Brake Servo question

[OverlandMan]

If the pedal is super hard and the brakes seem like they aren't 100% (ie: car is hard to stop) I'm guessing this would indicate a Servo problem or a vacuum leak off the booster somewhere. (Engine running obviously to create vacuum). Pedal doesn't go to floor or indicate air in lines. I rebuilt all the calipers and replaced the flex lines a year or two ago with virtually no miles since then.

In looking at the schematic, it looks like there is a metal vacuum pipe running down the frame. At the rear there appear to be at least a couple of hoses. I can't make out a part number but I'm guessing there would be another rubber hose at the front connecting to the booster itself from the metal pipe.

Does anyone have any pictures on the rear vacuum line locations? Is this the 5/32" or 3mm hose that gets used in the evaporative controls or is this a larger application? My experience with other vehicles is it's a larger diameter rubber vacuum line.

[Bitsyncmaster]

It is the large vacuum hoses running to the booster. It's been many years but I did replace those hoses. Don't expect the brakes to feel as good as modern cars with anti-lock. They even don't quite match up to my wife's 2004 Impala (not anti-lock) but that's getting close.

[PJ Grady Inc.]

Jeff,
The booster hose goes to a bridge pipe that runs down the frame backbone and crosses over to the R/H side before plugging into the back of the pass. side intake manifold. From there it travels into the L/H rear body pontoon where it feeds a vacumn canister to run the HVAC controls. It is about 10mm ID and is not associated with the emissions canister plumbing.
Your problem is likely a BAD BRAKE BOOSTER and not a hose or vacumn leak issue as the symptoms would indicate. I've seen this before.
Rob Grady


If the pedal is super hard and the brakes seem like they aren't 100% (ie: car is hard to stop) I'm guessing this would indicate a Servo problem or a vacuum leak off the booster somewhere. (Engine running obviously to create vacuum). Pedal doesn't go to floor or indicate air in lines. I rebuilt all the calipers and replaced the flex lines a year or two ago with virtually no miles since then.

In looking at the schematic, it looks like there is a metal vacuum pipe running down the frame. At the rear there appear to be at least a couple of hoses. I can't make out a part number but I'm guessing there would be another rubber hose at the front connecting to the booster itself from the metal pipe.

Does anyone have any pictures on the rear vacuum line locations? Is this the 5/32" or 3mm hose that gets used in the evaporative controls or is this a larger application? My experience with other vehicles is it's a larger diameter rubber vacuum line.

[Jonathan]

This may or may not help you with your troubleshooting Jeff, but I always thought this video did a really great job explaining how vacuum assisted brakes work (brake booster). It's not DeLorean specific of course, more just a general understanding of how the technology works.

I know you understand how the brake booster works Jeff, I just thought this would be a good thread to put the video clip in for others that are working on the same system.


https://www.youtube.com/watch?v=LThrL8Jjsgc

[OverlandMan]

It is the large vacuum hoses running to the booster. It's been many years but I did replace those hoses. Don't expect the brakes to feel as good as modern cars with anti-lock. They even don't quite match up to my wife's 2004 Impala (not anti-lock) but that's getting close.

I hear ya. They certainly are not comparable to modern vehicles. Currently though, they feel more like my 1948 CJ2A did with 4 drums and no booster assist. When I bought the car I recall they felt better from a power assist perspective, if that makes sense.



Jeff,
The booster hose goes to a bridge pipe that runs down the frame backbone and crosses over to the R/H side before plugging into the back of the pass. side intake manifold. From there it travels into the L/H rear body pontoon where it feeds a vacumn canister to run the HVAC controls. It is about 10mm ID and is not associated with the emissions canister plumbing.
Your problem is likely a BAD BRAKE BOOSTER and not a hose or vacumn leak issue as the symptoms would indicate. I've seen this before.
Rob Grady


Thanks Rob. I figured inspecting/replacing the hoses would be cheaper/easier than replacing the booster and would be where I'd start. Do you sell the servo? I seem to recall DMCH had them around $200+. Been a while since I looked though. This is just one of the many things I've got on my list. The list that keeps growing.




This may or may not help you with your troubleshooting Jeff, but I always thought this video did a really great job explaining how vacuum assisted brakes work (brake booster). It's not DeLorean specific of course, more just a general understanding of how the technology works.

