Power Brake booster bad?

[AR67GTX]

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?

 

[AR67GTX]

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

 

[twecomm]

Can't say about it being the correct booster, but... you can do a rebuild with parts from here.
Home - Harmon Classic Brakes
Worst part is getting under dash to remove and reinstall.

 

[AR67GTX]

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

 

[AR67GTX]

Looks like a Midland single diaphragm 9-1/2” from the Harmon website

 

[RJRENTON]

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

 

[AR67GTX]

Thanks, think I’ll see about doing an exchange for a rebuilt Bendix model if they will take the Midland one as a core.

 

[gtx6970]

Bendix booster is very different than the Midland Ross ( drum brake cars ) you have now

Wrong master cyl btw

 

[Dave6T4]

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.

 

[AR67GTX]

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.

 

[69L48Z27]

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.

 

[AR67GTX]

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.

 

[AR67GTX]

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.

 

[gtx6970]

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

 

[AR67GTX]

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.

 

[69L48Z27]

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

Car is 67 R/T. 11”.

 

[AR67GTX]

Car is 67 R/T. 11”.

My mistake - I mistakenly thought he was replying to a post of mine.