Replacing Master Cylinder--Need help!

[Andy Ring]

Help. I'm replacing my master cylinder in a 1972 T because it was leaking. I followed the advice on this site, and all seemed to be going slow, but well. I finished installing the new master cylinder about an hour ago. Along the way, I installed speed bleeder values (with the check valve built-in) and then bleed the brakes. My car is still up on jacks with all the wheels removed.

Ok, so here's the problem, I cannot rotate the front wheels easily. Is this a problem. Before I swapped the MC, the wheels would spin relatively easily by hand. After the work described above I could not spin the wheels by hand. Then I used a 2 foot wrench wedged through the lug nuts and could barely turn the wheels using all my strength. Is this normal right after the work I've done (i.e. temporary) or is this a symptom of something wrong.

I don't want to but all wheels back on and lower the car until I know.

Thanks for your quick input.

Andy

[}{arlequin]

could be your brakes dragging, badly... maybe the new master has issues and is not releasing pressure?

one thing you could do is to take off the wheels and have someone pump the brake pedal while you look at the caliper pistons/pads and see if they are retracting.

maybe you should pull the pads, retract the pistons and start to check again?

[911mot]

Remove the nuts holding the master cylinder on. Leave the pipes attached. If the wheels now turn then the problem could be the linkage behind the cylinder needs adjusting. How much pedal travel is there?

[Early_S_Man]

Andy,

First, be sure the proper 1.0 mm gap exists between pushrod and piston! If the gap is present, then what follows is important: It sounds like your old flex hoses are bad and acting like one-way valves. They need to be replaced, and you don't need the fancy stainless ones, either!

Normally, after applying brakes and parking ... the wheel or rotor should free up after one-half to one turn with medium drag, then it should turn freely.

[Andy Ring]

Thanks everyone for the advice. Some further info/response:

1) The car is still up and the wheels are off. I am alone. Pumping the brakes and releasing would not do anything since the front pads are hard up against the rotor. Same with removing the pads--I don't think I could right now because of how locked up the brakes are.

2) Regarding the pedal. The back wheels spin freely. Wouldn't this imply that the adjustment is correct? Also, it seems like there is a small amount of travel before the pedal engages the MC, then the pedal moves another half inch before becoming firm.

3) Regarding the brake lines. They seem to be ok. I actually have replacement stainless ones ready to go in, but I checked out what was there and decided to wait because they looked good.

Just to clarify, I have not rotate the wheels a full revolution because they are so hard to turn I have maybe just rotated them a quarter turn. I could put all the wheels on and lower the car and try to take it for a drive, but the brakes seem so engaged that its hard for me to believe they would release. Am I just inexperienced?

Thanks,

Andy

[ianc]

You can't tell by looking at the rubber flexy lines whether they're bad or not. When they get old, they swell inside and can have difficulty releasing pressure.

Are both rears free turning, but both fronts not? Follow MOT's advice, or just change to the new front stainless lines and report back,

ianc

[FrayAdjacent911]

Wow! Something I've actually DONE on my car and can comment about!!

Did you rebuild your brake calipers? I bet they're getting sticky, and should be rebuilt anyway. The seals and dust baffles wear out. Mine were pretty dang worn. Not to mention one of the cylinders was cracked and one piston was pretty messed up. I was given a pair of good calipers by another Pelicanite for a good price.


Added

Since you're doing the m/c on such an old car, you might as well do it all. (that's the way I think about these things!) I'd rebuild all four calipers, and replace the brake lines. My lines were old, but not bad, and my rear calipers were stuck and pretty much weren't helping at all. Unless you've done those things before, I'd suggest you commit to having the peace of mind knowing your brake system is in tip top shape.

[johnsjmc]

You can see if the front hoses are internally blocking fluid return to the master by "cracking" the front bleed valves .If the wheels now turn then your hoses are plugged . If they still are stiff then your calipers are seizing.

[petrolblue83911]

Not that this guy shouldnt consider rebuilding his entire brake system, but,

-did the wheels spin before you replaced the MC?

-did the front brakes stick before you replaced the MC?

-if not, I seriously doubt that all of a sudden either failed. Especially since you've probably already drained and then bled the system with fresh brake fluid.

-if you are confident that the MC is in correctly and that all the lines are properly attached, I'd get it down on the ground, fire it up and just drive it a few feet forward and backward. Then, jack it back up and see if the brakes have released. if they don't, then clearly you do have a problem, and then look at the calipers, pads, lines etc..

