Changing The Ratio In The Rear ?

[Stewart A.]

I have 2 meets that are around 20 hours of driving in my 1960 with 3.70 at 70 mph is going to do my head in.
I really want to drive it and have some representation of Corvettes and NCRS there.
So I was thinking of changing my rear end to be more comfortable. My rear at the moment is a single spinner and I don't want a posi at the moment.
I thought for the highway a 3.08 would be a better drive and much easier.
No.1 Is it a hard job to do in house or does it need a specialist to lap it in ?
No.2 Corvette Central has a video on the installation and was wondering if it was worth a look ?
No.3 What is the size of the ring and pinion in a 1960 Corvette (8.5'' ?), I believe they are all the same up to 63 ?
No.4 I think the GM passenger cars are also the same up to 63 ?
Any help would on this would be much appreciated. Stewy

[Joe L.]

Re: Changing The Ratio In The Rear ?

I have 2 meets that are around 20 hours of driving in my 1960 with 3.70 at 70 mph is going to do my head in.
I really want to drive it and have some representation of Corvettes and NCRS there.
So I was thinking of changing my rear end to be more comfortable. My rear at the moment is a single spinner and I don't want a posi at the moment.
I thought for the highway a 3.08 would be a better drive and much easier.
No.1 Is it a hard job to do in house or does it need a specialist to lap it in ?
No.2 Corvette Central has a video on the installation and was wondering if it was worth a look ?
No.3 What is the size of the ring and pinion in a 1960 Corvette (8.5'' ?), I believe they are all the same up to 63 ?
No.4 I think the GM passenger cars are also the same up to 63 ?
Any help would on this would be much appreciated. Stewy

Stewy-----

I agree; I don't like anything beyond 3.55:1 for a street car and I really think that, in most cases, a 3:08 or 3.36:1 is ideal BUT I'm talking about in a C2 or C3. A C1 is a different story. The 283 in a C1 doesn't have a lot of torque due to its relatively small cubic inch size. That's why GM generally used relatively low (numerically high) gear ratios in C1 Corvettes. However, in most cases, I think you'll be ok with a 3.36:1. I think that will perform adequately for you and it will give you a pretty comfortable cruise RPM. I would not go any higher (numerically lower) than 3.36:1, though. A lot depends on which engine option and transmission you have in the car.

If you're talking about changing the ring and pinion in your existing unit yourself, I don't think I'd go that way. Set-up on these things requires special tools and expertise. I'd leave that to an expert at it.

However, there's another way I'd think I'd go. That would be to purchase outright another complete differential unit which includes the gear ratio you decide to go with. That way, you can change out the complete unit yourself AND keep your original just the way it is in case you ever want to go back to it. This is a pretty easy swap-out on a C1. In this regard, most pre-1964 Chevrolet full size car rear ends are the same as Corvette. So, if you can find a good one with the ratio you decide on, it will bolt right in.

[Stewart A.]

Re: Changing The Ratio In The Rear ?

Thanks Joe I have a 350 in it at the moment, it has give or take 1 hp per cube. The original 283 is out of the car in resto.
I changed another car of mine to 2.75 (Ford Mustang) and drove 30 hours in a road tour and worked magic. I changed it when I got back and put the 3.55's back in it, 9 inch diffs are a dime a dozen over here so I did what you said would be a good idea and I now have a spare rear for the Mustang when I go for these crazy long hauls to car shows.
I know the car would pull a 3.08 easy in my Vette and would be much easier on the car for these massive road trips.
The only problem I can see is finding a spare case I can change to 3.08 for the long trips. I haven't started pricing them yet but being a C1 it is going to be pricey.
I figured that changing the rear myself would be tricky and best left for the differential shops over here.
The 3.36 would be a good all round gear but I do love the 3.70 and when I put the little slug back in with all the stock bits I think I will need a 3.70 to make it come alive. Stewy

[Wes S.]

Re: Changing The Ratio In The Rear ?

I've been running as 3:36 in my '62 for quite a while. it still pulls about 3200 rpm at the 70 to 75 mph range. I am running a crate 350 fom GM and believe it would go fine with a 3:08. As for a rebuilding, I agree a spare rear is a good idea. I think the solid axle rear is very easy to change ring an pinion on. The most difficult part of the change is setting the preload on the pinion. There is a crush sleve on the pinion bearings for setting the pre load which should be 15 to 25 inch/lbs for new bearings and 5 to 15 inch/lbs for used. Buy and exta crush, the prelaod will sneak up on you pretty quick and you will probably go by it the first time. Don't forget to put some non-harding sealer on the splines of the pinion gear to seal it from leaks. You obviously need an inch/lb dial torque wrench. From then on its easy to set the end play. I may be making light of the easy, but lugging that heavy thing might be the hardest part.
Wes

[Terry D.]

