71 power brake help?
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Junior User
Joined: Jul 2004
Posts: 80
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From: Independence MO
71 power brake help?
I'm working on a 71 Bronco for a friend, I put a new extreme power brake setup from the Bronco Graveyard on, as well as disc front brakes (GM calipers), prop valve came in the kit for disc/drum, all new lines and hoses, and new wheel cylinders. I bench bled the master cylinder, and then the entire system 3 times. I have about 16" of vacuum. Now, my problem is you have to just about stand on the brake pedal to get this thing to stop, the pedal is VERY hard to apply. I'm kind of out of idea's on what's going on.
Cranky Old Guy
Joined: Mar 2008
Posts: 3,562
Likes: 6
From: Raphine, Virginia
Make sure rear shoes are adjusted up properly, verify booster is not leaking by reading vacuum with it connected and disconnected/plugged. Even new parts come defective. Sounds like you did everything right, as long as proper bore size wheel cylinders were used on the rear. While vacuum reads a tad low, as long as it maintains over 12" that part should be fine.
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Junior User
Joined: Jul 2004
Posts: 80
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From: Independence MO
I double checked shoe adjustment, I have a slight drag on the drums. I have the same vacuum with booster supply unhooked and capped off. If I was sent a prop valve for a disc/disc setup instead of a disc/drum setup could that cause an issue?
Logistics Pro
Joined: Nov 2009
Posts: 3,885
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From: Lawrence Swamp
Sometimes Residual Valves wrk w/a disc/drum system (IF it is the solution it's placed down line from 'everything' ie just B 4 where the 2 back lines split). finding the right pressure can B tough (altho there R only a few: 2 lb, 7 lb & ?). Isn't there a few adjustable models?
Duplicating the master sz (the 2 chambers may B unequal sz)on the bronk w/the disc/drums ('76 & 77 only) may assist.
I put on a master from a Mark VIIIII (or some such crazy number - recommended by Chuck - BCB) but have disc/disc.
I thought prop valves were the same thru out but don't know - call Jeff's, go to tech assistance. yer a payin customer. Already sent a wrong prt...
Keep talkin, let us know how U do/any assistance we can offer.
Duplicating the master sz (the 2 chambers may B unequal sz)on the bronk w/the disc/drums ('76 & 77 only) may assist.
I put on a master from a Mark VIIIII (or some such crazy number - recommended by Chuck - BCB) but have disc/disc.
I thought prop valves were the same thru out but don't know - call Jeff's, go to tech assistance. yer a payin customer. Already sent a wrong prt...
Keep talkin, let us know how U do/any assistance we can offer.
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Junior User
Joined: Jul 2004
Posts: 80
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From: Independence MO
Well, I talked to Toms Bronco since I bought the disc kit from them (prop valve came in their kit). I checked a few things he had me look at, what I found is when I depress the pedal and start the engine, the pedal does not drop, so I think we have a faulty booster. Im going to get it returned and have Jeffs Bronco send me another (bought the booster kit from them). We'll see what happens!
Logistics Pro
Joined: Nov 2009
Posts: 3,885
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From: Lawrence Swamp
>since I bought the disc kit from them
o0OOPPps, sorry, wrong guy.
>. I have the same vacuum with booster supply unhooked and capped off
how ja test that? what's the process (just curious, don't use power breaks)?
TIA!
o0OOPPps, sorry, wrong guy.
>. I have the same vacuum with booster supply unhooked and capped off
how ja test that? what's the process (just curious, don't use power breaks)?
TIA!
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Junior User
Joined: Jul 2004
Posts: 80
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From: Independence MO
Yeah, all he had me do was run the engine with a vacuum gauge hooked to the intake manifold, then disconnect the booster supply, and compare both readings. If vacuum was higher with the booster supply unhooked and capped off, then that would indicate a leaking booster.
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Elder User
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Did you grind the knuckles? For the calipers to slide properly you have to grind down the knuckle or when you depress the pedal the caliper slides but is stopped by the knuckle. When you first put the caliper on the backing plate it looks like no material needs to be removed, but if you have somebody operate the brakes with the wheel turned in so you can see the caliper you can see where it binds.... and that is the material you need to grind away......
If you didn't grind down some of the knuckles.... that is where your problem is!
If you didn't grind down some of the knuckles.... that is where your problem is!
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