86 bronco II rear disc brake problems

[peatypaul@yahoo.com]

I currently have a 86 broncoII with a 302 v8. Im having issues with the braking performance. The brake pedal seems spongy for the majority of the travel then gets stiff with out any extra response to the braking. It does stop but not as fast as i would like. I am not able to make any sudden stops because the the pedal gets hard with no added braking powere no matter how hard i press. I recently installed a 95 explorer 8.8 with disc brakes. I replaced the front and rear calipers and installed a master cylinder from the explorer and an adjustable proportioning valve. I have recently installed a vacuum storage tank to help but not knowing if vacuum is the problem. Im not sure if there is any residual valves affecting the pressure. The only issue with the master cylinder is the resivour makes contact with the booster so i shimmed it out to clear and adjusted the booster pushrod out. any suggestions??

 

[adsm08]

Un-shim the master cylinder for starters. Your valve may not be adjusted right either, but your master cylinder shim is more than likely causing less than desirable operation.

If it just won't fit on there without the shim, try putting in the 95's booster.

 

[peatypaul@yahoo.com]

i looked into the explorer booster but it has a larger bolt pattern. I m thinking of getting a master cylinder with the dual resivour to fix the clearance issue but not sure what bore size i need

 

[adsm08]

Is yours the plastic reservoir or the bale-clip style?

 

[peatypaul@yahoo.com]

plastic.

 

[adsm08]

Try putting your original back in and see. I think the original master will work. Post down in the brakes section, those guys will know for sure.

 

[peatypaul@yahoo.com]

When i first did the dixc swap I had the original master cylinder in but it was even worse.

 

[Shran]

You don't need the proportioning valve or the vacuum reservoir, for one thing. I have a disc brake 8.8 from a 97 Explorer, a disc brake D44 from a '76 Bronco and my stock master and booster... the brakes work very well.

How sure are you that you got the master cylinder completely bled? I don't think that the shim would cause any issues if you adjusted the pushrod length to compensate for it.

 

[adsm08]

I don't think that the shim would cause any issues if you adjusted the pushrod length to compensate for it.

And if you did adjust the pushrod length then it should be ok. I'm sick right now and most of my assumptions are coming from the point of something else not being done right.

 

[peatypaul@yahoo.com]

Ive bench bled the master twice and the whole system a few times. still no change. I have the proportioning valve adjusted to operate mainly the front brakes in order to stop

 

[Shran]

So were you having problems with the fronts locking up or something?

 

[peatypaul@yahoo.com]

No problems with the front. Its mainly the lack of pressure when the pedal is pressed

 

[dirtcowboy]

Brake master cylinders are built to add more braking force to the front brakes stock, thats where the weight is, your prop valve is just making it worse. Take out the booster and put in a master from an E-350 Ford van, they have 1 1/8 pistons in them, lots of fluid movement.

 

[ThatGuy]

Or try swapping the lines around. That's what I had to do to correct my brakes. Now they will sling you trough the windshield.

Started with stock '91 Ex master cylinder and swapped in D44 an 9 inch from a '79 Bronco. Pedal spongy. Tried bleeding 3 quarts of fluid through it. Still spongy. Swapped in F-150 master cylinder for bigger piston. Still spongy. Bled 2 more quarts through it. Still spongy. Swapped lines around on master cylinder. Bled about 3 pumps per wheel. Got crazy braking power now.

That's my story.

 

[peatypaul@yahoo.com]

Got it all fixed and working great now. Thanks for the ideas. I ended up putting in the explorer brake booster with little bit of mod to hole pattern on the firewall. Its better than i expected.