Scout II on full widths, break pressure at the floor

vancetater

vancetater

Member
Ok here are the specs I have a 72/75 Scout II on 3/4 ton Chevy axles (hd 44 with disc up front 14 bolt drum in rear). I have brand new calipers, pads, rotars up front also new braided steel lines front and rear (new) the rear drums within spec and good wheel cyl. I recently replaced the master cyl and I have same issue my peddle has pressure and it stops fine but the pressure is at the bottom almost to the floor and when I go in water or mud it just fades to floor I know this is normal in the water and what not but I would like to have a higher peddle. Im wondering if I need to change my master cyl to a different style like a 1 ton Chevy or something I have tryed adjusting freeplay and the rod inside the booster and no luck what so ever:mad:
 
Sounds like you need a master that pushes more volume. With the Scout master it takes almost the full throw to get the brakes to engage because it was designed for use with way smaller brakes. Go with a Chevy 1ton as it was made for the bigger brake calipers and drums. It should bolt right in with miner fitting of the brake rod.
 
Thats exactly what I thought ,do you know what year Chevy 1 ton I need. I looked at a few but not sure what year to go off and most of them had hydro boost I still run vacume boost
 
According to the chevrolet 10-30 series light truck service manual:

jb5= front disc 11.86x1.29 rear drum 11.15x2.75 vacuum-double diaphragm

jb7= front disc 12.50x1.54 rear drum 13.00x2.50 vacuum-double diaphragm

jb8= front disc 12.50x1.54 rear drum 13.00x3.50 hydraulic-hydro-boost

jb7 is basically Dana 60 front disc with the smaller 14ff drum brakes with a vacuum booster and jb8 is Dana 60 front disc with the large 14ff drum brakes with hydro-boost.

fenco new/master cylinder (brake system) (nm1730) | 1978 chevrolet k30 1 ton p/u 4wd 8 cylinders l 5.7l 4bl ohv | autozone.com
 
Thanks for the link I will order it tomorrow and hopefully be able to stop better. Btw thanks for reserching and helping me out.
 
Ok I went and got the master but the bowls for the fluid are oppisit front is small and rear is large also the holes for the break lines are oppisit 9/16 front and 1/2 in rear do I just switch the stock lines up to bolt them up. Im pretty sure the larger bowl is for the front but why would it be in the rear? Let me know if this will function properly
 
I got it installed and now theay work great but I have to push the pedal very hard now.it feels like manual breaks now almost does not stop unless I smash down on the pedal.
 
It is deffinatly gonna be scary on the trail now I am having carb issues also cutting out when I go up a steep hill.:mad2:
 
Ok I need to fix this breaks suck way to hard to push what is the next step. I do not want to do hydro boost I have seen someone in hollister running same master with vacume boost. Did not get a chance to ask how it works but looked to be stock booster...
 
I am running a stock booster and master, with dana60 front and a 70 rear with 3/4ton disc, mine works great. Are you sure you have vacuum to the booster?
 
O ya cuz when it stalls its way harder and pedal goes up higher also if I give it throttle it gets a little easyer but not enough
 
Might be a good idea to swap a Chevy truck one in there. And the front brake line after the valve might not have enough flow for those big brakes.. Just my 2 cents though..
 
You are running brake components from two different vehicles.

Since you have the Chevy axles & brakes, you should run the Chevy master cylinder & prop valve from the same vehicle, and run the brake plumbing the same as the Chevy, otherwise, you will continue to chase your tail.
 
Only thing not Chevy now is booster and perportion valve but I have one off a 3/4 ton truck now but seems like to much work to modify the Chevy booster to fit on the Scout
 
Just some basics.

The manual master cyl has 1" piston. This allows it to be easier to push the volume needed. But with disc you need move vol so the pedal goes to the floor.

Next up is a 1.25" power assisted master cyl. Harder to press with the engine off, but with the engine on easier and moves more fluid.

1 ton master cyl 1- 5/16" piston. Comes in vacuum and power steering assisted.

Booster go bad all the time.

Put foot on brake peddle and start Scout, does the peddle go down a little bit like it should?


Edit... Found this. Should help

http://4x4trailmaps.com/4x4trails.php?trail_id=33
 
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Yep it goes down I know when a booster goes bad mine is fairly new in here. I will try to swap out the perportion valve but I do not see how that will affect it. The master I have now the only difference is the bore size is 1.25 the stock was 1" not much has changed
 
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