Power Brake Booster '70 B Body

Lost the brakes in my GTX. I have very low vacuum due to the cam so the brakes are usually sketchy at best but now I have nothing (extremely hard pedal). I believe it can only be the master cylinder or the power booster. All the vacuum lines are OK and I do have an aftermarket reservoir under the battery tray to increase vacuum reserves. Getting ready to dive in so I decided to look for a new power booster in case I need one but I can't find one anywhere for a '70 B body. What options are out there??? I prefer stock-ish look for the GTX but may stray from that if I can find something that will give me good brakes with 6" Hg at idle.

With only 6" at idle you may want to consider a Hydro-Boost setup. Of course, that won't look anywhere near stock. Those dual diaphram Bendix boosters are hard to find. Near impossible. Consider sending yours out for a rebuild if you have an original.

Yeah, I don't want to go with the hydro-boost, but it's a good idea.

If I end up not being able to find an original replacement I'll have to see if I can find a place that will rebuild mine.

Are the originals really a dual diaphragm unit?

Also, what is the chance that after sitting for 4-5 months the master cylinder is causing the very hard pedal and not the booster?

BOOSTER DEWEY

while they do fail, I would start looking at your vacuum reserve first.
see if you have a leak somewhere else.

put a vacuum pump on the booster and see if it holds vacuum and the brakes get better.

a bad master doesn't fail like that normally.
pedal to the floor for a bad master, or slowly falling when holding the brakes.

hard pedal is lack of vacuum or bad booster.

they also make the electric vacuum pumps to help too. you could hide that and thus still look stock.

I've looked at the lines and reserve tanks and they seemed fine (had my 6" of vacuum at the fitting to the booster.

I'll have to find a consistent vacuum source to check the booster. I have one of the hand units and I tried to pump up the booster but after 5 minutes I was only up to ~10" of vacuum. Not enough volume in that little pump.

I've seen the electric pumps, they're pretty expensive but I guess fixing the front of the car due to an accident would cost more!!

I had no idea what you were talking about so I searched the net. Not too bad of price and not too far away. Thanks for the information!!!!

Is it a disc brake or drum brake car? The boosters are different. Do you have a car with 15+ inches of vacuum? Even a new car. Run a long hose from that car to the booster on the GTX and see what it does.

But I will say that your booster is,bad, and the master is not causing this problem.

You might try removing the booster and run in them as manual brakes.

Booster Dewey is the place to go for booster rebuild.

I've got a couple more thoughts for you since about 6 months ago my '70 Road Runner lost its brakes (hard pedal, not going to the floor, but no brakes).

1. My car's problem was TWO bad Inline Tube metering valve/proportioning valve (split on '70, can't remember the correct name, but the part where you hold the little pin out to bleed the brakes). The quality control on those parts is TERRIBLE.

2. You can get a pretty close to original looking brake booster (dual diaphragm) which they sell on Ebay. I had to slightly (1/8") enlarge the hole in my firewall (not visible once installed) and I did not need to buy the "heavy duty bracket", maybe because my car was stock front disc.

the airgrabber hood is a good place to lose vacuum and the switch under the dash will also leak.

It is a disc brake car. When the weather improves enough (foot of snow on the ground now) I'll put another car along side and see what happens then. Thanks for the suggestion.

Wow, never heard of the metering valves doing that. Must have been preventing the fluid from reaching the caliper/wheel cylinders so it had a hard pedal.

Good call. I think I checked everything for leaks but I will double check before I spend any money on parts.

Booster Dewey if you need a rebuild...

Yep, that's exactly what the mechanic told me. After replacing it twice from two different vendors I was ignoring what was obvious.