924Board.org

[Llamaguy]

if you step on the brakes hard or even for a brisk stop the right rear locks up ,right away, any ideas?
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1987 924S Guards Red
1997 Suzuki Tl1000 Supersport

[dpw928]

A few possible reasons are 1) leaking brake fluid on pads causing them to swell, 2) Stuck caliper, 3) misadjusted parking brake cable, 4) Caliper piston in the wrong position, 5) bad proportioning valve.

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

[Doodle]

Could be a leaky wheel cylinder or in your case probably caliper, the piston is seizing in the bore of the caliper when the pedal is released instead of returning fully to the release position. Could be the brake pad slider pins are extremely dirty, rusted or worn in such a way as not to allow the pad to seperate far enough from the rotor. Try bleeding the caliper first. May as well do all of them while your at it. While you're under there check for physical damage or fluid leakage around the caliper assembly. Check the torque on the caliper retaining bolts. Buy a couple cans of spray type brake cleaner, wear some eye protection and spray everything down before dis-assembly.

Long shots, could be a crushed or otherwise restricted brake line to the one wheel allowing brake fluid to flow to the cylinder under pressure but not return fully on release. Could be a loose wheel bearing.
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Doodle
Pre 77.5 Mars Red

[Paul]

Brake fluid should be changed every 2 years, so I would suggest changing the fluid and bleeding the system.

[gohim]

No proportioning valve on a 924S, so that can't be the problem.

Misadjusted parking brake is probably not the problem either, unless you notice the braking malfunction is only occurring after the brakes are warmed up.

Replacing all of the brake fluid in the car (to remove contaminates), and bleeding (to remove air) will not hurt, but may not help either (unless the problem due to plugged lines from rust and contamination.

If the lockup occurs when you step on the brake, and not when you release the brake, I would not expect the problem to be found at the right rear caliper (the one you say is locking up).

Since the braking system on a 924S is split front and rear, and you haven't mentioned anything about the left rear caliper locking up, I would think that the problem could actually be on the left side. A siezed left caliper piston, plugged, or crushed brake line to the left caliper, would force all of the fluid meant for the two calipers to the right caliper. This could cause excessive movement of the right piston and brake lockup at the right rear.

This would probably be a good time to replace the seals in all four calipers, inspect and replace the brake hoses (as necessary), and replace the brake fluid. This would probably fix your problem. The caliper seals are fairly cheap ($10-$15 per wheel), and easy to install. This would give you the chance to throughly clean the crud from the caliper cylinders, and flush the flex hoses to make sure that there isn't any blockage.

[Lizard]

Gohim is correct here, although I just got new seals and boots for an M471 setup and it was $20 cdn a piece for the rear and $9 a piece for the front,

rebuilding the calipers is a VERY easy thing to do, however if you are not comfturable doing this yourself, take you calipers off and then take them to a rebuilding shop and they can do them right there, the whole process takes roughly 1 hour max for a shop with proper equip
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3 928s,

[emoore924]

I thought that the 924 had a diagonal circuit braking system -- the LF was in the same circuit as the RR, RF with LR. Soooo..., if I am remembering this right, if you're having problems with the RR and it has something to do with the circuit rather than being isolated to the one corner, you might want to check the diagonal??

Also, DK if you have access to corner weighing scales, but sometimes this can be caused by too much weight on the other diagonal..., i.e. too much weight on your RF or LR wheel casued by some change in your suspension, or even tire pressures. So you might want to check that too.

[gohim]

emoore,

The car being discussed is a 924S, which has the braking split front and rear like a 944. The 924 and 931 have the braking systems split diagonally.