New Brakes Work Terrible

[440sixpack]

I have all new brakes on my '78 J10 and they're awful. it's like you have a 10 tone gooseneck hooked to it when it's actually empty.


So I have turned drums and rotors , new pads and shoes, new slaves and calipers, new hoses, new MBM booster and master.

I've rechecked the rod lengths per MBM specs. re-bled the system. checked the vacuum source and performed the start up test on the booster and checked the check valve.


The ONLY think I haven't messed with is the combination valve. I just ordered a new master and I'm going to change it on the off chance it's defective. my next move is to swap the combination valve out with one off my parts rig. could this cause my problem ? any other ideas ? I'm about to take it to a pro and tell him I don't know WTF is going on.

[airman]

How did it stop before the brake job.

Andrew

[440sixpack]

I wish I knew . I hauled it home and did a full restoration.

[Kali]

I wish I knew . I hauled it home and did a full restoration.

If you're going FULL restoration, maybe consider upgrading to hydroboost. BJs has the kit. Unless you want to keep it stock.

[440sixpack]

Yes I'm trying to keep it as stock as possible. the vacuum booster should do a decent job if I can just find where the problem is in the system.

[ShagWagon]

Does your foot hit the floor or do you have pedal?

[joe]

the vacuum booster should do a decent job if I can just find where the problem is in the system.

Unless the pedal is rock hard, doubt it's the booster. The booster doesn't give you better, more powerful brakes. All it does is make the pedal easier to push.
Seems not necessary on all vehicles but often the prop valve(combination) button depending on what type you have type-W, or type-D needs to be either held-in or held-outward when bleeding the front brakes. Is it possible on the rear drums you mixed up the leading and trailing shoes? Even if you botched the rears the front discs should still pull you down "somewhat fair".

[Ristow]

are the shoes on correctly? primary shoe facing forward?


does the MC seem to have excessive stroke?

[babywag]

what size tires?
rear drums adjusted correctly?

[440sixpack]

Shoes are on correct, adjusted until they dragging pretty good.

This booster/master set came from MBM. I looked and now they don't list anything for full size Jeeps. I called their tech line and they said if I didn't have all the paperwork including the date of purchase they won't talk to me. I can't find it ,I bought this stuff over a year ago. so they're useless.


I'm wondering if I have a master with the wrong bore size. since nothing makes sense on this I'm going to put a new master I know is correct on as soon as it's out of the shop getting the new gears installed and see if that does it.


If that fails it almost has to be the combination valve or the booster. and I doubt it's the booster it passes all the normal tests.

[rang-a-stang]

can you lock any of the tires up if you mash the pedal hard? Did you replace all the soft lines? Does it feel like the only the front or only the back are biting?

[Mikel]

Does it make a difference if the booster is connected to vacuum or not?

[Mikel]

Unless the pedal is rock hard, doubt it's the booster. The booster doesn't give you better, more powerful brakes. All it does is make the pedal easier to push.
Seems not necessary on all vehicles but often the prop valve(combination) button depending on what type you have type-W, or type-D needs to be either held-in or held-outward when bleeding the front brakes. Is it possible on the rear drums you mixed up the leading and trailing shoes? Even if you botched the rears the front discs should still pull you down "somewhat fair".

Don't vehicles without power brakes often have master cylinders with a smaller bore to allow for lower braking efforts (at the expense of more stroke)?

[joe]

Don't vehicles without power brakes often have master cylinders with a smaller bore to allow for lower braking efforts (at the expense of more stroke)?

Mikel w/o some research I'm to lazy do do, you could be correct. I don't know the specific differences between std and PB masters but they are different.

[77Deepj20]

I've had a few bad out of the box master cylinders the last few years. You never did mention if the pedal was firm or sloppy ect.

Was the master bench bled before installation?

Unless the proportioning valve is clogged with rust or something it should work, never really had one go bad.

Is the pushrod between the booster and master in place and the correct length?