Need help ring and pinion

[NicoSlam]

I read most threads discussing ring and pinion changes but I can't seem to get a good understanding of what is needed. I have a 69SWB with a 250 and muncie three speed on the column with 3.73 rear. I want to change R&P to a 3.08 for better highway use. Majority of my driving is cruising. I found a 3.08 RR in 1971 C10. Being that I want to keep the 6 lug and my axle is 1" shorter then a 1971, I can't swap rear ends. Can I do a swap from one to the other? Using the rpm calc, 70x3.73x1x336/31=2829rpm. If I go with a 3.08 R&: 70x3.08x1x336/31=2336rpm. Thats a 500rpm reduction at 70mph. Any opinions would be great.

thanks
louis

[gonzo6869]

You might want to think about getting an OD tranny, like a 200R4 or a 700R4, not sure if they will fit with your engine though. If not upgrade to a 350 and a 700R4.

[LONGHAIR]

I assume that "swap from one to the other" means swapping the gears from one housing to the other?

If so, that is a "qualified" yes. They will physically fit.....but it is not a good idea. Installing used gears is more difficult than new and you are still "playing with fire". Many professionals will not even do it.
A new set is not going to cost you that much more than buying an entire axle just to get at the used gears inside.
Buy a new set and pay a professional to install them. You get a warranty, peace of mind, and a lot less hassle.

[cdowns]

i dont think there'd b much gas saving with that combe due to how hard the 6 needs to work getting up thru the gears

[Shaky]

Originally Posted by cdowns

i dont think there'd b much gas saving with that combe due to how hard the 6 needs to work getting up thru the gears

This.

I've done it to two trucks now (3.73 to 3.07). You get a minor gain in mpg. An overdrive transmission would probably buy you more.

[NicoSlam]

I spent all day today searching junk yards and talking to many people about what I am trying to achieve. Most made the same comments you guys have. I decided I will go with an early model NP440 (A833/MY6/NP833) 4 speed manual with OD. Looks as the gear ratio are close to the 700R and it gives me a final rpm of 2000prm @70 with my combo. Being I currently have a 3 speed saginaw, it should be a quick swap other than the floor shift install. I found two today. Both rebuilt with shifter for $700 ans $550. Going to take the plunge. I was going to buy used 20" boss 315, but that wont be till next month if they are still in the paper.

[airdale94]

Originally Posted by NicoSlam

I read most threads discussing ring and pinion changes but I can't seem to get a good understanding of what is needed. I have a 69SWB with a 250 and muncie three speed on the column with 3.73 rear. I want to change R&P to a 3.08 for better highway use. Majority of my driving is cruising. I found a 3.08 RR in 1971 C10. Being that I want to keep the 6 lug and my axle is 1" shorter then a 1971, I can't swap rear ends. Can I do a swap from one to the other? Using the rpm calc, 70x3.73x1x336/31=2829rpm. If I go with a 3.08 R&: 70x3.08x1x336/31=2336rpm. Thats a 500rpm reduction at 70mph. Any opinions would be great.

thanks
louis

500RPM doesn't sound like much, but with 3.73's you're almost at 3000RPM and 3.08's put you in the lower 2000RPM range.

When you set your gear's wear pattern with the blue dye I would try to match it more with wear pattern that's already on the gears than to spec. I would also use the shims from the 3.08 pinion and carrier. And see where that gets you first.