Brake Problems - 76FJ40 Need Expert Advice. (2 Viewers)

[chubot]

I originally pulled both rear drums to find a popping noise when I applied the brakes. The pop would slow with the truck and I could tell it was coming from the rear. The RR drum had some brake fluid and axle lube mixed in it. From what I could tell it had a brake fluid /axle lube smell so I replaced beatings and seals and wheel cylinders on both sides of the axle. Now for some reason I can’t get the brakes to work at all. I’ve bled them probably 20 times and just installed a new master from City Racer. I don’t see any visible leaks and the fluid in the reservoir doesn’t seem to be leaking down so I’m at a loss as to what the crap is going on.

 

[mp9999]

Both drums are not working? That would make me think you have the wrong master cylinder or it’s not working properly (not enough pressure).

 

[cruisermatt]

You probably don’t have the shoes adjusted tight enough.

I also have not had good luck with the aftermarket Mc’s.. if you replaced that in response to your issue, I would re-install your previous unit for now.

When we do replace master cylinders on pre-80 FJ40’s here in the shop, we use the +81 version which is still available from Aisin and that has been working very well for us

 

[3_puppies]

US spec rig? with disc on front?
X2 on adjusting the shoes, they will be tighter/snugger than you think

 

[chubot]

The previous MC was an aftermarket unit I installed when the one from the PO started leaking. I just readjusted the rear drums and tightened them a few more turns and I have an air bleeder I just bought so I’ll give it another try here shortly. The thing that has me scratching my head is that everything was working fine before I found the original leaking WC. I was wondering if there was another model year MC that would fit a 76 US 40, so I’ll have to look that up.

 

[dazerb]

I know this brake system can be notoriously hard to bleed... especially to the rear. Many threads on this struggle!
I have a later model CityRacer MC (pretty sure it's a 93) for my front disc (keep the rear drums) conversion along with a proportioning valve and it all works excellent!
I did replace rear seals, but the Wheel Cylinders were working good and not leaking. Again, I read over and over about how hard it is to get all the bubbles out of the rear.
I did a full bench bleed on the MC and I think that really helped. I REALLY tried not to introduce air by capping everything and doing one piece at a time.
74 fj40
Happy Wrenching!

 

[charliemeyer007]

So if you are using a one man brake bleeder like a mityvac, getting the nipple to seal when open for bleeding can be a PIA - I had to use Permatex non setting compound. +1 for screw the adjuster out to the drum. Apply the brake pedal lightly and move the rig a few inches forward and back to center the shoes. Then tighten the adjusters again, then back off like 3 clicks. Go for a short drive and see if the brakes seem to work and are getting hot on the drum.

 

[chubot]

So I tightened up the rear drums and I did bleed the brakes using the harbor freight air bleeder. It does seem to seal pretty good with the soft rubber nipple. The only problem is the hose is not very translucent. I have a much firmer brake pedal now with the truck off. When I crank it, the pedal gets a little soft but it has improved. I will bleed them again and see if I can get the bubbles out. I’ve never had any trouble with the brakes on this 40 and it would stop on a dime. If anything, the rear drums should probably have a little more pressure.

 

[chubot]

Bled the brakes one more time today and really firm pedal now but as soon as I crank the truck it’s just mush and goes to the floor. I’m at a loss now because I wouldn’t think it’s the booster right? Because it’s obviously working for the pedal to go to the floor right?

 

[ceylonfj40nut]

Bench bleed MC
Check that the pushrod distance is within spec using tool
Attach a hand vac pump on to booster to see if it holds vacuum (if not replace)
If booster has check valve take it out and test to see it is working
Tighten all drum shoes till snug
Gravity bleed for a couple of hours making sure reservoir does
Stays full.
I would do old school pedal pump and hold over gizmos if they dont seem to work right. Get another person to pump/hold.

 

[pb4ugo]

I haven't run drums brakes in decades, but have followed many threads about having problems bleeding stk drum brakes. A lot of folks have had success by putting the tires on and adjusting the brakes to the max, so the pistons can't move and the tires won't spin. Then bleed the brakes, once bled re-adjust per the fsm. .

 

[chubot]

Bench bleed MC
Check that the pushrod distance is within spec using tool
Attach a hand vac pump on to booster to see if it holds vacuum (if not replace)
If booster has check valve take it out and test to see it is working
Tighten all drum shoes till snug
Gravity bleed for a couple of hours making sure reservoir does
Stays full.
I would do old school pedal pump and hold over gizmos if they dont seem to work right. Get another person to pump/hold.

I haven’t put a hand vacuum pump on it yet but I did inspect the check valve and it seems to be fine. When I pulled the check valve out, a lot of air came out of the hole. I’m not sure if that means it’s holding pressure because I’ve never had to mess with a booster. I was thinking of a gravity bleed but I’ve never done that before either. I really appreciate all the input. I’ve been trying bits and pieces of everyone’s advice.

 

[brian]

Did you bench bleed the master?

 

[Pighead]

The pedal is supposed to sink a little when the engine starts, but shouldn't go all the way to the floor. Unless your pedal is too close to the floor to start with...
FSM has recommended pedal heights.

 

[igotta40]

Are you still getting air bubbles when you bleed the brakes?

 

[ceylonfj40nut]

If you replaced your calipers make sure the bleed valves are pointed up to let air out. Had a situation where I did all above and had a mushy pedal, only to realize.

 

[45Dougal]

FWIW; Each circuit on the master cylinder has a pressure switch which opens when you have pressure in the circuit.
They're both normally wired in parallel, and they cause the brake warning light to illuminate when there is insufficient pressure in one circuit (with handbrake off).
I've found it helpful to disconnect each circuit alternately at the master in order to confirm which circuit is reading low pressure.
It's a quick and easy test to help isolate your problem to either the front or the rear circuit

 

[chubot]

I did bench bleed the master and it’s hard to see if the air bubbles are completely gone when I use the harbor freight air bleeder. I do have a firm pedal when the trucks not running but pedal goes to floor when it is running. It looks like the booster is working, but there’s a woosh of air when I push the pedal. The check valve is working fine so I think today I’ll try to replace the air bleeder line with a clear see through line so I can see if all the bubbles are gone.

 

[chubot]

FWIW; Each circuit on the master cylinder has a pressure switch which opens when you have pressure in the circuit.
They're both normally wired in parallel, and they cause the brake warning light to illuminate when there is insufficient pressure in one circuit (with handbrake off).
I've found it helpful to disconnect each circuit alternately at the master in order to confirm which circuit is reading low pressure.
It's a quick and easy test to help isolate your problem to either the front or the rear circuit

I do have the pressure switch connected but there’s no light on my dash on this 40. There’s some holes there though.

 

[chubot]

I replaced my air bleeder hose with clear hose and re-bled the brakes. I’m getting solid fluid from the left rear but when I get to the right rear there’s a lot of air. I’m thinking I got some bad wheel cylinders from rockauto.