I know you understand how the brake booster works Jeff, I just thought this would be a good thread to put the video clip in for others that are working on the same system.


Thanks Jonathan. I actually saw that prior when I was searching threads on this topic. It's a nice basic theory video on how the booster works.

[PJ Grady Inc.]

Thanks for the enquiry Jeff,

DMCH List is up to about S270- at this time. I have known good used ones at lower prices. If interested PM, email or call for more info.
Rob
I hear ya. They certainly are not comparable to modern vehicles. Currently though, they feel more like my 1948 CJ2A did with 4 drums and no booster assist. When I bought the car I recall they felt better from a power assist perspective, if that makes sense.



Thanks Rob. I figured inspecting/replacing the hoses would be cheaper/easier than replacing the booster and would be where I'd start. Do you sell the servo? I seem to recall DMCH had them around $200+. Been a while since I looked though. This is just one of the many things I've got on my list. The list that keeps growing.



Thanks Jonathan. I actually saw that prior when I was searching threads on this topic. It's a nice basic theory video on how the booster works.

[David T]

Thanks for the enquiry Jeff,

DMCH List is up to about S270- at this time. I have known good used ones at lower prices. If interested PM, email or call for more info.
Rob

Before assuming the booster is bad at least see if there is any vacuum in the hose AT the booster. Maybe the hose is not connected to the motor and plugged off? If you just go ahead and replace the booster and the problem is that the vacuum hose isn't connected to the motor, you will not have fixed the problem but you WILL have spent money on a part you don't need.

[OverlandMan]

Before assuming the booster is bad at least see if there is any vacuum in the hose AT the booster. Maybe the hose is not connected to the motor and plugged off? If you just go ahead and replace the booster and the problem is that the vacuum hose isn't connected to the motor, you will not have fixed the problem but you WILL have spent money on a part you don't need.

Agreed. Which is why my OP was asking for a picture of where the hose(s) are/connect/etc. This way I can do a quick check in my garage. At least I assume this would be a quick check.

At least with the info already provided, I think I can find them... but again, a picture is worth a thousand words.

[David T]

Agreed. Which is why my OP was asking for a picture of where the hose(s) are/connect/etc. This way I can do a quick check in my garage. At least I assume this would be a quick check.

At least with the info already provided, I think I can find them... but again, a picture is worth a thousand words.

Pull the hose off the booster (at the booster). With the motor running see if a piece of stiff cardboard, like a tag, will stick to the end of the hose. If it sticks you have vacuum, if it slides off you don't. If you have a vacuum gauge all the better. To replace the booster you have to pull the vacuum hose off anyway.

[DMCMW Dave]

Pull the hose off the booster (at the booster). With the motor running see if a piece of stiff cardboard, like a tag, will stick to the end of the hose. If it sticks you have vacuum, if it slides off you don't. If you have a vacuum gauge all the better. To replace the booster you have to pull the vacuum hose off anyway.

And make sure the check valve is good. That plastic connector at the master is not just a right angle connector, it is a one-way valve. If the check valve fails open, going from full throttle to hard braking gets pretty exciting. If it's plugged, the power assist will be down.

[David T]

And make sure the check valve is good. That plastic connector at the master is not just a right angle connector, it is a one-way valve. If the check valve fails open, going from full throttle to hard braking gets pretty exciting. If it's plugged, the power assist will be down.

Yes, you MUST remove the hose from the booster and if the check valve comes loose with the hose you have to remove it too. The main purpose of that check valve is to hold some vacuum after the motor stops so if you are moving you still get 1 or 2 pumps on the brakes with some boost. Of course when you lose vacuum altogether the adrenalin kicks in and you can push that pedal all the way down to the floor! With both feet if you have to! If the brakes are still hard to stop the car and the booster is working, you could have some bad brake hoses or stuck calipers. Does the car pull to one side when you stomp on the brakes? On one car both front calipers were stuck and it was difficult to stop the car even with both feet and it stopped straight because BOTH front wheels didn't have working brakes. I have also seen where the calipers were freshly rebuilt and still wouldn't work because the hoses collapsed inside working like check valves.

[PJ Grady Inc.]

