Outer Limits 4x4 Board

Hey OL'ers,

Need some help. Got a '78 BJ40 with a B diesel donk - came with stock drums all round. Before I bought it, someone put disc front end on it. The brakes have always been pretty suss - feeling very spongy and occasionally the pedal falls to the floor. My master cyl was all old and rusty (looked cactus) and someone along the line told me to replace it with a 60 series one, which will work better with the disc front.

So I replaced it this afternoon, bleed the shit outta them, and they are still shitty and spongy. I'm running out of things that could be busted. I've recently replaced the disc rotors and pads on the front...

Two questions:

* What is the tank thingo that is under the passenger floor (is it like a vacuum tank?)
* Any ideas on what could be causing my brakes to be spongy?

the canister thing is the vacuum canister like you expected. There realy isnt all that much to do with brakes, so if you arent actually loosing any fluid, it has to be either still air trapped in the master cylinder, or the master is passing fluid past the seals somehow. Id still go with air. tried bench bleeding the master before putting it on?

Bench bleed, ay?

* Runs off to google to find out what that is **

the canister under the floor on the pax side is the vacuum booster. it hooks up to the vacuum pump on the back of the alternator. if your braking is suss, make sure you these bits work as they should. also replace all pads and check the calipers, sometimes the pistons in the calipers get seized, some times they leak.

go over the rear drum brakes as well, back off the adjuster before you try and take off the drum, makes things a lot easier when you remember, discover this. since your in here replace the pads and check the wheel cylinders. also check the flexible lines that go to the calipers from the diff. these crack, age and can leak. if your brake stuff hasnt been touched you'll no doubt bust some hard lines getting everything undo. spray these with wd40 before you undo them to make things easier. if you bust a hard line, take the end and get new ones from a brake place. get a spare made at the same time. the flexible lines to the calipers are available from repco for about $12.

you can replace your handbrake cable too which will help if its stretched or busted.

if you get through all of that your brakes should be a bit better.

Thanks shorty... When I bought it, it had the disc front end, but the rotors were so rooted and the pads were worn. Myself and a mate ripped them off, rebuilt the caliper and pistons, cleaned it all up with brake cleaner, installed new rotors and pads on the front.

I might investigate some braided cable to go from the diff to the caliper (that small 1 foot length) as this rubber hose looks old.

I have been looking around the net and I think I might have to bleed the brakes more - like do it for a good while each side and churn through some fluid.

Bleed the rear proportioning valve and check the adjustment of the rear brake shoes also.

Matt

There is no rear prop valve as far as i know...

a BIG tip with old brake lines try to do the up a little before undoing them the seem to release a lot better

when bleeding the brakes always statrt from the wheel closest to the diff brake line to chassi or your just moving the air back n forth n not getting it out

Thanks for the tips Grimmy

Just a heads up. 60 master cylinder has no proportioning. 60s have a proportioning valve mounted under the master that regulates bias front to rear. 40 masters (early and late) have internal proportioning in the master. Would have been a better choice to get a late model 40 master (for disc front, drum rear). 60 master will still work but would be better with the proportioning valve.

If you are confident you have no leaks and you have adjusted up your rear brakes properly (important or you will always have a shitty pedal) then you might need to adjust the pushrod inside the booster.

Thanks for the advice Ray. The rears have always locked up first in mine... What do you mean by saying "adjusted rear brakes properly"?

Is yours a twin rear wheel cylinder or single wheel cylinder drum setup on the rear? If you have access to a workshop manual for your model it would be helpful. Basically (this is for single wheel cylinder) with the drum off, you adjust the shoes out via the adjusting mechanism so the drum can only just fit back on. Then through the little access hole on the backing plate (with the wheel on) adjust it more 1 click at a time while spinning the tyre until you feel it start to drag. Do the other side, pump the pedal a couple of times then spin the tyre again. If it feels looser repeat final adjustment until you feel slight drag and you're done.

If you have twin cylinders each wheel then you need to do the front one first till you get drag, then the rear one, pump pedal and repeat if necessary.

ok, so I adjusted the rear drums, they seem to be working fine and can slow the truck down.

