Booster ?

Building 32 coupe and would like to put Power Brakes on it was looking at post and debate about 7 or 8 inch booster Have disc all four wheels what has some one used and brand would be nice Thanks

Most of the 7" boosters are a single diaphragm, the 8" or usually a dual diaphragm which helps the braking power with a bit less pedal effort. I've used both, the 7" will stop a car just fine, but the 8" dual diaphragm takes a bit of the pedal effort out of it. Big thing is to make sure the master cylinder you get is designed for 4 wheel discs, the diaphragm IMO is just a personal preference deal. Hope that helps, somebody will probably chime in with a bit more thorough explanation....

The first question to answer is whether your engine makes enough vacuum to produce any usable boost. You really need at least 15" for a booster to work ok. Any less and it's not going to do you much good to go to the trouble of installing a booster.

Use a Mustang Hydro boost off the power steering pump

Jerry brings up an interesting option, hydroboost. Here is a link to a discussion about them....
https://www.stovebolt.com/ubbthreads...09913&page=all
https://www.amazon.com/Universal-Hyd.../dp/B074DZCB49

Another option I might pursue is to use a straight hydraulic system with no booster at all. You can jockey the brake pedal length and the master cylinder piston diameter to arrive at a system that works well.
https://www.jalopyjournal.com/forum/...ooster.757027/
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Running ls1 motor with straight axle with manual steering . brake pedal mounted for master cylinder under floor..if I was going to go manual brakes what would be good master cylinder to use ? size bore and brand

You'll want to lean on the manufacturer that you buy parts from, but I would begin with maybe a 7/8" or 15/16" bore master cylinder and a 6:1 or 6.5:1 pedal ratio.
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Go with Tech, call the manufacturers, I have a 32 & a 37 both with boosters, and quite honestly if the mc is sized right you don't need either one on 4 wheel disc, a bunch of rod shops use no booster on the 30's cars, I didn't believe them and wasted my money to find out they where right

One problem with underfloor pedals like I have is the actuation ratio may only be 4:1, which won't work without a booster. You need something in the 6-7:1 range for manual brakes. Then you get lots of pedal travel. What size of booster you need can vary with the calper and rotor combination. I have Wilwood 6 piston front and 4 piston rear with 12 inch rotors. I wouldn't bother with any single diaphragm booster. I ended up with an 8 inch dual. The second diaphragm only adds about 25% more force. With Willwoods, no rear pressure reduction is needed. A change from a 1 inch MC to a 7/8 inch made the brakes a little too sensitive and made for more pedal travel than I liked.

I'll throw this out there-I have under-the-floor Pedals too, however I am running a 7" Dual Diaphragm Booster. My engine also does not create enough vacuum, and I am running a Concept One Serpentine Pulley system which negates the use of Hydroboost Pump (I'm not sure I'd want those Hydraulic lines running that close to my Exhaust anyway, it's tight under there)-

So, I investigated about every other avenue I could find, and it presented a few choices:

1. Buy one of those electric, aftermarket Vacuum Pumps, offered by Summit, Stainless Steel brakes and the like (which I did, but I wanted to mount it under the car to keep any noise out of the cabin-these MUST be mounted upright, and, they are a bit noisy, so they were out)-

2. I found that Electric Cars use a Pump made by Hella (Hella makes good stuff), and they offer three Pumps: UP28, UP30 and UP32-the difference being the designed life (the UP28 is designed for 600 hours of use, the 30 & 32 are 1200 hours)-the other upside is that they are a Vane pump (read: quiet and long lasting), and this design allows it to be mounted at any angle-I went this way, and doubled up on rubber mounting just in case-

I found out later that these Pumps are also used in early 90's Mustang Cobras, Audi's, VW's and some GM Car products-there is another design that is used in Diesel Pickups (Ford Dodge, GM), but I don't who manufactures them-go on Ebay, type in electric vacuum Pump-you'll be surprised-

Hope this helps-

1999 up ford super duty pick ups use an electric vacuum pump and they're usually on the RH inner fender near the middle by the fender. I'm currently trying to decide if I want to use my vac booster or go with a hydraboost I have. I'm leaning the vac booster since it's 2 less lines I have to run. The car stopped alright before with the stock MC so the better MC should be a big help already. :LOL:

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