I believe that Jeff said in his first post that he rebuilt the calipers and replaced all flex hoses about a year ago so assuming good parts and correct procedures were used we can move on back to the power booster. Did you read the initial post David?
By all means check for sufficient vacuum to the booster before replacing it.
I must reiterate that I've only had a few DMC's in all the years with a hard pedal combined with poor, as in weak, braking and except for one pinched hose on a frame R&R they were all bad boosters. i would concentrate on this area before revisiting the recently done caliper/hose work since no brake pulling was mentioned as a symptom. Again I like to thoroughly examine the most likely cause first before jumping to another area of the brake system.
Rob


Yes, you MUST remove the hose from the booster and if the check valve comes loose with the hose you have to remove it too. The main purpose of that check valve is to hold some vacuum after the motor stops so if you are moving you still get 1 or 2 pumps on the brakes with some boost. Of course when you lose vacuum altogether the adrenalin kicks in and you can push that pedal all the way down to the floor! With both feet if you have to! If the brakes are still hard to stop the car and the booster is working, you could have some bad brake hoses or stuck calipers. Does the car pull to one side when you stomp on the brakes? On one car both front calipers were stuck and it was difficult to stop the car even with both feet and it stopped straight because BOTH front wheels didn't have working brakes. I have also seen where the calipers were freshly rebuilt and still wouldn't work because the hoses collapsed inside working like check valves.

[David T]

I believe that Jeff said in his first post that he rebuilt the calipers and replaced all flex hoses about a year ago so assuming good parts and correct procedures were used we can move on back to the power booster. Did you read the initial post David?
By all means check for sufficient vacuum to the booster before replacing it.
I must reiterate that I've only had a few DMC's in all the years with a hard pedal combined with poor, as in weak, braking and except for one pinched hose on a frame R&R they were all bad boosters. i would concentrate on this area before revisiting the recently done caliper/hose work since no brake pulling was mentioned as a symptom. Again I like to thoroughly examine the most likely cause first before jumping to another area of the brake system.
Rob

I did read the original post but he said HE rebuilt the calipers. Since we don't know exactly what he did it is possible they could be stuck. If he kinked or twisted the hoses they could be bad. Hard to assume "correct procedures" when you don't know the OP's skill level. I mentioned checking the hoses and calipers AFTER making sure you have vacuum on the booster. If the poster finds he doesn't have vacuum at the booster he MUST find and fix that BEFORE doing anything else. Hard to tell if the booster is good or bad if you don't have any vacuum on it!

[PJ Grady Inc.]

I agree he should check for vacuum first and if he has good vacuum I think he probably has a bad booster. I find it hard to foresee what he could have done to the calipers or the hoses that would result in a hard pedal and no brake pull even if he used inferior parts or assembled things incorrectly but maybe you have some ideas?
Rob

.
I did read the original post but he said HE rebuilt the calipers. Since we don't know exactly what he did it is possible they could be stuck. If he kinked or twisted the hoses they could be bad. Hard to assume "correct procedures" when you don't know the OP's skill level. I mentioned checking the hoses and calipers AFTER making sure you have vacuum on the booster. If the poster finds he doesn't have vacuum at the booster he MUST find and fix that BEFORE doing anything else. Hard to tell if the booster is good or bad if you don't have any vacuum on it!

[OverlandMan]

I did read the original post but he said HE rebuilt the calipers. Since we don't know exactly what he did it is possible they could be stuck. If he kinked or twisted the hoses they could be bad. Hard to assume "correct procedures" when you don't know the OP's skill level. I mentioned checking the hoses and calipers AFTER making sure you have vacuum on the booster. If the poster finds he doesn't have vacuum at the booster he MUST find and fix that BEFORE doing anything else. Hard to tell if the booster is good or bad if you don't have any vacuum on it!

Here's my original blog posts pertaining to the brake job I did a while back now:
http://dmctx.blogspot.com/2013/06/brake-system-rebuild-part-i.html
http://dmctx.blogspot.com/2013/06/brake-system-rebuild-part-ii.html

As you can see, I'm not a complete idiot. I have some background in automotive mechanical work and know my way around these cars decently, though I'm still humble enough to know there's stuff I don't know and I don't mind asking questions (hence this forum/other forums/vendors/communities/etc.).

My original post was asking if anyone could send me a picture of where the vacuum lines connect in the engine compartment area. That said, checking the vacuum lines and the one-way valve should be a relatively straightforward and quick procedure. Rob's input regarding the servo is very helpful in that if I verify the aforementioned isn't the culprit, this is where I'll go.

