Looking for thread re. brake fluid leak

[Henrik]

I have a slight brake fluid leak coming from the bottom of the brake booster. Of course, it could be the master cylinder or the joint b/w the master and the reservoir - not sure at this point. Is there a thread already here on the dmctalk that expands on this, i.e. how to take it apart and how to trouble shoot?

[DMCMW Dave]

It is the master leaking from the rear seal. The joint between the master and the booster is not sealed on purpose. If there is fluid there the master is failing.

[Henrik]

Thanks Dave. There is nothing about brakes in the FAQ Links to Quick Answers section (http://dmctalk.org/showthread.php?7972-DMCTalk-Frequently-Asked-Questions-Links-to-Quick-Answers). I would like to learn more about the issue I'm having, teardown, bench-bleeding etc. Is there a link to some good discussions here in the community?

[Rich]

I would like to learn more about the issue I'm having, teardown, bench-bleeding etc. Is there a link to some good discussions here in the community?

Am not seeing a thread here about how to do that but it's probably a method similar to that for any other brake master. On that topic you can cruise the web and find a lot of how-to's for it such as this one:
LINK: http://secondchancegarage.com/classic-car/rebuilding-master-cylinder.cfm (http://secondchancegarage.com/classic-car/rebuilding-master-cylinder.cfm)

I do recall a few threads here that deal with just the bench-bleeding. Again, probably similar to bench-bleeding a non-D cylinder.

Before you start you may want to at least read this short thread about rebuilding a D master in order to set your expectations:

LINK: http://dmctalk.org/showthread.php?3571 (http://dmctalk.org/showthread.php?3571-Master-cylinder-rebuild&highlight=rebuild+brake+master)

[Henrik]

Thanks Dave and Rich.

Before anyone tells me I'm lazy I wanna say pre-emptively: I'm lazy!

A little searching yielded a ton of info on the subject. Here are a few links:

http://dmctalk.org/showthread.php?45-How-To-Bench-bleed-a-brake-master-cylinder&highlight=bench+bleed
http://dmctalk.org/showthread.php?10327-Brake-Master-Toast&highlight=bench+bleed
http://dmctalk.org/showthread.php?3992-Bench-bleed-master-cylinder&highlight=bench+bleed
http://dmctalk.org/showthread.php?8868-Mystery-of-the-unbleedable-brakes!&highlight=bench+bleed
http://dmctalk.org/showthread.php?8213-Brake-Master-cylinder-and-Caliper-removal&highlight=bench+bleed
http://dmctalk.org/showthread.php?6000-Brake-reservoir-question&highlight=bench+bleed

[David T]

Thanks Dave and Rich.

Before anyone tells me I'm lazy I wanna say pre-emptively: I'm lazy!

A little searching yielded a ton of info on the subject. Here are a few links:

http://dmctalk.org/showthread.php?45-How-To-Bench-bleed-a-brake-master-cylinder&highlight=bench+bleed
http://dmctalk.org/showthread.php?10327-Brake-Master-Toast&highlight=bench+bleed
http://dmctalk.org/showthread.php?3992-Bench-bleed-master-cylinder&highlight=bench+bleed
http://dmctalk.org/showthread.php?8868-Mystery-of-the-unbleedable-brakes!&highlight=bench+bleed
http://dmctalk.org/showthread.php?8213-Brake-Master-cylinder-and-Caliper-removal&highlight=bench+bleed
http://dmctalk.org/showthread.php?6000-Brake-reservoir-question&highlight=bench+bleed

If the master is leaking where the plunger goes the master needs to be rebuilt or replaced. If the reservoir is installed the wrong way and is hitting the booster the seals will leak. If the seals are not installed correctly it will leak. If it is overfilled it will leak.

