Disc brake seizing on

2700 Views 11 Replies 5 Participants Last post by evilC, Mar 11, 2009

RecklessRob

Discussion Starter · Mar 11, 2009

Hi

I have just fitted a set of rear discs to my 1972 gp beach buggy.
They work great until they get hot, then they start to seize on. The more they seize the hotter they get, they worse they get.

I have reasonable pedal travel when cold but no travel when they get hot.
The hand brake is not over tight, and I have adjusted the pedal give more travel.

They work fine for about 4-5 miles then over heat and stick on.

Any suggestions ?

Rob

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evilC

· #2 · Mar 11, 2009

Either the pistons are sticking or the line pressure is not releasing. Is the pedal set so that there is free play between the plunger and the m/c piston?

Whats the overall brake set up as a matter of interest.

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Moby5153

· #3 · Mar 11, 2009 (Edited)

Brake pedal pushrod freeplay........ in case it's that causing it....

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wolfrace

· #4 · Mar 11, 2009

what type of calipers are you using and what master cylinder?

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RecklessRob

Discussion Starter · #5 · Mar 11, 2009

I have discs front and rear, 3 output master piston, ie 1 line to rear 1 to front left, & 1 to front right.

There are some short flexible hoses (3") long from rear copper into the brake calipers.
They came with the brakes but are not needed, so I have removed these to see if they were breaking down inside.

I will double check the free play on the pedal to match the illustration sent.

I will try theses out tonight when I have someone handy to bleed breaks again.

Thanks for suggestions so far

Rob

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RecklessRob

Discussion Starter · #6 · Mar 11, 2009

The calipers are marked as VARGA C34 (could be VAROA)

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Bada Ben

· #7 · Mar 11, 2009

RecklessRob said:
The calipers are marked as VARGA C34 (could be VAROA)

Varga is the name of the manufacturer, Varga are Brazillian, they make a lot of VW pattern Brake parts.
What master cylinder are you using ? is it new. or an old one with a residual pressure valve on the rear line ?

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RecklessRob

Discussion Starter · #8 · Mar 11, 2009

The master cylinder is about a year old, and the brake line goes from the outlet on the cylinder straight to the t piece behind rear the bulkhead, to 2 copper lines, to 2 hoses, to 2 copper lines, into 2 calipers

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Bada Ben

· #9 · Mar 11, 2009

RecklessRob said:
The master cylinder is about a year old, and the brake line goes from the outlet on the cylinder straight to the t piece behind rear the bulkhead, to 2 copper lines, to 2 hoses, to 2 copper lines, into 2 calipers

Yeah but, is it a M/Cyl for a beetle, a beetle with drum brakes all round, or a beetle with disc brakes at the front ?

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RecklessRob

Discussion Starter · #10 · Mar 11, 2009

Ah Ha !

I see what you mean.

Don't know.

How can you tell, and what are the implications ?

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wolfrace

· #11 · Mar 11, 2009

coz if your using a drum master it will cause the brakes to ratchet up.cars with disc brakes all round keep asmall amount of pressure in the lines to stop the pistons backing off ,increasing pedal travel.as you press the pedal the piston will adjust itself in the rear caliper,if it was kept there by residual pressure the next time you press the pedal the piston would not move enough to click up the ratchet adjuster.think that makes sense.also try and find out if the kit disc is thicker than the caliper was ment for(ie golf)thats why most rear disc pads are a lot thinner than front ones

isnt this fun.my advice stick to drums:crazy:

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evilC

· #12 · Mar 11, 2009

aquarius said:
coz if your using a drum master it will cause the brakes to ratchet up.cars with disc brakes all round keep asmall amount of pressure in the lines to stop the pistons backing off ,increasing pedal travel.as you press the pedal the piston will adjust itself in the rear caliper,if it was kept there by residual pressure the next time you press the pedal the piston would not move enough to click up the ratchet adjuster.think that makes sense.also try and find out if the kit disc is thicker than the caliper was ment for(ie golf)thats why most rear disc pads are a lot thinner than front onesisnt this fun.my advice stick to drums:crazy:

Sorry to contradict you but the opposite is true. On a normal caliper its the small designed in movement in the caliper seal that prevents the piston from backing off too far.
If you have residual pressure valves in the system then the whole thing WILL rachet up. The pads will be held against the disc generating heat. Next time the system is pressurized the pads give a little more and heat up further until after progressive uses fade has set in. the residual pressure valves can only be used where there is a positive return usually in the form of a spring so that rachetting doesn't occur.

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