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Junior Charter Member
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354 Posts
Discussion Starter · #1 ·
Ok..here's one for you.... After my "no Brakes" inncident, I'm all replumbed. '82 master cylinder directly fed to a T then to the front disks, same general theorey in the rear drums. 3/4 mile into the test drive seems like the front brakes locked up on their own. Had to get a wrench and open the bleeders. After getting home seems like there might still be just a bit of drag somewhere.....another day!!

Fire away!!!!!!!
 

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Premium Member
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16,561 Posts
The MC piston is not fully returning when you release it. Could be the rod is too long (add spacers), rod is binding on the side of MC bore, or the snap ring that holds the piston in is partially dislodged and is keeping the piston from returning.

Cheers, Rod
 

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Junior Charter Member
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354 Posts
Discussion Starter · #4 ·
M/c is a new one. I'll recheck free play of the rod but I think it is fine. As I said, the brakes seemed as if they came on by themselves?!?!?! I went to shift from 4th to 5th and the car bagan to stop. As I let out the clutch it almost stalled!!
 

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Senior Charter Member
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1,218 Posts
Are you sure you didn't install a drier's trainer brake pedal in the passenger side? My wife always thinks there is one in mine. :D :D
 

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section 8
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5,136 Posts
Dr Stebo , I have dents inthe floor of some of my cars from that . If its not the master something is binding, hardware caliper etc . Some masters have the residual valve for the rear brakes right in the master if you have the line hooked up to the wrong port on the master this could be the problem. I had a 66 gt that had a rust problem. If you loosen the master bolts doe the brakes free up ??? Bob
 

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ASE Tech & Shop Teacher
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1,936 Posts
Snakeski. If opening the bleeder helped, you have pressure still holding. If the builder performed the "pedal mod" as recommended for manual brake cars, and described in the build manual, he/she may have not gotten the pushrod pushing straight enough.

Check and see if the pushrod is pointed straight into, or at an angle to the stroke of the master.

Too high of an angle may have (even temporarily) tilted a piston in the master causing it to bind in the bore, hence holding pressure. If like dv/dt says the pushrod is at such an angle that it binds, re-align it.

You can often find or make a correct pivot hole for the pedal arm in the pedal box. Easier with body off, but can be done with a 90 degree drill.

If that's not it, does all re-plumbed mean all new hoses?

If old hoses, I've seen them get a kink or fray on the inside liner, and act like a one-way valve. Let's pressure in, and doesn't release it.

If new, or old hoses, you may have a hose getting pinched, you may have a hose with a twist in it, too tight of a curve in it causing it to kink.

Any of those can cause it have the one way valve syndrome.
 

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ASE Tech & Shop Teacher
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1,936 Posts
BOB, great call, I'd missed that one. If that's it, (residual check valve) You Da man!
 

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FFCobra Captain
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11,720 Posts
My bet is the snap ring is twisted. Take off the M/C and make sure it's in there the right way. The snap ring holds the cylinder in the M/C.

If it's bent, then you'll have just the slightest bit of drag on the pads. As you drive, that generates heat and the fluid expands. Because the M/C piston isn't fully released, the fluid applies more pressure to the brakes. If you let the car cool down, the fluid will shrink and you're brakes will feel fine.
 

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Junior Charter Member
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354 Posts
Discussion Starter · #12 ·
well it certainly seems like the piston sticking, but I don't see why, yet. I can see the snap ring from inside the footbox and it doesen't seem to be keeping anything from moving. I did not find the "heat soak" post but there is a lot of interesting reading out there!!! Guess I will have to pull everything apart and try again!
 

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Premium Member
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1,198 Posts
There was an earlier post about a similar issue. Are you using DOT5 (silicone) fluid? If everything mechanical is OK, may be worth looking at.

c
 

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FFCobra Captain
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11,720 Posts
I only keep bringing up the snap ring because I had the same problem as you're having to the "T". I wound up replacing fluid & calipers all the way around and was being lazy (not saying that's you) about not wanting to disconnect & remove the M/C to get a clear view of the snap ring.

On mine, only one of the ends was twisted, so the M/C was only engaged by about 1/16", but that's all it took to not let the fluid get back into it.

Unless you can see very clearly that the snap ring is flat all the way around, take off the M/C just to cross off that possible problem.
 

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Moderator
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12,662 Posts
Dan is correct in that the MC Piston MUST totally return home.. if it dont, you have a problem just like yours.


You can also get a very similar problem if your brake line gets very hot by being tooooooo close to something hot. This I dont understand, but it also can cause the exact problem you are describing.

cobraearl
 

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Senior Member
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334 Posts
Dan is absolutely correct, in fact his earlier post saved me. Pull the MC and check the clip. I had the exact same issues.

Mark
 

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ASE Tech & Shop Teacher
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1,936 Posts
Snakeski, on the lock-up issue. Most masters use the forward line routed to the rear brakes, and the rearward line routed to the front brakes.

Bob had the idea, I'm just explaining it further and reminding you to check your line routing.

Here is why it's important.

Some disc/drum cars have the residual pressure check valve in the combi-valve. BUT,
some masters made for a disc/drum system will have it in the master itself.

What does the check valve do?

It holds 10 psi on the rears to keep the little cups in the wheel cylinders from seaping fluid.

If your lines are routed wrong, you'll have pressure on the fronts which likely gave you your lock-up issue.

Please let us know what you find.
 

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Junior Charter Member
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354 Posts
Discussion Starter · #18 ·
finally got around to pulling the M/C!! Could see from the cockpit that the piston was not fully against the snap ring. When I got it off and looked I found one of the ends of the snap ring had broke off and was lodged between the piston and the rest of the snap ring. Hope that fixes all. Time to bleed it all out!!!!

Thanks again. You guys aalways have the answer somewhere in the pile!!!
 

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section 8
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5,136 Posts
that'll do it excellent .Bob
 
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