Rear Brake Upgrade for 1985.5
01-30-2007, 05:56 AM
#31
Race Director
Originally Posted by jerhofer
When the previous owner installed the big Red's, he also changed the master cylinder to the later model which has the proportioning valve on the master cylinder.
01-30-2007, 06:35 AM
#32
Burning Brakes
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Did a little digging around on this one and think I have an interesting tidbit about the valves.
Yes, non-ABS 951's do have the proportioning valve threaded in the rear hard brake line postion on the master cylinder, but apparently the 5/18 variety. Anecdotally, it appears the non-ABS 944S model were blessed with the more desirable 5/33....meaning that it allows roughly twice the hydraulic power to reach the rears before it begins limiting the pressure.
Probably a factory decision that early 951's were more skitish in the rear than the less powerful 16V NA and thus needed the lower limiting threshold.
But for serious performance driving, the 5/33 gives you more inital bite upon calling on the binders, although advisably in a straight line
When I swapped the OE 5/18 out of my Turbo S for the 5/33 I noticed an immediate improvement in decel when hard on the whoa peddle, less nose dive and haven't yet encountered any new tail end skittishness to date.
Yes, non-ABS 951's do have the proportioning valve threaded in the rear hard brake line postion on the master cylinder, but apparently the 5/18 variety. Anecdotally, it appears the non-ABS 944S model were blessed with the more desirable 5/33....meaning that it allows roughly twice the hydraulic power to reach the rears before it begins limiting the pressure.
Probably a factory decision that early 951's were more skitish in the rear than the less powerful 16V NA and thus needed the lower limiting threshold.
But for serious performance driving, the 5/33 gives you more inital bite upon calling on the binders, although advisably in a straight line
When I swapped the OE 5/18 out of my Turbo S for the 5/33 I noticed an immediate improvement in decel when hard on the whoa peddle, less nose dive and haven't yet encountered any new tail end skittishness to date.
01-30-2007, 10:47 AM
#33
Racer
Thread Starter
Originally Posted by tifosiman
The valve just screws onto any cylinder, it isn't part of it.
01-30-2007, 10:51 AM
#34
Race Director
I guess my point is that the valve is not technically part of the cylinder, it is a bolt-on part, that's all. 
Just wanted to clarify (so that one doesn't expect the valve to come with a new cylinder if they purchase one). Hope that makes more sense.
Have fun with the new brakes on the DE!
Just wanted to clarify (so that one doesn't expect the valve to come with a new cylinder if they purchase one). Hope that makes more sense.
Have fun with the new brakes on the DE!
01-30-2007, 10:57 AM
#35
Burning Brakes
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Mental note on the trial and error method: If you can see where you just were through the windshield, you probably should apply the brakes more gingerly the next time around
Have fun at your DE, let us know how it all works out! Inquiring minds want to know.
Have fun at your DE, let us know how it all works out! Inquiring minds want to know.
01-30-2007, 02:09 PM
#36
Racer
Thread Starter
Originally Posted by TheRealLefty
Mental note on the trial and error method: If you can see where you just were through the windshield, you probably should apply the brakes more gingerly the next time around
Have fun at your DE, let us know how it all works out! Inquiring minds want to know.
Have fun at your DE, let us know how it all works out! Inquiring minds want to know.
Years ago I installed basically the same brake system on a 911SC with a turbo motor. The velocities were much higher than those I will be reaching with this car. so when the rears were grabbing more than the front, it became very interesting. To say the least, it was very easy to rotate the car. I just wasn't sure which way it would rotate!!
Last edited by jerhofer; 01-30-2007 at 04:51 PM.