[Mark D]

While I'm sure it's possible to rebuild a rusty/leaky brake master cylinder I don't think I've ready any threads about people rebuilding... Most simply replace it, I know that's what I did. I took one look at the rusty mess and had no desire to go any further. I considered it $176 well spent. I bought a DMCH reproduction that matches the original 60/40 valving specs. Other crossover parts apply 50/50 pressure to front and rear brakes and may change the braking performance of the car.

http://store.delorean.com/p-7478-master-cylinder-brake.aspx


If yours is leaking it probably looks like this.
http://dmctalk.org/attachment.php?attachmentid=29995&d=1407726823


http://dmctalk.org/attachment.php?attachmentid=29996&d=1407726829


Removal is easy....remove the access panel in the floor of the luggage compartment. Disconnect the two hard brake lines and cap them off. A line wrench (AKA flare nut wrench) is helpful to prevent rounding off the fittings. Remove two nyloc nuts holding the master cylinder to the brake booster... remove the master cylinder (and attached reservoir) from the brake booster. The studs that hold the MC in place are part of the brake booster:

http://dmctalk.org/attachment.php?attachmentid=29997&d=1407726834


You'll probably have to do some paint/rust repair on the booster as well as on your frame if it has been dripping for any lengthy period of time.

Once you're all done it'll look like this :-)

http://dmctalk.org/attachment.php?attachmentid=29998&d=1407726839


http://dmctalk.org/attachment.php?attachmentid=29999&d=1407726844


To clean the internal nooks and crannies of the reservoir (once it's removed) fill it with a handful of small washers and a generous squirt of brake cleaner. Plug the holes with your fingers and shake it up until all the rusty film is dissolved into the brake cleaner. Rinse and repeat until it looks brand new. Then empty out all the washers.

After the new master is installed bleeding the air out of the system is easy if you use a pressure bleeder. Motul makes them for around 75 bucks or you can build your own from a garden sprayer for about half that price. No bench bleeding of the master is required... Just fill the reservoir and push fresh brake fluid through using the pressure bleeder.

Pics of the brake bleeder I built here:
http://dmctalk.org/showthread.php?7264-Questions-About-Bleeding-the-Brakes&p=106069&viewfull=1#post106069

I just upgraded it the other day with a 0-30psi gauge from Mcmastercarr for about 10 bucks:
http://www.mcmaster.com/#3846k6/=t86ypy

The exact same cap that fits the DeLorean reservoir worked on my E46 BMW so it'll probably fit other european cars too.

[Henrik]

Oh my, Mark, that looks real nice and thank you for the step by step procedure. Looks like you had your brake booster out and gave it a do-over as well. Is it easy to remove too? I will be working on it tomorrow night.

Question #1: How do I know for sure that the master cylinder is shot (i.e. leaking)? Isn't there a good chance the leak may be due to a poor seal b/w the reservoir and the master cylinder? The reason I ask is that the reservoir seems kind of wiggly...

Question #2: Has anyone thought of some sort of a deflector to keep the brake fluid from dripping on the frame if it ever starts leaking again? I really don't wanna have to remove the tank close-out plate, empty out the coolant, pull the coolant pipes and drop the tank AGAIN (to clean/paint the frame) if there is another leak in the future.

[Henrik]

If the master is leaking where the plunger goes the master needs to be rebuilt or replaced. If the reservoir is installed the wrong way and is hitting the booster the seals will leak. If the seals are not installed correctly it will leak. If it is overfilled it will leak.

Just saw this. Thanks David.

[Mark D]

Oh my, Mark, that looks real nice and thank you for the step by step procedure. Looks like you had your brake booster out and gave it a do-over as well. Is it easy to remove too? I will be working on it tomorrow night.

Question #1: How do I know for sure that the master cylinder is shot (i.e. leaking)? Isn't there a good chance the leak may be due to a poor seal b/w the reservoir and the master cylinder? The reason I ask is that the reservoir seems kind of wiggly...

Question #2: Has anyone thought of some sort of a deflector to keep the brake fluid from dripping on the frame if it ever starts leaking again? I really don't wanna have to remove the tank close-out plate, empty out the coolant, pull the coolant pipes and drop the tank AGAIN (to clean/paint the frame) if there is another leak in the future.

