B-Body Vac booster better than G-Body?

Mark E.

I have done the vacuum conversion on my car. I have the 12 inch 1LE front brakes. I use a B-Body 1 1/8 master cylinder and currently have a G-Body vac booster. The booster is leaking vacuum and I need to replace it. I have heard of people using the B-body Vac booster and have 2 questions.
1) Is it better than the G-body booster?
2) Do I need the B-body pedal, or is a vac G-body pedal ok?

Mark E.

Well I guess I am going to Pick and Pull to do my homework.
I was just hoping someone had been down this road before.
I will post my findings when I am done.


Slow GN Fizz!
G-body is a smaller dual diaphram booster, while the B-body is a larger single diaphram unit. I don't know if the larger b-body size will fit well on the firewall. Haven't heard of a greater benefit either way.
HTH, CaptRob

Mark E.

So the B-body booster only comes as a single diaphram?

I have read that a dual diaphram is better in an old Chiltons type reference book I have. Sound reasonable?

If that is the case, I guess I will try to find my reciept and check the warranty on the leaking one I have that I purchased less than 1 year ago.

Thanks for the help.

Louie L.

Habitual Line Stepper
Staff member
I dont know if the B bod unit comes only in a single. Im not brake system literate:D But i did have a vac conversion on my car with the large diameter single diaphram booster. I went back to the power monster.


Active Member
I tried the vacuum conversion also, but went back to the PM.

I bought a complete unit from the junkyard off an '86 Regal - $50.
I don't trust junkyard parts, so I bought a lifetime warranty master cylinder - $40.
The Casper vacuum block for the TTA wasn't available yet - I bought one of the two GM had - $85.
I installed the assembly & the vacuum booster unit from the junkyard leaked vacuum - lifetime warranty one - $90.
A couple times on the street when pulling out into heavy traffic (read WOT- maximum boost & no vacuum to operate the vacuum brake boost unit), I would have somebrain dead about 2-300' up the road also pull out. By the time I would realize the road is totally blocked (by the brain dead in the Toyota or the suv), i'd be over 40 mph & have to use both feet on the brake pedal to stop (also the traffic behind me is moving 40 - 50 mph.
I bought a vacuum booster pump for the early '80s Citation to give me vacuum to the brake booster all the time - $240.
After about a year the vacuum brake booster developed a vacuum leak. The leak was not steady & varied with every application & release of the brakes. Troubleshooting my IAC was a real hair puller until I figured out the vacuum brake unit was leaking. No problem, lifetime warranty, I got & installed another unit.
The now third vacuum brake booster developed a leak in abou a week. My last trip home from work with this vacuum booster unit was a nightmare. The computer was adding fuel to the leak & the TR was ideling at approximately 2k rpm or 70+ mph. At the seemed like thousands of RED lights, using both feet to hold the brakes, the TR would not idle & would die unless I fed it more footfeed - however it took both feet to hold the brakes. I guess I was fortunate the seat didn't break loose from the floor.
I got my money back for the vacuum booster & have a Citatation unused vacuum boost pump for sale & bought a lifetime warranty PM. My IAC is now adjusted properly & the PM always works (so far). The only problem with the PM install was that the old unit had blown the fuse.
You can do what you want & I have two friends local who have had no complaints about their vacuum conversions. I just couldn't see the difference in price - PM lifetime warranty - $199. Vacuum conversion - $505 & couldn't set IAC.

Mark E.

Thanks for the input. The vacuum setup works perfect in my wifes car so far. Like you, my booster is giving me problems. I may just try to find a good junkyard booster if I get grief trying to get a warranty for my booster. My PM did work good while it worked. When it went out, I had the worst brakes I have ever had in any vehicle I have had so far. Thanks again,

Red Regal T

Senior Member
Originally posted by Roger

You can do what you want & I have two friends local who have had no complaints about their vacuum conversions. I just couldn't see the difference in price - PM lifetime warranty - $199. Vacuum conversion - $505 & couldn't set IAC.



Mark what symptoms are you having with the booster?I'm having similar probs as Roger but can't get the bl #'s right since the conversion.Well I can pinch off the booster hose and the bl's will be perfect!!!

Mark E.

My car would idle high every now and then when I put it in park. It had done this for a while. I cleaned the IAC. I had put a new one on a few years ago so I thought it was ok.

What made me start wanting to fix it was when I hit the brakes a few times from about 100 mph. It felt like glazed pads. Hard pedal and not the braking I expected. This was hitting them hard immediately after punching it. I changed the pads and adjusted the rear brakes. It was better but not fixed. I found if I held it in 2nd to around 4500 and then let off and hit the brakes, they worked great. Plenty of vacuum available to make the bad booster work.

When I compared my car to my wife's, I found her booster will hold vacuum and mine will not. I just checked her car that had not been driven for more than a day, and the booster is still holding vacuum. Mine looses it in less than a minute.

I am not looking forward to climbing under that dash to unbolt the booster.