MTFCA Forum

No, I don't mean your Halloween pumpkin! I mean your rear axle pumpkin.

I recently drove my 1927 coupe for the first time since the restoration. I drove it 10 miles on two separate occasions. The last was today. After each drive, I touched the pumpkin to see how hot it was. Each time, it was very, very hot. I described this in my September 17 post entitled, "Has Anyone Experienced This?", and it generated considerable discussion. I haven't made a final decision, but I probably will have the rear axle redone. Having said that, I would appreciate if some of you would tell me "How Hot Does Your Pumpkin Get".

It is normal for the axle to heat up when running, and higher speeds generate more heat. Some heat is from internal friction and some is engine heat. I don't know how hot is within a normal range. I would think you could put your hands on it even after miles of highway driving in warm weather, but I haven't actually tried that.

Pat, The exhaust from the muffler is real close to the pumpkin so I put temporary metal sheet between it and the pumpkin. It didn't make any difference.

Someone with more experience will need to address this. My general experience is that rear axles will run 20 to 30 F hotter than ambient temperatures at higher road speeds, but that may not apply to Ts. A newly rebuilt axle might run a little hotter than a well-used one.

Pumpkin heat is probably more common than we know. I, personally, have never felt my pumpkin after a drive, but, if we all did, I’ll bet it would be hot. It is really nothing to worry about as long as it is properly lubricated up to the proper level. Any part where friction is involved will produce heat. Like digging up snakes just to kill them, it is easy to find things on the Model T to fret over, but if you just ignore the snakes, they won’t bite you and you can enjoy your Model T much more. Jim Patrick

Proper way

How was the side thrust clearance set when the rear end was assembled? A warm rear end is ok but if its too hot to keep your hand on, then something is in need of attention. Exhaust impinging on the housing will heat it some but...... about the only thing that can generate excessive amounts of heat is thrust washers set too tight. Incorrect gear mesh will make lots of noise before generating that kind of heat.

Dan McEachern wrote: ↑

Sun Nov 19, 2023 11:04 pm

A warm rear end is ok but if its too hot to keep your hand on, then something is in need of attention.

I think that's pretty much the standard for what is too hot, in this case.

I read somewhere that if you can keep your hand on something for no longer than 5 seconds, the temperarure should be about 135F. I've checked this with a digital thermometer and found it to be surprisingly accurate... if that's any help to you.

The rear axle will pick up heat from hot air passing under the car from the engine and radiator when out on the road. Axles normally generate heat from both mechanical friction and fluid friction in the lubricant. How much heat is normal depends on speed and duration of operation and the ambient temperature.

I would limit road speed on a newly rebuilt axle to 25 to 30 MPH for the first 100 miles and avoid long, hard climbs.

If I get a chance, I'll run my car on the highway today and see if I can get an idea of how much the axle warms up.

Objective measure is best way, just get an inexpensive laser heat temp gage and measure. Useful for lots of T parts, like the cooling system.'


These pics were on the forum years ago and useful too. You might get such a tool and measure the temp to see if it's in range.

Once had a rear axle after just restoring with bronze thrusts. On that one did note that when turning the assembly with thumb and fingers thru the drive shaft opening, there was a tight drag at just one spot, but didn't give a concern. Should have.

The pumpkin got fairly hot to touch running on jack stand. Cooled down, drained some lube, and bronze flakes appeared in the lube. Had to redo, by adding more clearance to the thrusts by taking one down evenly.

Removed axle to redo....


Infrared Pic of T parts on warmed up T

Note the heat of the oil in the pan sump, when the engine is warmed up to operating temps, right around 185 degrees F. (85 C.)


And this one of the rear axle near the pumpkin, about 105 F, (43C). About normal IMO. Some heat there too, with the nearby muffler being much hotter.

One thing to check is rear end lube. I have heard of someone forgetting to add it.

Just answering the original question... After 10 miles, the rear is warm but not too hot to touch. I definitely have engine oil working into the diff, and I'm slowly oiling my breaks on one side. So my seals aren't great but temp doesn't seem to be an issue.

Nv Bob wrote: ↑

Sun Nov 19, 2023 10:45 pm

Proper way

THAT'S how you eat pumpkin pie! And any pie for that matter. Won't go into the last time I felt a warm rear end though