Good Luck!-I went through this last winter with my 914, -not the most fun project, but you'll learn alot about the brake system by the time your done!

Good luck!

[Andy Ring]

Once again, thanks everyone for your advice. Its raining cats and dogs here (Montauk, NY) and I am without a garage, so I'm not going to be able to make any progress today. However, here's an update: I put the wheels back on and lowered the car and drove it last night. The brakes released after some driving, but anytime I used them they got stuck again for a least another 100 feet and then released. Very noticable at low speed like if you are at a stop sign. I only drove around the block, so I don't know if it will improve with a little more use (like twice around the block).

Regarding some of your questions above: Both rears spin freely and both fronts don't (at least that was what was happening when the car was up on jacks). I tried opening the bleed valve when the wheel was frozen and no fluid came out and the calipers didn't release. Bear in mind that I also replaced the bleed valves with the type that have a built-in check valve (did this yesterday). Could that be causing the problem?

I'm a little puzzled about the lines/calipers since they seemed to work before I replaced the MC yesterday. I didn't replace the lines with the stainless ones I have because I know I will need to rebuild the calipers soon and I figured I would do that then and I just wanted the car back on the road for the dog days of summer (probably a mistake in retrospect).

Also, checked the free play of the pedal and it seems that there is at least 1mm of play before it engages the MC.

Anyway, thanks again...

[}{arlequin]

i'd guess it's the lines swelling/collapsing... it's a warning system of sorts, which also lets you know the age of the lines, which is why they're favored by some over the stainless lines (not to mention the price diff.)

i had a similar problem, even on an incline the car wouldn't roll, b/c something was keeping the pressure on, after driving sometimes 2, 3, and even all 4 wheels were hot, which meant that the brakes were dragging.

i figured it can't be all 4 calipers or lines failing AT THE SAME TIME, so i guessed it was the m/c. it was. after replacing it everything went back to normal.

if the rears spin but not the fronts, replace front lines and see what happens

[DW SD]

My first thought it: Does the piston on the MC return when you remove pressure? If it does, it seems that the front calipers are hanging up.

Brakes are SO important, seems like a good time to go through everything? If you had a resulting accident, you'd kick yourself for not doing everything.
My $0.02.

Doug

[Trefor]

Whatever the solution it definitly sounds like pressure is not release correctly for your front circuit.

Was everything clean before, during & after installation. Ie any dirt in MC, lines or calipers is real bad. Disasemble & flush lines with new fluid.

Is this happening to both front calipers? We're the caliper pistons retracted before inserting new pads? Remove pads, note position of pistons. Pump the pedal once! Check pistons, did they move??

Push pistons back into bores, try pump test again. NOTE: keep fingers clear of pistons, very high pressure. & Don't pump to many times as pistons will fire out of caliper.

If during any of that you notice a piston stuck, you have to get the calipers rebuilt.

[Bill Verburg]

It may be that the tipping valve is not working properly. When pressure is relieved on the brake pedal the actuating rod releases pressure on the m/c pistons allowing them to push back, the front wheel circuit has a valve tipped by the piston for the front circuit on it's way back. This releases pressure and fluid flows back to the m/c reservoir.

Check to see that fluid returns to the reservoir is refilling.

Of course the rubber lines may(probably are) still be swollen internally and the caliper pistons may be corroded as well.

[petrolblue83911]

it's interesting that when you open the bleeder valves that you cant get fluid to flow out of them...this would lead me to believe that something is amis with the MC or the proporting valve?

[Bill Verburg]

no p/v in a '69 or '72

[ianc]

it's interesting that when you open the bleeder valves that you cant get fluid to flow out of them...this would lead me to believe that something is amis with the MC or the proporting valve?

Or that the calipers need rebuilding...

ianc

[Walt Fricke]

The only time I had anything like this happen it was due to new stainless pistons being a hair too large. Hardly your problem. And you had no reason to mess with the calipers/rotors/pads when replacing the MC.

