Steering, Suspension, & Brakes

tips, technology, tools and techniques related to non-driveline mechanical components

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Jim Stabe
Jim Stabe
San Diego, Ca
(726 posts)

Registered:
02/28/2009 10:01AM

Main British Car:
1966 MGB Roadster 350 LT1 Chevy

authors avatar
Power brakes are phenominal
Posted by: Jim Stabe
Date: March 15, 2019 10:55AM

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.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5819 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

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Re: Power brakes are phenominal
Posted by: BlownMGB-V8
Date: March 15, 2019 12:28PM

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

Jim


Jim Stabe
Jim Stabe
San Diego, Ca
(726 posts)

Registered:
02/28/2009 10:01AM

Main British Car:
1966 MGB Roadster 350 LT1 Chevy

authors avatar
Re: Power brakes are phenominal
Posted by: Jim Stabe
Date: March 15, 2019 01:12PM

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.


MGBV8
Carl Floyd
Kingsport, TN
(3780 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

authors avatar
Re: Power brakes are phenominal
Posted by: MGBV8
Date: March 15, 2019 03:30PM

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


ex-tyke
Graham Creswick
Chatham, Ontario, Canada
(1083 posts)

Registered:
10/25/2007 11:17AM

Main British Car:
1976 MGB Ford 302

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Re: Power brakes are phenominal
Posted by: ex-tyke
Date: March 15, 2019 03:42PM

Quote:
I am looking for a better booster than my OEM booster.
...I, too, am in line to see how this develops.


Jim Stabe
Jim Stabe
San Diego, Ca
(726 posts)

Registered:
02/28/2009 10:01AM

Main British Car:
1966 MGB Roadster 350 LT1 Chevy

authors avatar
Re: Power brakes are phenominal
Posted by: Jim Stabe
Date: March 15, 2019 04:37PM

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.


MGBV8
Carl Floyd
Kingsport, TN
(3780 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

authors avatar
Re: Power brakes are phenominal
Posted by: MGBV8
Date: March 15, 2019 07:01PM

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:

[forum.britishv8.org]



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



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