All this said, I still haven't had a chance to test this out. I'm finalizing a long fuel system rebuild project and need to get her running again before I can even check for vacuum. I'm hoping to accomplish this weekend. The weather is starting to get nicer down here now and I guess I'm looking ahead at some of my upcoming jobs on the car, hopefully not fuel-system related!

[David T]

I agree he should check for vacuum first and if he has good vacuum I think he probably has a bad booster. I find it hard to foresee what he could have done to the calipers or the hoses that would result in a hard pedal and no brake pull even if he used inferior parts or assembled things incorrectly but maybe you have some ideas?
Rob

.

I saw one car where the calipers just had new seals but the pistons had the plating all corroded (he reused the old pistons). Also the car could have been flooded. I never said the poster was a complete idiot, (or even a partial one!) I just can't know his skill level. Anyway you have to assume anything is possible but you always start with the easiest and/or most obvious. No need to go fussing around in the engine compartment if you have good vacuum at the booster. That is why I suggested starting there. If, after checking and not getting vacuum at the booster, you just follow the plumbing back til you find the problem. I mentioned the hoses because that is a VERY insidious problem and hard to find and unless you have seen it before, you don't expect it.

[PJ Grady Inc.]

I was trying to cover your back man!!! I figured you weren't an idiot and even if you had been the symptoms didn't match anything I could conceive of that you could have done to create a hard pedal condition. THAT'S WHY I KEEP STEERING THIS BACK TO THE BOOSTER IF ANYONE IS LISTENING?
I tried to explain exactly how the hose is routed, as clear pictures of the areas concerned are hard to come by, and I don't have time to set up a photoshoot right now. Did you look at the section of the manual I referred to as that is clearer than most pictures will provide. Could anyone else who has more time on their hands send Jeff some pictures... David....anybody??????

This is my last post on this thread until you can confirm vacuum to the booster in which case you need to bite the bullet and install one. It's not an easy job and time consuming to describe so I'm not going there until you decide you need one. BTW I have a low mile used one someone is expressing interest in so this thread may have just gotten me a sale in which case I thank you and if not then it could be yours if you so desire.
It just depends who pulls the trigger first. I may have another one available soon so no pressure here! Take your time. I'm sorry folks but I know of no way to absolutely positively confirm a bad booster without replacing it but the symptoms in both cases seem pretty clear to me IMHO.
Rob



Here's my original blog posts pertaining to the brake job I did a while back now:
http://dmctx.blogspot.com/2013/06/brake-system-rebuild-part-i.html
http://dmctx.blogspot.com/2013/06/brake-system-rebuild-part-ii.html

As you can see, I'm not a complete idiot. I have some background in automotive mechanical work and know my way around these cars decently, though I'm still humble enough to know there's stuff I don't know and I don't mind asking questions (hence this forum/other forums/vendors/communities/etc.).

My original post was asking if anyone could send me a picture of where the vacuum lines connect in the engine compartment area. That said, checking the vacuum lines and the one-way valve should be a relatively straightforward and quick procedure. Rob's input regarding the servo is very helpful in that if I verify the aforementioned isn't the culprit, this is where I'll go.

All this said, I still haven't had a chance to test this out. I'm finalizing a long fuel system rebuild project and need to get her running again before I can even check for vacuum. I'm hoping to accomplish this weekend. The weather is starting to get nicer down here now and I guess I'm looking ahead at some of my upcoming jobs on the car, hopefully not fuel-system related!

[OverlandMan]

I was trying to cover your back man!!! I figured you weren't an idiot and even if you had been the symptoms didn't match anything I could conceive of that you could have done to create a hard pedal condition. THAT'S WHY I KEEP STEERING THIS BACK TO THE BOOSTER IF ANYONE IS LISTENING?
I tried to explain exactly how the hose is routed, as clear pictures of the areas concerned are hard to come by, and I don't have time to set up a photoshoot right now. Did you look at the section of the manual I referred to as that is clearer than most pictures will provide. Could anyone else who has more time on their hands send Jeff some pictures... David....anybody??????