I'd remove the special bleeder entirely to see what fluid appears (just in case somehow those play a role in this, however unlikely - you could also just reinstall you old bleeders to check this part out also but it shouldn't matter). Remember, it takes some pressure to push air or fluid past those special bleeders. If none does, compress a piston (using whatever you usually do when changing pads, or channel locks against the caliper and the pad ears). (This is a quick and dirty way of bleeding at the track, minus removing the bleeder altogether - crack the bleeder, squeeze, squirt, retighten). If they move the way you are used to from brake pad changes, and fluid comes out of the bleeder hole, the pistons most likely are not stuck. If stuck, pull the calipers and rebuild them.

Put things back together and get them stuck again. Remove the rear (closest to the MC) connection of the flexible line. See what happens (other than fluid runing out of the MC side of the line - have a rag or cap handy, and if none does that is a clue too). If you have the "old rubber line flap forms a one way valve" disease, this should demonstrate it. Besides, you were going to replace these lines anyway. Do it when done here.

If everything seems to be working properly out here beyond the MC, then it pretty much has to be the MC. That also would explain the fact that both fronts acted up at once. The only other change that connects both fronts is the bleed valve change, and it is really hard to see how this could have anything to do with any of this. I put this most likely problem last because it is the hardest to deal with (swapping an MC in a non-power assist with the MC down under is a special kind of pain).

The MC has two pistons inside, one in front of the other. When retracted each uncovers a hole in the MC bore which connects directly to its tube up to the reservoir. Something (and not the most likely - an actuating rod set too long, because you checked on that with the free play) is preventing the pressurized fluid from rising back up in the tube to the reservoir. It only moves a little way up, but move it must.

Possibly, when reinserting the nasty rubber plug which holds the reservoir line end for the front brake circuit into the MC, something got kinked shut?

The two MC pistons are not joined together. The actuating rod presses on the rear piston, moving it forward. When it passes the reservoir hole, pressure starts building. This pressure not only operates the rear brakes (I think that rear on the MC = rear on the car, but I could have that backwards - easy to tell when down under there looking at the lines, harder to remember), it also pushes the front piston forward (there is a solid piece in there too, but that only comes into play if the rear piston fails to generate pressure, so you at least have front brakes). The front piston then covers its hole, and so on. The front piston has a spring in front of it, which causes it to retract when no longer pushed from behind. I think there is also a spring between the two to push the rear piston back, but looking at an exploded diagram is worth many words and beats memory for accuracy. And as I recall somewhere in here there is a bolt coming in from the side which sticks into the cylinder and prevents the front piston from coming too far back.

What could prevent the front piston from retracting far enough to uncover the hole? Maybe the spring is screwed up or even missing. Debris under the piston (which has a rubber cup doing the sealing)? Hard to say. The reservoir hole could simply have debris in it. But the MC is new!! Well, yes. A shop owner buddy once cautioned me to pull apart new MCs and clean them out. He said he'd found all kinds of stuff in there on occasion, left over from the manufacturing and assembly. I once found some little white plastic bead-like debris from who knows where, I think in a caliper when rebuilding it. I thought of what he had said (and I had ignored) when I found them.

So the final step, if you get there, is to remove the MC and either replace it with another one (or your old one? did that actually fail, or was this one of those "it is an old car" things) or disassemble it, check that the reservoir passageways are clear, clean it out with brake cleaner fluid, relube (brake fluid should do if you don't have a tube of hydraulic fluid grease), and maybe figure out how to check and test the MC without having to reinstall it.

If you don't have a diagram, make one as you pull parts out so you can get things back in proper order, facing the proper way, and so on.

Just suggestions, of course.

Walt Fricke

[Bill Verburg]

the tipping port is at 26



another possibility is that the stop screw/bolt #8 was mis adjusted somehow on initial assembly

an exploded view of the m/c

[Andy Ring]

First, thanks all for the time you have spent helping me out. Nothing is more fustrating than setting out to "fix" your car and ending up hours later having actually made negative progress. In this case misery does love company--at least I now have a path out of the darkness--although it may involve pulling out the *&#! MC again which was no fun in the first place.

One final piece of the puzzle which just occured to me and seemed benign at the time. When I removed the original MC (which was leaking), I noticed that the safety switch on the new MC had different electrical hook-ups (it only had one terminal, whereas the old one had 2). So, I just swapped them putting my old switch into the new MC. When I did this, I did a cursor look at them to make sure they were compatible. However, all this talk about the tipping valve and internal workings of the MC is getting me to think that perhaps it was longer and could have affected things.

Anyway, I will do some work tomorrow and get back to you.

Andy