[shortbus]

Brake upgrade went bad

I changed the master cyl. on my cj5 to one from a ford E350.
I used my old stock cj booster and inserted a rod in the new M/C to make up for the deep hole in it. I did this thinking I would get better braking power for my 38.5 SX'S and the dana 60'S. It will stop now but the pedal is kinda soft and is no where near locking the tires up. I bench bled the M/C and bled the brakes with a tube and bottle. What do you think?

 

[Maine Jeepah]

Bleed it more.

Gravity blled it overnight if you have to.
Then if no change start to worry.
MJ

 

[Azzy2000]

If you can pump the pedal and make it firmer... Keep Bleeding.

Edit.. Also make sure your spacer for the pushrod is the correct length... could be too short.

 

[Scout Dude]

larger diameter master = more volumn, less pressure
smaller diameter master = more pressure, less volumn

You need to smallest master available to fill your wheel cylinders or calipers and that's it...going too big will not help in the end.

 

[shortbus]

I need more pressure and more volume. With the old master I didn't have enough volume to fill the calipers. It wasn't even close to stoping. I have enough volume now but I need a little more pressure. The old stock M/C has the same bore diameter as the E350, the 350 might be just a hair larger. I can lock the front up in gravel if I really stand on it.

 

[Bigburlynakedguy]

2psi residual pressure valve may help too. They keep the pads closer to the rotor when the pedal is released, affectively decreasing the amount of throw to engage the piston in the caliper. 10 psi for drums.

 

[DUG]

larger diameter master = more volumn, less pressure
smaller diameter master = more pressure, less volumn

You need to smallest master available to fill your wheel cylinders or calipers and that's it...going too big will not help in the end.

You must have been sick when the went over hydraulics in class.... Of cours eI never remember them teaching about "volumn" so maybe I was sick the day you where there


check it, the volume of fluid the master moves in relation to the volume of the wheel cyl/caliper piston volume is what makes pressure.

He went from little tiny D30/AMC20(?) brakes to big ole one ton D60 brakes. This makes for a increase in the combined volume of the wheel cylinders/caliper pitons. It is a even greater increase if he had front drum brakes before. The stock CJ master simply would not move enough fluid to build good pressure at the wheels, there is not enough fluid in the piston of the master to fill the caliper/wheel cyls enough to get decent pressure. By switching to a larger master cylinder (whether bigger bore or a longer stroke) he is moving more fluid into the same space thus creating a higher pressure.

Basically, with the stock master he was trying to fill a 5 gallon bucket with 3 gallons of water.

From your symptoms I would say bleed it some more, possible even "bench bleed" the master again with it on the Jeep. However, if your pedal ratio is way off from what the Ford master wants you may still not be moving the correct amount of fluid to get good braking.

 

[shortbus]

Believe I have it figured out!! The rear brake star adjusters were rusted solid and the shoes were about 1/4" away from the drums= maxing out the rear cylinders and stealing the volume of the M/C. It makes sense, if you can't get enough volume you wont get any pressure.
Well I fixed all this stuff and it allmost put me through the windshield. I can stop at 30 mph in about 20 feet(roughly).
I can't lock the tires up on the road but I can hold good with the T/C in low(auto tranny) and not need to shift into neutral. Before with brand new brakes pads and shoes ,adjusted properly I couldn't hold in low.barely slow it down.
Thanx to everyone that helped me with this, and if anyone is wondering how the master fit on the stock CJ booster,it bolted right on no drilling but you need to make a spacer that is 7/16 round and 1.250"long with one end rounded and the other end spot drilled to make a dimple. Also need to run new lines to the Prop, valve.