This is my last post on this thread until you can confirm vacuum to the booster in which case you need to bite the bullet and install one. It's not an easy job and time consuming to describe so I'm not going there until you decide you need one. BTW I have a low mile used one someone is expressing interest in so this thread may have just gotten me a sale in which case I thank you and if not then it could be yours if you so desire.
It just depends who pulls the trigger first. I may have another one available soon so no pressure here! Take your time. I'm sorry folks but I know of no way to absolutely positively confirm a bad booster without replacing it but the symptoms in both cases seem pretty clear to me IMHO.
Rob

Rob,

I appreciate you input and help. My previous post was aimed more towards David after he posted this:



I did read the original post but he said HE rebuilt the calipers. Since we don't know exactly what he did it is possible they could be stuck. If he kinked or twisted the hoses they could be bad. Hard to assume "correct procedures" when you don't know the OP's skill level. I mentioned checking the hoses and calipers AFTER making sure you have vacuum on the booster. If the poster finds he doesn't have vacuum at the booster he MUST find and fix that BEFORE doing anything else. Hard to tell if the booster is good or bad if you don't have any vacuum on it!


Guess I was a bit offended in the presumed assumptions in that statement. All is well. Hopefully I'll get a vacuum check done this weekend and go from there. I'll PM you or call your shop first if it turns out I do need a new booster.

[David T]

Rob,

I appreciate you input and help. My previous post was aimed more towards David after he posted this:



Guess I was a bit offended in the presumed assumptions in that statement. All is well. Hopefully I'll get a vacuum check done this weekend and go from there. I'll PM you or call your shop first if it turns out I do need a new booster.

My apologies to Ovelandman getting caught in the crossfire between me and Rob. We seem to have differing opinions on what the ultimate problem is, Rob is assuming the booster is bad and I am assuming there is a plumbing problem causing a loss of vacuum. When troubleshooting you (anyone) always seem to have a guess as to what the ultimate problem is and you use that bias when trying to figure out what is wrong. Sometimes it can cause you to go down the wrong track. I was trying to avoid replacing the booster just because it is a pain to do although it may turn out that is what is necessary.

[PJ Grady Inc.]

Looks like we need to send David to one of those "sensitivity training " classes! We know you meant no offense David but maybe you weren't totally PC on this one. We still love you man!!!!

P.S. "If we can't have some fun while doing this then why bother" (as in working on Deloreans!). I'm quoting Stephen Wynn talking to me at a company "dealer" meeting back in 2004 and I still agree with that statement. Do you guy's all know it was both his birthday and his & Elaine's 38th wedding anniversy this week? Three cheers for the birthday boy and his lovely wife;)


Rob,

I appreciate you input and help. My previous post was aimed more towards David after he posted this:



Guess I was a bit offended in the presumed assumptions in that statement. All is well. Hopefully I'll get a vacuum check done this weekend and go from there. I'll PM you or call your shop first if it turns out I do need a new booster.

[PJ Grady Inc.]

Once vacuum has been determined to be present at the booster David tell us what you'd do next to avoid replacing the booster. If vacuum is present it is the booster. I said I wouldn't post on this until the vacuum supply is checked but you keep sucking me in. Now I'm done so you can have the last word. This isn't really crossfire as much as a pointless debate.


My apologies to Ovelandman getting caught in the crossfire between me and Rob. We seem to have differing opinions on what the ultimate problem is, Rob is assuming the booster is bad and I am assuming there is a plumbing problem causing a loss of vacuum. When troubleshooting you (anyone) always seem to have a guess as to what the ultimate problem is and you use that bias when trying to figure out what is wrong. Sometimes it can cause you to go down the wrong track. I was trying to avoid replacing the booster just because it is a pain to do although it may turn out that is what is necessary.

[David T]

Once vacuum has been determined to be present at the booster David tell us what you'd do next to avoid replacing the booster. If vacuum is present it is the booster. I said I wouldn't post on this until the vacuum supply is checked but you keep sucking me in. Now I'm done so you can have the last word. This isn't really crossfire as much as a pointless debate.

If vacuum is present at the booster AND if the check valve is not stuck closed the chances are very high that the booster is bad. The only other possibility (and I admit it is a long shot but I have seen it) is that both calipers on either the front or the rear axle are stuck. As for the booster, there is a place that repairs them. Look up
boosterdeweyexchange.com 503-238-8882

I have not used them for a Delorean booster but they have helped me with other makes. DMC also had a kit to repair the booster (or servo as it is called in the parts manual) under part # 109038. I don't know if anyone has any. Worth checking around if you want to try fixing it yourself. Again, start with the simple stuff and verify vacuum at the booster. I can't wait to see how this turns out. I hope we are both right.

