Rear End Operating Temperature

35ragtop

35ragtop

Senior Member
Hi guys,
I am wondering if there is an ideal operating temperature for a flathead Ford rear end. (ring and pinion).I have just rebuilt a 3.78 for my 34 pickup and first time around the block it seemed a bit warm to me but that could be because of all new bearings etc. I also wonder if pinion bearing pre load would effect the temp. (too tight = runs hot ?).
I'm guessing but I think it would be about 120 deg F ,just too hot to leave your hand on for too long.
Your opinions appreciated
Dave
 
I guess the logic would be first ambient temp. So if its 90 degrees out of course it will
get warmer anything that spins gets warmer. Old rule back in the day if you can
hold on to it, the temp is around 140 degrees.. goes for the ****** too....
 
Yes tight bearings and preload will have an effect on temperature. I would get an inferred heat gun if you are really concerned about checking it and see what the temperature really is.
 
A hand held infrared thermometer device is the best way to check. My old rule of thumb was if you could hold your hand on it for 3 seconds the it would be between 160 & 180 degrees F. The helicopters have overtemp warning devices that are preset to 235 degrees for a warning light indication. If it runs at over 200 degrees F for a long time then I'd be wondering what's going on. 180 degrees F is fine for one that is breaking in. They will generally start to run cooler after the first 500 miles or so.
 
Thank you for that info. I will run the truck around a bit before getting too worried. I was pretty fussy when it came to setting it up, so I am confident about the preload being right.
Once again the Barn is a big help
Dave
 
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