What is an acceptable axle hub temperature?

[Silly Seville]

Hey Guys,

Has anyone ever shot their axle hubs with a thermo-gun immediately after towing a significant distance? I ask because I have noticed something peculiar about mine. I have a 28' tandem axle trailer with 4 wheel hydraulic actuated drum brakes. I serviced the wheel bearings a month ago, used Mobil 1 full synthetic grease and have Buddies installed. Also adjusted the shoes so that they were "just" scratching the drums when spun by hand.

After pulling 10 miles in moderate traffic, (several stops at city speeds) and 20 miles of 55mph highway use; I hop out to do the "hand to hub" temperature check. The driver side is always just warm, with the forward axle slightly warmer than the rear. However, the passenger side is HOT. Like, I don't want to keep my hand on it hot! Both axles too. So, I'm trying to figure out if this is a failing bearing issue, or a brake issue showing up as hot hubs. Is there a standard "too hot to hold" criteria for axle hub temps? I was always taught that you should be able to leave your hand on the hub indefinitely under normal circumstances without it being uncomfortable. I bought a thermo-gun and am going to take some base line readings tomorrow. Just wanting to know if anyone else experiences these wildly divergent temperature differences.

 

[freeisforme]

Re: What is an acceptable axle hub temperature?

Warm is normal, but too hot to touch is a problem unless you just came down a long mountain road dragging the brakes.
I'd back off that brake adjuster and see if the heat goes away. All the brakes should be adjusted the same, one being tighter will get hotter since the trailer can't tell that one is grabbing harder than the rest.

 

[LippCJ7]

Re: What is an acceptable axle hub temperature?

If its uncomfortable to touch after you just did the work I think your fine, if it were a bearing you wouldn't be able to touch it, I think your brakes are seating and its normal, also keep in mind that the tried and true method of touching your hubs is determined by the area you tow in, try that in Colorado at the wrong time and you are going to burn your hands, brake heat transfer to the hubs cannot be understated, it would be worth taking a look at but keep in mind that you are still touching the hubs, and that is a good sign and probably an indication of brake heat and not a bad bearing.

But the only way to know for sure is to take a look...

 

[boaterinsd]

Re: What is an acceptable axle hub temperature?

Hey Guys,

Has anyone ever shot their axle hubs with a thermo-gun immediately after towing a significant distance? I ask because I have noticed something peculiar about mine. I have a 28' tandem axle trailer with 4 wheel hydraulic actuated drum brakes. I serviced the wheel bearings a month ago, used Mobil 1 full synthetic grease and have Buddies installed. Also adjusted the shoes so that they were "just" scratching the drums when spun by hand.

After pulling 10 miles in moderate traffic, (several stops at city speeds) and 20 miles of 55mph highway use; I hop out to do the "hand to hub" temperature check. The driver side is always just warm, with the forward axle slightly warmer than the rear. However, the passenger side is HOT. Like, I don't want to keep my hand on it hot! Both axles too. So, I'm trying to figure out if this is a failing bearing issue, or a brake issue showing up as hot hubs. Is there a standard "too hot to hold" criteria for axle hub temps? I was always taught that you should be able to leave your hand on the hub indefinitely under normal circumstances without it being uncomfortable. I bought a thermo-gun and am going to take some base line readings tomorrow. Just wanting to know if anyone else experiences these wildly divergent temperature differences.

I saw its a fluid system, so tell me is the one circuit on the right side and one on the left . Or is the front axle and rear axle separate? I am thinking a bad hose might be an issue not allowing the fluid to completely return after a brake event. Try jacking up a wheel after using the brakes on both sides and see if the right has more of a drag.

 

[fondafj]

Re: What is an acceptable axle hub temperature?

