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Power Brake Booster '70 B Body #2250019 02/08/17 11:40 PM 02/08/17 11:40 PM
Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington V VITC_GTX OP master
VITC_GTX OP master V Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington	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. Last edited by VITC_GTX; 02/08/17 11:44 PM.

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2250029 02/08/17 11:52 PM 02/08/17 11:52 PM
Joined: Jan 2004 Posts: 1,249 North Carolina 4 469runner pro stock
469runner pro stock 4 Joined: Jan 2004 Posts: 1,249 North Carolina	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.

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2250034 02/08/17 11:58 PM 02/08/17 11:58 PM
Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington V VITC_GTX OP master
VITC_GTX OP master V Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington	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.

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2250112 02/09/17 01:26 AM 02/09/17 01:26 AM
Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington V VITC_GTX OP master
VITC_GTX OP master V Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington	Are the originals really a dual diaphragm unit?

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2250113 02/09/17 01:27 AM 02/09/17 01:27 AM
Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington V VITC_GTX OP master
VITC_GTX OP master V Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington	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?

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2250123 02/09/17 01:42 AM 02/09/17 01:42 AM
Joined: Jan 2003 Posts: 5,357 Rancho Cordova, California (Sa... hemi71x master
hemi71x master Joined: Jan 2003 Posts: 5,357 Rancho Cordova, California (Sa...	Originally Posted By VITC_GTX 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. BOOSTER DEWEY RF-4C Phantom 69-370 Zweibrucken, Germany

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2250132 02/09/17 01:50 AM 02/09/17 01:50 AM
Joined: Feb 2003 Posts: 8,671 A Andrewh master
Andrewh master A Joined: Feb 2003 Posts: 8,671	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.

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2250144 02/09/17 02:13 AM 02/09/17 02:13 AM
Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington V VITC_GTX OP master
VITC_GTX OP master V Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington	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!!

Re: Power Brake Booster '70 B Body [Re: hemi71x] #2250145 02/09/17 02:14 AM 02/09/17 02:14 AM
Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington V VITC_GTX OP master
VITC_GTX OP master V Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington	Originally Posted By hemi71x Originally Posted By VITC_GTX 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. BOOSTER DEWEY 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!!!!

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2250155 02/09/17 02:36 AM 02/09/17 02:36 AM
Joined: Dec 2003 Posts: 4,951 northwest USA N NANKET master
NANKET master N Joined: Dec 2003 Posts: 4,951 northwest USA	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.

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2250603 02/09/17 08:31 PM 02/09/17 08:31 PM
Joined: Jul 2011 Posts: 956 Chicago PurpleBeeper super stock
PurpleBeeper super stock Joined: Jul 2011 Posts: 956 Chicago	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. 70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2250611 02/09/17 08:42 PM 02/09/17 08:42 PM
Joined: Feb 2005 Posts: 464 C cmansell mopar
cmansell mopar C Joined: Feb 2005 Posts: 464	the airgrabber hood is a good place to lose vacuum and the switch under the dash will also leak.

Re: Power Brake Booster '70 B Body [Re: NANKET] #2250726 02/09/17 11:40 PM 02/09/17 11:40 PM
Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington V VITC_GTX OP master
VITC_GTX OP master V Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington	Originally Posted By NANKET 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. 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.

Re: Power Brake Booster '70 B Body [Re: PurpleBeeper] #2250727 02/09/17 11:42 PM 02/09/17 11:42 PM
Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington V VITC_GTX OP master
VITC_GTX OP master V Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington	Originally Posted By PurpleBeeper 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. 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.

Re: Power Brake Booster '70 B Body [Re: cmansell] #2250728 02/09/17 11:43 PM 02/09/17 11:43 PM
Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington V VITC_GTX OP master
VITC_GTX OP master V Joined: Mar 2003 Posts: 4,925 Tri-Cities, Washington	Originally Posted By cmansell the airgrabber hood is a good place to lose vacuum and the switch under the dash will also leak. Good call. I think I checked everything for leaks but I will double check before I spend any money on parts. Last edited by VITC_GTX; 02/09/17 11:43 PM.

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2256462 02/20/17 04:56 AM 02/20/17 04:56 AM
Joined: Apr 2014 Posts: 623 Zombieland Car Nut mopar
Car Nut mopar Joined: Apr 2014 Posts: 623 Zombieland	Booster Dewey if you need a rebuild...

Re: Power Brake Booster '70 B Body [Re: VITC_GTX] #2256536 02/20/17 01:06 PM 02/20/17 01:06 PM
Joined: Jul 2011 Posts: 956 Chicago PurpleBeeper super stock
PurpleBeeper super stock Joined: Jul 2011 Posts: 956 Chicago	Originally Posted By VITC_GTX Originally Posted By PurpleBeeper 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. 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. Yep, that's exactly what the mechanic told me. After replacing it twice from two different vendors I was ignoring what was obvious. 70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"

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