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. 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

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

[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...ht=bench+bleed
http://dmctalk.org/showthread.php?10...ht=bench+bleed
http://dmctalk.org/showthread.php?39...ht=bench+bleed
http://dmctalk.org/showthread.php?88...ht=bench+bleed
http://dmctalk.org/showthread.php?82...ht=bench+bleed
http://dmctalk.org/showthread.php?60...ht=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...ht=bench+bleed
http://dmctalk.org/showthread.php?10...ht=bench+bleed
http://dmctalk.org/showthread.php?39...ht=bench+bleed
http://dmctalk.org/showthread.php?88...ht=bench+bleed
http://dmctalk.org/showthread.php?82...ht=bench+bleed
http://dmctalk.org/showthread.php?60...ht=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-mas...der-brake.aspx


If yours is leaking it probably looks like this.






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:




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 :-)







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?72...l=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.



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-...ower-unit.aspx

And here's a photo of the bolt pattern on the back of the mounting bracket.



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

http://store.delorean.com/c-358-6-3-...ge-manual.aspx