Brake Pedal Travel and Warm Hubs

[UPFINN]

This week I finished rebuilding my wheel cylinders and installing a remote reservoir. No more leaks!

I bled over half to 3/4 of a gallon of fresh dot5 through the system at 15 psi. I am sure there is no air left in it with that much bled, and I also bled about 16 oz from the air pack. Now for some reason my pedal seems to travel down further before the brakes grab and resistance begins.

I set the shoes at the top and bottom adjust points both to .015, as done by many. Feeler gauge was quite stiff to get in at the ends of the shoes but a lot of slop in the middle of shoes. My shoes looked to have at least 3/16 of thickness before rivets. I had no drag.

I am measuring about 1/2 to 3/4 inch of free play at the top of the pedal travel, and there is about 1/2 inch of threads visible on master push rod. The pedal has to go down at least 3 inches before any braking occurs. Very hard braking puts it almost even with the gas pedal. Is this acceptable?

My hubs are also getting hot, but not the drums. Last year when I repacked bearings I set the inner nut to 50ft lbs, backed off 1/4 a turn, and set outer to 130. The little cork piece was in the key way. Hubs were cold when driving right after service, but after 700 miles, gear oil washed grease from bearings. Either the seal wasn't preloaded enough or the keyway cork was too old and small.

For the last service, I repacked bearings and set inner nut to 50 ft lbs, backed off 1/8 turn, and set outer nut to 130 again. Filled key way with cork and rtv. Drove it 15 miles yesterday evening with an outside temp of 55F, average speed of 45mph, and the hubs were very warm. Not uncomfortable to touch though, just concerning. Will everything loosen up with use, or will I "burn up" the bearings?

Here is my reservoir location and bleeder setup. The fluid level can be seen from outside of the truck through the crack in the panel corner.


Magnetic bleeder/siphon bottle.


Pedal with no foot.


Pedal free play.


Full pedal travel before braking.

 

[cattlerepairman]

Did you measure with the engine running and/or air pressure over 60 psi present?

 

[UPFINN]

Did you measure with the engine running and/or air pressure over 60 psi present?

Yes it is aired up to around 90 psi.

 

[Kaiser67M715]

you should definitely feel more pedal without the booster, when you get air, the pedal will actually sink a little as well. I think you have another issue, I get pedal pressure at about 1.5 inches, maybe less, with only 1/2 inch free play.

try two person bleeding, possible the pressure pot introduced air in the system, or there is a leak elsewhere in the system--this will show up as bubbles with two people, but isn't always noticeable with a vacuum or pressure pot--I think the pumping action cause the leak to make air bubbles in the stream as the fluid moves back and forth over it, where as the pressure pot or vacuum only draws it over once, so it doesn't create a bubble.

 

[UPFINN]

you should definitely feel more pedal without the booster, when you get air, the pedal will actually sink a little as well. I think you have another issue, I get pedal pressure at about 1.5 inches, maybe less, with only 1/2 inch free play.

try two person bleeding, possible the pressure pot introduced air in the system, or there is a leak elsewhere in the system--this will show up as bubbles with two people, but isn't always noticeable with a vacuum or pressure pot--I think the pumping action cause the leak to make air bubbles in the stream as the fluid moves back and forth over it, where as the pressure pot or vacuum only draws it over once, so it doesn't create a bubble.

Once the brake pedal goes down 3 inches it is very firm and the truck stops fast. Can't really get it any further than level with the throttle pedal even if mashing it. I bled 3 quarts all together. I don't see how any air could be left. I bled 16 oz from the air pack first. Only way air could have gotten is is when I put on the master cylinder cap for the last time. I was sure to top it off before putting on the cap, but as I was plumbing in the little npt fitting for the remote reservoir, a bleeder on the rear axle started leaking. Caught it within a minute, but I had lost a bit of fluid so there may have been little air space in the top of the master. I was told that any air caught in the master would work it's way up to the remote res.

There was air in the power bleeder hose, but when it reached the remote reservoir it rose to the top of the res and the fluid sunk down. I figured the same principle was at work in the master cylinder reservoir.

I know a lot of air pack or master cylinder issues cause a pedal that can be pumped and getting harder and harder, but steady pressure causes it to sink. My pedal is hard and I can hold it forever, but it is just low. Very puzzling.

Anyhow, might try bleeding air pack again tomorrow but otherwise trucks going for some drives and parades for Independence Day festivities.

 

[gringeltaube]

If your pedal doesn't feel soft/spongy at all then you may want to check your brake shoe's adjustment again: Lift both sides of each axle so the wheels can spin freely. Then get a 11/16th box wrench, choose either one of the top adjusters and little by little "open-up" (the shoe) until you start feeling resistance - not just hearing it dragging - that, while doing full rotations. Back off that adjuster a tad until no more resistance is felt and do the same with the other one. After finishing all six wheels go for a test drive to see if it changed (for the better…)
I bet it will!

