Brake Gremlins, trying to find the culprit..

[Mike B]

I have Brake gremlins... coming and going for a while now and I'm at a loss what it could be;

 

Symptoms;

- occaional pull hard to the right, you can feel the car want to pivot around the front right wheel under sharp application of the brakes.

- soft pedal feel, (can be exlained by pad knock back, but I have my doubts!)

- loss of abs on front right wheel (but no warning lights are on)

 

I have bled, re-bled, re-re-bled, every corner, changed fluid, checked pads, calipers...no sticky pots, no change and no problems, no bulges in the braided lines, no leaks, no fluid loss, everything is in good working order.

 

I am no master mecanic, so could someone who is rule out some of the following and perhaps suggest their own theory;

 

My own thoughts are;

 

1) is there a stock biasing mechanism? does it bias left and right or just front and back? could it be manfunctioning?

 

2) I know there are 2 cylinders inside the master cylinder, could the first be knackered? letting fluid past and changing the bias through the brake travel? the right pull alters in serverity from none to lots but there is no discernable pattern.

 

3) I know my alighnment is slightly out - I don't have enough front camber on.. could this be a problem... I personally doubt it!

 

4) abs not working has really got me now.. it's not been raining so cant do a proper test, but in the full power stops I have had the right front wheel can lock, before I bottle a potential flat spot and ease up. Could such a different brake bias overpower the abs intervention ability?

 

any thoughts greatfully received.. the problem is getting worse not better, and I need guidance before I start replacing components!

[Chris Wilson]

UK or J-Spec brakes? If J-Spec sounds like a classic case of sticking caliper sliders. Has it got a long pedal?

[Mike B]

Hi Chris,

Thanks for the reply. 6 pot rotora with 355 disks, all pots are free and easily movable independantly when the pads are removed..

 

BUT the pads do have uneven wear.. intake side of the pad is 5mm thick, exit side of the pad is 7-8mm - it's a long pad, photo enclosed. I have asked Rotora and they volunteer no information as to whey the pads wear unevenly or if they could cause any problems...

 

edit, yes the pedal travel is long, until I pump and then the pedal travel is smaller, hence why rotora suggested - pad knock...?

[Chris Wilson]

What pad compound? How much longitudinal end float between pads and caliper end stops? Car usage? Do they pull only when hot, or only cold, or both? Fixed or floating discs?

 

Some taper wear is normal, you'd have to *ugger about with compounds and cooling and be SURE to have optimised piston differential sizing to stop all taper. Pulling is NOT normal though. Again, what's the pedal like? Soft or hard, long stroke or right up near the top? Have you got a helper there?

[Mike B]

Hi Chris.. again thanks..

What pad compound?

I belive it is a compound pad, some metallic in there as well yet they do work well when cold.

 

How much longitudinal end float between pads and caliper end stops?

I'm guessing here - you range of pad movement inside the caliper housing? if so they are not loose, but there is more play than on a standard oem disk/caliper.

 

Car usage?

4-5 times a week, maybe 150 miles a week max. all country roads and dual carriageways. I do use them hard from time to time.,, not at the moment though!

 

Do they pull only when hot, or only cold, or both?

pull more when warm, and I'm not trusting enough to get them hot now.

 

Fixed or floating discs?

if you mean those new disks that have floating mounts they are all solidly bolted in place...

 

Some taper wear is normal, you'd have to *ugger about with compounds and cooling and be SURE to have optimised piston differential sizing to stop all taper. Pulling is NOT normal though.

 

Again, what's the pedal like? Soft or hard, long stroke or right up near the top?

Pedal is fairly soft on this car.. I originally fitted the brakes on my silver sup before.. they were immediate hard weapons on the silver car... on this vvti they are soft and on first application the bite is soft and low, maybe 50% of the overall travel.. on second immediate application.. it's becoming a habit now, the bite engagement is at 30% of the total pedal travel.

 

Have you got a helper there?

when I need one, if I can tear her away from the paramount comedy channel.. my garage is, I have been told, a less amusing place to hang out.

