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

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....

QuoteIMHO 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

https://www.mgexp.com/forum/mgc-forum.48/new-brake-boosters-again.2096630/

Nevermind, the PBR VH40 boosters are remote only.

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

On this thread, Jim?  

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

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

https://www.speedwaymotors.com/Speedway-Dual-Diaphragm-Power-Brake-Booster-7-Inch-Chromate-Finish,8446.html?sku=91031432&utm_medium=CSEGoogle&utm_source=CSE&utm_campaign=CSEGOOGLE&gclid=EAIaIQobChMIgeeQneXJ4QIV7h-tBh2dyweGEAQYAyABEgLEkPD_BwE

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

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.

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

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 ½ inch socket on a 1/4 inch wobble drive extension. 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, ¾ 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.

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

Pretty clean install Larry, worth keeping in mind.

Jim

Is that 7" diameter booster, Larry?

It is a 7 inch booster;

https://www.speedwaymotors.com/Speedway-Dual-Diaphragm-Power-Brake-Booster-7-Inch-Chromate-Finish,8446.html?sku=91031432&utm_medium=CSEGoogle&utm_source=CSE&utm_campaign=CSEGOOGLE&gclid=EAIaIQobChMIgeeQneXJ4QIV7h-tBh2dyweGEAQYAyABEgLEkPD_BwE

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

Larry,  What is the piston diameter of your Wilwood master cylinder?  Thanks.

The piston diameter is 1 inch. This is also rather commonly found in OEM master cylinders.

I have now driven a few hundred miles with the new booster and I can report that it works even better than I expected. It allows the true power of the Wilwood front brake conversion to be realized. Pedal effort is low, very much like any modern car, but the brakes are easy to modulate. The highest speed stop I have tried was from 90 mph and it was effortless. This is almost a bolt in conversion with only minor fabrication needed, and probably has the biggest improvement vs time or cost of anything that can be done to an MGB. I am hoping someone who already has the stock MGB booster tries this and provides an independent assessment of the advantages...

Thanks for the update, Larry!

I plan to, maybe this Fall.  Do you think it would provide similar results with the OEM master cylinder size?

With a smaller bore master cylinder the booster will appear to be even more powerful but there would be a somewhat longer pedal travel than what I have. However, if you have stock brakes pedal travel will be stock, but I assume you have upgraded brakes...
In any case,  you will need a new master cylinder since the MGB cylinder flange is too narrow.

I have always had stock brakes.  Still have the original front rotors on the car.  

I guess you don't get them turned when you replace the pads?

I may have had them turned once in 1991.  I need to measure them again.  I'm sure they are at or below minimum specs by now.