m715 brakes

[newworld]

i have braking problem. rolls under braking...will not come to a dead stop in gear. all braking system was replaced, new lines, new pads, adjuster wheels etc. only thing not replaced was drum.

i have a front/rear reservoir i think came from a j pickup truck etc. brake pedal is hard not soft.

but even if you stand on it, truck will creep forward or back if in drive or reverse.

dont really know what to think about this.

 

[dmetalmiki]

Study the relevant T.M.s and adjust all the wheel cams and adjusters. Jacked up safely, check one wheel at a time.

 

[newworld]

i jacked up each wheel and got so i cant turn wheel by hand when brakes applied....even though lets say fronts are adjusted but back are not....should that hold the truck?? and prevent the rolling?

i have an autobox and it rolls in reverse and drive. its quite scary even with pedal depressed down bigtime.

Study the relevant T.M.s and adjust all the wheel cams and adjusters. Jacked up safely, check one wheel at a time.

 

[Nailhead]

It sounds like your MC bore is too large, and doesn't provide enough force to the wheel cylinders.

 

[newworld]

i lifted up wheel and adjusted until i cant turn wheel with my force. i concentrated more on fronts than backs.

i do have a high idle...but brakes do not hold the vehicle and it rolls in gear.

when i bleed brakes i do get a steady flow.

the master came from gladiator j type pickup truck...it has dual setup, reservoir for front and another for back.

 

[newworld]

if bore for mc is too large...how to fix? as i mentioned it is not stock....previous owner converted to j type truck cab and used the master from it. i did use 1/4 inch brake line in some places when replacing the brake lines

 

[porkysplace]

i lifted up wheel and adjusted until i cant turn wheel with my force. i concentrated more on fronts than backs.

i do have a high idle...but brakes do not hold the vehicle and it rolls in gear.

when i bleed brakes i do get a steady flow.

the master came from gladiator j type pickup truck...it has dual setup, reservoir for front and another for back.

What are you using for a proportioning valve ?
Is the master cylinder for drum brakes or disc/drum?

 

[newworld]

i dont have a proportioning valve. my setup is the following: brake rservoir has 2 chambers, and 2 connectors one for each, one goes to front and one goes to back. i hooked up copper nickel line to each and then it goes to each wheel from these 2 lines ie a splitter. my brake pedal is very hard...but doesnt brake

 

[newworld]

are you saying i need to change out my master cylinder?

 

[porkysplace]

are you saying i need to change out my master cylinder?

What year is the master cylinder off of ? It sounds like you have a late model master cylinder.

 

[newworld]

i dont know exactly possible '73? but im not sure. it was defintely from a j series pickup

 

[porkysplace]

i dont know exactly possible '73? but im not sure. it was defintely from a j series pickup

73 was about the time they started using disc brakes , if it is a disc brake master that could be your problem

 

[newworld]

your suggestion may be exactly my problem...i researched here this

From the archives....using the Jeep dual master cylinders is not recommended in the M715:

Quote:

Caution to all who are considering installing dual piston master cylinders: the 60's and 70's vintage civilian Jeep master cylinders are NOT suitable for use in an M715. Warning is straight from a Wagner Brake Engineer. Those Jeeps used different diameter wheel cylinders on front than on rear. M715's have 1-1/16" diameter units front and rear.

 

[bcowanwheels]

YOU DIDNT DO SOMETHING RIGHT, go back thru it all. don't drive it till fixed

 

[quickfarms]

your suggestion may be exactly my problem...i researched here this

From the archives....using the Jeep dual master cylinders is not recommended in the M715:

Quote:

Caution to all who are considering installing dual piston master cylinders: the 60's and 70's vintage civilian Jeep master cylinders are NOT suitable for use in an M715. Warning is straight from a Wagner Brake Engineer. Those Jeeps used different diameter wheel cylinders on front than on rear. M715's have 1-1/16" diameter units front and rear.

A proportioning valve will solve that problem.

The issue with the disc master cylinder is that it does not have the residual pressure valve in it.

Does the pedal go to the floor?

Does the pedal pump up?

There could be a lot off issues on this brake system.

Did it ever work right?

 

[quickfarms]

YOU DIDNT DO SOMETHING RIGHT, go back thru it all. don't drive it till fixed

It could be miss matched parts

Did it every work right?

 

[newworld]

let me answer some questions raised here....when i got the truck po removed all rear brake lines and fronts were not working. i did a total refresh, all new lines, all new pads, spring etc etc for all 4 wheels.

the brake pedal is very hard....not soft at all.

all brake cylinders are standard m715 i think they cost $35 each from one of the vendors, and with wheel off, i can see the cylinders expand etc.

everything is new except for brake master cylinder which is a dual cylinder i think from a civilian gladiator model. it does have a brake booster behind it.

when bleeding, fluid does come out and i bled the correct way ive been doing brakes for years, however this is first drum brake system i have done.

it could be a matter of adjusting properly, it could be a matter of not getting enough pressure to the wheels due to bore diameters etc etc....

i dont know.

It could be miss matched parts

Did it every work right?

 

[newworld]

as for residual valves...the brake master is alot higher than the wheels. my understanding is you need this if brakes are level or master is below cylinders etc to prevent fluid from going back into reservoir.

 

[gerrykan]

A non-working vacuum booster can sometimes make a very hard pedal.