power brake master cylinder problem?

[delorean928]

When I bought my D in last october, I brought it back home on it's own power (10 hour ride) and among the problemSSS I got, I had a problem with the braking system.
When I was stopped at a light by example, I was holding the brake pedal and after a few seconds the pedal was going down a bit. Not at the floor but deep enough to worry. I have no brake fluid leak.
I checked for vacuum leaks and no problem at the master cylinder. Lately when it was time to check this problem I tried to hold the pedal with the engine OFF and it holds the pressure well. The pedal does'nt drop down. I was planning to change the brake fluid cause I don't know how old the oïl is in there.
Could it be a typical brake master cylinder problem??? :(

[Jonathan]

Have a look at this video explaining how vacuum assist braking works.


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

It's not uncommon for it to be difficult to push the brake pedal when the car is off and there is no vacuum in place.

Your foot going to the floor when the car is running and you are using the brakes at a light or otherwise to me says you will need to rebuild your master cylinder or replace it with a new one (preferably designed for the DeLorean as the specifications are unique for our cars in terms of % going to front and back via the fluid connections).

[delorean928]

I tought that the braking system was vacuum assisted on DeLoreans :jawdrop: That's why I checked for vacuum leaks around the front of the car.
It is possible to rebuild the master cylinder??? I read somewhere that it was not. Is there a kit we can buy somewhere?

Thank's for the link for how power brakes work. I like very much these videos :)

[David T]

I tought that the braking system was vacuum assisted on DeLoreans :jawdrop: That's why I checked for vacuum leaks around the front of the car.
It is possible to rebuild the master cylinder??? I read somewhere that it was not. Is there a kit we can buy somewhere?

Thank's for the link for how power brakes work. I like very much these videos :)

First thing I do would be to flush the brake system with fresh brake fluid. You don't know how old the stuff is in there and you might also have air. If the master cylinder needs to be rebuilt you should be rebuilding all four calipers too. It is getting harder and harder to find kits anymore, no one wants to sell a cheap kit when they can use it to rebuild your old one and make more money. Try AutoZone and look up a 1986 Saab 900. You can also look at SpecialTauto for kits and parts. You might also have a bad hose and when you push on the brakes it swells the hose. If you change any you should change them all. Pull the vacuum hose off at the booster and see if it is wet inside with brake fluid. If it is, the booster has to be rebuilt/replaced. Pull the carpet and see if there is a puddle under the padding on the driver's side. Might as well also flush the clutch too unless you have an automatic.

[delorean928]

Pull the vacuum hose off at the booster and see if it is wet inside with brake fluid. If it is, the booster has to be rebuilt/replaced. Pull the carpet and see if there is a puddle under the padding on the driver's side. Might as well also flush the clutch too unless you have an automatic.

So I was right it is what we call a power brake! (vacuum assited) Thank's for all these precious infos. I was planning to change the clutch fluid.

[Jonathan]

It is possible to rebuild the master cylinder??? I read somewhere that it was not. Is there a kit we can buy somewhere?

I can only speak to what I did on my car and that was to replace the master cylinder with a new one (NOS). The one I bought is shown here on the Houston webstore:

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

I understand the brake boosters are considerably less likely to fail, but was surprised/relieved to see on the same brakes page (6-3-0) of the parts store that you can buy replacements.

I am betting it is your master cylinder that is the problem, but like David said, look at the other areas as well. Flush the fluid and then ensure it is properly bled of any air. Puddles under the car or in the drivers footwell are obvious signs.

If you do go ahead and replace various aspects of the braking system like the hoses, master cylinder, rebuild the calipers, etc., you might want to check out the kits available on most vendors websites. Josh has some great looking performance kits for sale and there was a thread on the forum here recently talking about a brake upgrade to some degree, although I'm not sure of the status of that kit.

[delorean928]

Thank's a lot for your help. I'll work on this soon and let know the results here later in case it could help someone else.

[delorean928]

Problem solved :) I changed the master cylinder and bleeded the lines and the car brakes very well :)
Thank's to all for the help and infos!

[Timebender]

Needing to resurrect this, as my breaks are suddenly not braking without a lot of force. I did check my carpet today- after testing the car a few days ago, and the carpet feels damp- not wet, below,the pedals. Could be it's just needing a good cleaning as I didn't feel any wetness there or at the bottom of the floor. I recently did some work on my engine - a Chevy 350, and could swear I hear a vacuum leak somewhere - engine runs a little rough, and when I took it for a test soon there was a lot of hesitation when accelerating, plus the car was a lot harder to stop.
So where is the booster exactly, and where does the line end up in the engine compartment? I've only really had the car about a month and have been attacking little issues one by one.

Thanks!

Greg

[sdg3205]

Remove the access panel under the hood with the rubber plug to access the master/booster. Vacuum taken off right plenum of intake IIRC.

Brake master won't leak into cabin, but the clutch will if you have a 5spd.

