33willys

iTrader: (1)

I have a '39 Chevy sedan, stock LM4, 4L60E and Ford 8.8 with 3.73 gears. Car weighs 3200 lbs. For some unexplained reason I'm going to put a C4 'Vette rear end under the car. It has 2.59 gears. Will these gears be to tall? Don't need blazing hide boiling starts, the car is just a cruiser with some long distance trips. Should I just wait 'till the swap is done and see if works for me?

Michael Yount

iTrader: (1)

Simple math - ratio of the gears means you'll be about 32% lower revs at a particular speed than before. You (hopefully) have an idea of what that'll do to you at highway speeds rev-wise. I'd wonder if it's so long that it keeps dropping out of 4th when pulling up hills and such -- or constantly locking/unlocking the converter (if you have that).

1964SS

iTrader: (1)

I'd say you will be way too tall for an the overdrive transmission. You might as well get the correct ring and pinion and swap it at the same time.

Haggar

Well, his transmission gears are the same as the 700R4 that came with the vette.

One thing with the vette, it has really good aero, so gets away with it on the highway. If you have more drag, it might cause issues at those speeds. I have a 92 C4, with those 2.59s, I personally hate them, way too long.

Tire size may also come into play. Vette tires are around 25.5" tall.

Personally, if you want highway, I'd be looking in the 3.08-3.42 range.

If you don't want to mess with changing gears, sometime you can find the 3.08 Dana 36s, it was the performance gear option with the 700R4/4L60. Dana 44s are better, and always had at least 3.08 gears.. but $$$$. I have a complete 3.33 dana 44 diff/batwing that was going to go into mine.

Michael Yount

iTrader: (1)

The other reason the C4's got away with it (had to for CAFE regs!) was that the TPI small block was tuned for peak torque at relatively low rpm, so they made gobs of torque off-idle. We used to race them in SCCA Showroom Stock -- lots of folks took a while to learn that the quickest laps around Road Atlanta happened when shifting them at about 4500 rpm.....

Doug G

My car had 2.73's from the factory, and with a 350/350 combo and 28" tall tires it drove fine.
It was fun messing with ricers on the street with 1st gear going to 80 They never expected an old muscle car winding out the speedometer on the hiway.

With your 2.59's, your OD trans won't be happy unless you plan to cruise at 125+

Get some better gears in say the mid 3's range.

KW Baraka

iTrader: (7)

Do you know if the donor car had a 4L60E....or a T56?

Off hand, I'm with Haggar....go with something in the low 3.00's.....

Also, I wouldn't go with more than a 2200-2400 stall TC.

KW

33willys

iTrader: (1)

Thanks for the input...and bad news that I expected. Yes, the 2.59s are way too tall with overdrive. Aftermarket gear for the C4 are not cheap at over $400, then install kit. Was hoping against hope that the general votes would be good to go.

rpturbo

iTrader: (47)

Although many will probably advise against it, I've had good luck putting used STOCK GM gears back in. I don't know if there were other factory gears for that rear, but if so they may be a option. The best luck I have had is to reuse basically everything. I do not get a new crush washer or anything. When I put the pinion in, I use exactly what shims were behind the pinion I am removing. On GMs I would say over 80% of the time it works perfect.

I found this out on Ford Mustangs back in the fox days. Any 8.8 from 87+ (not 86) you could do this on and basically never have a issue.