Steering, Suspension, & Brakes

I have C4 Corvette suspension and brakes in my car with dual master cylinders and a balance bar (race car stuff). Even with 5/8" master cylinders installed the car's braking still required a heavy leg to get it to stop quickly. I'm getting old and I don't like having to push that hard anymore so I decided to install vacuum boosters. That is vacuum boosters (plural) because I have two separate braking systems for the front and rear brakes and the master cylinders are located inside the passenger compartment behind the dash. When my car had a turbocharged 215 Olds and stock front brakes with Jag XKE rear brakes, I installed a remote booster from an MGC that worked on both the front and rear brakes. The car's stopping power was phenomenal. I scared more passengers with the stopping ability than its acceleration. So I decided to install 2 boosters - one for the front brakes and another for the rears. I found a dual circuit booster setup from a company in the UK that looked like it might be the answer. I wanted to mount it out of the engine compartment but the only place in the car it would fit is on the shelf in the front of the trunk. There were a couple issues putting it there. I didn't want to lose that space in the trunk and the plumbing routing would have been a lot longer. The front brake hydraulic lines would have to go from the master to the trunk and then back again to the front brakes. The vacuum line would have also been longer than I wanted. Besides the plumbing issues the cost of the unit was $400 plus the shipping from the UK. If I ever had a problem with the unit the car would be down for an extended period and I would have to pay shipping both ways.

I finally discovered a single circuit vacuum booster that was only 7" in diameter and was available from a distributor in California. I could buy two of them for $230 (for both) and free shipping. These units were designed for the Australian market and were OEM fitted to several cars. I found a good place to mount the units right under the headlights in front of the front wheel. I had to move bracing members on both sides but it gave me a few advantages. I mounted the front booster on the passenger side and was able to tie into the front brake circuit at the junction of the hard line and flex line to the right front wheel. This means that I only have to penetrate the front of the passenger footwell with one line from the front master cylinder. The rear booster mounts on the drivers side and required 2 penetrations of the front of the drivers footwell, one for the master to booster line and one for the booster output that connects the existing line to the rear brakes. I didn't have to do anything to the existing plumbing aft of the instrument panel. Vacuum runs will be much shorter since both boosters will be right next to the engine. I fabricated a vacuum reservoir out of 1 1/4" thin wall tubing that spans the distance between the two boosters to ensure braking since I have a boosted engine. I installed a one way valve between the engine intake and the reservoir to prevent boost from getting to the reservoir even though the boosters have one way valves built in - belt and suspenders. It took about 17' of brake line to plumb it up but that ia about half of what it would have been if I mounted the boosters in the trunk.

So how does it work? I took it for a drive this afternoon and the feel is exactly how I wanted to be - slightly easier braking at low pedal pressure around town and it will throw you through the windshield if you really stomp the pedal in a panic stop. Full disclosure, I have 275 section tires on the front and 315's on the rear and they are 200 treadwear rated so they are very sticky and wheel lockup takes place at pretty high G force. I want to dial in the front/rear balance and then do some measured stops. I think I can come close to a 100' stop from 60 mph which is what the supercars do with their huge carbon brakes.

Thanks for the update Jim. A few of us are also considering a brake booster.

Jim

There's a lot more detail in part 6 of my journal on this site. BTW I took the 5/8" masters out and put the 3/4" back in at the same time. I wanted to have the extra volume and higher pedal. Not sure if it was necessary or not.



Edited 1 time(s). Last edit at 03/15/2019 02:24PM by Jim Stabe.

I am looking for a better booster than my OEM booster.

Quote:

I am looking for a better booster than my OEM booster.

...I, too, am in line to see how this develops.

Carl- Are you looking for a higher boost ratio? The one I used is only about 2:1. The advantage for me is that I don't have the big clunky booster in the engine compartment. I'm not sure what effect using separate boosters for front and rear brakes has but in the end all it is doing is doubling the input line pressure so it shouldn't matter.

Yes, I would like a bit higher ratio. I guess need to do some digging & find out what it is now.

I wouldn't mind using a remote booster, if need be. Although, I guess that means 2 booster for me, as well.

Here's your original brake booster thread:

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Edited 2 time(s). Last edit at 03/16/2019 10:34AM by MGBV8.

Has anybody considered the hydro boost system?
GM used it on everything from the astro van to the cadillacs. Others have used it as well including Land Rover variations.
Most used the power steering pump for power but many also used an electric pump and accumulator.
The actual unit is small, powerful and bullet proof.
I just put one on a Vixen 21 motor home and it transformed the vehicle.
Food for thought.
Cheers
Fred

Having just completely re-engineered my brakes and now having had time to try them out a bit, I have to say that I'm quite satisfied with their performance and have no inclination to look at power boosters. In my case it was mostly a matter of proper sizing of the hydraulic components. My master cylinders are probably as small as I could go without getting into trouble and the online calculator shows the system to be capable of a .7g deceleration with somewhere around a 70-80lb pedal pressure. In use it feels just about like it should, not too heavy and not too light. It's also worth mentioning that my pads (Porterfield R4S) have only a .41 coefficient of friction, leaving a generous path to lower pedal pressures.

I cannot emphasize highly enough the need to use the brake calculator when modifying a braking system. It may seem like a lot of work putting in all of the various vehicle parameters to get a good result, but the more sophisticated the calculator is, the more closely it will approximate real life results. I could have NEVER, not in a million years have gotten the brakes I have now without it. It showed me exactly what effect every change I made to the system would have, and allowed me to make the changes that made the most sense for my specific setup. For instance, I have a balance bar with two masters and was able to set the bar to the center, and so far I haven't touched it to make adjustments. I will of course, but it has yet to be either necessary or desirable, that's how close it was right out of the box.

Jim

As a reminder, about a year ago I described how I put in a 7 inch diameter dual chamber booster that fit on the stock MGB pedal box along with a matching master cylinder (many will fit). Works far better than the stock MGB booster.

I haven't forgotten, Larry!

[forum.britishv8.org]

Dumb idea category ? If you are at smallest piston size(s), in master and don't want hydro or vacuum boost, change the mechanical ratio on the pedal ? Perhaps something like a, locked in index position, offset bushing for pedal pivot and relocate push rod hole ?

Something like this, Art? :)

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Well one can do that sort of thing. It's equivalent to fitting a smaller master but as you say if that's already done... the thing with increasing the leverage by moving the fulcrum point, is it also increases the pedal travel.
Without a servo, that's your limitation. When your foot hits the floorboards.

One can increase the available travel by lifting the pedal, but then you may have to lift your leg back to get from the throttle to the brake, as in my Land Rover with its smaller master. Or move the throttle pedal back. Or elastic floorboards.
There's a lot to be said for a servo.

Ivor