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Brake issue

vc commodore

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I've had a search through and had no luck finding a solution

I have 4 wheel discs on my VC and when the brakes have got some heat in them, ie about 20 minutes of stop start driving, all 4 of my brakes lock on. The brake pedal also goes hard...

The car was off the road for 4 months, for a few running repairs....

Work done with the brakes.....I have cleaned and greased all caliper slides using bosch RB17 rubber grease....I have removed and cleaned the master cylinder out and bled all the brakes....I have had all 4 rotors machined and I replaced the rear pads....I have backed off the hand brake cable, so the handbrake doesn't work at the moment

When the brakes cool down ie after about 10 minutes, the brakes aren't locked on.....Any ideas where to look next? I've never struck this before, hence asking for any clues where to go next
 

vc commodore

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Tried disassembling the calipers & cleaning the bores out & putting new seals in when reassembling them?
No.....I just greased the slides up with rubber grease....With the rears, I pushed the pistons back into the calipers and they went back in smoothly....I can try the fronts and see if the pistons slide back in smoothly, before I go down the re-con route...

Thanks for the advise....Will wait to see if any one else comes up with other possible causes
 

losh1971

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I have had brake piston issues before where a small amount of rust forms the tiniest bump on the seal mating surface, inside the seal groove. It was causing the piston to stick. I cleaned out the grooves with a seal pick and refitted the seal. Took me a long time to figure out the issue. Changed MC and mucked around with dismantling the caliper probably three times before i saw the rust bump.
Only thing is it seems odd that all four brakes are locking on.

Do you always use rubber grease on the slides? I always use slide grease due to the low melting point of rubber grease. I use a tiny amount of rubber grease inside the caliper when overhaling them.
 

vc commodore

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Only thing is it seems odd that all four brakes are locking on.

.

This is why it has me bamboozled...I could understand 1 or 2, but all 4 has me stuffed. And it definately is all 4 because I have smoke coming from all 4 when I take it for a run to see if I have fixed the problem...

And no, this is the first time I have used rubber grease....Stems from me trying to fix the issue to begin with......I cleaned all the slides and used this grease to try and fix the problem.....
 
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Lacksballs

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Check the booster, the push rod maybe seized internally or master cylinder piston sticking?

If it was me, I'd loosen off the master cylinder from the booster to see if the wheels/brakes release... I doubt that it is all the calipers at fault!

Good luck.
 

vc commodore

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Check the booster, the push rod maybe seized internally or master cylinder piston sticking?

If it was me, I'd loosen off the master cylinder from the booster to see if the wheels/brakes release... I doubt that it is all the calipers at fault!

Good luck.

Makes sense, the booster might be causing the problem....The master cylinder was checked, when I bench bled it prior to re-fitting.....Everything else has been triple checked.....

I did forget to mention, the original booster crud itself out of the blue....With the engine running, my brake pedal was as hard as a rock.....So I put a 2nd hand one on and now all this headache.....Will remove the 2nd handie and put a known good one in and see what happens from there and report back
 

vc commodore

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Can anyone confirm whether VB through to VK brake boosters have any adjustment in them, with the rods? I have just checked one I have here and can't find any adjustment....

Reason I ask is, the place I bought the 2nd hand booster from is claiming the rod will need adjusting
thanks
 

vc commodore

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Thought I'd update this thread....Turns out, the 2nd hand booster I bought had no adjustment with the pushrod, which was causing it to lock the brakes on.....I ended up getting hold of another booster which had an adjustable push rod and the problem is solved.
 

losh1971

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Great good outcome. Thanks for the update.
 
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