[JFP]

The brakes on my wifes 94 CSE are'nt as good as they should be. The brakes work 'eventually' but there is very little initial bite. Being an automatic the problem seems worse at slow speed (sub 10 mph) and not as noticeable above 25 mph.

The pads, discs, brake lines all seem OK and I can't see any signs of leaking fluid from say a cracked caliper.

I took it to the local garage who are honest & cheap, the brakes all register the correct stopping force on the MOT tester and they sat the pistons slide Ok within the calipers. they could'nt figure out what was wrong with them.

I noticed that there does'nt seem to be a brake servo.

The local garage chap said his technical book mentioed a SAAB diagnostic brake checker, but only on later versions, however he has'nt got one and was'nt sure how to connect it if he had.

Any thoughts on what the problem might be ?

 

[mark e]

It could be to do with the pad compound. Some pads require a little bit of heat in them to attain maximum friction (race pads btw don't work UNLESS they are hot)

The difference between low speed and higher speed braking is simple to explain. The kinetic energy to be dissipated and friciton generated for a given pedal force will vary with the square of the speed ie in other words, the pads will warm up much quicker when stopping from a higher speed. It can also depend on how old the pads are...

One way to try this would be to do some higher speed stops and then try it from lower speed and see if you get the same efficiency once the brakes are warmed.

If that doesn't sort it there's another possibility that occurs to me. From lower speeds the engine will be running at lower revs and therefore the vacuum assistance generated for the brake servo may not be as great. Others may want to correct me on this...

 

[gadgeteer]

The servo is hidden away behind/underneath the battery on the passenger side.

I'd suspect the vacuum hose is leaky.
Its the hose going to the rear of the intake manifold, just next to the oil cap.

 

[billj]

Did it ever perform any better than this in the past, or does it just not seem good enough? There is no vacuum operated servo on the ABS 9000 (turbos from '87 and non-turbos from '88) - the braking assistance comes from a pressurised chamber in the ABS unit/master cylinder, which is pressurised by an electric pump. If the pressure is low, you should get the ABS light coming on and staying on. Does the light work (comes on briefly on startup)?

Another possibility, especially since it's an automatic, and if your wife doesn't drive very hard, is that the pads have become glazed through light use. If this is the case, taking them out and refacing them with sandpaper (or just replacing them with new ones) might make a difference.

However, I find the 9000 brakes simply don't have an impressive initial "bite". My dad's Nissan Primera wants to stand on its nose when you touch the brakes, but I don't like it. Both my Aero and my new CSE (test-drove it last night and picking it up this evening - whoopee!) need a bit of effort to stop them, but they do stop well when you apply some braking force.

 

[mark e]

Originally posted by BillJ:
There is no vacuum operated servo on the ABS 9000 (turbos from '87 and non-turbos from '88) - the braking assistance comes from a pressurised chamber in the ABS unit/master cylinder, which is pressurised by an electric pump. ][/b]

Hmm... that may be true for the 9000 but my 93 9000CS 2.3T DOES have vacuum assistance on the ABS. I know becuae I've tried fitting an Ecotek and by the time I can get it to make the right "noise" I start suffering from loss of brake efficiency :-((

And I've not managed to get any better fuel economy either. I can see how it should work on naturally aspirated engines but (and maybe this is due to the fact I have a hybrid turbo) as my turbo lends "assistance" most of the time setting the Ecotek up at idle doesn't work.

Mark

 

[longblackcoat]

My 1992 9000 CS has the Trent Saab stage 2 brakes - Group N Grey Iron Discs and Ferodo DS Compound Pads. £300 all in and bugger me, do they stop the car.

When I originally test drove the car I thought it was OK but that the brakes were pretty wooden. The upgraded brakes (using the standard calipers) are eye-poppingly powerful and well worth £300 of anyone's money.

Oh, and although they're race-compound, they work very well when cold (WAY better than standard) and then get even better when hot. Only downside is the amount of black dust thrown up.

lbc