[Timebender]

Yeah I saw the big panel that you can get to the master cylinder - interestingly my master has a sensor on the cap of the reservoir, which I've never seen on other DeLoreans. That's the one?

[Timebender]

Remove the access panel under the hood with the rubber plug to access the master/booster. Vacuum taken off right plenum of intake IIRC.

Brake master won't leak into cabin, but the clutch will if you have a 5spd.

I had mentioned the moisture as someone on another thread said if the booster was bad, brake fluid would end up in the driver footwell.

[sdg3205]

All deloreans have that switch. It's the low fluid switch. It operates via float.

Yup, that's what you're looking for.

If you suddenly have a soft pedal, check your fluids first. Perhaps you're low and your brake light is burnt out? Or perhaps the harness wasn't in place on the resovoire cap?

Edit - technically they are correct. The clutch uses the same "brake fluid." Aka dot 4. But the brake doesn't leak into the car as far as I know. Only a failing clutch master will.

[Timebender]

All deloreans have that switch. It's the low fluid switch. It operates via float.

Yup, that's what you're looking for.

If you suddenly have a soft pedal, check your fluids first. Perhaps you're low and your brake light is burnt out? Or perhaps the harness wasn't in place on the resovoire cap?

Edit - technically they are correct. The clutch uses the same "brake fluid." Aka dot 4. But the brake doesn't leak into the car as far as I know. Only a failing clutch master will.

So as I thought, due to a higher than loud whooshing sound in my engine compartment along with a rough idle (and acceleration problems like the engine has the choke on), there's a hose going from the intake manifold now to nowhere... there's a hard line on the passenger side of the engine bay, and one on the driver side - I'm guessing one is for the brake booster and the other for the hvac control knob/valve in the cabin, as turing that gets no external air (vent mode) into the car.

The hose coming off the engine is larger, and it can almost reach the hard line on the passenger side, but even if it's close it's too large of an opening. Could be there was a connector between it and the pipe. I'm assuming since it looks like a brake line, it could be the one to the booster (though odd it's on the right).

Or it could be the other, but I know it's best to take the vacuum from the intake vs. off the carb manifold for the brakes.

If I plug it the engine runs smooth as silk (surprise..).

Which pipe does what? I can hook up another smaller vacuum T'd off something for the one on the driver side. Or run the big line to it with an adapter/stepdown.

Greg

[sdg3205]

So as I thought, due to a higher than loud whooshing sound in my engine compartment along with a rough idle (and acceleration problems like the engine has the choke on), there's a hose going from the intake manifold now to nowhere... there's a hard line on the passenger side of the engine bay, and one on the driver side - I'm guessing one is for the brake booster and the other for the hvac control knob/valve in the cabin, as turing that gets no external air (vent mode) into the car.

The hose coming off the engine is larger, and it can almost reach the hard line on the passenger side, but even if it's close it's too large of an opening. Could be there was a connector between it and the pipe. I'm assuming since it looks like a brake line, it could be the one to the booster (though odd it's on the right).

Or it could be the other, but I know it's best to take the vacuum from the intake vs. off the carb manifold for the brakes.

If I plug it the engine runs smooth as silk (surprise..).

Which pipe does what? I can hook up another smaller vacuum T'd off something for the one on the driver side. Or run the big line to it with an adapter/stepdown.

Greg

I'd have to double check but I think the vacuum line off the right intake plenum joins a T-junction.

[Ron]

Greg, check out #50 thru #54 here- http://store.delorean.com/c-365-7-3-0-electricalmechanical-controls.aspx

[PJ Grady Inc.]

I can only speak to what I did on my car and that was to replace the master cylinder with a new one (NOS). The one I bought is shown here on the Houston webstore:

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

I understand the brake boosters are considerably less likely to fail, but was surprised/relieved to see on the same brakes page (6-3-0) of the parts store that you can buy replacements.

I am betting it is your master cylinder that is the problem, but like David said, look at the other areas as well. Flush the fluid and then ensure it is properly bled of any air. Puddles under the car or in the drivers footwell are obvious signs.

If you do go ahead and replace various aspects of the braking system like the hoses, master cylinder, rebuild the calipers, etc., you might want to check out the kits available on most vendors websites. Josh has some great looking performance kits for sale and there was a thread on the forum here recently talking about a brake upgrade to some degree, although I'm not sure of the status of that kit.

It is often pointless to rebuild the brake master unless you have the cylinder sleeved first. The cast iron bore usually is pitted so it must be sleeved to achieve a smooth sealing area. We have brass sleeved units that will last longer than new ones. Brass is self-lubricating which means there is much less chance of the seal sticking to the bore surface causing a torn seal on cars that sit for extended periods. Brass is not susceptible to pitting the way iron is. We also offer it with a cleaned reseviour as these tend to hold debris and are also hard to find nowadays. We do all our rebuiling inhouse to assure the quality of these and other safety critical parts.
Rob