More brake woes

Whitechameleon · Whitechameleon's Garage

Took Rosy out for first good drive today and discovered that after about 10miles the new brakes are now grabbing on the other side now and pulling the car over to the right and under firm, but not hard braking the right side front will lock up. (this is exactly what was happening to the left before the caliper rebuild.)

Getting sick of this now.

Anyone have any ideas as to why? Everything at the front has been replaced, Discs, pads, both calipers recon'd and new flexis.

Please help?

Oh Haha · 03-18-2006, 01:18 PM

Wow, that sucks!!!
Gonna throw a couple ideas at you. Did you cycle the caliper pristons in each caliper before bleeding again? You may have one side pushing the pads out before the other side. Remove the pads and replace with a thin piece of wood or metal to prevent the pistons coming all of the way out.
Have a helper SLOWLY push the brake pedal until the pistons move out a bit. Do this a few times for each caliper. After doing this, bleed the calipers again using the helper/pump method.

If this procedure doesn't help, then i would think your master cylinder has problems. If the problem is exactly the same as before, I would look there.
Hope this helps, man. I did my brakes this year and ran into a few problem along the way but worked them out. No, it wasn't the same problem as yours.

johnsjmc · 03-18-2006, 02:24 PM

If you rebuilt both front calipers then I would suspect a corner balance issue. The mastercyl and even air in a line should affect both fronts as they are both in the same supply circuit . A rough corner balance can be done with a jack and a tape measure. Search tripod method. I,ve seen this (premature lockup on one corner) several times before.

Whitechameleon · Whitechameleon's Garage

Thanks chaps,

i can see this is gonna be one of those annoying jobs.

If it is a prob with the master cylinder would it do it on the same side as before though? as since it's been rebuilt the problem is on the other side???

Oh Haha · 03-18-2006, 03:24 PM

Are you saying that BEFORE the rebuild the problem was on, say , the passenger's side. and now, AFTER, it has moved to the driver's side?

Whitechameleon · Whitechameleon's Garage

Yes, i know, strange isn't it?

Oh Haha · 03-18-2006, 03:41 PM

WTF?!!!!!!!

Sorry, nothing else to say about it right now.

Jim Smolka · 03-18-2006, 03:47 PM

As a SWAG, try swapping the pads side to side. I like the idea of making sure all pistons are moving OK. Also, check that the groves on the pistons are in the correct position. Also, check that the bleeders are on the top of the calipers and not on the bottom (don't ask...)

Whitechameleon · Whitechameleon's Garage

Quote:

Originally posted by Jim Smolka
Also, check that the groves on the pistons are in the correct position.

Not too sure what you mean by that?

I know the bleeders are on the top as i was made aware of this before i did the job.

Jim Smolka · 03-18-2006, 04:09 PM

The part of the pistons that mates to the brake pads have an 'offset' on then (grove). Anyway, there is a 'correct position' that the piston must be alligned.

Thank the person who told you about the bleeders on top trick. I like to learn things the hard way...

Nine9six · Nine9six's Garage

The step on the piston face that Jim speaks of should be set at 20 degrees. It is on the face of the piston that contacts the brake pad. Here is a photo of the alignment of the step to 20 degrees.
Hope this helps...

Oh Haha · 03-18-2006, 07:09 PM

I was thinking about the piston orientation but I thought that was really just to keep teh brakes from squealing. Worth a shot, though.

Nine9six · Nine9six's Garage

Oh Haha,
You are correct. I was simply trying to clarify Jim Smolka's post for Whitechameleon.

Gunter · Gunter's Garage

The 20deg off-set is not just for squealing; it's more for even pressure against the rotor when brakes are applied during running.
Squealing is not destructive, it's just a nuisance and treated with a combination of shims and special "glue" between pistons, shims, pads.
If the pistons are stuck, or frozen, they cannot retract and pull the glued-on pads away from the rotor. (See Bentley SC Manual 470-11)
Another issue that is often overlooked is centering the calipers in relation to the rotors. If the calipers are too much to one side, the new pads will make contact even before brakes are applied. Centering requires shims under the mounting bolts.
In this case, the MC/vacuum booster may be screwy; hard to tell from a distance. I would lift the car, remove the wheels, remove the new pads, install the old, thinner pads and exercise the pistons by pushing them back into the calipers (Channel-lock pliers work well) and out again with the pedal 3-4 times making sure that they move easy. Check/Set the 20deg required for ATE brakes (That should have been done during the rebuild) You can make a 20deg template from cardboard and use channel-locks to rotate the pistons. I have a pair with ground-off teeth just for that purpose so I can grab the outer edge of the piston without damaging it. If all of that doesn't work, concentrate on the MC/booster.

Nine9six · Nine9six's Garage

May I suggest a pair of electrical channel locks for this job.
They have plastic covers over the jaws, and will not marr
the pistons. Scratch your pistons, and get ready to spend
more money.

Nine9six · Nine9six's Garage

Quote:

Originally posted by Gunter
The 20deg off-set is not just for squealing; it's more for even pressure against the rotor when brakes are applied during running.
Squealing is not destructive, it's just a nuisance and treated with a combination of shims and special "glue" between pistons, shims, pads.
If the pistons are stuck, or frozen, they cannot retract and pull the glued-on pads away from the rotor. (See Bentley SC Manual 470-11)
Another issue that is often overlooked is centering the calipers in relation to the rotors. If the calipers are too much to one side, the new pads will make contact even before brakes are applied. Centering requires shims under the mounting bolts.
In this case, the MC/vacuum booster may be screwy; hard to tell from a distance. I would lift the car, remove the wheels, remove the new pads, install the old, thinner pads and exercise the pistons by pushing them back into the calipers (Channel-lock pliers work well) and out again with the pedal 3-4 times making sure that they move easy. Check/Set the 20deg required for ATE brakes (That should have been done during the rebuild) You can make a 20deg template from cardboard and use channel-locks to rotate the pistons. I have a pair with ground-off teeth just for that purpose so I can grab the outer edge of the piston without damaging it. If all of that doesn't work, concentrate on the MC/booster.

While I have not come across glued on pads, it is my understanding
that piston retraction is accomplished by the seal ring
per this text.

Gunter · Gunter's Garage

Exactly. The pads can only be pulled away from the rotor if they have a connection to the pistons when they retract. That connection is the special goop that comes with some brake pads/shims.
When the pistons are frozen, that mechanism doesn't work.
Various manufacturers like Girling, ATE, etc. have experimented in different ways to elimminate squeal with some success. (Anti-squeal shims, goop)
Squealing happens when the pads vibrate between rotor and piston; it's not destructive.