SAAB WIS ONLINE

Vibrations while braking

SERVICE INFORMATION
Bulletin Nbr: 510-1919
Date: ........... june 1998
Market: all
Vibrations while braking


Cars affected

All Saab 900 M94-

Background

If a customer experiences vibrations during braking, it can be due to two possible causes:


- Excessive irregularity of the wheel hub.

- Excessive thickness variations of the brake disc.


If the total run-out of the brake disc/hub exceeds 0.08 mm, both the brake disc and wheel hub must be replaced.

If only the brake disc is replaced when a significantly uneven wheel hub has been confirmed, front assembly vibrations will reappear after 1 000-2 000 kilometres of driving.

If only thickness variations of the brake disc have been confirmed, that is, the wheel hub is not significantly uneven, replace only the brake disc.

It is important that both the hub and brake disc run-outs are measured in order to avoid the problem with reappearing vibrations.

Checking brake discs and wheel hubs

Refer to Service Manual 5:1 Brakes for checking the brake discs.

See below for checking wheel hubs.



1. Remove the wheel, brake caliper and brake disc.

2. Make sure the hub is clean and free from impurities. Only one dial is used. Make a recess in the tool as illustrated so that the wheel hub will not make contact with the tool.

3. Rotate the hub and check the run-out (the value between the greatest and the smallest readings).

If run-out exceeds 0.03 mm, the hub must be replaced.

Important

The dial will jump about 0.03-0.05 mm at each bolt hole, this is normal.


4. Fit the brake disc, brake caliper and wheel.

Tighten the wheel bolts with a torque wrench.

Tightening torque 120 Nm (89 lbf ft).