Brakes locked up and soft pedal. (1 Viewer)

[jamarquardt22]

So Im trying to track down some brake problems.

Here is the background.
Since my axle swap I have been dealing with brakes that pull. The old setup was IFS with V6 calipers, master cylinder and dual diaphragm booster. Drums in the rear on a early taco axle.

This setup worked perfectly for me. It stopped straight and was predictable.

My axle swap did away with the V6 calipers and replaced them with a FJ80 stock brake setup.

It has pulled to the left when braking hard at speed. I started by replacing pads and rotors. No change.

I then attempted to rebuild the front calipers. I found a frozen piston on the first one I tried to rebuild. I ordered aftermarket reman calipers and Installed them.

I think the front calipers are working now as It seems to stop straighter but I was loosing brake pressure and needing to pump the brakes. This pointed to a bad master cylinder.

I have now replaced the IFS V6 MC with a FJ80 ABS MC from a 96. I bled the system at all 4 corners. I did skip the LPV above the rear axle. Then with the engine not running I pumped the brakes to see if it would build pressure. It did not. I then started the engine and pumped the brakes. still no pressure. But when I tried to move the Truck It appeared that the brakes were locked up. It would stall out the truck. I don't know yet if it is the rear, front or both.

The non abs FJ80 MC is a known upgrade for mini trucks. And I was unable to find any facts about not using a abs MC.

So what do you all think is going on? Could This be a issue that I have rear drums? Or That I don't have abs? Or a bad used MC.

 

[brian]

an non abs fj80 master...is going to be from a disc front drum rear truck.
the 96 fzj80 abs master is going to have been from a disc front and disc rear truck..not sure if a master intended to run rear discs now trying to deal with drums is the issue....but it sounds like a good starting point.

 

[caz]

I'm with Brian. I've always read that when going to rear disk you need to remove the residual valve from the MC.

Not sure what that looks like but it would be worth researching that term.

 

[jtaco1]

Put the rear up in the air and see if the tires can be moved by hand, if not then that is the problem area. It is possible that since the new MC was designed around discs front and rear, you may need a residual valve on the rear line to make it work. They come in a few pressures.

There may be a topic on Pirate about it, recall a conversation a few years back about something similar.

 

[dci blair]

New, reman, or used master installed?

 

[jtaco1]

Also, did you bench bleed it before install?

 

[Pacer]

Pushrod adjustment.
The brakes are being applied when you bolted the MC to the firewall.

 

[jamarquardt22]

New, reman, or used master installed?

Used

 

[jamarquardt22]

Also, did you bench bleed it before install?

No. How do I do that?

 

[jamarquardt22]

I'm with Brian. I've always read that when going to rear disk you need to remove the residual valve from the MC.

Not sure what that looks like but it would be worth researching that term.

See, I've been reading the other way. That you need to add a 10psi residual valve for the drums. But that doesn't make sense to me. Since the lines seem to hold unwanted excessive pressure

 

[jamarquardt22]

Pushrod adjustment.
The brakes are being applied when you bolted the MC to the firewall.

Could be I would expect the pedal to stop before the floor though. It dosent.

 

[shmukster]

Not knowing if the used MC is good is a good place to start as far as not building pressure. I would also definitely bleed the valve over the top of the rear axle. And, seems like the brakes not releasing problem would be what Pacer suggested- a pushrod adjustment, probably the one between the MC and the booster. Whenever I swapped masters from a different type of vehicle I checked the pushrod height from the mounting face of the booster and the depth of the piston from the back mounting surface of the MC. A little clearance is necessary so the pushrod in the booster isn't moving the MC piston when they are bolted together. I will be interested to see just what you come up with Andy! Good luck, keep us posted.

 

[jamarquardt22]

Not knowing if the used MC is good is a good place to start as far as not building pressure. I would also definitely bleed the valve over the top of the rear axle. And, seems like the brakes not releasing problem would be what Pacer suggested- a pushrod adjustment, probably the one between the MC and the booster. Whenever I swapped masters from a different type of vehicle I checked the pushrod height from the mounting face of the booster and the depth of the piston from the back mounting surface of the MC. A little clearance is necessary so the pushrod in the booster isn't moving the MC piston when they are bolted together. I will be interested to see just what you come up with Andy! Good luck, keep us posted.

I should of bled the lpv. I was pressed for time. I'm also thinking if I loosen the MC from the booster with out breaking the lines the brakes may release if it's a puss rod thing.
It won't happen today but I've got some things to look at now.

 

[shmukster]

I changed the MC on a 95 4Runner way back when, bled the brakes at least a dozen times couldn't get a good pedal. Finally drove it (unsafely) to a friend's garage who had a lift. Soon as it went up in the air he asked if I bled that valve. I said 'what valve"? We bled the four wheels and the valve and got a full firm pedal. Very educational and I might add, humbling, got my balls busted severely for that.
For sure if you lossen the MC-to-booster nuts and the wheels free up you're on the right track. Good luck!

 

[dci blair]

If you deem the master faulty, I can get you a new non abs for $70, or an abs version for $140.

 

[jamarquardt22]

Update:
I got to work on the 4runner today. I found the locked up brake. nothing to do with the MC swap. The passenger side rear drum was frozen. It popped loose as I turned the bolts into the drums to remove them.
I bleed the LPV and got no air out of it.
I looked into how to bleed the MC. I sort of feel that as much bleeding that I have done, there should be no air left in the MC. Since it looks like I need a helper for it, (now that its installed) Im going to skip it for now. If Im totally off track someone tell me please.

I have not yet gotten to check into the MC pushrod,(whatever its called)

Right now Im leaning towards trying a residual valve.

 

[Crusha]

Andy, for the record, that MC was in perfect working order off of a driving truck with a blown engine.

 

[jamarquardt22]

Andy, for the record, that MC was in perfect working order off of a driving truck with a blown engine.

They don't go bad often. I think I need a residual valve for it.

 

[jamarquardt22]

Can someone check which port on a ABS MC goes to the front and rear? I found this on Pirate post 15 and 16 got my attention.
FJ80 MC for rear disc brakes? - Pirate4x4.Com : 4x4 and Off-Road Forum

 

[jamarquardt22]

ok, I went ahead and switched the lines. I also tried to bleed the MC before reassemby I now have some pedal feel but I haven't gotten to bleed the brakes again yet.