[Chris Wilson]

OK, a brief stab at a few ideas. You basically don't know the compound, which suggests generic pads from the caliper supplier. Treat it to some decent pads, which, IMO, means choose between Performance Friction and Endless, *IF* they list these pads. I hope the makers haven't used an "odd" pad shape forcing you to buy only from themselves?

 

Get your helper away from the TV, use bribery or force, as you feel inclined Jack the front up safely, and remove both front wheels. Put 3 wheel nuts on the studs and tighten firmly against the disc bells, on both sides of the car. Use washers if the studs bottom out in the nuts before the bells are held firm. Get her to press the pedal firmly a couple of times, but not more often, you don't want to drain the vacuum from the servo. If this may be a problem do the test with the engine idling *IN PARK* or neutral, handbrake hard on. Once the pads are settled get her to press the brake pedal HARD whilst you VERY CAREFULLY look for flex in the caliper mountings or disc and bell. With the engine running you can do this a multitude of times without losing the servo assist. Without servo assist you may well not see the flex, if it exists. You are looking so see if the caliper is not mounted absolutely parallel to the disc surfaces, in both planes, and as the pistons force the pads against the disc this inaccuracy is shown by the caliper shifting to align itself with the disc faces, or indeed, the disc or bell itself flexing. There should be NO caliper or bracketry movement, or disc, AT ALL. If there is you need to address the misalignmnt. Even a barely notecable flex will give a long pedal and odd wear or pulling. I suspct one side will have misalignment, and it will be the side opposite that to which the car pulls. Whatever, you can generally say that the problem will be the side OPPOSITE that to which the car pulls. If you a dial gauge check for disc run out with the bells bolted up as above. More than 3 thou inch is poor, more than 10 thou and it needs sorting as that is bad.

 

Fitting new pads will make a big difference, once taper wear starts it self propogates, and the geometry of the piston to pad backing plates is severely compromised. Don't panic if you find no flex, you may be lucky and find parallel faced new pads will be the panacea you need. Spend more than you think is modest on good pads, like good tyres they will transform your driving pleasure, and be cheaper, long term. Avoid Performance Friction Z rated pads, they are made to be a zero noise pad for the ultra noise intolerant US market, get a race pad like 03 compound. They work fine from cold and are very disc friendly with low disc wear. This is important as the discs are bound to be made of recycled junk Treat it to matching compound pads on the rear Hope that helps. If it was here I'd fix it, assuming that the calipers themselves are not so *rap as to be the cause of the trouble in themslves, but as you say they were OK on another car this shouldn't be the issue.

[Mike B]

Chris you are a star, thankyou.

I will do as you suggest... and report back. It won't hurt to get a set of new pads either way, I will start hunting.

What you say does make complete sense in cause and effect, as the pads are now quite well worn, and the brakes were like razors when new, but I could swear their positive feel was lost over time, even on the silver car which had excellent feel when they went on as a brand new part.

Jurgen did tell me a story of one of his cars that was not right; he took it to a brake specialist in Tyne&Wear who diagnosed misalignment and fabricated the nescessary ajustments which cured the problem.

 

Terry did tell me to be careful removing the old uk spec's and fitting these. I was in two minds but the weight saving on these rotora's (over 3kg per wheel) won me over.

Having read one of your earlier archived posts on brakes, and their balance misalignment when oversizing the fronts, I am now beginning to wish I spent more time reading the forum and less time looking at pretty pictures.

 

Still saving for a set of 18's lol.

[Jurgen-Jm-Imports]

yep had to get my rx7 fronts aligned evenly when i fitted the 8 pots, so much better now and pad wears evenly the guys used a vernier and shimmed it level somehow.

[Mike B]

Thanks matey, going to have a check tomorrow possibly, I spent this evening with a large hacksaw in Morrison's carpark sawing my good lady's exhaust into 2 pieces.

It fell off on the dual carriageway and she dragged it a respectable distance.. it would not come off easily. Now I have a credit token for my helper!

[Mike B]

Update;

 

stripped the fronts as Chris suggested, bolted the bells in place, ran the car, found helper and checked for caliper/disk movement.

 

Driver's side; showed no movement on hard brake application; this was the driver's side, the disk also ran true and straight through the caliper with no discernable warp whatsoever.

