Need advice on brake issue please!

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75Dart440

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I put a 440 in a 75 Dodge dart (originally a 318ci), the original brake booster doesnt fit anymore. I got an 8" dual diaphram booster that came with a bracket that raises it up to clear valve cover and a new linkage to connect it to the pedal. After installed, it feels like there is no brake assist. The brake pedal is rock hard and car is very hard to stop. It feels harder than manual brakes. engine is producing about 14psi of vacuum at idle.

Any advice or thoughts would be great!
 
Did it all work fine before the BB install?How old are your hoses?They do colapse from the inside.Need more info.
 
You have to switch to the ealier "Hemi" style Power booster (Dual Diaprham they are called I think) and Master Cylinder (Has 30/70 Tanks and Lines exit on Fender Side ).

Hope this helped!
Later,
Bruce B.
 
7071DartGTReg said:
You have to switch to the ealier "Hemi" style Power booster (Dual Diaprham they are called I think) and Master Cylinder.

Hope this helped!
Later,
Bruce B.
Click to expand...

Missed that somehow?
What is the Vacuum reading on the Power Booster end of Vacuum Hose?
Did you use the Power Booster Rod or the Manual Booster Rod?
I remember that causing an issue with my Dual Diaprham but back then you still could pick parts for these cars in a local Parts Yard!
Also, I have pics of mine installed if you need.

Later Again,
Bruce B.
 
The brakes worked great with the 318ci, before the BB swap. I did the swap over the corse of about 3 or 4 months. The hoses wouldn't colapse in that period of time. And i do have a dual diaphram booster.
 
I have the same problem with my 68 Barracuda with power drum brakes.Do you have drum or disc?I,m gonna try a 4 wheel bleed of the system to see if there,s any change to the hard pedal.Let me know if you get yours figured out.
 
14 Hg of vacuum isn't a lot when power brakes usually require around 20 Hg to operate properly. It would seem though that you should be seeing SOME assist. Like maybe have power assist the first time you hit the brakes slowing down. It never has any assist at all? If not then somehow somewhere the booster ain't seein a vacuum signal.
 
Does the booster have a working check valve in the vacuum supply line ?
 
It is front disc rear drum. It has no assist what so ever. It does have a working check valve. Its a new booster, check valve, master cylinder, bracket and pedal linkage. I bench bled the master before i installed it. I am wondering if it has to do with the master cylinder or maybe because it is a smaller diameter booster it needs alot more than 14 hg to operate.
 
Have you ruled out the possibility of a bad booster?
 
I have thought about that possibility. but when i pull the check valve off the booster after it has been running you can hear air rushing back into the booster. I know it is holding vacuum. How else can i test the booster. I even ran a long vacuum line from an 05 chevy silverado to my dart to see if i could get any assist while i was just parked. It didnt feel any different then.
 
If the booster has sat on the shelf a while, the piston the diaphragm rides on could be stuck with rust. I've seen it happen.
 
where did the booster come from im about to buy one and dont want the same issue if its in the booster lol
 
Same thing can happen with the master cyl if your car sat around for awhile. The brake fluid absorbs water and the bore will rust and pit.
 
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