Hubs are still hot

[pinbill]

Hello-

I am at a loss, both my front hubs were getting too hot to touch and I repacked the bearings, changed the pads, calipers, and rubber brake hoses. I took it for a ride on the highway without really braking on the way to the on ramp, drove 15 minutes, and then took an uphill off ramp. I could keep my hand on the hub for as long as I wanted. On the way home I tried some more aggressive braking and they got hot again. My mail man said if the back brakes are not working either because of improper adjustment or a bad proportioning valve, it can make the fronts hot.

Today I inspected and adjusted the rear brakes and drums. THey looked good.
Went for a test ride for 10 minutes with some heavy braking. The rears locked up fine and when I got home were at 171.

It seems like the problem is in the brake system, but I don't know where to go next. I mixed dot 3 brake fluid in when I worked on the brakes three days ago and will flush the whole thing Friday, but it just doesn't seem like thats the problem. Didn't check the spindle bearings but the hubs don't get hot unless I use the brakes. Not sure if replacing the master cylinder or the proportioning valve would help because the back brakes are working fine. Anyone have any ideas?

Thanks,

Bill

 

[1986Blazerk5]

Are your hubs unlocked? mine get hot in the front but not too hot to touch with hubs unlocked i think it is normal but not sure.

 

[pinbill]

yeah, they are unlocked. thanks for the reply.

bill

 

[OL AG '89]

I gotta ask a couple of stupid questions first to get to the meat of the problem.
If you jack the truck up and spin the fronts, do they spin freely?
When you have them spinning and then stop them with brake do they again spin free or do they feel kie they tighten up?
If they tighten up check the calipers and see if they are releasing all they way?
Is this on both fronts or more on one than the other?

It sounds like you have might have crud in the lines. I think also if you mixed the DOT 3 with the 5 you might also have some seal damage, if I remember these do not play well torgether.

 

[pinbill]

They spun pretty nice after I did the brake hoses. Will try to jack it up again tomorrow and spin the wheels after I apply the brakes.

The drivers side gets hotter sooner, but the passenger side read 171 after the test drive.

What seals could be damaged?

 

[ryan77]

I took mine out today the hubs were warm but not hot, you have to have something dragging or a bad bearing, or something.

 

[Barrman]

The caliper piston seal can be crudded up and not let the piston move back after you release the pedal. Could be the piston is all corroded as well. You wrote that it has new pads and calipers though. Do the jack it in the air, spin the tire and then hit the brake test. See if you can spin it after you hit the brake. You probably should do this with the tire off so you aren't getting 2-1/2 feet of leverage. Just by grabbing the lug studs you should be able to spin the rotor. Try this cold and then go out and do a bunch of braking and try it again while everything is warm.

How does your master cylinder look inside? Can you run your finger through it and come up with all kinds of slimy goo on it? If the answer is yes, then you need to pull it apart, clean and inspect it. Then put it back on if everything was ok or put on a new one. If there is a bunch of crud in there, the pressure is not being released from the system when you let go of the pedal. This was my reason for having you do the cold and hot test above. Clogged up master isn't a problem until everything starts to expand. The only thing that can move is the caliper piston which applies the brakes.

 

[pinbill]

Update: I went and did all the tests and the brakes do feel like they are hanging up when hot. I also opened the master cylinder, the two oils had not mixed, and it didn't look good. It also has a leak on the back passenger side. I read about some testing to see if the ports are clogged. Which might be the case, when I did the hoses the old oil that came out was very nasty. Will let you know how it goes.

Thanks for all your help,

Bill

 

[rlwm211]

bearing preload is critical

When you adjusted the bearings how much "preload" did you apply"?​

The bearings can run hot if they are too tight. This also causes the grease to run out as well.​

I adjust mine as follows:
I snug the bearings with the spanner socket and rachet until they bind slightly. This ensures the bearings are fully seated on the races.​

I back the bearings off until there is lateral play (wobble) in the hub.​

I turn the socket back in until the 'wobble' just goes away, and maybe a few degrees more. (maybe 10)​

I put the locking washer in and then the outer nut and lock the spindle nut in place.​

If you have too much preload, even just 30-45 degrees of rotation, you can cause a heating problem and also ruin bearings eventually.​

If you have the bearings properly adjusted, then it is back into the brakes and the possibility that you have calipers that are very old, and probably frozen, or near to that. DOT 3 and DOT 5 being mixed is also a problem as it causes the seals to swell and could be causing the piston to bind.​

Hope this helps​

RL​

 

[armytruck63]

Bite the bullet and get all new DOT 5 for your brake system. Even if this is not the cause of your current problem, you are just asking for trouble mixing DOT 3 and DOT 5. The manual specifies DOT 5 for some very good reasons.

