19 replies to this topic

[evl666]

Lc torana with a total rebuild. Overhauled calipers, new seals in the master cycling we and perfectly working brake booster. New lines as well. If I drive it for say a 5 minutes the brakes work fine but then if I drive it a bit long the front brakes start to lock on. I’ve adjusted the brake booster clearance and like I said it works fine till it gets drive a bit further than a few kms. Got me stumped

[Kevrev]

You don't happen to have a 4 wheel drum brake master cylinder fitted by chance?

There's a residual pressure valve needed for drum brakes that keeps about 10lb of pressure in the line.

If there's one fitted to the front brakes it would cause the front brakes to lock on.

The valve is fitted under the brass seat that the brake line seals on.

 

https://www.freeases...heck-valve.html

[evl666]

When the master got new seals and pistons I pulled the olive out out and made sure it was a disk/drum configuration. About after an hour after pulling up at home the brakes have unlocked. They weren’t totally locked on but really tight.....just managed to push it by hand in the garage

Edited by evl666, 19 July 2019 - 09:39 PM.

[LJ RB30]

When they are locked on pull  the vacuum line out of the booster & see if they release.

[DMLC71]

Might be an idea to see if the booster push rod is the correct length
Cheers

[S pack]

Were the calipers with new pads fitted a very neat fit over the rotors?

[liswar2]

Booster push rod , was my problem in the past with a rebuild , as there is a difference between lc and lj length ,
Depends on which you have ,
My brakes did the same thing , so swapped the shorter push rod for the longer version , problem solved ,
Yes big nut master cyl and double diaphragm booster.

[holdentoranaman]

same thing happened after paying reputable person to rebuild big nut master .apparently a bad batch of seals requiring push rod to e slightly shorter to clear port.when it happens loosen 2 nuts holding master cylinder to booster to see if thats the problem.

[evl666]

Sorry guys....I’ve been busy but haven’t had a chance to touch the car. At the time I unscrewed the master from the booster and it made no difference so it’s not the push rod length. Yes the pads and discs are new and were a tight fit but still spin freely when cold. I’m going to take it out for a short drive and see if I can get to to lock on then have another fiddle.

[Potta]

Sorry guys....I’ve been busy but haven’t had a chance to touch the car. At the time I unscrewed the master from the booster and it made no difference so it’s not the push rod length. Yes the pads and discs are new and were a tight fit but still spin freely when cold. I’m going to take it out for a short drive and see if I can get to to lock on then have another fiddle.

 

Mine was like this when I got it to the point where I could push it forwards but not backwards.

 

A caliper rebuild fixed it for me. The pistons weren't going back in the bores properly.

[evl666]

That’s what I’m thinking Potter. Was going to pull the brake calipers off and wack some new pistons in there and try again. I’ve already put a new seal kit through them

[Potta]

That’s what I’m thinking Potter. Was going to pull the brake calipers off and wack some new pistons in there and try again. I’ve already put a new seal kit through them

 

Need to let them soak in metho, give the bores a gentle rub if there is any pitting or rust, and also use a liberal amount of rubber grease when you put them all together.

 

That's what Dattoman told me and it seemed to work quite well.

[evl666]

Question...just want to check something while I’ve got the calipers apart....the seal that sits inside the piston bore of the calipers is that tapered and goes in a certain way or is it my imagination?

[rodomo]

The annular groove that it sits in is is tapered. The seal itself is square section...…………….if my memory is correct?

[evl666]

Thanks rondomo. I’ll finish rebuilding the calipers and fitting new flexible lines today and see how we go

[grumpy xu1]

Question...just want to check something while I’ve got the calipers apart....the seal that sits inside the piston bore of the calipers is that tapered and goes in a certain way or is it my imagination?

Verniers might help you determine that, or pm or ask datto aswell maybe ?

[evl666]

Ok guys....so rebuilt the calipers again this time with new pistons and put new flexible lines. Took it for a drive did the same thing again. Cracked the nut where the front brake line goes into the master cylinder and she was still under pressure so it had to be the master. I grabbed a new master I had and threw it on...low and behold it works perfectly fine. Grabbed the the big nut master, striped it down and it looks like the tiny hole in the front port was blocked solid. So it a like when the heat caused everything to expand the fluid couldn’t flow back into the master causing the pressure to build up

[RallyRed]

good feedback mate..and good find too.

[grumpy xu1]

Great result mate ! Gary.

[liswar2]

Good to know for the future , just in case ,
Great detective work agent 86