15 replies to this topic

[Potta]

I'm pretty sure that the disc pushes the rotor back out.....that's how they automatically adjust....

Maybe the caliper piston needs a lube? Or it could be a master cylinder issue? Ie not releasing pressure when it should?

I'm no expert, but that's what I would check first.

I'd also wait for Datto or someone of similar experience to comment before you listen to me.

[ls2lxhatch]

LS1LX had the same problem.

See this thread for details.

[TerrA LX]

That's a bit of a worry.

[TerrA LX]

They are brakes your talking about, why not fix the problem?

[ls2lxhatch]

You may not have the same problem as LS1LX. There are other things to check suggested in the thread.

It would be worth seeing if you can get your hands on a set of worn pads to try in the calipers.

If the problem is brake pressure related then you would expect both calipers to hold on the same.

[S pack]

Yes I to want to fix it.

I spoke to hoppers and they believe that they have never heard of problems with the PBR calipers

He suggested to crack the line at the different stages,i.e. bleed nipple then hose etc. and see if its retaining pressure and work out where the tight spot is.

I found with our VS V6 (OEM calipers) when I fitted new DBS Gold front rotors and Bosch pads that there was very minimal clearance and the effort required to spin the road wheel by hand was unusually high. Was a bit worried about it but all came good after a while.

All disc rotors are made with a small amount of runout which kicks the pads back.
If you can push the pads back and the disc will spin relatively freely then machining the pads or the discs will probably not solve the problem.
You might have a blockage or restriction in the brake line to that caliper or in the caliper itself, one or both of the pistons may not be moving freely in their bores or the guide pins that hold the main body of the caliper to the bracket are dry, binding and need lubricating.
Visually check the brake piping to ensure it is not crushed or kinked anywhere along it's length.
I would first bleed the brakes and compare the pedal effort and flow of fluid from the bleeder nipples on both calipers (make sure you crack the bleeder nipples the same amount) to see if one flows easier than the other, this may indicate if there is an obstruction in the brake line or caliper.
Do LX models have a proportioning valve? Maybe there is a problem in it.

[dattoman]

Discs don't have "factory" runout
If they did the car would have shudder from day one.... like BA falcons and VT commodores... lol
The seals actually pull the pistons back as the internal groove is cut on an approx 3 degree angle... so when you apply pressure the pistons actually roll the seals as they apply... when you release the seals roll back

Make sure everything sits square , the pads are flat and that the pistons move in the calipers easily and the slides move freely
Don't use anything petroleum based for lubrication as this makes the rubber seals and boots swell making the problem worse

[rexy]

You still have the adjustable rod between your new master and the booster I presume? Check that it isnt "too long" leading to minor activation of the master with the pedal released. I scored my hatch cheap due to its prior owner being unable to find this issue. He had incorrectly reassembled things after painting. When I looked at the car he had all the front brakes in bits and had given up!

[S pack]

Discs don't have "factory" runout
If they did the car would have shudder from day one.... like BA falcons and VT commodores... lol
The seals actually pull the pistons back as the internal groove is cut on an approx 3 degree angle... so when you apply pressure the pistons actually roll the seals as they apply... when you release the seals roll back

Make sure everything sits square , the pads are flat and that the pistons move in the calipers easily and the slides move freely
Don't use anything petroleum based for lubrication as this makes the rubber seals and boots swell making the problem worse

Shudder occurs when there is excessive lateral runout in the rotor.
Disc rotors can have up to a maximum .004" lateral runout - source GMH LC & HQ shop manuals.
You are correct the seals grab the pistons and pull them back when the brake line pressure is released.
The runout in the rotor then knocks the pads away from the braking surface.

Rexy you could be onto something. As the master cylinder has been changed to one from a different model the master vac pushrod might not be adjusted correctly.
Also a swollen primary cup can block or partially block the compensation port causing residual line pressure.

[ls2lxhatch]

If the problem was related to residual brake pressure then you would expect both front calipers to hold on.

[S pack]

If the problem was related to residual brake pressure then you would expect both front calipers to hold on.

Theoretically correct but always expect the unexpected. Process of elimination will eventually find the true cause.