#1: If the rear seal on the master cylinder is shot you'll probably see dampness and fluid staining around the two nyloc nuts on the brake booster and you may also see evidence of fluid leaking past where the MC fits inside the booster. My MC was definitely leaking at the rear seal as you can see in the photo below. Notice how it's relatively dry up near the reservoir and how wet it is at the rear of the MC.

http://dmctalk.org/attachment.php?attachmentid=30001&d=1407770113

From what I understand failure of just the two donut shaped seals where the reservoir meets up with the MC is relatively uncommon. If those have failed chances are the rear seal on the MC has also failed. You should be able to move around the reservoir slightly when installed into the MC due to the fact that the only thing securing the reservoir in place are the two pins that pass through the base of the reservoir.

#2: I considered making a stainless deflector as you're describing but I hadn't heard many complaints about leaks after replacing the master cylinder. As long as you flush the system with fresh fluid every 2-3 years you shouldn't have to worry about leaks anytime soon.
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To answer your other question about the brake booster, yes I removed mine completely so I could sand blast and paint it. To get the booster/bracket assembly out you remove the MC first. Then there are four nuts on the inside of the car in a V shaped pattern near the pedal box that you need to remove and you also have to disconnect the brake pedal linkage from the booster.

This diagram shows the brake booster bracket that is mounted through the firewall near the pedals. The brake booster is mounted to this bracket with four nuts in a square shaped patern. Once you have the booster/bracket assembly removed from the car then you can separate the bracket from the booster and repaint each separately. This diagram shows how it all goes together. Getting at a few of the nuts that hold the booster bracket to the firewall can be a bit tricky...I used a combination of different socket extensions with swivel heads to be able to get access to each nut. I don't believe it's possible to leave the bracket attached to the car and only remove the booster by taking of the four nuts in the square shaped pattern. The whole works has to get pulled out as an assembly. Chances are you've got paint damage on the bracket so you'll want to remove both anyway.

http://store.delorean.com/c-356-6-3-0-master-cylinderpower-unit.aspx

And here's a photo of the bolt pattern on the back of the mounting bracket.
http://dmctalk.org/attachment.php?attachmentid=30003&d=1407772472


See this diagram here (Item #7) for the clevis pin to remove:

http://store.delorean.com/c-358-6-3-2-brake-pedallinkage-manual.aspx

[Henrik]

Mark D, you must be a technical writer and a teacher. Thanks for a well-written and clear explanation with pics and all. Not sure whether our Administrators are continuously prowling all the posts (or if you have to bring them to their attention specfically) but the info you have provided is def worthy of being moved to the How-To section.

Thanks again.

[DMCMW Dave]

Question #1: How do I know for sure that the master cylinder is shot (i.e. leaking)? Isn't there a good chance the leak may be due to a poor seal b/w the reservoir and the master cylinder? The reason I ask is that the reservoir seems kind of wiggly...
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Here's a better shot of the back end of the master. Once you understand that it's vented at the base, you can see why there is really no seal between the master and the booster. If the master leaks, it will run out the vent area. This area should be dry.

30005

[Mark D]

Mark D, you must be a technical writer and a teacher. Thanks for a well-written and clear explanation with pics and all. Not sure whether our Administrators are continuously prowling all the posts (or if you have to bring them to their attention specfically) but the info you have provided is def worthy of being moved to the How-To section.

Thanks again.

:wave2: thanks Henrick, no problem with the explanation and the photos. It hasn't been long since I did all this work on my car so it's still pretty fresh in my memory. I also have a huge folder full of pictures that I took as I was doing all the work so that helps too. I remember having some of the same questions you're asking before I started... I'm glad I can help make it easier for you.

I've also gotten a lot of help from Dave (and Julee) at DMCMW.

[David T]

Here's a better shot of the back end of the master. Once you understand that it's vented at the base, you can see why there is really no seal between the master and the booster. If the master leaks, it will run out the vent area. This area should be dry.

30005

In fact, it is vented for a reason. If it should leak you don't want the brake fluid getting into the booster. Kind of like the weep hole in the water pump so the coolant doesn't go through the bearings and wash out the lube. If the master cylinder leaks at that point it is a very bad sign and should be fixed before driving. The master cylinders don't usually get rebuilt because by the time you see it leaking, the inside bore is all corroded and it costs to much to resleeve it. Besides, it is getting very hard to find kits to rebuild them. If the master cylinder is leaking you should figure all of the calipers are also corroded and should also be rebuilt. While you are at it you should also replace all 4 brake hoses. Now you are rebuilding the whole brake system! Much cheaper to flush and bleed it every 2 years.

