What does "excessive brake fluid pressure" mean?

[Johnny]

What does "excessive brake fluid pressure" mean?

My BJ7 is now roadworthy but I have a serious problem with the rear brakes. All is fine at startup, when I drive even as little as around the block I notice the brake pedal becoming very stiff, I mean hard as a rock! When I start a drive the pedal freeplay is fine but as I proceed the stiffer the brake pedal becomes. Eventually the brakes start to overheat. It seems only the rear brakes are affected. I jack up the car and you can't even move the wheels by hand, the front brakes are fine, wheels move fine. I've adjusted the rear brakes, by backing out the rear adjusters, and all is well again. I might add that the brake lights come on and stay on. I've bled the rear brakes twice now and do not notice a problem. In fact, once the car sits for awhile the pressure releases and all is fine again.
What could be causing this problem?
Thank you in advance.

 

[GregW]

Re: What does "excessive brake fluid pressure" mean?

I would guess that the brake lights are a different problem and may have been staying on longer than you think. I'd check the rear flex line where it branches to the rear wheels at the axle. It may have deteriorated inside and formed a valve of sorts that keeps the brakes applied. If it is an old line, I'd just replace it.

 

[anthony7777]

Re: What does "excessive brake fluid pressure" mean?

johnny, sorry to hear about your problem, you may have a master cyl. pushrod out of adjustment, or vent hole in the reservoir vent cap clogged, wheel cylinders might be bad staying on, brake shoe springs bad/broken or installed incorrectly, or even the handbrake over adjusted, as you know i also own a bj7, dont ask how i know, good luck.

 

[Johnny]

Re: What does "excessive brake fluid pressure" mean?

I would guess that the brake lights are a different problem and may have been staying on longer than you think. I'd check the rear flex line where it branches to the rear wheels at the axle. It may have deteriorated inside and formed a valve of sorts that keeps the brakes applied. If it is an old line, I'd just replace it.

Yes, the brake lights were staying on before so I replaced the brake switch and all was well again, however, now there on again due to the excessive pressure build up. The rear flex line is new as is all the brake pipes.
Thanks for responding Greg.

 

[Johnny]

Re: What does "excessive brake fluid pressure" mean?

johnny, sorry to hear about your problem, you may have a master cyl. pushrod out of adjustment, or vent hole in the reservoir vent cap clogged, wheel cylinders might be bad staying on, brake shoe springs bad/broken or installed incorrectly, or even the handbrake over adjusted, as you know i also own a bj7, dont ask how i know, good luck.

Interesting you mentioned the vent hole. The cap won't tighten by hand, must be stripped out, but it does tighten enough to hold on. I replaced the inner rubber seal and slit it to provide an escape. I don't remember checking the hole though. I also thought it might be the master cylinder, but wouldn't that affect the front brakes as well?
Oh, I forgot to mention the wheel cylinders are new as is all the brake pipes and hoses.
I will check the brake springs and the mounting of the rear cylinders, if I recall they were a bear to get on.
It's odd that if left overnight all is fine. I've pumped the brakes many times to try and get them to fail to no avail. Only when I drive the car, at first all is fine, even without using the brakes I can feel the brake pedal firming up. Really strange, what's going on here?
Thanks anthony for responding.

 

[GregW]

Re: What does "excessive brake fluid pressure" mean?

I also thought it might be the master cylinder, but wouldn't that affect the front brakes as well?

Oh, I forgot to mention the wheel cylinders are new as is <span style="font-weight: bold">all the brake pipes and hoses</span>.

Did you replace the lines from the reservoir-to-MC? Those pipes connect to the front of the MC (the pipes that go to the brake cylinders are closest to the firewall).

 

[bob hughes]

Re: What does "excessive brake fluid pressure" mean?

Just a couple of ideas, and shooting from the hip, as I do not have the manual in front of me.

Isn't there a pressure regulator to the rear wheels? at the junction where the front and rear lines come together, it may only be a 3 or 4 way junction, not sure, the idea being to send most pressure to the front. If this has gone pearshaped or there is a blockage it could be the cause of a pressure build up to the rear wheels, taking pressure and not releasing it immediately.

Alternatively, there is a brake pressure switch in the line that controls the brake lighting system, this could have disintegrated sending rubbish into the line causing a jamb some where.

I would suggest that you blow out the lines and see what you get in the jar.

By the way are you running with a servo? and were the lines and in line brake fittings new?

Bob

 

[Randy Forbes]

Re: What does "excessive brake fluid pressure" mean?

If it only happens when the engine is running, I'm thinking there is a problem with the servo, though I can't explain how the fronts are escaping the pressure build-up.

Don't you just love these cars; if there're two (2) ways for a part to fail, it will do both?!

 

[anthony7777]

Re: What does "excessive brake fluid pressure" mean?

randy, yes a servo problem came to mind but my 63 bj7 does not have one and i dont think any of them did, unless perhaps he or a p.o. had one installed? or later bj7's had them?

 

[GregW]

Re: What does "excessive brake fluid pressure" mean?

randy, yes a servo problem came to mind but my 63 bj7 does not have one and i dont think any of them did, unless perhaps he or a p.o. had one installed? or later bj7's had them?

I believe they were an option for the BJ7s. Later with the BJ8s, the servo became a standard part. The servo output goes to a brass fitting and branches out to all the brakes from this single source. So a servo issue pretty much has to affect the entire system, not just the rear.