Problem is, I'm pretty sure the front discs are providing about 20% braking power.


What I have done so far:
* New front brake pads
* New front rotors
* new fluid in the entire system
* thoroughly bled throughout
* new 60 series master
* reco'd brake pistons / calipers
* Adjusted rear brake shoes to slightly drag
* adjusted brake pedal free play
* ensured master cylinder piston rod is correctly engaging master cyl within tolerances

What I suspect could be at fault:
* front rubber brake lines from diff to disc are old and could be expanding
* need a proportioning valve to push more fluid to front brakes
* booster could be cactus (doubtful)
* 60 series master could be wrong - should I swap for a newer model 40 series one?

De-lux wrote:ok, so I adjusted the rear drums, they seem to be working fine and can slow the truck down.

Problem is, I'm pretty sure the front discs are providing about 20% braking power.


What I have done so far:
* New front brake pads
* New front rotors
* new fluid in the entire system
* thoroughly bled throughout
* new 60 series master
* reco'd brake pistons / calipers
* Adjusted rear brake shoes to slightly drag
* adjusted brake pedal free play
* ensured master cylinder piston rod is correctly engaging master cyl within tolerances

What I suspect could be at fault:
* front rubber brake lines from diff to disc are old and could be expanding
* need a proportioning valve to push more fluid to front brakes
* booster could be cactus (doubtful)
* 60 series master could be wrong - should I swap for a newer model 40 series one?

Anyone got any updates or advice?

De-lux wrote:

Anyone got any updates or advice?

You could always come around and fit my setup and see if mine all works - I bought my new setup months ago but havent got around to fitting it yet.

At least it will cancel out your mechanical skills being the problem if it all works

replace the flexible lines. you can get them from repco for $15-20 each. quick easy fix and something worth doing if they look cracked at all. Also worth while getting the correct brake booster for your setup. Try and find one out of a later BJ that had disks up front.

yeah cheers shorty... I just picked 'em up from repco, $21 each side. Hopefully this makes a bit of a difference to it all. I'll report back this afternoon.

Mick do you need brakes with Lafondas hefty frame in the truck?
surely she can slow it up?

Mate I need Porsche brakes on all corners to stop with the extra weight...

With the motor running....press the brake pedal a few times, does the pedal firm up?
Nex question, how do the rear shoes look? are they wearing evenly across the face? There may be some grooving but that is irrelevant, just put a steel rule acress the shoe face to see if it is flat.

thanks for the info bumpy.

Over the weekend I replaced the two rubber hoses which went from diff to caliper... It didn't fix it much. I did notice that there is another rubber hose from chassis to diff. I'll replace this one too, mind you, I am doubtful that it will fix anything.

I'm pretty sure that the rear brakes are working fine now that I have adjusted the shoes, but the biggest problem is still the lack of pressure to the front discs. I suspect this would be fixed with a brake proportioning valve... Does anyone know what one looks like that came standard with a 60 series?

I'll try and get a pic of the 60 series one in my 40 tomorrow. It sits under the master cyl. You'd probably be better off getting an adjustable proportioning valve for it so you can dial in your own bias to suit. I just don't know if they are legal or not. Mine pulls up pretty well on 35s but could still do with a little more pressure on the front. Mine has the entire system off a 60. Front discs/calipers, rear drums/shoes/cylinders, booster, master and prop valve.

Edit: Here's the 60 proportioning valve with 60 booster and master cyl:

are you sure your expectations are greater than what the BJ can do when running the size rubber you are? What do your creepies weigh per corner? I'm sure this isnt helping.

The braking in my 42 is fine (not great) with the 33's but I would think its border line. I rarely ever lock them up, but then again I'm rarely in situations that they need to be locked up.

I'm not expecting this to stop on a 5c piece, but I just want the confidence that if a kid runs out in front of me I can stand on the brakes and brake with enough force to pull the truck up without the rears locking and fishtailing into a bad scenario.

I suppose as they are now, the braking is pretty good - there's not much in the braking system that I haven't replaced or reconditioned. Perhaps down the track I might investigate disc rear just for that added vote of confidence...