[s-cars] [urq] S-Car Brake system conversion- Read- no more PSpumpintegration <question>

Sun Mar 15 17:58:56 PDT 2009

You could just get a Tilton (or other) master cylinder with a smaller bore and/or re-drill the hole on the brake pedal for the master cylinder push rod. On the V8 944's that I build we have to delete the vacuum assist to make room. We just re-drill the hole in the pedal about 10mm closer to the pedal pivot to increase leverage. Pedal travel increases some, but the feel is great and there is no possible way for the assist to fail. 

Another route is to delete the assist, leave the stock master cylinder, and increase the size of the brakes. Larger brake pistons have the same effect as smaller master cylinder pistons - travel increases slightly, but so does leverage. Perfect excuse for going for some big reds! Our V8 951 race car uses a stock 944 master cylinder, stock pedal drilling, but 996TT huge reds and the brakes are awesome, not too stiff, not too soft, and has enough stopping power to lock the 11" wide front slicks at high speeds.

-Cody Forbes

> Guys,
> 
> Thanks for all your input. My mechanic is just about to do a 20vt
> conversion on an Urq and his plan was to do this conversion and use
> BIG brakes because this will be a track whore.  
> 
> His thought was to have an additional vac reservoir for track days
> because of that very reason Dennis. 
> 
> Ingo, you might have something there, Vac assist helper?hmmm.
> 
> I'm so sick of the idiot brake light and hard pedal, I just want it
> ffixed. My dilemna is strap a rebuilt POS PS pump on or go this route
> with some unknowns.  
> 
> My thought was, since I won't be tracking it in the next 3 months,
> get it working ala Dennis' and work on the vac assist issue later. 
> 
> Anymore thoughts would be great.
> 
> Thanks
> Brian
> 925-989-8997 PST
> 
> Leal and Trevor, you can chime in anytime ;-)
> 
> --- On Sun, 3/15/09, Ingo Rautenberg <ingo.rautenberg at gmail.com>
> wrote: 
> 
> From: Ingo Rautenberg <ingo.rautenberg at gmail.com>
> Subject: Re: [urq] [s-cars] S-Car Brake system conversion- Read- no
> more PSpumpintegration <question> 
> To: dgraber460 at aol.com, urq-bounces at audifans.com, cody at 5000tq.com,
> vinnieb2 at yahoo.com, s-car-list at audifans.com 
> Cc: urq at audifans.com
> Date: Sunday, March 15, 2009, 7:33 AM
> 
> 
> Interesting but not surprising. I wonder if something could be done
> on the order 
> of the old 4kq assist pump (maybe additional electric-driven vacuum
> pump). The 
> 4kq system, for those that recall, had a vacuum assist pump driven by
> the 
> camshaft. Not doable directly, of course. But that's essentially what
> you 
> need -- a vacuum assist helper.
> 
> 
> Ingo Rautenberg
> 
> -----Original Message-----
> From: dgraber460 at aol.com
> 
> Date: Sun, 15 Mar 2009 10:18:14
> To: <cody at 5000tq.com>; <vinnieb2 at yahoo.com>;
> <s-car-list at audifans.com>
> Cc: <urq at audifans.com>
> Subject: Re: [urq] [s-cars] S-Car Brake system conversion- Read- no
> more PS 
>  pumpintegration <question>
> 
> 
> I have an UR S6 with brake issues as well, so I can empathize with
> those 
> feelings! My car is briefly activating the anti-locks on every stop
> as the 
> speedo crosses 10 MPH on decel.
> In the FWIW department, I have switched my URQ over to the vacuum
> system from a 
> CGT, and it works fine for daily driver duty. However, I have tracked
> the car 
> twice since and found that 4 laps on a small tight course is all I
> get from the 
> vacuum system. In the? fifth lap on both courses the brakes went rock
> hard.?Still functional enough to keep me out of trouble, but the
> assist was 
> gone. Pulled into the pits and let it set for a few minutes and all
> went back to 
> normal. Four more laps and repeat.
> In the past when I have tracked a car with regular brake fluid (not
> SuprBlue) I 
> have encountered boiling brake fluid which required a much longer
> recovery time, 
> and felt much more disconcerting on use. The brakes would almost go
> away 
> completely.
> I'm definitely not suggesting you take either option and modify your
> brakes 
> in any way. That is totally your responsibility, but thought this
> information 
> might be of interest.?
> 
> 
> Dennis Graber
> Denver, CO
> 720-838-0558
> 
> 
> -----Original Message-----
> From: John Cody Forbes <cody at 5000tq.com>
> To: vinnieb2 at yahoo.com; s-car-list at audifans.com
> Sent: Sat, 14 Mar 2009 9:54 pm
> Subject: Re: [s-cars] S-Car Brake system conversion- Read- no more PS
> pumpintegration <question>
> 
> 
> 
> Without GOOD engineering a vacuum assisted system is not exactly a
> good idea 
> on a turbocharged car which is exactly why Audi went to hydraulic
> brake 
> boosters anyways. The '95 A6 system would likely not be suitable. It
> could 
> 
> likely be made to work, but I don't think it's worth the risk of a
> failure
> at the wrong time. The modern cars use a venturi vacuum pump to create
> vacuum for the brakes even when on boost, but these venturi's fail
> (get 
> clogged) on a somewhat regular basis.
> 
> -Cody Forbes
> 
> brian bilotti wrote:
>> S-Heads,
>> 
>> Anybody done this conversion? I'm sick of having brake issues with
>> the PS pump. My mechanic says that the A6 has a vac assisted set up
>> that eliminates the need for PS pump integration.
>> 
>> The need for some off the shelf parts and a check valve is all I
>> need.... I'm told.
>> 
>> ANY info would be great!
>> 
>> Thanks
>> 
>> Brian
>> 
>> 
>> 
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