 

[Johnny]

Re: What does "excessive brake fluid pressure" mean?

Yes, all brake lines, hoses etc. are new. I did rebuild both clutch and MC.
Thanks for considerations.

 

[Johnny]

Re: What does "excessive brake fluid pressure" mean?

randy, yes a servo problem came to mind but my 63 bj7 does not have one and i dont think any of them did, unless perhaps he or a p.o. had one installed? or later bj7's had them?

I believe they were an option for the BJ7s. Later with the BJ8s, the servo became a standard part. The servo output goes to a brass fitting and branches out to all the brakes from this single source. So a servo issue pretty much has to affect the entire system, not just the rear.

You're correct, it was an option and my car doesn't have one. I did replace the brake light pressure switch and that now works okay, unless of course I drive the car.

Good idea about the pressure balance connections. I could have them wrong. I'll check them with my BN7.

 

[gblawson]

Re: What does "excessive brake fluid pressure" mean?

I don't know if it might be similar, but in the bottom of my MC on a '53 TD, i have a tiny vent hole the size of a pin...it was clogged and the system built up back pressure and wouldn't release...kept getting tighter as i used them....? Don't know if there is a similar hole or not in AH MC? I had to search for it and clean it out with a pin.

 

[Johnny]

Re: What does "excessive brake fluid pressure" mean?

:frown: Boy, this problem just keeps on frustrating. I know I'm going to be so pleased when it's found and fixed. But, until then here's the latest update;
" As you know I have a working BN7 so from time to time I use it for comparisons. So I double checked the brake pipe connections at the 5 way switch with those of the BN7. Unfortunately they all matched the BN7." I also removed the rear brake drums and double checked the (new) brake shoe locations. I really didn't see anything out of the ordinary (remember, the brakes work fine until I drive the car) but I reversed (switched ends)on the non-pushing (trailing shoe)anyway since I had them all off. After I reassembled them I gave the brakes many hard pushes trying to set them, per the manual. All worked perfect. Lowered the car down and went for a drive. I didn't get around the block till I noticed the brake pedal getting harder and harder as I drove What can it be? Of course as usual after returning to the garage the brakes are almost fully on. The next morning all is well again.

My next step is to take out the MC pushrod and see what's going on there, unless some of you might be able to offer another suggestion.

 

[Shane]

Re: What does "excessive brake fluid pressure" mean?

Hey John,

This is a wild stab, but is there anywhere where the exhaust pipe crosses under the brake line? If so, maybe there's a heat shield you could try. I guess if you let it idle for a few minutes then tried the brakes, if they harden up, then that might give you another direction to look in.

I'm off on Friday, I could come over and brainstorm if you want...

Shane

 

[bob hughes]

Re: What does "excessive brake fluid pressure" mean?

Johnny

If the fluid is expanding due to heat, it should fill up the fluid resevoir and not cause a problem.

When the rears tighten up, have you physically checked the fronts as well? If they are still free then logic would say that the problem is after the 4 way union and not related to the MC.

The back cylinders are free to slide on the back plate I pressume that they are free?

Have you tried releasing pressure from the rear bleed nipples once you are locked up? If there is a problem in the line, this would show it, you either get fluid out and the brakes relax, or nothing comes out, then you could rule out mechanical and concentrate on the lines and rear cylinders, though if both back wheels are locked it is more lightly to be the lines.

Just an idea - before I got my Eeezee bleed I used a 4 inch length of clear 1/4 inch poly pipe mated to a about 2.5 metres of 1/8 inch poly pipe and slipped it over the nipple. The 1/8 inch pipe was draped up and over a lamp stand so that it was above the level of the Resevoir and dropped down to the collection pot on the floor, release the nipple and pump the pedal slowly, fluid would travel up to the top of the pipe on the stand. Stop pumping and the level would drop back to even up with the resevoir - a cheap way of removing air without too much fluid loss. Do this when the brakes are locked, if the fluid does not drop back quickly then problem is in the hydraulics for sure.

Bob

 

[Johnny]

Re: What does "excessive brake fluid pressure" mean?

If I remember the brake lines are on the opposite side. Of course you can come over, anytime. Call first though to make sure were home.

 

[Lin]

Re: What does "excessive brake fluid pressure" mean?

I don't think that there is any relationship, but I will offer this thought. When I put disc brakes on the front of my 59 Bugeye, I worked carefully to make sure that everything was adjusted properly. However, when I drove the car the exact same thing happened that you are experiencing. Eventually, in the Bugeye's case,I discovered that there was a check valve in the master that must be removed when converting to disc brakes.
Lin

 

[Johnny]

Re: What does "excessive brake fluid pressure" mean?

Thanks Lin, that does give me an idea though. Looking back through my records I don't see any MC purchases listed, or even rebuild kits. So, it's possible I didn't do anything to the MC. I don't know why but the front brakes aren't affected and work fine. Again I pulled the rear hubs off and checked the springs. Strangely, the manual ( in the MMM)section call for two types of springs the shorter spring should go near the brake adjuster. MOSS lists only one type of spring and you'll need 4, that's what I have 4 springs all the same size. I'm really beginning to think the MC is at fault.

 

[GregW]

Re: What does "excessive brake fluid pressure" mean?

Hi Johnny,
Looks to me like one of your shoes is installed backwards. That looks like the left side brake. So the shoe on the left in the photo should be flipped so the leading edge is at the adjuster. The leading edges on the other side of the car will be mirrored as you sit looking at the assembly.