Dual or single diaphragm booster?

[SD455]

Currently sorting out an A body with d52 front callipers, and rear drum brakes. The car pull 14HG of Vacuum warm, and currently has 1/18" bore master and a 9" single diaphragm booster in place. Brakes are OK for just cruising, but try bedding in pads, or doing a panic stop and they really fall short. I cannot lock the front wheels and pedal effort is beyond what reasonable.

I'm wondering if converting to a dual diaphragm 8" or 9" booster will solve the problem ( no room for an 11" single ) or if I should be looking at converting to manual brakes? In my mind 14HG of vacuum while not optimal should do the job in almost all cases. I'm not interested in converting to Hydraboost.

For those that are interested I'm currently running Hawk HPS pads on the front, and stock replacement shoes on the rear. There is a adjustable proportioning valve, and an RPV in the rear circuit.

Thanks

[Apogee]

Given your vacuum level, a dual-8" or dual-9" booster would make a world of difference in your brake feel and performance. The factory single-9" unit was intended to be used with power drum brake applications, which require less pressure than disc/disc or disc/drum applications.

Tobin
KORE3

[SD455]

I see the 8" dual readily available, with the 9" being slightly harder to find. I re tested my vacuum again today to make sure my memory was correct and once warm it pulls nearly 14hg, and will bounce around from 12-14hg depending on idle/timing. I have no plans to make changes to the engine that would decrease vacuum and I can see at some point changing cams to increase vacuum so assume this is the worst it will be. I'm not opposed to going back to manual, but never did achieve what felt like optimal braking without a booster.

Reading a little on another thread that yourself and Ron were commenting on I want to make sure I'm moving in the right direction and gain as much overall brake pressure as I can. With that in mind is a dual 9" the best overall choice, and in terms of difference what percentage would it increase? Looking at the charts the differences seem nominal from smalls to largest, but there seems to be a few different ways to calculate what the total system pressure is at the wheel.

Thanks!

[Apogee]

Moving from a single-9" to a dual-9" booster should basically double the gain/boost of the system. Moving from a single-9" to a dual-8" unit would be about a 60% increase in gain/boost, all other variables kept the same.

Tobin
KORE3

[Skip Fix]

My factory 81 Trans Am dual booster works fine unless vacuum gets below 10". 14" should be no big deal for a dual. In fact the factory even reduced the pedal ratio over the 11" single booster disc/drum setup up.

[SD455]

Hi Tobin,

I inquired about a dual 9" to the folks at The Right Stuff this was the response I got. Not trying to argue, just wondering where they got that info from or how they have made that calculation as it seems wildly different than yours. I wasn't able to find any charts online that support your calculations, although you seem like a much more reliable source with some real world experience.

"We do not carry a 9" dual booster. We have an 8" inch dual that will provide 10-15% more assistance than your 9" single.

Best Regards,

Heather Ross
The Right Stuff Detailing
p 800.405.2000
f 614.523.3659
www.getdiscbrakes.com "

[Apogee]

You're free to argue all you like, but I don't know how they're calculating their gain factors, or what losses they're estimating through the booster. That said, their number looks low based on both my calculations and experience. The dual-7" boosters provide about 10-15% more gain than a single-9" unit in my experience, making them more or less comparable in my mind. The dual-8" units should clearly make more boost/gain than a dual-7" unit, so something isn't adding up. Maybe TRSD provided the specs for a dual-7" instead of dual-8" unit, but I can only make less than educated guesses at this point...that would be a better question for TRSD I would think.

Tobin
KORE3

[gray86hach]

http://www.tuffstuffperformance.com/...od/prd8672.htm