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.

[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.