Hello!
First, here's my setup:
1965 C10
283 CID rebuilt, bored to .060"-over
Holley 1850 4bbl carb
SM420 transmission
3.08 rear end
29.6" tall tires
Current fuel economy: 16-18 in town (w/o much wind). 17-19.5 on highway (also no/low wind)
The problem is that the main bearing on the SM420 is going out, as is the throwout bearing. Clutch (made by Sachs) is good.
* I know I can rebuild it, or I can replace it. If I replace it, I would like to consider a transmission that has overdrive, and I would like a floor shifter, like I have now.
* I talked to "the old guy" at the well-respected transmission parts house/rebuilders in Tulsa, and he told me that, although parts for the SM420 are somewhat still available, they're getting harder to find and more and more expensive when you can find them. He recommended the NV4500 from a 93-95 Chevy/GM 3/4 to 1-ton truck, stating that it would pretty much bolt right up with minor modifications, and that I could change it from an hydraulic clutch setup to a manual one using my existing linkages, with some "tweaking". He did not mention the speedometer - I want to keep my mechanical cluster.
Questions:
1. With my current setup, I'm getting what I consider respectable gas mileage. Would it be unreasonable to expect better with an overdrive transmission? Will I realize enough RPM improvement that will result in better mpg's without lugging my engine at 60-70 mph?
2. If I did get an OD unit, what ratio would I need to look for in the OD gear? Would the NV4500, as built, work in OD with my 3.08 rear end?
3. If not, what rear end ratio would I need to change it to?
4. If I go with the NV4500, what do I do in order to keep using my mechanically driven speedometer?
5. I know the Dodges and GMs used the NV4500, and I know they can both be used on the '65 Chevrolet, with some "adapting". For me, from my reading, the Dodge version would be a "no" because it would place the shifter way too close to the bench seat. Where would it come up in relation to where it does now on the SM420 if I use the GM-version?
6. What about motor mounts - will they have to be changed, and, if so, to what?
7. What about an additional crossmember - one thread showed pictures without it. Should I plan to put one in if I go with the NV4500?
8. Can I retain my mechanical clutch and linkages, and, if so, how?
9. If not the NV4500, then is there a different one you'd recommend?
10. Lastly, does anyone have any pictures of the swap to an NV4500 (from whatever earlier transmission)?
A big THANKS in advance for all your help! I've read everything the search feature came up with on this type of swap, but these are things that I just couldn't find the answers to, or, in the very least, need clarification on.
- Todd
