[alexis]

I had to replace a brake hose the other day. It had a ridiculously big bulge in it. In the process I found out what a bad state my brakes are in. The pads are nearly worn through. Everything is rusty. Discs don't look great and to cap it all off I managed to shear the bleed nipple off. :evil:

So I decided I needed to rebuild the system. I spent a few hours last night reading about 9000 ugrades but am not sure if its a god idea or not. There is no real doubt that the stock brakes cannot take too much punishment without giving into the inevitable heat. The 9000 calipers are bigger, the pads are bigger and the discs are bigger. So they can take far more heat before fading.

This is all well and good. But... as was pointed out by a few people, and confirmed by my further reading today, the bigger caliper piston diameter gives increased clamping force leading to an upset in the front/rear balance. So although the front brakes may be able to take more heat, this extra capacity will be used up doing the rear brakes job to some extent. Also, beacuse the braking force is restricted by a tyres grip, the actual stopping distance will be increased. Not so great in emergencies.

There are some really good articles here on the subject of brake balance.
Particuarly relevant to what I am asking about is this graph.

So I was hoping for some insight, particuarly from Alex who seems to be very knowledgeable on the subject, on peoples' opinions on this. Pretty please .



Now just a polite request to give the moderators a rest; if you haven't yet heard of the 9000 upgrade then rather than ask about it here :nono;, please do a search for '9000 brake' within the two 900 forums and read all about it . Just to get you started you need a 900 with an '88 or later brake system (rear handbrake) and '88 (turbo) or '90 (non turbo) 9000 front brake components. Rears are the same. Its a very easy job.

 

[trackside]

Fitting late 9K calipers on a 900 just replicates what is already on a 9000 - has anyone complained about severe front bias on a 9000?. Ive done the conversion and it's been a great improvement. I too had worn standard components and after many years of Saab ownership I was never very happy with the stock setup. Doing the 9k conversion alows you to use stock components and not pay out for fancy performance pad compounds and grooved disks. As for the fronts doing more work - my pads have been on for 35k and are only 1/2 way worn - hardly symptomatic of more work. You could always fit rear pads with a higher friction compound if it realy bothered you.

 

[alexis]

The 9000 is a heavier car and will produce different axle loadings under deceleration thereby requiring a different brake setup.

Hey, I'm not knocking the conversion (although it may appear I knock every mod talked about on here), I'm just asking the questions based on the articles I read and mentioned above. If you say its worth doing then I believe you and I don't doubt for a second that the brakes will be far more effective when driving quickly along a good B road.

However, the only concern I have is in the ability of the setup to stop the car in an equal or lesser distance than the stock setup from 90mph on the motorway. In this instance the heat generated is not as much of an issue since you only need to make the stop once and the most important thing is to slow all four wheels to the limit of grip. Personally I think this is a very important issue.

 

[trackside]

The 9000 went from the same front calipers as the late 900 to the the bigger ones without any change to the rears as far as I know. If you at all concerned just refit new or recon stock 900 parts and buy the best tyres you can - tyres probably have more effect on braking distance than brakes.

 

[alexis]

The 9000 went from the same front calipers as the late 900 to the the bigger ones without any change to the rears as far as I know.

Thats a damn good point. I'm probably being a bit pedantic about the whole thing, the difference is only small. I'll do it!

 

[trackside]

I will mention that the extra unsprung mass of the thicker disks and heavier calipers makes the front end feel a bit less nimble -I guess that's why alloy brake components are so important. Also the brake hoses can be custom made with some swivel joints instead of tyring to attach the old brackets and rigid lines. There are several online parts suppliers for brake lines and attachments.