[Mark D]

Yeah if you've got a failing master cylinder and you are unsure of the last time you had the brake system flushed with fresh fluid then chances are your calipers are probably filled with goo. Mine looked like this...

http://dmctalk.org/attachment.php?attachmentid=26168&d=1395930529

http://dmctalk.org/attachment.php?attachmentid=30008&d=1407856735

It's a rabbit hole once you start down the path of replacing or rebuilding parts. I replaced the brake master, got seal rebuild kits for the calipers, and bought new flexible brake lines. I didn't want to rebuild rusty calipers so I sand blasted them and replated in yellow zinc. I figured hey, as long as I'm replating those I should do the exhaust brackets too. And oh, while I'm repairing that paint damage from the master cylinder leak on the frame I should re-paint the suspension parts. Might as well get lowering springs and new shocks since I've got the suspension torn apart. Might as well replace all those worn rubber bushings too while I'm in there. And so on and so on...

[alexwolf1216]

Yeah if you've got a failing master cylinder and you are unsure of the last time you had the brake system flushed with fresh fluid then chances are your calipers are probably filled with goo. Mine looked like this...

http://dmctalk.org/attachment.php?attachmentid=26168&d=1395930529

http://dmctalk.org/attachment.php?attachmentid=30008&d=1407856735

It's a rabbit hole once you start down the path of replacing or rebuilding parts. I replaced the brake master, got seal rebuild kits for the calipers, and bought new flexible brake lines. I didn't want to rebuild rusty calipers so I sand blasted them and replated in yellow zinc. I figured hey, as long as I'm replating those I should do the exhaust brackets too. And oh, while I'm repairing that paint damage from the master cylinder leak on the frame I should re-paint the suspension parts. Might as well get lowering springs and new shocks since I've got the suspension torn apart. Might as well replace all those worn rubber bushings too while I'm in there. And so on and so on...

That is eerily familiar to the path I took, but I didnt repair the spot on the frame yet.

[Mark D]

That is eerily familiar to the path I took, but I didnt repair the spot on the frame yet.

I let myself get pretty carried away... Once you get to a certain point it's almost easier to just do everything. In these photos I hadn't pulled the steering rack or removed the radiator yet which ended up happening before I started finally putting the car back together.

http://dmctalk.org/attachment.php?attachmentid=30010&d=1407857642
http://dmctalk.org/attachment.php?attachmentid=30009&d=1407857642
http://dmctalk.org/attachment.php?attachmentid=30012&d=1407857855
http://dmctalk.org/attachment.php?attachmentid=30011&d=1407857855

[Domi]

Amazing! Good luck to re-build all of these parts together :wrenchin:

[Henrik]

If the master cylinder is leaking you should figure all of the calipers are also corroded.....

Not sure I understand why a leaky MC would cause corrosion of the calipers.

[Henrik]

#1: If the rear seal on the master cylinder is shot you'll probably see dampness and fluid staining around the two nyloc nuts on the brake booster and you may also see evidence of fluid leaking past where the MC fits inside the booster. My MC was definitely leaking at the rear seal as you can see in the photo below. Notice how it's relatively dry up near the reservoir and how wet it is at the rear of the MC.

http://dmctalk.org/attachment.php?attachmentid=30001&d=1407770113

Mark D,
Here is a picture of my BB and MC - basically the same angle/position as your photo. Going by your assessment above I defintiely have a leak at the back of the MC. The bottom of the horizontal part of the MC is bone dry whereas the bottom of the BB is full of oil and crud. Note the dissolved paint below. I've got some grinding and painting to do....
30013
BTW, I flushed the brake systems and replaced all four flexible brake lines last year so that part should be fine.

[David T]

Not sure I understand why a leaky MC would cause corrosion of the calipers.