[OverlandMan]

... I can't wait to see how this turns out. I hope we are both right.

I hope that's not true for my sake :smile:

I'm hoping a vacuum line has been dislodged or something super easy.

[PJ Grady Inc.]

Damn it David you drew me in again! I have about 100 of these kits in stock but they probably wouldn't solve a leaky booster as it is only a rod bellows and seal kit. I got a bunch of them every time I bought a dealer inventory. I can supply as many as you want for $25- a kit if someone wants to give it a try.
I would think that the issue would be with the inner diaphragm and not the rod seal. Not having ever rebuilt one I can't say for sure. You need special tools to disassemble them and that combined with a low failure rate, and high liability from a safety standpoint, make them one of the few parts of this car I have never attempted to rebuild.
Rob


If vacuum is present at the booster AND if the check valve is not stuck closed the chances are very high that the booster is bad. The only other possibility (and I admit it is a long shot but I have seen it) is that both calipers on either the front or the rear axle are stuck. As for the booster, there is a place that repairs them. Look up
boosterdeweyexchange.com 503-238-8882

I have not used them for a Delorean booster but they have helped me with other makes. DMC also had a kit to repair the booster (or servo as it is called in the parts manual) under part # 109038. I don't know if anyone has any. Worth checking around if you want to try fixing it yourself. Again, start with the simple stuff and verify vacuum at the booster. I can't wait to see how this turns out. I hope we are both right.

[David T]

Damn it David you drew me in again! I have about 100 of these kits in stock but they probably wouldn't solve a leaky booster as it is only a rod bellows and seal kit. I got a bunch of them every time I bought a dealer inventory. I can supply as many as you want for $25- a kit if someone wants to give it a try.
I would think that the issue would be with the inner diaphragm and not the rod seal. Not having ever rebuilt one I can't say for sure. You need special tools to disassemble them and that combined with a low failure rate, and high liability from a safety standpoint, make them one of the few parts of this car I have never attempted to rebuild.
Rob

Maybe you can sell them to Booster Dewey? Let him do it and take the liability? I know boosters can be rebuilt, I have had several done over the years. I understand the kit doesn't have the main diaphragm but maybe you don't need it? And if you do I am sure Booster Dewey could match something up. We are getting ahead of ourselves here again, we are waiting to find out if there is vacuum on the booster.

[DMCMW Dave]

OE replacement boosters are readily available, although not particularly inexpensive. Used ones are as well, as the failure rate is overall, as Rob mentioned, pretty low.

[SpudMurphy]

I wonder how that all turned out?

I have the same problem - initially I had absolutely NO vacuum at the servo .. there was no vac tank in the car either !!!

Anyways ... if anybody wants to check the vacuum plumbing route on a Delorean I posted a thread here ....

http://dmctalk.org/showthread.php?17895-How-to-Brake-Servo-Vacuum-Route

[David T]

An old thread. My guess it it was something really simple (stupid) and the OP never closed the thread. Very often we assume the worst, most complicated things when it almost always turns out to be the simplest things. Like maybe the hose got squeezed or kinked. Out of plain courtesy it would be nice to hear how these do turn out. Maybe he just sold the car?

[SpudMurphy]

An old thread. My guess it it was something really simple (stupid) and the OP never closed the thread. Very often we assume the worst, most complicated things when it almost always turns out to be the simplest things. Like maybe the hose got squeezed or kinked. Out of plain courtesy it would be nice to hear how these do turn out. Maybe he just sold the car?

I used to post a lot on a guitar forum and always went back to my thread and described the outcome. People come back to me years later saying how much it helped.

You may be right Dave, insofar as he may have sold the car - it's ironic that I have the same problem - but I know that vacuum is getting there.

[David T]

If you have vacuum at the booster the check valve *could* be stuck. If you are getting vacuum into the booster and it doesn't work, the booster must be rebuilt or replaced. Measure the vacuum at the motor and at the booster. Should be the same. If not, you have a leak. The vac tank is for the A/C, not the booster.