I use an IR gun every time I trailer to keep an eye on tires/hubs/brakes. Things to consider when checking temperatures is outside ambient temp and sunlight.... the side in the sun often runs 10-15 deg F warmer. My trailer has disk now converted from drums, in both cases the running temp in normal driving is 90-160 deg F. A few panic stops and the hub temps rise quickly, longer highway miles and they settle in around the lower range... on a cool night of long highway runs they will run as low as 80 deg F.
My thoughts are the cool side is as much of a problem as the hot side and agree with the other recommendation of readjustment or disassemble to see the problem. It would be surprising to have a bearing problem you could not hear by spinning the jacked up tire unless the preload is way too tight.
Glad to hear you are checking, and invested in an IR gun --- my personal experience with a frozen caliper resulted in 4 burned finger tips doing the "touch test". I check temp after 10 miles every tow and at every fill up.

 

[Bob's Garage]

Re: What is an acceptable axle hub temperature?

I use an IR gun every time I trailer to keep an eye on tires/hubs/brakes. Things to consider when checking temperatures is outside ambient temp and sunlight.... the side in the sun often runs 10-15 deg F warmer. My trailer has disk now converted from drums, in both cases the running temp in normal driving is 90-160 deg F. A few panic stops and the hub temps rise quickly, longer highway miles and they settle in around the lower range... on a cool night of long highway runs they will run as low as 80 deg F.
My thoughts are the cool side is as much of a problem as the hot side and agree with the other recommendation of readjustment or disassemble to see the problem. It would be surprising to have a bearing problem you could not hear by spinning the jacked up tire unless the preload is way too tight.
Glad to hear you are checking, and invested in an IR gun --- my personal experience with a frozen caliper resulted in 4 burned finger tips doing the "touch test". I check temp after 10 miles every tow and at every fill up.

I also use a IR gun and really like it better than burning my hand.

I have found that on a really hot day, as stated above, the temp. will get to 135 deg. (The highest I have recorded.) Normal around 90/95. You want both sides to be close in temp. and there will be some variation between front and back hubs. but not more than say, 5-10 deg.

One thing I noticed, when fooling around with the gun, is that the hubs, wheels and even the tires were very close to the same temp.

For comparison, I am towing a 6600 lb rig, tandem axle, both with surge operated disc brakes.

The brake lines, by the way, are a single line system, with the main hose (or tube) going to a splitter, forward of the front axle, with "trunk" lines leading to the front caliper, then the back, on each side. I believe drums are the same system. When bleeding the brakes, you start the process at the most distant bleeder from the master cylinder and work forward.

 

[SingleShot]

Re: What is an acceptable axle hub temperature?

Like above, I have a 29' travel trailer tandem axel that I changed bearings last July before 5K trip to yellowstone. After installing and adjusting the brakes like you, I took a quick 25 mile highway trip and checked my bearings. At that time I did not have my IR gun but I did find two wheels p front, and d rear were hotter than the others. I readjusted thos brakes and found they were dragging more. In short running from SE wi straight to Rapids city day temps reached 90 F my wheel temps held around 125f on the high side. For your hot wheels, I would check the brake drag as that will heat up wheels quick, and double check your end play on those hubs. Too tight is worse than loose. I set my end play to ~ .005, as your bearings heat up this number will get less. And I did use the same grease as you Mobile1.

 

[Silly Seville]

Re: What is an acceptable axle hub temperature?

Thanks for all of the thoughtful replies Guys, that helps a lot! I'll try to respond to the various questions, and then fill you in on my findings.

brake heat transfer to the hubs cannot be understated Agreed! When the hubs were at their hottest, it was right after coming down an exit ramp to enter a truck stop...makes sense except that only one side was hot...

is the one circuit on the right side and one on the left The main line runs down starboard side frame rail to a set of tee's above the axles. Those tee's then split a pair of lines over the axles to the port side. Interesting that the hot side is also the side with the tee's. Maybe there is a pressure imbalance here?

outside ambient temp and sunlight.... the side in the sun often runs 10-15 deg F warmer. Agreed! I tried to factor this in because the hotter side, was in fact, traveling in the sun for the entire distance. But in my case, I think the 10-15 degree variation would not have been noticeable to my hand...only a temp gun.

