In the course of discussion I feel it might be useful to have a diagram or two…
Mine too Mike, mine too…
I tried that and the brakes are sh** without the booster so if you do be sure to leave a lot of distance!
Yes, Michael, I understand not liking to do things twice. 400 miles, obviously not even used. Four years- if that was mostly sitting, yes, that can be a problem, especially depending on the environment. And fluid should still be changed every 2-3 years, which maybe you have. But even under poor conditions, one would think it would at least go 4 years. And you did say the problem was even before now. I do not like blaming bad quality parts, but maybe that is the case. I just keep rebuilding the old. I have had the same M/C and servo since 1981, just keep rebuilding. Maybe they are original. But the car is used every year. And I do not mind a few pits in the bore.
Tom
Michael
It won’t be an engine bay heat issue. I thought my MC issues were caused by heat, but they weren’t.
The notion that it’s heat is driven by the fact that the issue often doesn’t manifest itself until you have been driving for some time. I think that the heat is a condition that just aggravates the underlying fault. Once you address the underlying fault, the heat is no longer an issue.
By the way when I pulled the MC it looked perfect inside, it wasn’t until I put the seal kit in that the stiffness was apparent. I did give a light hone to the bore.
Cheers
On the basis that you didn’t report half a reservoir bottle of brake fluid having chewed into your paintwork and that you reported losing half a reservoir of brake fluid, you already know that your seals don’t seal.
kind regards
Marek
I still have the binding brake problem and it’s clear that it only occurs when the engine compartment is hot. Tomorrow I’m going to wrap the master in some kiln type insulation and take the car for a 20+ mile drive. If the brakes don’t bind then I’ll remove and disassemble the master and check the nylon spacer, which, based on conversations on this forum and beyond, seems to be the culprit. It’s just too tight.
So, assuming the weather plays ball for me over the next few days, I’ll give it a try and let y’all know what happens.
The leak was due to poor sealing between the bottle and hose. Any fluid fell onto the aluminum closing panel, so not a problem. I mentioned it for completeness, but it’s not relevant to the problem. I rebuilt the master yesterday. The spools, particularly the large one, are very tight fitting. But I don’t think it’s bad enough to explain the problem. I did find some ridges on the flapper bit, but that fits so loosely, I can’t imagine that was a problem either. The plastic keeper at the end of the assembly isn’t a tight fit, and I didn’t get a new one with the kit. But I can’t see how that could cause the problem. So maybe with the new seals it will work better, maybe not. I’ll get it installed later and we’ll see.
Sigh!! So the rebuilt master works perfectly. Smooth as silk when I bleed the brakes, good strong flow. Fully installed, the reaction valve is working perfectly according to my vacuum gauge. The pedal is firm, a little more free travel than I will eventually allow, but fine. I go down the road a mile, tap the brakes down a little hill and the car comes to a full stop at the same place it always stops. After a little while, the brakes unlock. There’s nothing on the vacuum gauge to suggest that the slave is locking up. So once again, I’m stuck. The only clue is that the left front brake is hotter than the others. As it happens, I have a caliper rebuild kit and a spare set of brake cylinders on the shelf. I /m going to throw that in and see if it makes a difference.
Michael,
Did you back off the adjusting screw I mentioned a few posts back?
Given that you put a new master cylinder in, and given that you say it is not vacuum related, it may be that the new master cylinder piston is prevented from completely retracting (by the adjusting screw) and is keeping fluid locked in the master cylinder and not letting it vent back into the reservoir when you release the brakes.
Dennis 69 OTS
If that was the case, the pedal would be firm throughout it’s range. It has a little free play at the top, as it has always had. Which suggests that the pedal adjustment isn’t the problem. But I’ll give it a look tomorrow.
If it is absolutely not vacuum, then it may be the master cylinder seals swollen a bit or plastic bushing which prevent the piston from retracting completely. If it does not retract completely because of internal problem you will still feel the little free play that you do
Maybe try the following when the brakes are next locked (from past post)
Put a string on your brake pedal. Take the car for a drive and when you feel the brakes stick, pull the string hard to be sure the brake piston is all the way back. If the brake sticking goes away when you do this, the problem will be fixed when the stiff piston retracting problem is fixed
The pedal shaft isn’t bolted to the piston. So pulling on the pedal won’t retract a stuck piston. The bolt takes up the free play, so there may be value in adjusting it to completely eliminate movement. Then if the MC locks, the pedal will become loose. But based on the way it feels, I’m really inclined to think that it’s somewhere else. What I think I’ve eliminated so far is the master cylinder and the vacuum servo. It could be the slave cylinder or a sticky caliper. I’m just not relishing pulling the servo and slave unit, otherwise it would already be out of the car and apart on my bench. Anyway, considering how hot the brakes became, tearing down a caliper for inspection seems like a good idea.
I am not quite understanding. I suggest that (as a troubleshooting test) if you put a string on the pedal and pull it back when the brakes are stuck, that if the piston is stuck in the master cylinder, this will pull the piston back and expose the hole that fluid (which is locked into the brake circuit) can vent back to the reservoir thus releasing the locked brakes.
Dennis, Michael is saying when your string pulls the brake pedal back up, it will simply pull the push rod away from the MC piston. The rod is not attached to the MC piston, thus the rod/pedal will not pull a stuck piston back out.
Michael, I would once again suggest disconnecting the vacuum at the intake manifold. But, if not, I believe you are reporting that you can see your vacuum gauge while driving, and when you apply the brakes, the vacuum drops and as soon as you leave off the pedal, then the vacuum returns to its max reading, about 20 inches.
How much hotter is the left brake than the other three?
Tom
You are so right
Apologies for this wrong track
The left front is about 100F hotter than the right, 400 vs 300. That’s worth looking at.
I have the gauge plumbed into the rear section of the servo. When the servo is engaged, the vacuum reading drops (pressure increases) in proportion to braking effort. When the brake is released, it returns to about 20 inches, which is where it stays while the brakes remain locked. So unless there’s something I’m not getting. the servo isn’t a factor. That doesn’t eliminate the slave cylinder itself, but I don’t think there’s a problem on the vacuum side.
Michael, as before, your vacuum test results do seem to indicate that is not the issue. Agreed, the 400 vs 300 does seem to be a significant difference. How quickly are you reaching theses readings? I checked mine recently, and after a long, but casual drive, mine were only 170F or so. So may not be comparable, but are they both hanging up, since maybe both are high. Or were you just using them more? Is one 100 F higher, or just tough to get good readings on shiny metal? With both hanging up, I am still looking at the slave. Just one hanging up, then, with you on the caliper (or hose but you indicated it was recent.) (As a side, I assume you are calling the servo the vacuum booster, and the slave the hydraulic portion of the booster assembly. I typically call the whole thing the servo. We all have different terms, and I just do not want to confuse myself with the terms.)
Tom
Tom
I think both sides are too hot, considering that I only went a couple of miles at most. So some common component would seem to be the problem. Nevertheless, I’m going to start by rebuilding the left caliper, only because I have a kit left over from another project. I suspect I’m going to have to drop the servo/slave assembly before I’m done, I’m just procrastinating.
I don’t know if this has been mentioned, I haven’t read all the posts; how confident are you that the flexible hose on that side is in good condition?