Thread: 960 Brakes help
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Old 12-06-2017, 08:22 AM   #4
Janspeed
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Join Date: Sep 2005
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Your post does not mention what car. i assume it is the '92 965 in the sig.?
A car from 1992 is old... and it is a good idea to do a complete overhaul on the brake system because all parts will be old.

Brake pads are never made of rubber... any pad that's available for streetuse should work OK. (Racing pads might need to warm up to perform properly, they are not very suitable for streetuse)
And new rotors will not warp easily , specially not it the brakes perform badly (= not able to put heat in the rotors! Rotors warp because of excessive heat and temperature shocks)
New rotors should be installed on clean rustfree boltflanges. Any rust on those can cause the brakes to feel like they are warped. (attention to detail matters)
On a 900 (and 700) it can also be the case that the mushroom bushings in the lower control arms are shot. Very common problem on these cars. Also the cause of weird movement in the front suspention when driving backwards. These can also be the cause of brake judder and making the brakes feel like the rotors have warped when in fact they are not.

about ABS sensors: they do not wear, they either work (= produce an electric signal) or they don't.
however, It sometimes does happen that corrosion on the ABS tooth rings or debris on the tip of the ABS sensor cause bad signals = problems for the ABS.
It's a good idea to clean the toothrings and sensor ends to ensure proper functioning. The (only!) sensor for both rear brakes is in the rear diff cover.

don't fixate on the pads and rotors. (unless they are obviously totally worn out but that's easy to see). Slotted rotors will not increase the brake performance at all. They are there for cooling and expelling gasses coming from hot pads. Not needed on any road car. The stock brakes should be able to provide plenty of stopping power.

Instead make sure the entire brake system itself is functioning 100% (your post suggests that there is something seriously wrong, a well sorted stock 900 should be able to brake really hard.)

- it is smart to change old rubber flex hoses. They can cause all kinds of annoying and potentially dangerous problems. (internal swelling, cracking due to dryrot causing fluid leaks) if in any doubt, change them.
- the front calipers do 70+% of all brake work. So, if you are disappointed about the performance start by checking the front brakes first for quick wins. Make absolutely sure those front calipers are working perfectly. Make sure all pistons can move freeling inside the caliper, that the pads are not stuck on the edges inside the caliper (remove debris/crud/rust), that they can move freely along any slidepins. Here attention to detail matters.
- Brake fluid is hydroscopic, it attracts water. old brake fluid will have captured water in it. This water will easily boil inside the brake fluid. Boiling water turns into compresseable steam... these steam bubbles prevents you from putting proper pedal pressure on the brakes. That's why you need to flush the system with clean new fresh DOT4 brakefluid and make sure to bleed the system perfectly. Start bleeding the rear brakes first en move your way to the front brakes.
(be careful not to snap any bleednipples. Remove rust with a small wirebrush, give all bleednipples a shot of penetrating oil. Give all bleednipples a light tap on the end to shock them lose. only then try to open any of those for bleeding. If you snap one off you have an annoying problem...
- bleeding tips: tap the calipers to shake lose any trapped airbubbles. Then bleed again. If you keep having problems bleeding the system, try jacking the car up at the end where you want to bleed. It could help air to reach the high point (= your bleednipple) easier.
Brake bleeding can be done with a helper but easybleed toolkits are not very expensive and will make it a oneman job.
- With the engine running check if the brake booster is able to hold vacume , check if the oneway valve inside the brakebooster hose still functions like it is supposed to.

If everything is OK after checking/correcting and you still have a soft pedal that does not hold pressure then you might have a worn (internally leaking) master cilinder. Replace... and bleed the entire system again...

finally: in the whole equasion of braking the TIRES also play a crucial role. If the tires are old the rubber compound will have hardened. (check the 4digit production date code on the sidewalls of the tires) Your car can have perfect brakes but if the brake forces can't be transmitted to the road then the car will not perform very well. The tires will lose grip early while braking and ABS will prevent the wheels from locking up by releasing brake pressure (you can hear and feel it in the pedal)... increasing brake distance...
Fresh new grippy tires will reduce your brake distance.
At least make sure you optimise tire grip by using the right tire pressure (when i had my 940 i found 2.5bar/36psi to be optimal on 205/55x16 and for 195/65x15 i used 2.4bar/35psi for optimal grip.

Last edited by Janspeed; 12-06-2017 at 09:50 AM..
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