 

Passenger's side; here there was movement, not so much to the eye, but when you put your fingers so they touch the disk and caliper a the same time you can feel the disk move on application. It's as if the caliper is trying to twist the disk on hard application.

Also the disk was not perfectly straight - there was a definate free running section of disk and a section that catches the pads.. a slight warp. When braking I feel no warp at all.....

 

So this kind of fits; the passenger side is not braking as hard as the drivers side causing the car to have a tendancy to creep right. and there is a lot of pad knock; on such big disks this could explain it... right?

 

So... I'm tapping Jurgen up to get the caliper aligned (have him check both I would think).. and shall I get the passenger disk skimmed? or both skimmed.. there is plenty of meat on them and just a very very slight warp of the passenger side... as well as some new pads; I was thinking H6, but these look like they are only goingto start working at 200 degrees c..?

 

PAD TYPE: H2

COMPOUND: CERAMIC

DRIVE TYPE: STREET/LIGHT TRACK

DISC TEMPERATURE RANGE: 0-500 C/0-932 F

AVERAGE COEFFICIENT OF FRICTION: .25-.5

 

PAD TYPE: H6

COMPOUND: HIGH-CERAMIC

DRIVE TYPE: TRACK/RACE

DISC TEMPERATURE RANGE: 200-660 C/392-1220 F

AVERAGE COEFFICIENT OF FRICTION: .44-.55

 

PAD TYPE: H8

COMPOUND: CERAMIC-METALLIC

DRIVE TYPE: RACE/ENDURANCE

DISC TEMPERATURE RANGE: 300-800 C/572-1472 F

AVERAGE COEFFICIENT OF FRICTION: .5-.62

 

BIG thanks go to sir Chris who seems to have been dead on with this diagnosis!

[Chris Wilson]

What make of pads are these? What make of discs? If a big vented disc takes a warp they rarely grind and stay true. I'd replace them with AP or Alcon ones, *IF* they are available to fit your bells.

 

Before anything else try releasing the caliper bracket and caliper bolts a turn or so, get someone to press the brake hard, and re torque them. With a lot of luck they may re align and stay re aligned, worth a quick go?,

[Mike B]

What make of pads are these? What make of discs? If a big vented disc takes a warp they rarely grind and stay true. I'd replace them with AP or Alcon ones, *IF* they are available to fit your bells.

 

Before anything else try releasing the caliper bracket and caliper bolts a turn or so, get someone to press the brake hard, and re torque them. With a lot of luck they may re align and stay re aligned, worth a quick go?,

 

The pads are Rotora; I have not checked to see if they are universal pads.. they may be a rotora one off. The disks are also rotora, and the warp is tiny.. teeny tiny!

 

this is the first UK web page I found for the rotora pads;

http://www.amber-performance.co.uk/info.php?i=389

 

I did indeed think of releasing, wire brushing and re-seating the bracket.. but I had not thought to have someone stand on the brake pedal when you torque them. Obvious now you think about it...!..

 

Perhaps the bell housing and hub could do with a good clean and re-seal too...

[Gaz Walker]

I'd bet I can get those pads from Endless Mike.

 

If you draw round them and send me some measurements I can have a look into it...?

 

Gaz.

[Mike B]

Yes matey; will do on monday!

I also need a T4 turbo/manifold gasket and you need to charge me for that heat shield!

[Gaz Walker]

Yes matey; will do on monday!

I also need a T4 turbo/manifold gasket and you need to charge me for that heat shield!

 

Don't currently have those gaskets in Mike, you can have a word with Kevin next week he will be able to help.

 

I'm waiting for the replacement wrap to come so I know how much it is, then I'll send you a bill

 

Gaz.

[Mike B]

UPDATE;

 

Many Thanks to CHRIS WILSON,

 

instructions followed to the letter and problem 100% cured; you were bang on!

 

pedal feel is much imporoved, brake balance perfect.

 

Sir, you are a star, a credit to the club.

 

for all those that have aftermarket brakes, check the alignment when you put them on.. it makes perfect sense and a massive difference.

[Chris Wilson]

Glad to have helped, I'm no star, just an old bugger that has seen most brake and handling / suspension problems too many times to want to recall Thanks for the kind words.