I have a Chrysler 7/14” rear diff open 2.93 gears. After driving for approximately 30 miles I checked the tire temps, the front and rear wheel bearing temps. My infrared gun gave it up a while ago so I just used my calibrated MKV fingers to test temps. Outside temp in the mid 80s tires and front bearings were fairly cool maybe 110 degrees same as tires IDK. I couldn’t continuously touch the rear hubs so I’m guessing maybe 150 ish. You can hold 140 but not 150. The hubs weren’t hot enough to cause a burn. When I get to HF I’ll buy a new IR gun. I changed the rear fluid about 2000 or so miles ago everything looked fine. I don’t have any noise that I can hear. What did you say? My question is Is it normal for the rear bearings to be running maybe 40 50 degrees hotter the the fronts? Thanks
That seems hot, especially for a car that has what, maybe, 2,000 lbs supported by the rear axle? I have seen trucks with 10,000 lbs on the rear run that warm, and stuff with high angle CV joints get that warm (or warmer) during highway usage. But a car under lightweight, low load conditions should be no more than 30 or 40 degrees above ambient.
I don’t think the brakes are dragging That’s what I was thinking the rear has maybe 1500 lb load. I never had a rear axle hot unless I was abusing it. I’ll keep an eye on it. I’m going to Lloydfest next week, trailering the car but still don’t want a breakdown during the festivities. The car will be getting a Ford 8.8 in the future, just don’t have time to install right now. Thanks guys Daniel
Think about how the heat would radiate. Ie if you suspect the bearing, and you can’t keep a hand on the drum, the bearing would be much warmer/hotter. The heat would have to radiate through the axle, the hub flange to the brake drum and to the outside of the drum. That’s a lot of m***. And to be that hot after driving when air is cooling things off, means if it’s a bearing, you could cook an egg on it. How did the hub/flange of the axle feel?
I just felt where the hub flange stick out of the wheel, next drive I’ll climb under or remove wheel and check at brake drum, also check the pumpkin. Dan
I will Jack it up and rotate by hand and see if I hear any noise, both sides are hot about the same temp near as I can tell. Damn I need to buy a new IR gun handy things they are. The last one lasted over 30 years. Dan
I still have (and use) the IR thermometer I bought 30+ years ago when I had my powdercoating business. It cost $1200 then.
First, that's no way to treat your MKV girlfriend. Second, on the 8.75 the gear lube is for the inner bearings and gears, the outer tapered bearings are greased. The seal is inboard of the outer bearing. Not sure on the 7.25. Blew mine up... https://differentials.com/chrysler-7-25-differential-parts/ I check the outer bearing temps at the end of the housing tube, not the brake or hub. As said, brakes are their own heat generators.
Just normal stopping drive several miles at 60 mph slowed to 15 or so turned on my road - gravel - drove easy with very little braking about 2 miles and stopped in my driveway Dan
Thanks Rod looks like the 7-1/4 is the same as 8-3/4. I bought a new IR gun and will check temp at the axle housing where the bearing resides, also the pumpkin. Dan
The place to start is to be sure the gear lube level is correct. Your Dart has a 7 1/4 rear, right? I believe those rear wheel bearings are lubed by the axle gear lube (I know an 8 1/4 wheel bearings are, and I believe the modern 7 1/4 are as well). If the level is low, the bearings may not be getting enough lube. If they are external and need to be grease packed, have you ever done that? A hard run, or a bit of tire spin, or a bit of brake drag, or exhaust dumping on the axle tube, or trapped hot exhaust in the rear axle area, can all bring the temp up pretty fast, for a short time. On an 80 degree day, a 150 degree axle hub temp is getting up there, but I don't believe its in the danger zone yet. i would not be concerned until you can get an actual temp reading and compare those numbers with the temps of other parts in the area.
Picked up a new IR gun today, will take for a drive and get accurate readings at bearings and pumpkin. I changed fluid a couple thousand miles ago, I don’t have any leaks but I’ll recheck the level. I have abused this rear axle some. Dan
Dan, my avatar has a 9IN with the A20 bearings that lube off the center section, also disc brakes. I can go on a 20,50 or even a 100 mile run and lay my hands on the outer ends of the tubes. They are hot but I can lay my hands on them for 5,10 seconds or so depending on hard I ran. Everything always seems fine. I'd be careful laying my hands on the drums.
Anyone who has watched your build videos knows that! That rear was designed in the late 50s early 60s for the lighter, less powerful A body. Economy and light weight were the focus. A warmed over V8 pitched around gravel roads in a heavier car with wide tires was the edge of the design envelope. Nothing wrong with that but just know if you are dancing on the edge, Danger is the point, to quote Ryan.
I bought a new IR gun which should help in diagnosing, anytime I want to feel how warm something is I approach slowly. The 5-10 second timeframe you talk about is about what I have. Both side sides felt similar. Thanks Dan
I figured I’m on the edge hence the 8.8 Ford rear laying in garage waiting on being shortened etc. I just don’t want to break it not because the 7-1/4 is anything special but because I had a rear come unglued at over 100 once. That was enough for me, my **** puckered so hard I’m still picking out pieces of the seat 40 some years later. LOL Dan Danger is the point
Drove to my Nursing Home/Disabled taxi job. Drove about 12 miles like a little old lady stopped and took temp readings. The hubs are each 145, the axle tube where the bearing resides was 135 cover about 1/3 up was 145, brake drums 165 When I got work 15 miles more using my brakes in town driving the temps were the same except brake drums were 200, after sitting 5 minutes the hubs were 165. I might have the brakes adjusted a wee bit too much. Monday I’ll investigate the brakes. It coasts fine. I don’t think I have anything bad going on since the temps are mostly equal side to side. Dan
Get a helper, raise the rear up. Have them apply the brakes for a bit, let off and immediately turn a tire. See if any drag at all. Then try again (no more brakes on) and see if the drag, if any, is gone. I’m sure you know about this, but sometimes the small things get over looked.
Dan, I think you are going to be OK. The temps across the board are pretty consistent, with slightly higher temps near the brakes ans wheels. The two places the generate the most heat, and the two areas that have tires and wheels keeping the heat from dissipating from. I have seen many 7 1/4 rear ends die. All of them were failed spider gears from single wheel burnouts, unless some one thought they could do neutral drops. Those 7.25 spider gears are pretty small, when one tire is making smoke, and the other isn't doing anything, the speed those spider gears are spinning is crazy. The speed removed the lube from the spider gears and their shafts, and something locks up, a split second before the boom. Don't want to blow up the 7.25? Limit the single wheel smoke show to 10 seconds at a time. Or blow it up! It already has a trailer ride home....
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