Menu toggle

Brake proportioning valve

Tam Lin

New member
Has anyone upgraded the ratio of their brake pressure proportioning valve on a 944S/944S2 and do you have the old valve to sell me?

I'm going to fit rear S2 callipers on my 924S next year as part of a general brake lines/brake overhaul, as I want to bring the brake balance a bit further back on corner approach (I already have Wilwood DynaPro 4 pots on the front), but obviously if I panic brake, I don't want to emulate the standard early-911 crash profile..
 
I thought the 'upgraded' proportioning valve increased brake bias to the rear so isn't it one of the 'upgraded' ones you require if you want to increase rear brake bias.

In anycase if you install larger calipers to the rear you will automatically increase your rear brake bias because the pressure acting on a larger piston area will result in a larger braking force. You will also probably notice an increase in pedal travel due to the larger volume of fluid in the system.
 
All correct, however at present I have no proportioning valve of any kind, and no ABS, so putting S2 calipers on the rear might not only move the brake bias backwards, it might cause the rear to lock up spectacularly when I'm not expecting it: been there, done that. Used to track a Cerbera.

So I want to put in the early proportioning valve (5/18 I think) to reduce the chances.
 
Erm, piping up about something I don't know anything about here, but front:rear proportion on brakes is something you need to get right I'd have thought rather than fitting and hoping for the best. Too much front means the rears aren't working to their best effect and those new rear calipers are in vain. Too much rear and - as you've said - you'll be spinning faster than a Labour Special Advisor on a busy day.

Would it be possible to consider an adjustable one - possibly an aftermarket (racing) one, or something from another car. Mk2 Golf GTi's had adjustable brake bias valves on the rear axle, which adjusted with the suspension position. If you put lots of heavy things in the car, the suspension dropped, and the adjuster adjusted so that there was more braking at the rear of the car. (Played havoc with the wide boys who lowered their cars and didn't re-adjust the adjuster, but that's neither here nor there.)

Possibly think about something like this?


Oli.
 
There are a few variable proportioning systems that have been used on cars. I know of systems that use an inertia weight so the harder you brake the more is sent to the rear. Modern EBC systems also vary the brake force distribution across the axel as well as fore and aft.

Anywayback on topic - I've done an extensive check in the PET and all 944's, 968's and post '85 928's used the same proportioning valve so i'd think your 944 does have one. It will either be mounted on the ABS unit under the front drivers wing or the master cylinder. Either way the part number is the same wether it is an S2, turbo or a lux.

Replacing the proportioning valve to a pre-'85 928 one is a job on my list since upgrading to big blacks to move the bias rearward a tad, but i've not been out on track yet to feel what the car is like under really heavy braking. On road the stock balance seems to be perfectly fine despite the bigger brakes up front.
 

Posts made and opinions expressed are those of the individual forum members

Use of the Forum is subject to the Terms and Conditions

Disclaimer

The opinions expressed on this site are not necessarily those of the Club, who shall have no liability in respect of them or the accuracy of the content. The Club assumes no responsibility for any effects arising from errors or omissions.

Porsche Club Great Britain gives no warranties, guarantees or assurances and makes no representations or recommendations regarding any goods or services advertised on this site. It is the responsibility of visitors to satisfy themselves that goods and/or services supplied by any advertiser are bona fide and in no instance can the Porsche Club Great Britain be held responsible.

When responding to advertisements please ensure that you satisfy yourself of any applicable call charges on numbers not prefixed by usual "landline" STD Codes. Information can be obtained from the operator or the white pages. Before giving out ANY information regarding cars, or any other items for sale, please satisfy yourself that any potential purchaser is bona fide.

Directors of the Board of Porsche Club GB, Club Office Staff, Register Secretaries and Regional Organisers are often requested by Club members to provide information on matters connected with their cars and other matters referred to in the Club Rules. Such information, advice and assistance provided by such persons is given in good faith and is based on the personal experience and knowledge of the individual concerned.

Neither Porsche Club GB, nor any of the aforementioned, shall be under any liability in respect of any such information, advice or assistance given to members. Members are advised to consult qualified specialists for information, advice and assistance on matters connected with their cars at all times.

Back
Top