It is not a case of a leaky master cylinder causing the calipers to fail. When the master cylinder leaks it means the brake fluid got corrosive enough to make it leak. When it leaks it means the calipers are also corroded and also will start to leak soon. Typically the calipers don't leak immediately but after you start driving and wear the pads a little the pistons move and then the seals leak. To save time and brake fluid you might as well do the whole system at once. Yes, this kind of thing can grow into a bigger and bigger job but you have to remember you are working on a 30 year old car and parts were not meant to last this long without service. There are a lot of jobs like this. You can cheap out and do things piecemeal but you are only delaying the inevitable. I also understand budgets and finances and it can be expensive doing a big job all at once as opposed to a lot of smaller, cheaper jobs all the time but what is reliability and safety worth?

[DMCMW Dave]

Not sure I understand why a leaky MC would cause corrosion of the calipers.

It's more of a condition indicator than a cause.

[Henrik]

OK, David and Dave. I see your point. Thanks.

[Mark D]

BTW, I flushed the brake systems and replaced all four flexible brake lines last year so that part should be fine.

It's probably no coincidence that suddenly your old master cylinder started leaking after a fluid flush ....Brake systems are interesting in that a 30 year old untouched system might not leak a drop but as soon as you introduce fresh brake fluid the seals start giving out. I think it was Dave S. who coined the term "Delicate Balance of Crud". The theory is that all the gunk and thick goo around the seals are holding the system together and when you upset that balance the crud starts to dissolve away and the degraded seals start to leak.

That being said, it's much better to have a system that doesn't leak because the seals are new and fresh fluid rather than an old system held together with crud. It can be a frustrating path to go from crud based homeostasis to a fresh system because like Dave T said, once you replace one thing you'll most likely end up refreshing everything.

At the very least I'd check each caliper to make sure there is no dampness around the pistons. If you find you have leaks or you want to be proactive caliper seal rebuild kits are pretty cheap and it's an easy (but messy) DIY project. As an alternative to rebuilding yourself, most of the vendors also have a rebuild/swap program where you ship in your old calipers and they send you rebuilt ones ready to go.

[NightFlyer]

It's probably no coincidence that suddenly your old master cylinder started leaking after a fluid flush ....Brake systems are interesting in that a 30 year old untouched system might not leak a drop but as soon as you introduce fresh brake fluid the seals start giving out. I think it was Dave S. who coined the term "Delicate Balance of Crud". The theory is that all the gunk and thick goo around the seals are holding the system together and when you upset that balance the crud starts to dissolve away and the degraded seals start to leak.

Precisely why I haven't touched my clutch yet - still running the Dunmurry fluid :biggrin:

[Henrik]

It's probably no coincidence that suddenly your old master cylinder started leaking after a fluid flush .....

All good points and I have clearly set in motion the chain of events where one failure gets fixed only to be succeeded by another. I ordered my new MC today. What's next I wonder? The brake pedal breaking in half ? :dunno: The BB came out quite easily... but contorting your body and tools to get to the four little nuts on the other side of the firewall truly was an excerise in agility and patience. It's like the pedals are purposedly lined up to block off access the BB nuts! - but it worked out.

[Henrik]

Precisely why I haven't touched my clutch yet - still running the Dunmurry fluid :biggrin:

Impressive....

[Mark D]

Precisely why I haven't touched my clutch yet - still running the Dunmurry fluid :biggrin:

Lol...somehow I knew you'd not miss the wide open door I left for you to point that out. I'm going to be really sad if I ever hear you have to change that fluid.

[Mark D]

All good points and I have clearly set in motion the chain of events where one failure gets fixed only to be succeeded by another. I ordered my new MC today. What's next I wonder? The brake pedal breaking in half ? :dunno: The BB came out quite easily... but contorting your body and tools to get to the four little nuts on the other side of the firewall truly was an excerise in agility and patience. It's like the pedals are purposedly lined up to block off access the BB nuts! - but it worked out.

Hey that's great you got the brake booster pulled. I remember letting a few curse words fly getting some of those nuts off. Who knows what will go next, hopefully not the pedal itself!

[NightFlyer]

Lol...somehow I knew you'd not miss the wide open door I left for you to point that out. I'm going to be really sad if I ever hear you have to change that fluid.

