Booster/brake help! (1 Viewer)

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Sep 25, 2008
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I have a 71 FJ40,SBC,T400,ARB's,Bobby Longs,488 Gears,Skyjacker 4" Lift,35" tires,and the brake system is mini truck outers on the front, and the monte carlo disc conversion on the rear. I have owned it & wheeled it for over 3 years now. My issue is, and has been brake pedal assist. I have assist, but not enough. I have a factory single diaphragm booster (new) and the original dual reservoir master cylinder. The system works, just not well. If I am trying to stop on any steep incline, up or down, you have to put an enormous amount of effort to hold the vehicle. All lines are new,pads are new OEM, SS brake hoses,calipers removed,cleaned and checked etc. My assumption is that the original single diaphragm booster does not offer enough assist for the 4wdb's. I am planning a SOA,shackle reversal,traction bar etc conversion soon and would like to correct this issue at the same time. Please chime in and let me know if you think I am correct, and what would be the easiest fix. I have access to one of those MAF complete GM conversion master/booster combos, but I don't want to install it unless I get a confirmation that it could be the fix!!
Thanks, Jerry
 

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Oh...Durka Durka Durka.
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Remove the hose going to the brake booster and install a vacuum gauge.

How much vacuum are you indicating at this connection?
 
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vac gauge

Sorry I did not include that info in my first post. Running a GM HT383, very mild cam! Have 17hg @ idle in park 15-16ish in gear @ about 700-750 rpm.
 

inkpot

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Numbers sound OK, but you need to check and see if it is getting to the vacuum booster. Also need to do a bleed down test to see if the booster and line is holding the vacuum. John
 
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LEAK TEST

Roger that! Have done a leak test with vac pump! Tests OK. Check valve only lets air out, and had an extra one to test also! This booster does give a slight amount of assist-just not enough. If you start the engine with the brake pedal depressed, it will depress a little further, as well as easier. Problem not super noticeable just running around town, UNLESS you have to stop fast. I guess what I am really wondering is do different boosters, whether they be different in size, shape, or # of diaphragms produce more or less assist depending on their design and intended usage?
Thanks Again!
 

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Oh...Durka Durka Durka.
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I guess what I am really wondering is do different boosters, whether they be different in size, shape, or # of diaphragms produce more or less assist depending on their design and intended usage?
Thanks Again!



Yes, they do.

I would find a 60 series brake booster and swap/try that before going to a GM unit...

:meh:
 
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What did you end up doing?


I installed a 8" dual diaphram booster with a 1" GM master. I have 17 inHg at idle. v6 4Runner calipers front and GM calipers rear. The efforts is decent, but unable to lock up the wheels.
 
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I have the same engine / brake setup in mine, used a booster out of a 97 toy forerunner, bolted right up - more than enough stopping power
 

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