 

[ODdave]

i bet your hydro booster is bad, there is a small bleed off port that gets plugged and the pressure from the ps pump will actually apply the brakes as you are driving. Learned this on my civy truck.

 

[pinbill]

Got all Dot 5 ready to go, master cylinder installed, buddy coming over at 7 to bleed. If this doesn't work then I will loosen up the bearing nuts just a tad. At this point at least I will have a completely rebuilt brake system. Will let you know how it goes.

 

[pinbill]

Brakes bled, MC installed, 20 minute test run complete, still 180 on both sides at the hub near the wheel. Tomorrow I plan to loosen up the bearing nuts a bit, test the hydro booster, and go from there. If they still get hot I guess I will change the bearings. Any more input would be greatly appreciated.

Thanks,

Bill

 

[littlebob]

Just a couple of other things I can think of.

Old brake hoses often deteriorate from the inside and act as check valves. If ther is a rubber line
going from the frame to a splitter to each wheel I would change it.

Is there a proportioning valve(front to rear, diagonal). I worked on a truck(89 3/4 ton chevy) and we changed rubber lines and calipers before we found the valve to be at fault.

I've never owned or worked on that model, but things to check.

Another member I know locally just had an issue with a rubber line on his Duece that did the same thing on one of his wheels. I would change the rubber at each wheel too, but if it is doing it to both, I would change the one going to both first.

Good Luck!

 

[watkinssr]

Dot5 and Dot3 will cause all kinds of problems. Some well meaning friend did that to my harley one time and it pretty well turned into jelly inside the lines...**** near killed me when I went to brake and nothing happened. I had to tear the master cylinder and calipers apart and replaced the lines (on a motorcycle not a big deal).

 

[OL AG '89]

What does the TM say????

TM 9-2320-289-20 U N I T M A I N T E N A N C E M A N U A L

TRUCK, UTILITY, TACTICAL, 3/4 TON, 4x4, M1009​

(2320-01-1 23-2665)


The tapered end of inner bearing assembly must be facing toward the outboard (cap end) of the
axle shaft. The tapered end of the outer wheel bearing assembly must be facing toward the
inboard (splined end) of the axle shaft. Failure to follow this warning may force wheel off truck
during operation, causing serious injury or death to personnel.

Paragraph
8-4. ROTOR AND WHEEL BEARINGS MAINTENANCE.

Also look at Par 6-7...... I think or maybe 6-4....... about bearing and spindle removal.

I said earlier mixing DOT 3 and 5 is a HUGE NO-NO..... I would first stop everything clean ALL brake lines and components. 3 & 5 DO NOT MIX. They destroy seals or at the very least soften them to uselessness.

Once you have cleaned the brake lines, clean them again.... seriously!!
All components clear of MIX.
Now put it all back together and FOLLOW THE TM...
Can almost guarantee it will go together correctly and you will be done ......

 

[watkinssr]

HOw would you even begin to clean out fo the lines in this case? I've had it happen in motorcycles, and like I said...I always replaced the lines and tore down the components. But as long as the metal lines are.

 

[Barrman]

Pressure bleeder with de natured alcohol is a great way to clean them out.

Or, if he bought his BFS from Spruce mountain at $30 per gallon, he either got the yellow or the purple. Fill the pressure bleeder up with a color that does not match what is in the truck now and bleed until the new color is all that comes out.

I swapped my M715 over from DOT 3 to BFS by flushing with alcohol in the pressure bleeder, then slowly bled in the BFS. Using a catch container for what comes out the bleeder lets you look real close at the liquid. I love pressure bleeding.

 

[watkinssr]

pressure bleeding rocks.

 

[watkinssr]

I really need to check and see if what is in my cucv. since it doesn't really drive, I've never got around to checking it.