911 Brake Questions

[gflynn]

I put S4 fronts and 930 rear calipers on my '85 Carrera. Anyone have info with regards to brake proportion valve changes? I'm locking up at high speed and heavy braking; Not sure which end, but I suspect the rear.

I also have very bad front brake squeal, especially at lower speeds. I'm using gas slotted rotors front and stock 930 rears. Do the slotted rotors squeal, or should I use different pads? I'm using OE Jurid pads for the street. Thanks.

[Kahuna]

Lots of relevant info here;

http://www.pelicanparts.com/MotorCity/wmv/brakes.htm

there are some other pages linked that also have info

[Bill Verburg]

The link posted by Kahuna was to one of my pages it is a useful(I hope) reference of what the factory has done over the years. There are other pages dealing with specific installations such as my 964 calipers to my Carrera, and general upgrade pages. Thom Fitspatrick(widebody911) also has a nice photo essay of adapting 930 brakes to his 77, as does Jack Olsen on their respective pages.

As to your specific question. The S4 front with 930 rear caliper combo has a hydraulic bias of 1.796 which is fine and should cause no problems as long as 78-89 930 sized(or better) rotors are used. You do not need a p/v. You need to identify which end is locking first, sans ABS you want the front to lock just before the rear.
If the rear is locking first there are several suspects;

• you did update the mc to a 930 one , right?
• glazed pads
• oil or similar on pads/rotors
• pads/rotors not properly bedded together
• more aggressive pad compound at one end
• pad compounds that work at a different temps at one end

squeeling is often the result of an aggressive high temp pad compound Pagid orange are notorious for it while the less aggressive Pagid blue makes no noise. Here is a link to some of the Pagid compounds;
Pagid

and

Pagid

[gflynn]

Thanks for the info. I do have the 930 m/c, and the pads are new Jurids. The rotors are new, factory 930 rear and aftermarket 2-piece slotted fronts.

It appears upon inspection that the right front pad is not contacting the rotor completely flat. The pad is scuffed under the smaller, trailing (in relation to rotation) piston on both the inner and outer pad. The left front looks good. I've 'excercised' the caliper to insure free piston movement, so I'll hope for the best now. If not I'll excorcise the entire caliper.

[82SC]

sorry to barge in on your thread...but anyone contemplating a setup like gflynn I am selling my rear 930 calipers in the classifieds

MJ

[Kahuna]

Just a mite curious here, What are you going to use for rear caliper/rotors with your 930 fronts?

[Clark Griswald]

That piston not contacting sounds like your problem. I would check for air in the lines first.

Also, did you remove the factory bias valve?

[Bill Verburg]

Clark raises a good point that I neglected to mention the p/v shoud be removed with that combination.

Here in upstate NY its common for the caliper to get cocked because of corrosion. Cleaning, exercising, and lubing are the cure. Another good reason not to use these cars in the winter.

[gflynn]

Thanks to all for the replies.

I'm using the 930 calipers (rear) in the rear, with S4 in the front.

Please tell me how to remove the bias valve; Did'nt realiize it was not compatable with this system.

I'll re-bleed the system to clear any air or particles; Great advice.

I also talked to someone who said that my front rotor set-up is prone to squeal anyway, so I may not be able to totally eliminate the squeal. I'm using a 2-piece slotted rotor. I'll have to change these rotors to 930 fronts, as this car is driven on the street. Anyone need almost new rotors?

[Bill Verburg]

The p/v is to the left of the power boost vacuum canister. It has no effect until 33 bar line pressure is reached. Beyond that point line pressure to the rear is reduced by.46 effectively shifting the bias to the front. Your setup is already more front biased than normal, the p/v will make it worse.