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
(720 posts)

Registered:
02/28/2009 10:01AM

Main British Car:
1966 MGB Roadster 350 LT1 Chevy

authors avatar
Re: Power Brake Boosters
Posted by: Jim Stabe
Date: March 17, 2019 10:32AM

I ran across this on the internet this morning. [brakepower.com]


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5812 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: Power Brake Boosters
Posted by: BlownMGB-V8
Date: March 17, 2019 12:10PM

The booster itself is a vacuum canister, and should hold enough for one or two boosted applications, maybe more depending on how hard you hit the pedal. An aux canister will add more uses between. You can base the size on the booster itself.

Jim


MGBV8
Carl Floyd
Kingsport, TN
(3761 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Power Brake Boosters
Posted by: MGBV8
Date: March 17, 2019 12:43PM

Yeah, a reserve canister is not going to help an engine with low vacuum to begin with. I guess that means using an electric vacuum pump, like Bill suggested.

Here is a Brake Bias calculator to go with the one Jim S. posted.

[www.tceperformanceproducts.com]


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

Registered:
02/28/2009 10:01AM

Main British Car:
1966 MGB Roadster 350 LT1 Chevy

authors avatar
Re: Power Brake Boosters
Posted by: Jim Stabe
Date: March 17, 2019 02:09PM

This is the calculator I used to design my brake system. It is an Excel spreadsheet so I couldn't post mine on this site but you can download it - it is the attachment in the first post. I like this one because it takes center of gravity height into account as weight is transferred during a stop. It came out pretty much on the money for my car.
[locostusa.com]


88v8
Ivor Duarte
Gloucestershire UK
(689 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: Power Brake Boosters
Posted by: 88v8
Date: March 17, 2019 02:58PM

My TR6 with its big cam, made 7" at idle. And it does matter, because if you're tootling down the high street at pretty much idle, that's how much vacuum you have when some pedestrian walks out in front of you.
So I fitted an electric vac pump and a vacuum switch, gave me 19".

Worked well for the five years I ran the car.

Ivor


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5812 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: Power Brake Boosters
Posted by: BlownMGB-V8
Date: March 18, 2019 10:06PM

Thanks for the link on that spreadsheet. After inputting values it is obvious from the results that I have a problem in the front calipers. Must be some stuck pistons, blockages, or something. Didn't think it was working the way it should.

Jim


MGBV8
Carl Floyd
Kingsport, TN
(3761 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Power Brake Boosters
Posted by: MGBV8
Date: April 10, 2019 09:40AM

Finally went out & measured the vacuum on my engine. Warmed up, it pulls 17" with an occasional dip to 16". When I reve the engine to 2500rpm or so & let off, it jumps to 21". That seems pretty normal at my altitude of 1450'.

The MGC, over the years, had a number of different booster ratios available ranging from 1.6 to 3.0. Rather than changing my booster to something else, I would like to source a stock size booster with a higher boost ratio. If, there is such a thing.

Hmm....
Quote:
IMHO the PBR VH40 units, either in dual NA spec or solo EU, AU configuration, are state of the art direct replacements for the OEM calibration of the Girling MKIIB units. I have only spent a little time going through some barely legible spec information to conclude the VH40 PBRs have about a 30% more effective boost than the OEM Girlings which compare nearly equally to the larger Lockheed substitutes. -Robert Kirk
[www.mgexp.com]




MGBV8
Carl Floyd
Kingsport, TN
(3761 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Power Brake Boosters
Posted by: MGBV8
Date: April 11, 2019 02:49PM

Nevermind, the PBR VH40 boosters are remote only.


mgb260
Jim Nichols
Sequim,WA
(1991 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Power Brake Boosters
Posted by: mgb260
Date: April 11, 2019 04:43PM

Carl, I saw a picture recently of a dual diaphram street rod booster in a MGB but can't find it now.


MGBV8
Carl Floyd
Kingsport, TN
(3761 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Power Brake Boosters
Posted by: MGBV8
Date: April 11, 2019 09:12PM

On this thread, Jim? ;)

Mike Stemp posted some pics of his on page one. Seems the way to go.


mgb260
Jim Nichols
Sequim,WA
(1991 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Power Brake Boosters
Posted by: mgb260
Date: April 12, 2019 01:09AM

Carl, Yep, that is the one. I looked everywhere except page one on this thread. Speedway has them:

[www.speedwaymotors.com]



Edited 1 time(s). Last edit at 04/12/2019 01:11AM by mgb260.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5812 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: Power Brake Boosters
Posted by: BlownMGB-V8
Date: April 12, 2019 09:08AM

Helpful video on that link too. Not too long.

So to be clear, the advantage of the dual diaphragm is that it doubles the pressure applied to the M/C? (for the same booster diameter)

Jim


MGBV8
Carl Floyd
Kingsport, TN
(3761 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Power Brake Boosters
Posted by: MGBV8
Date: April 12, 2019 09:54AM

I don't think it doubles, Jim. Just eyeballing the 7" dual booster, the front diaphragm looks to be a good bit smaller than the rear.

