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Power Brake booster bad?

AR67GTX

AR67GTX

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First off, I’ve never been inside a booster unit’s guts before so my knowledge of their inner workings is sparse.

I have a used booster I put on my 67 GTX years ago and it’s never seemed to do much as brake effort remains high. But since holding the brake pedal down while starting the engine causes it to drop a bit and then firm up, I figured it was working - at least somewhat. Finally I got around to pulling the hose on the check valve and putting a vacuum pump on it and . . . nothing. It can’t build or hold any vacuum inside the unit.

That’s kind of surprising as it’s an AC car with the vacuum line for the doors plumbed to a nipple on the check valve and the AC door vacuum pods all work fine. That and that the booster seems to do something when I start the motor had me thinking that everything was holding vacuum fine. But now it appears I’m just operating on manual brakes. I disconnected and capped the check valve vacuum nipple off to the AC while testing so all vacuum was applied to the booster only.

Sound right - I need a new booster?
 
And while I’m at it, does this look like the correct booster? 11” drums all around. Stock cam.

P1010287.jpeg
 
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Better pictures. Thanks on the reference. I didn’t figure rebuilding one of these with a crimped housing was a do-it-yourself project.

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Looks like a Midland single diaphragm 9-1/2” from the Harmon website
 
AR67GTX said:
Better pictures. Thanks on the reference. I didn’t figure rebuilding one of these with a crimped housing was a do-it-yourself project.

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IMO.....it appears to be a MIDLAND ROSS single diagram booster, which were zinc dichromate plated with clamp band. Original units were single diagram Bendix boosters used with power drum or disc brakes ....the HP engines USUALLY use with HEMI, 6 BARREL. CARS with disc brakes/drum brakes rear (10") used the BENDIX TANDEM DIAPHRAGM BOOSTER. I'm sure there are exceptions. There is/was a company called BOOSTER DEWEY in Oregon (??) that is an excellent rebuilding service.....don't do it yourself...requires special tools....and parts......google search for their name phone number and website.......
BOB RENTON
 
Thanks, think I’ll see about doing an exchange for a rebuilt Bendix model if they will take the Midland one as a core.
 
Bendix booster is very different than the Midland Ross ( drum brake cars ) you have now

Wrong master cyl btw
 
With drum brakes, stick with the Midland Ross single diaphragm booster like you have now. Using a Bendix dual diaphragm with drums is overkill and will make your brakes very grabby.
 
I would use a Bendix single diaphragm booster which appears to be what the Harmon site indicates was original. My motor has a stock cam.

Yes, the master cylinder was a NAPA expediency replacement 20years ago when I found the old one leaking and I was finishing up a brake job.
 
Here’s what mine looks like. Dirty picture is from sitting, 1979 until I restored it. Confident this is original to the car. 11” drums all around.

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69L48Z27 said:
Here’s what mine looks like. Dirty picture is from sitting, 1979 until I restored it. Confident this is original to the car. 11” drums all around.

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Thanks. I didn’t see an exact match for that on the Harmon website and their identification page but some of the models they represent in photos are the 2-bolt MC model so kind of hard to compare for a 4-bolt MC one. But looks to definitely be a Bendix single disphram.

Nice looking restoration.
 
I finally went back out to the garage to retrieve my 67 service manual and it indicates that both the Midland-Ross single disphram and Bendix single diaphragm units were used for drum brakes that year. I couldn’t find any differentiation as to which was used for 10” or 11” drums and there is very little information on the Bendix where the full rebuild details are shown for the Midland. Also I’m not sure if the Bendix uses the same lever assembly as the one on my Midland so now I’m back to probably sticking with the Midland-Ross unit as Dave6T4 said.

I’m learning more about PB boosters tha I ever anticipated I would need.
 
69L48Z27 said:
Here’s what mine looks like. Dirty picture is from sitting, 1979 until I restored it. Confident this is original to the car. 11” drums all around.

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Is this a 10inch drum brake car ? If so that style booster seems to be the most common ( not sure what manufacturer it is )
And the Midland Ross on 11inch drum brake cars.
Bendix on Disc brake cars
 
Bill - they are the 11” police package brakes - same as drums on your 66 Hemi unless it has power disc.

It is a Midland Ross unit. I got the booster out and on the bench. Nothing like crawling under the dash of a factory AC Mopar and twisting your arm and hand into all sorts of impossible places to get the bolts out. I’m going to send it off to Harmons for rebuilding.
 
gtx6970 said:
Is this a 10inch drum brake car ? If so that style booster seems to be the most common ( not sure what manufacturer it is )
And the Midland Ross on 11inch drum brake cars.
Bendix on Disc brake cars
Click to expand...
Car is 67 R/T. 11”.
 
I have a 1969 Dodge Coronet Frankenstein car, it is a survivor. I have a leak at the check valve. Turn it one way, it leaks, move it a bit and no leaks. Trying to find a replacement check valve with a grommet. Problem, I do not know the product line that the booster came from or the year. Parts people just laugh at me when I as if they have the part. Need some info on booster make and maybe a year range. Stuck in the drive way and need to get the windshield gasket replaced. Any assistance greatly appreciated.

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canblue said:
I have a 1969 Dodge Coronet Frankenstein car, it is a survivor. I have a leak at the check valve. Turn it one way, it leaks, move it a bit and no leaks. Trying to find a replacement check valve with a grommet. Problem, I do not know the product line that the booster came from or the year. Parts people just laugh at me when I as if they have the part. Need some info on booster make and maybe a year range. Stuck in the drive way and need to get the windshield gasket replaced. Any assistance greatly appreciated.

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Just looking at your first pix, it appears to be a SINGLE DIAPHRAGM BENDIX BOOSTER.....but it would correspond to what ever tge car came with. Most often, a single DIAPHRAGM booster was used with drum brakes, either 10-11" diameter. Midland Ross boosters were usually a yellowish color and an external clamp band. What vehicle, model year and engine??? FSM should be able to tell. The BENDIX TAMDUM BOOSTER IS TOTALLY DIFFERENT IN DIMENSIONS.........just my opinion of course........
BOB RENTON
 
Thanks for the reply.
The booster feels like it was painted black. The car was stripped of a lot of items and parts
scrounged from other vehicles long before I bought it. Did not find this out until many years later. The car has 10inch drum brakes in the rear and disks from a 74 Duster on the front. The engine was originally a 318 to a 383 to a 400 cu in 1972 block. The alternator is a GM brand. The interior was from a 68 Charger. The Charger rear seat covers were modified to fit on the Coronet seat frame. Other parts???
 
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