Warm hubs and correct wheel bearing adjustment (again...): The 1/8th-of-a-turn should be taken more like a reference and not as the absolute recipe...
Every hub may react a bit different to the same method applied, mainly due to tolerances between parts; specifically the condition of the spindle- and spindle-nut threads. Also, not all nuts were created equally, and not all of them have been treated nice... e.g. tightened via hammer & chisel, instead of using the correct socket...!
BTW: these nuts should spin-on firmly, with no play to be felt! Never use a nut that shows any movement, axially or radially!

What we do want here is a Zero-play/NO-preload scenario, after bearings are well seated on their races.
I have found that it is easiest to start with a bit of "excess" play and then work my way "down", until that play has just "disappeared". Eventually this requires two or three steps, and of course, every time the outer nut has to be firmly tightened again!

It should be clear to everyone doing this that by tightening the outer nut, the lock-washer will press the inner nut to only rest against the spindle(thread) itself, NOT against the seal and/or bearing cone! This has to be seen as a strong nut-counter nut assembly, exactly adjusted and holding everything in place - with the additional safety feature of the lock-washer, once the tab is bent over, of course.
During the adjusting process, while there still is any play, it can be felt- and heard- best if the whole wheel/tire assembly was still bolted on, and rocking it vertically.
Needless to say, this all should be done with the brake adjusters backed off, or at least ensuring that there is no contact between shoes and drum.

Another reason for warm or even hot hubs could be new aftermarket seals with excessive preload. See this post... or this thread, starting at post #15.



G.

 

[UPFINN]

You know, come to think of it, when I took off the drums they were tight. Now that is strange, since I set the adjusters both to .015 last Fall with no drag. For some reason they got tighter over winter . Another problem, I noticed the .015 feeler gauge I used last Fall may not have been .015. May have been 14, 16, or even 13. The label is scratched off. I have new ones now. I will use a micrometer to measure the difference. I really wish I measured pedal travel before tearing everything apart.

I noticed while adjusting that the center of the shoes had a lot of gap compared to the end. The .015 feeler gauge would not touch both shoe and drum.

I see a lot of "experts" here set both adjusters to .015, but if you have to tighten the top, you loosen the bottom. While the top may now be .10, the bottom could be .20, REVERSE of what original spec is supposed to be. For me to correct this would require pulling wheels again..From my observations, the adjusters seem to affect each other oppositely. This morning I will draw a pencil line at the current adjustment, tighten top, and observe pedal travel. If no change, I will return adjusters back to original point.

Next possible cause of low pedal would be air in the master cylinder? Would bleeding at the air pack remove it, or will I need to pull the master cap? Maybe a bubble is trapped in the remote res hose, but I would expect that much air in master would overcome hydraulic/gravity pressures.

As for wheel bearings, I am thinking that I will drive a longer distance tomorrow at 55mph, and monitor. If more heating occurs, I will back off inner nut a little bit more.

I reused the old outer seals. They seemed to be in good shape.

 

[cattlerepairman]

As for wheel bearings: If, after a drive of 30 mins or more, they just get warm - i.e. you can leave your hand on the hub for several seconds without fear of getting burned - I would not obsess about it. I would take action if a hub gets too hot to touch for any length of time.

 

[UPFINN]

Is it safe to set the top minor adjustment until brakes drag slightly AFTER both top (minor) and bottom (major) were previously set to .015? Wouldn't the bottom of the shoe be too far away if top is set closer since they effect each other opposite? I really should tighten the major adjustment, but I see no correlation between adjuster and shoe movement direction. Don't want to remove wheels again..

Also, when I was measuring with the feeler gauge, the very top and bottom of shoes were almost dragging and the center of shoe was well over .015 away. Adjustment points the gauge slid in with slight drag.

Dad and I took the truck for a 20 mile drive this afternoon to get a chain to go across the back of the troop seats. Also picked up an ir thermometer gun. Ran great.

Back hub's run between 115 to 123F, fronts around 100. Back drums 110 to 130F. Front drums around 145. Outside temp, mid 70s to around 80. Brake pedal went halfway down still. Seems like you have to press it harder a bit too. No fluid loss in remote res. No fluid out air pack vent, no fluid out master cylinder boot.

I opened the 5/16th npt oil cap on the back of the air pack, and a good bit of clear yellow/brown liquid came out. Smells "deucy", like oil, brake fluid, diesel. The cap has never been removed, as the original paint was unbroken. No fresh purple dot5. Over the past few years I have added air tool oil to the line running from the compressor. Maybe it was just a mix of oil, water, and old brake fluid that leaked out during long periods of no operation (Winter).

I called a friend of mine who is 80 miles away, specializes in 5 tons now, used to have deuces. Said as long as hubs don't burn you when you touch them, they are fine. Recommended as by many on here, turn the top adjusters out a bit. Hydrovac may be in need of rebuild if leaking, and watch for spray out of vent and other pedal issues. He has a new master cylinder to install, might as well when I do the air pack.

This evening I crawled under the truck and tightened the top adjusters, and sure enough, I gained another inch of pedal! Pedal stops around 4.5" instead of 3.5". Had my neighbor come over and test the pedal and he said it does not seem to be mushy.

Here is after backing the top adjusters out as mentioned above until dragging, after minor and major originally set to .015.