Advise on rear end gear change..3:31 vs. 3:73

[prager]

Hello all.. I currently have 3:31's in the Lark, am thinking of changing to 3:73's over the winter..Dana 44 unit.. Question is..Will this give a big seat of the pants speed move? Is it worth messing with? I was thinking of the 373 because of the carrier change thing by going any larger than that. The car has a pretty healthy 355 witha aTremec 5 speed behind it.. It does pretty well now...but , would there be a noticable improvement with the 3:73 change? Gas mileage aside..town cruiser...just want more off the line, but yes...that once a year road trip low rpm cruise would be cool too...Any advise?? Thanks!!!

[63t-cab]

I'm certainly no expert on this,but I'd leave it a 3:31. or say 3:54 (kinda split the difference)

[1954khardtop]

Is 5th gear overdrive? If so you'll like the 3:73s. Ive got a T5 5speed in my model A roadster with 4:11 gears. It turns about 2100 rpm at 65mph.

[starliner62]

Going from a 3:31 to a 3:73 would be like adding two more cylinders.(kind of)

[PackardV8]

Yes, it will give a bigger dig off the line. With the Tremec, the 3.73 would be perfect.
No, with the overdrive fifth gear, you won't notice much difference in cruise noise or economy.
Maybe, ask around. There are Avanti owners with 3.73s who would like a 3.31 to lower their road noise.

jack vines.

[okc63avanti]

My 63 R1 Avanti was an automatic with a 3:31 ratio open (standard) differential dana 44 rear end. In its new life as an R2+ with a Tremec TKO 5 speed the rear end was rebuilt. It now sports an Auburn Gear Posi-Trac unit, 3:73 ratio rear, new alloy flanged axles and rear disc brakes. I've done the math and with my 215/70/15 tires at 70 MPH in 5th gear (OD ratio 0.64) I will be turning about 2100 RPM which is lower than the original automatic and 3:31 which turned about 2900 RPM at 70 MPH.

[Mike Van Veghten]

As others have said...depending on your overdrive ratio...
If it works out to where the actual "final drive" is back to the 3.31 area...that's what you want.

Then yes, you WILL...feel a good seat of the pants pull. In fact...depending on your idea of a "healthy" 355...the thought of higher h.p.'s...."normally" will steal low speed power. So, again, yea, with more first gear...you should feel a much better kick in the pants feel.

Mike

[prager]

Thanks everybody!! I guess my mission is clear!! I'm gonna do the swap over the winter. Can a guy buy the ring and pinion from just anyone, as long as it's for a 44, or are there centain models that will or won't do? Also, will I have to reset the axle end play and all of that or should everything stay pretty well in check? I did set it at .002 when I put it all together..Think it will move with a ring and pinion change? Thanks!!

[PackardV8]

As I mentioned earlier, in your South Bend/midwest area, it would be surprising if there weren't a ready-to-run complete 3.73 rear axle nearby. It is a common gear ratio, especially in Avanti. Many Avanti owners would or already have swapped the 3.73 for a 3.31 to quieten the car at highway speeds. Look around for a couple of months before getting into the slippery slope of new gears, new TwinTraction, new bearings, new brake drums, new seals, plus setup labor.

jack vines

[prager]

Thanks Jack, I'll be looking around for sure..The carrier I have now was an open type, but I installed a lock right into it and went to the moser flanged axles, with disc brakes. I think all I need is the ring and pinion gears and some time to do it..I'm not sure which will be easier to get...

[sweetolbob]

Richmond gears for the 44 will set you back about $150. Widely available at most any FLAPS.

Bob

[prager]

Thanks bob..And a huge thanks to Jack Vines... A phone conference..got the whole deal worked out..Thanks again to all of you too!!! Great ideas, and helpful input!! Thanks!!