Not much info out there on actual booster ratios. Did find this on Ebay:

"A 7" Dual booster gives you 27% more stopping power than a 7" single"

I think the MGB booster is a 6", so a 7" dual booster should be quite an improvement.



Edited 2 time(s). Last edit at 04/13/2019 11:45AM by MGBV8.


88v8
Ivor Duarte
Gloucestershire UK
(689 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: Power Brake Boosters
Posted by: 88v8
Date: April 25, 2019 04:19AM

Well, I'll tell ylou something about boosters you probably already know; they can leak.

The Bendix Hydro Vac on my Rambler had 56 years in service, it was working, but I thought it was time for a refresh, so I sent it for rebuild.
On return, they mentioned that it had a big vacuum leak and on their test rig it didn't work at all.
Now, their test rig doesn't have a 327 vacuum pump, so it was working on my car.
And even with the engine off, it held some vacuum.

But as I now realise, it wasn't working very well. The brakes now are a lot sharper.

And, I've had an intermittent problerm where the engine won't idle. Happened after a long run when it was thoroughly hot. Couldn't find any cause, thought it was bad petrol.
And. it used to pink on acceleration even though the timing is correct,.

Now, both those problems have gone.
Cause? I guess, the vacuum leak.

The more stuff you have, the more there is to go wrong.

Ivor



Edited 1 time(s). Last edit at 04/25/2019 04:20AM by 88v8.


302GT
Larry Shimp

(201 posts)

Registered:
11/17/2007 01:13PM

Main British Car:
1968 MGB GT Ford 302 crate engine

Re: Power Brake Boosters
Posted by: 302GT
Date: July 13, 2019 09:11AM

I bought the dual diaphragm booster from Speedway referenced earlier in this thread and installed it along with a new master cylinder (the master cylinder was needed because the stud spacing is much wider than the MGB master cylinder hole spacing). The boost is much more effective than stock, pedal effort is far lower but the brake feel is still very progressive.

The booster fits the MGB location without modifying the mounting surface. However, for ease of installation (relative) I shortened the mounting studs on the booster so that the retaining nuts could be tightened with a 1/8 inch drive inch socket. I also had to make a clevis to adapt the booster input push-rod to the MGB brake pedal. The booster push-rod is threaded 3/8-24 and clevises fitting that are way too big. I made the clevis from 1/8 inch thick, inch wide bar stock. I bent it around a 3/8 inch bolt (to get the proper spacing), welded a 3/8 stop nut to the end, then drilled through the clevis and threaded it 3/8-24, starting the tap in the stop nut. To finish, I drilled the clevis for the brake pedal pin, then compressed the ends in a vise so that the cotter pin would go in the end of the pedal pin. I also shortened the booster push rod as needed. The master cylinder fits on the booster with no clearance problems with the hood. Plumbing was simple because I have 4 wheel disk brakes and had no need for proportioning valves or pressure retention valves. But there are many master cylinder options besides the Wilwood cylinder I used. Just about any GM, Ford, or Chrysler cylinder will bolt up to the booster and these are available for disk/drum configurations with built-in pressure retention valves for the drum circuit. I do not know if these alternative master cylinders will fit in terms of hood clearance, but for reference the Wilwood cylinder I used is 8.15 inches long, 3.22 inches high from the center of the bore, and 3.14 inches wide at the reservoir. The widest part of the reservoir is about an inch from the side of the engine compartment and the height of the front of the reservoir is about equal to the top of the channel containing the fender bolts. Note: the Wilwood master cylinder came with a push rod extension that goes between the booster and master cylinder. This may be needed but not included with a different master cylinder, but the extension rod is available separately from Wilwood.
booster.jpg
clevis.jpg



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

Registered:
10/25/2007 11:17AM

Main British Car:
1976 MGB Ford 302

authors avatar
Re: Power Brake Boosters
Posted by: ex-tyke
Date: July 13, 2019 11:43AM

Damn you, Larry.....now you've got my project wheels turning.
...nice installation summary.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5812 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: Power Brake Boosters
Posted by: BlownMGB-V8
Date: July 14, 2019 11:12AM

Pretty clean install Larry, worth keeping in mind.

Jim


MGBV8
Carl Floyd
Kingsport, TN
(3761 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Power Brake Boosters
Posted by: MGBV8
Date: July 15, 2019 05:42PM

Is that 7" diameter booster, Larry?


302GT
Larry Shimp

(201 posts)

Registered:
11/17/2007 01:13PM

Main British Car:
1968 MGB GT Ford 302 crate engine

Re: Power Brake Boosters
Posted by: 302GT
Date: July 31, 2019 08:14AM

It is a 7 inch booster;

[www.speedwaymotors.com]


MGBV8
Carl Floyd
Kingsport, TN
(3761 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Power Brake Boosters
Posted by: MGBV8
Date: July 31, 2019 12:06PM

Thanks, Larry. Please post your review of the swap. This is something I have pondered for quite some time.
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