Drum brake troubles (1 Viewer)

[arnott1t]

Hoping you can provide some advice on fixing my drum brakes on the front of my troop carrier.
I had to wheel cylinders with seized adjusters. I replaced all wheel cylinders with new.

Previous symptoms were a low pedal. I need to pump the pedal once and would have brakes on the second application. I thought this was caused by the lack of adjustment of half of the shoes.

I’ve since replaced all wheel cylinders and bled the brakes three different times. They still require pumping in order to engage. I’ve adjusted them from factory spec to so tight they can’t be turned by hand. Neither made any difference towards pedal height.

Well the truck is on the hoist and brakes applied one full application The front brakes are hardly engaged. A second Pump locks them up.

With the drums off one pump hardly moves the wheel cylinders.

All this I think is pointing to my master cylinder now but I’m really unsure.


Looking for any advice mud might have

 

[Curt]

What wheel cylinders did you get? i had issues with air being trapped in non oem units that took lots of bleeding to get a hard pedal.

 

[middlecalf]

In addition to Curt’s suggestion I’d bleed the master cylinder.

A caution - don’t pump breaks without the drums on. If the cylinders do move you can actually move them too far and they’ll blow their top so to speak. Fixable but messy and you’re back at ground zero wrt trapped air.

 

[tls3601]

Possible weak booster? How old is the master cylinder?

 

[John McVicker]

I will say that properly adjusting the 40 drum brakes is a major pain. Undoubtedly all you need to do is adjust the brake drums a bit tighter.

I tighten them to where they won't turn by hand...then back off only 3 clicks. I know the FSM says to back off 5...but 3 is best...maybe even 2.

I then go for a test drive and coast to a stop and feel the drums with my hands. If they are cool to the touch they are too loose and need to be tightened one click at a time until they feel warm (warm, not hot) to the touch. At this point in the adjustment process, cool is bad...warm is good.

Like I said, a major pain, but once adjusted correctly, you'll be good for a long time.

 

[arnott1t]

Well I’ve adjusted them so tight that they wouldn’t turn and still had a low pedal.

Pulled the master and tested on the bench. Had little to no pressure out the front port. It would push some
Fluid but not much.

Grabbed a spare. It was pretty much the same.

Grabbed another spare. Seemed better and would flow healthily out both ports. Installed and now am bleeding like mad again. So far pedal is still s***.

 

[arnott1t]

What wheel cylinders did you get? i had issues with air being trapped in non oem units that took lots of bleeding to get a hard pedal.

Just some from rock auto. Non oem but looked good

 

[Curt]

I purchased the same ones, beck arnley distributed ones. I found a couple threads that suggest the internal is missing a baffle or something that allows air to get trapped into the top of the cylinders and cause bleeding issues.

 

[arnott1t]

So frustrating. This thing isn’t bleeding like any other truck I’ve owned. Being a real pain

 

[PG45er]

Did you try "bench bleeding" the master cylinder. If you haven't then that could be the problem. There are you tube videos on how to do it. HTH

 

[arnott1t]

Bench bled yes. Then I built a pressure bleeder cap. Pressure bled all corners for 1/2 a volume of the reservoir. Put all the tires on. Adjusted one last time
And went for a drive.

Same thing as always. One pump to get the brakes to engage. Rear would lock on the first application and could lock all 4 on the second.

Proceeded to drive the wee out of it and hammer brakes a few times.

Much to my surprise the next stop peddle was high and firm. Stayed like that the rest of the drive. Best cruiser brakes I’ve had. Control my 37s well.

Not sure what the spirited braking did but it worked. I’m guessing some air in the master as it was acting so funny.

 

[65swb45]

Properly working troopie drum brakes are amazing. My HJ would toss me like a rag doll at the windshield if I wasn’t careful.

All OE parts.

 

[middlecalf]

Pads finally got set

 

[JohnnyC]

Did you try removing the top of the cylinders fill with fluid and put back together while they are on the truck ?

You have air and or just not adjusted correctly ... need to adjust them with the wheels on

Manual bleed them

 

[Warloc]

I have had that same pedal on my 40, no matter what I did with brake adjusters and bleeding the pedal needed to be pumped. I recently replaced my mater cylinder and now no more pumping even with oriniginal booster, but new wheel cylinders 1.125 diameter (early 71).

 

[arnott1t]

Ya I’m not sure what it all is. Every time I get in I have a low pedal needing a pump for brakes to really grab.

Then I kick the pedal as fast as I can. Stab it with my foot. Then brakes are set until I park again and are right at the top of the travel. No pump required.

 

[Billsboat]

I’m very interested in this thread. Before I took the thing (66fj40) apart for a frame off restoration I had the same issue with my brakes. I never did resolve the problem. Someone suggested they needed a vacuum bleed...it did not work. I got a new master...it did not work. The wheel cylinders look as if they had not been used, but I don’t know how old they r because they were on the truck when I got it about 6months ago. My theory is that the PO had changed out the brake pads and wheel cylinders and tires and never figure out how to property bleed the brakes and just let the rig sit for years, the tiers look to have next to no miles, but are all dry rotted. For my frame off I’ve replaced all the brake lines both hard and soft, so I’ll be starting from scratch once I get the tub back on. Also I’ll be following this thread closely

 

[John McVicker]

To get best results the wheel cyls MUST be OEM. Front and back wheel clys are different sizes.

Personally, I think it best to rebuild OEM clys as opposed to new non OEM.

YMMV.

 

[Billsboat]

To get best results the wheel cyls MUST be OEM. Front and back wheel clys are different sizes.

Personally, I think it best to rebuild OEM clys as opposed to new non OEM.

YMMV.

Hi John, thanks for your in put! At this point I’m willing to try anything. Will oem have anything on them that shows they are oem?

I hope this is not hi jacking...still seems on topic. Someone plz let me know if I am. Thanks

 

[thebigredrocker]

The wheel cylinders on my 71 all had teq surrounded by a circle. Below is the master off my 76, same logo. Perhaps slightly larger.