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Ok, some general questions for those who have gone down this path. 41 COE: How many of you have run 60+ on the original 1.5 ton rear ends? I'm planning V8/700R4 and want to know if there is any reason to think the rear wouldn't like that. Granted there are different ratios, but generally what RPM can I expect at 60 w/700R4 overdrive? Which of you would run the split rims that fast? Old trivia I know, but if it helps me, it will probably help someone else looking the threads over. As always, my warmest appreciation for the information and knowledge. Tom

*This truck will never carry a load and weighs about 5K.

Empty weights for 1941 trucks

Rated gross weights for 1941 trucks

The empty truck weighs no more than 4,000 lbs. Which model truck do you have - the rated net load is between 3,300lbs and 9,000lbs.

Safely driving-at/stopping-from 60+MPH: that is important safety-question.

It is a medium wheel-base 41 COE that has a van body added to it by a movie studio for the movie Jeepers Creepers. There were 3 of them and Tim Glace (another stovebolter) has one of the others. I just had it weighed for DMV and it came in at 5140. Some of the weight is the frame I used which was a tractor frame and is C-capped from the door pins back meaning they placed a frame around a frame. It is very stout and not much sway. Anyway, that is what he weighs. I'm mostly curious about the rear ends ability to spin faster than it was designed to do so. I plan on the disc conversion, and other things. In the meantime, can the rear end, and wheels handle more than 45.

I'm sure a lot of these heavy trucks exceeded 60 downhill back when they were the only thing haulin freight cross country - how fast it can spin isn't the right question, how long it'll last doin it is what you should wonder - have you replaced the rear axle bearings? even inspected them? looked at the condition of the gears? .... and as Tim points out, how it'll handle at 60+ is another question, the front ends weren't designed for it ..... your rear gears will be 5.43 at best, quite possibly 6.17, using your tire size and gear ratios you should be able to figure RPMs

Bill

If you are up grading the motor & trans, especially the motor to a V8, why would you run the old rear-end? You probably have 411 or lower gears. Go to a higher ratio rear end, 370 gears would be better. What ever you do, you need to use the correct torque converter to match the trans with the rear end gears to make the trans work right & not heat up.

The weak link will be the 700R4 aka 4L60. It wasn't used o.e. in anything over 7200GVW rating (light 3/4 or heavy half ton, 6 lug wheels). The later 4L60E is better but still light duty. 4L80E would be my choise.

Thank you guys!

Original Rear: The reason to run the original rear end is to preserve the original look. I do have an NPR rear end that may eventually work it's way under the truck, but the hubs are larger, need to have wheels made, and ultimately it starts to lose the factory look. I will probably get there, but would like to fire it up and run it around until I complete the mods needed to the new rear end. Other options are too wide.

Torque converter: How can they be matched and how does it get hot? My thoughts are that the converter, after sufficient RPMs engages and stays that way until RPMs drop. My plan is to use a very low stall because I have a moderate cam installed. That will allow it to get moving without hesitation. What variables can be considered for converters other than stall, and proper fit?

4L80E: My research found the need for this to be computer controlled is the only reason I'm looking at the 700R4 which can be used without. Seems if they put 700R4s in full sized chevys to work, that a beefed up rebuild should be OK for a non-working, slightly heavier truck.

These are just my justifications and thoughts, and I appreciate everything you guys have replied with, and I'm taking it all in.
Tom

Tom,

Assuming you have the following:

34" tall tires
6.17 rear
1:1 trans ratio (stock trans)

To reach 60 mph the engine will be spinning at 3700 prm.

If you add an OD trans with a .8 ratio the rpm drops to 2960 at 60 mph.

Hope this helps,

Mike B

OK I looked up the movie to see the truck.
Looks like 7.00-20 dual wheels. Nice big rolling radius. My truck has the same.
If you have a 5.43 diff, you will be fine. Standard its doing 3000 at 60 mph. A 6.17 is that much worse.
With .8 OD you'll get 2400. OK for a bigger motor. The original 216 probably wont pull it without a lot of throttle.
Anyway the diff. The front pinion bearing is uncaged needle type. I dont know a lot but I think these are designed for load not speed, with revs they tend to bind and grind. That said, they were designed to do 50 and 60 aint much more. Add in modern oils and I think you will be fine if you dont exceed 60 by much.
All the other bearings are monster size, barrel type and I dont think they will mind the extra speed.
From what I have seen the diffs never wear out and this would include any abuse they ever got.
I plan on running mine all day at 60, and I dont expect issues.

If you get serious, clean out the rear axle housing- my diff unit was clean enough but the housing was full of old hypoid gunk, like about 1/4 " of it right through. Running it faster may dislodge this and let it float around.