It has become a mission to try to squeeze as much life as is possible from that fluid :biggrin:

Personally, I think it's good for at least another 33 years at a minimum :wink:

[Jonathan]

Precisely why I haven't touched my clutch yet - still running the Dunmurry fluid :biggrin:

Wouldn't that be Ann Arbor/POG fluid? Or did they leave that part of your car alone?


BTW, I flushed the brake systems and replaced all four flexible brake lines last year so that part should be fine.

I don't know if you already looked at your calipers, but this is the only how-to that came to mind when mentioning brake work. Not sure I've seen one solely on the booster or master (but Mark's pictures and write-up could certainly count as one!)

http://dmctalk.org/showthread.php?1939-Rebuild-Your-Brake-Caliper

[Henrik]

I am curious about the o-ring (pn 105544) between the master cylinder and the brake servo. I do realize that it is not meant to contain any leaks from the MC. So:

What then is the purpose of the o-ring?
Is the o-ring a face seal or a radial seal? Given the size of the new o-ring it kinda straddles the lip of the brake booster, i.e. it doesn't sit fully on top nor within the BB's recess; it's somewhere in between....
Check out my old MC (attached pic). Is the o-ring designed to get squeezed out like that? (I am refering to where the o-ring is drooping out of the MC's "drain" slot.)

[Mark D]

I can only guess that the intent would be to create a seal between the master cylinder and brake booster except for the area around the drain...perhaps to prevent water and debris from getting down inside through the upper edge/gap. Sealed at the top and open at the bottom since it's less likely for water to flow upward. Mine looked exactly like what you have pictured so it's not a fluke that you have a seal there.

That is a complete guess on my part, but the only thing I could think of that remotely makes sense.

[DMCMW Dave]

I can only guess that the intent would be to create a seal between the master cylinder and brake booster except for the area around the drain...perhaps to prevent water and debris from getting down inside through the upper edge/gap. Sealed at the top and open at the bottom since it's less likely for water to flow upward. Mine looked exactly like what you have pictured so it's not a fluke that you have a seal there.

That is a complete guess on my part, but the only thing I could think of that remotely makes sense.

The booster is a diaphragm with vacuum on one side of it. The other side has to be vented or it would not move. The only reason for the "seal" would be to keep water and crud from above from getting into the booster. Seal is cheap, if you don't want to wait any sealant would work as well. The seal looks like a hunk of sponge.

[Henrik]

Thanks Mark D. Makes good sense.

Dave,
Just wanna make sure I understand you:

The booster is a diaphragm with vacuum on one side of it. The other side has to be vented or it would not move. The only reason for the "seal" would be to keep water and crud from above from getting into the booster. Aha! Clever!


Seal is cheap, if you don't want to wait any sealant would work as well. The seal looks like a hunk of sponge. Now you're gettin' cryptic on me. I have the brand new O-ring from DMCH (and of course, a new MC). Should I install the MC and O-ring onto the brake booster, torque it down as normal and pretty much expect that the o-ring will automatically squeeze itself out of the groove (like in my picture above) and thereby create the "vent"?

[Mark D]

Yeah I think what Dave said confirmed my theory that the seal is there to keep junk from getting in from the top while still allowing the vent at the bottom to do its job. When you install the master to the booster the seal will compress like in the photo of your old one and push out the vent hole.

What Dave was getting at in the second part of his post was that if you didn't already go buy a new seal from DMCH that you could probably just use RTV sealant around the top and that would accomplish the same goal.

[DMCMW Dave]

Thanks Mark D. Makes good sense.

Dave,
Just wanna make sure I understand you:
Aha! Clever!

Now you're gettin' cryptic on me. I have the brand new O-ring from DMCH (and of course, a new MC). Should I install the MC and O-ring onto the brake booster, torque it down as normal and pretty much expect that the o-ring will automatically squeeze itself out of the groove (like in my picture above) and thereby create the "vent"?

Yes. I offered the alternative because the seal is pretty inconsequential and most folks are not all that enthused about shipping a $2.50 part alone.

[Henrik]

Thanks Mark and Dave!