Red Diamond 372 Max Criusing RPM

I posted this over on the L, R & S forum but I thought I'd see if I get any responses here.

I have a 1962 R185 with the 372, 5 speed overdrive transmission (0.823:1), 9.00-20 rubber and a 2-speed rear with a 5.57:1 ratio on the high (cruising) side. The engine is governed at 2850 RPM's. The way it's set up now I can run 55 MPH at about 2150 RPM's. I keep going back and forth about changing the rear end gears to something more cruise-friendly like a 4.88:1 (1900 RPM at 55 MPH) or even a 3.73:1 (1500 RPM at 55 MPH). I'm afraid if I go with the 3.73 that it will lay down like a dog whenever I get to any sizable hill. Does anyone have a similar set-up that works well as a compromise between speed and power? I may just leave well enough alone and stick with the 5:57 gears as I sometimes pull a trailer. Any thoughts or words of wisdom would be much appreciated.

Redk5guy

I'd leave well enough alone.

Due to it being a 50+ y/o rear it's extremely unlikely you'd find a new ring & pinion or a used carrier with a higher ratio for that matter.
I perused a couple parts manuals to see what ratios were available way back when,not much different than today really. Didn't see any higher than 4.3x so 3.73 was probably not used.
RD engines were "slow turning" with a relatively low torque rise built to use the torque,not for speed.

Wondering,why do you keep posting the same question in 2 sections? Not really necessary even though it's falls under either category.

Thanks for the information, I'll probably leave it alone.

As far as posting in both forums, I thought they were totally separate with different readers and posters in each. As you can see I'm still a newbie and learning how the forums work. Sorry for the duplicate posts, won't do that anymore.

Redk5guy

There will be some who only read certain forums, there are others who may have vehicles that fit both forums. It would be acceptable to post something over on the L,R,S, as yours is in that category,, However it might work to just post a notice in one of the forums that there is a Question that you would like some info on in the other forum, then post the full question in the forum that you best fit in. You got info in both areas.


For the others that read this forum, What do you consider Larger trucks? I will ask this same Question in the other Forum also.

Lloyd

Redk5guy, you might be interested in this R-185 Sales Engineering Bulletin I ran across on ebay. If you look at the third picture closely you can read some numbers that might answer your question.

http://www.ebay.com/itm/Vintage-1953-In ... 35d0b3091b

In case it disappears before you see it, it says in the example that cruising speed with a 372 is 2530 at 50mph with an F-52 OD tranny (.825:1), 10x20 tires and 7.16 rear end.
Sounds to me like yours was specced pretty darn good for modern highway speeds.


Lloyd, to me a pickup is less than 10,000 GVW, medium is up to 26 or 28,000 and heavy is above that. I think modern pickups are pushing the 10K mark, but in the vintage truck context, that's my way of thinking.