Inliners International Forums General Discussion Truck Talk Tranny/Rear End

Ok, A question for all you guys out there. I have a 55 Chevy 1/2 ton, 3 speed on column and 3.9 gears. Not being one to drive slow (read under 65)I know I need to do something...having trouble trying to decide between a new ring and pinion so 3.55 gears, bigger tires, an overdrive tranny or all three. What would/have you done?

thanks

Chevy Girl-

You can definatly increase your top end by going with a set of 3:55's, Taller tires (30") and a T-5 tranny from a Camero/Firebird. I have a 292 /tri-power and it has all of the above, and I cruise at 65MPH @2,000 RPM's. That worked out to 18 MPG for 3,000lb car. At 75 MPH, it was only reading 2,200 RPM's but the milage dropped to 13MPG. I guess the secondaries started to come in.

Good Luck!

RapRap
1940 Chevy Coupe

Easiest & cheapest way to gear up would be taller tires.

A Borg Warner overdrive from a '55-'62 GM car would be perfect for your 3.90 rear gearing, and is a virtual bolt-in. You could keep the column shift too. Only problem might be finding one in good shape. The later Saginaw overdrives are good too, but the shift linkage would have to change.

Best solution - but more work and $$ - is an overdrive T5 transmission from an S10 truck. Floor shift only, see "tech tips" for details.

My 2cent worth is to go with a taller tire and maybe the OD tranny .Then if your still not happy with final RPM at 65 then do the gear change. hope this helps }[oooooo]



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NovaMan/Twisted6/Larry

Love those old electric overdrives. Besides the gear reduction, you get clutch-free shifting and free-wheeling. Just don't forget to lock out the OD going down a grade - no engine braking! And same when parking, use the handbrake or your truck will roll away.

Thanks for all the advice. I need to do some RPM calcs and see where a comfortable cruise speed will be. I know some of the T5s have a .73 OD.

I'll post my results

Ok, heres what I get

Assuming keeping the 235, 30" tires, 3.55 rear gear and a T5 with a .73od I come up with 82 MPH in 5th at 2500 RPMs.

Is it reasonable to assume a 235 can withstand 2500 rpms for a sustained period of time or am I going to put too much wear on it? Am I correct that a 235 should max around 3000 rpms but not for any great length of time?

I am more than happy with the 82 mph, just want to make sure I'm not expecting too much.

Your calculations are correct but unless you have a very healthy 235, it'll be hard pressed to pull that much gear in overdrive 5th. As long as your route is only dead flat roads, you may be OK, but any grades at all will require backshifting. I recommend staying with the factory 3.90 ratio which came in OD-equipped passenger cars.

Where are you finding 3:55 gears for a 2nd series '55 1/2 ton? If you are talking about Patrick's, I know they have 3:36 gears available, unless they have come out with 3:55's recently or something I'm not aware of?

The factory did have 3:36 gears available for the 55-62 1/2 tons, but not sure of which years specifically, as my Hollander interchange manual is somewhat vague on this. Probably were used in trucks with automatics. Rare nowadays.

Do you intend to keep it as original as possible, or maybe upgrade to 5 lug wheels?

Not sure how original we are going to stay. We do want to upgrade to front disc and eventually get some ac in it. I got some info on a possible front suspension upgrade that I need to review so may be doind something there too. Right now jsut trying to fill time until I can get back to body work