When bleeding the brakes, you start the process at the most distant bleeder from the master cylinder and work forward. I made sure I followed this sequence to the letter...per Titan-Dico's technical info. No air in my brake system. (hopefully)

First results; I jacked up all wheels before taking boat for a spin around town again. Wheels turn free, no hanging up and no bearing noise. Checked Buddies, and they are oozing a slight amount of grease out, so I know that are full, (as springs indicate)

As I was unable to duplicate the exact running conditions, these results may be flawed. (This day was a full 15 degrees cooler out than previous trips. Went 13 miles on back country roads between 40 and 50 mph stopping only at occasional stop sign and slowing for curves. Did have a brief sprint on the interstate to 65 mph, then came down a ramp to a mall parking lot and jumped out and took readings.

Here they are:

Front left 110
Rear left 104
Front right 141
Rear right 136

That's a 30 degree spread side to side. The left side numbers seem reasonable, but the right side not so much.
Also, I should mention that the hand test revealed that the right side was not as hot during this test as in previous trials. (probably because I didn't drive as far and it was cooler out this day)

One other thing, then I'm going out to re-bleed and readjust the shoes on the right side. Is it possible that under "emergency" style stopping, that the right side brakes would actuate faster given their closer proximity (hydraulically speaking) to the master cylinder? I ask this because when I was in traffic last week, I had to use extra firm brake pressure for a yellow light idiot in front of me. (that's the guy or gal in a small car that wants to stop prematurely for a yellow light when a 15k lbs. rig is behind them doing 50 mph) Anyway, as I'm stabbing the brake pedal pretty hard, I instantly feel the trailer brakes grab and almost yank the truck back and to the right, indicating that the right brakes were activating first. I don't want to replicate that kind of stopping condition again to see if it does the same thing, but could that be a component of my heat issue?

Thanks for taking the time to read this long post!

 

[Bob's Garage]

Re: What is an acceptable axle hub temperature?

One other thing, then I'm going out to re-bleed and readjust the shoes on the right side. Is it possible that under "emergency" style stopping, that the right side brakes would actuate faster given their closer proximity (hydraulically speaking) to the master cylinder? I ask this because when I was in traffic last week, I had to use extra firm brake pressure for a yellow light idiot in front of me. (that's the guy or gal in a small car that wants to stop prematurely for a yellow light when a 15k lbs. rig is behind them doing 50 mph) Anyway, as I'm stabbing the brake pedal pretty hard, I instantly feel the trailer brakes grab and almost yank the truck back and to the right, indicating that the right brakes were activating first. I don't want to replicate that kind of stopping condition again to see if it does the same thing, but could that be a component of my heat issue?

Thanks for taking the time to read this long post!

If I was the one who was having this problem, I would begin to believe that the left side brakes may not be grabbing. All the braking pressure seems to be on your right side, hence the swerve to the right.

With disc brakes it's easy to tell, the working ones are shinny, but drums aren't so simple. But that is where I would be looking now.

 

[four winns 214]

Re: What is an acceptable axle hub temperature?

Here they are:

Front left 110
Rear left 104
Front right 141
Rear right 136

The temps on my tandem axle trailer hubs are fairly even from side to side regardless of position of the sun. I believe your issue is mal-adjusted brakes, air in the lines of the side with the lower temps, or some other issue that preventing even brake pressure from being applied to each side.

 

[fondafj]

Re: What is an acceptable axle hub temperature?

I should clarify my post, kinda typed it hastily. I check both the tires and hubs every stop with the IR, tires show the sun temperature delta not the hubs.
I doubt bleeding the brakes will modulate a side to side problem. I would readjust the shoes and if the problem still exists pull the drums to look for contaminated linings. Look up the factory recommendation for adjustment... My 12" drum adjustment was adjust until you could not spin the wheel then back off 12 clicks. More than I would have done for auto brakes.
One other not very likely item .. but stranger things have happened. make sure you have both left and right backing plates on your axles. Surge brake drum assemblies are designed to be free backing..... if placed on the wrong side of the trailer they would not be very effective.