Re: Changing The Ratio In The Rear ?

Stewart
Open rear ends are not pricey. New ring and pinion is under $200, set up will be around $300, at least around here it is. I agree with Joe, 3:36 is good but with your 350 a 3;08 will be no problem. A little sluggish off the line but a dream on the highway.
Terry

[Tom P.]

Re: Changing The Ratio In The Rear ?

With you combination, the 3.08 would be not only an excellent swap, but your 350 will EASILY pull a 3.08 gear from a full stop.
EARLY Corvettes ONLY offered the 3.08 ration in 62, but pass cars had 3.08s 59-64.
The rearend center sections are 100% interchangeable for 55-64 pass cars and 56-62 Vettes. ALTHOUGH, the 55-56 center sections are not as beefy as the 57-64s. At one time, a 3.08 NON-posi from a pass car was as common as dirt, but not so much now. The 3.36 is a little more common, but if you can locate a good 3.08, you'll be much happier with it, ESPECIALLY on the hiway.

You also mentioned that you weren't interested in a posi------------at this time. If at a later date you should desire to have a posi rear, Eaton now makes a posi unit for these early Chevy rears.
If you should ever be interested in converting a NON-posi rear to posi, here is a link to the procedure that I posted on another site.
http://www.chevytalk.org/fusionbb/sh...hp?tid/223912/

[William C.]

Re: Changing The Ratio In The Rear ?

I swapped my '62 to a 3.36 several years back when I was going on a Road Tour. No Problem pulling the gear (327/360) and kept the revs at speed down to a more tolerable level, great if you plan on road tours or similar activities. I grabbed a complete unit at a swap meet, and put the 4.11 in a bag for "someday".

[Robert S.]

Re: Changing The Ratio In The Rear ?

I did the swap in my 60, but it is a posi rear end. The option of a spare pumpkin makes the most sense. I had a serious problem with the posiafter the swap. Watch the length of the drivers side axle. Mine had to be shortened about one quarter inch since the new gears moved the ring gear. Not a big problem if you know what to look for. The interference can be spotted with a tape measure.

[Jack H.]

Re: Changing The Ratio In The Rear ?

That's a reasonably common request/issue from youse guys outside North America (desire for low numeric rear end) and understandable when you consider the price structure you face for pump gas vs. those of us here.

I remember taking a tour of Tom Falconer's (UK Judging Chair and owner/operator of Claremont Corvette outside London) 'cave'. That's where he stored take off parts. It was AWASH with 3.70/4.11/4.56 rear ends and VOID of 3.08/3.36 equivalents!

It seemed to me that there was an opportunity here for 'arbitrage' IF the cost of transcontinental freight wasn't an issue because the high gear rears are desirable Stateside... Folks here seem to value stop light to stop light 'tire burner' setups more than they do economic highway crusier cars!

[Tom P.]

Re: Changing The Ratio In The Rear ?

I did the swap in my 60, but it is a posi rear end. The option of a spare pumpkin makes the most sense. I had a serious problem with the posiafter the swap. Watch the length of the drivers side axle. Mine had to be shortened about one quarter inch since the new gears moved the ring gear. Not a big problem if you know what to look for. The interference can be spotted with a tape measure.

SOMETHING is bad wrong here!!!!!!!!!!!!!!!!
That SHOULD NOT have been necessary!!!!!
I'd certainly be interested in knowing what/how this occured!

[Robert S.]

Re: Changing The Ratio In The Rear ?

I got my new gears from Tom's Differentials. The old gears were 10 tooth pinion and 37 tooth ring gear. The new gears were 12 tooth pinion and 37 tooth ring gear. Pinion gear diameter went up 20 percent. (that's a big guess on my part.) Anyway, on reassembly, the rear end made terrible clanking noises while turning. No problem, add more posi lub. This didn't work. Had the fluid changed on the 2000 mile trip that we took with the new gears. Rear was quiet for three turns, then the horrific noises returned. Got home and dissassembled the rear axle. In desperation, I shoved a tape measure in the drivers side of the housing and also measured the length of the axle. The two were nearly the same. Axle was slightly longer. Took the pumpkin to the shop that put in the gears and had them look at it. The clutch pack was destroyed. They put in a new clutch pack and machined about 1/4 inch off of the drivers side axle and the problems were gone. Been happy ever since.
I did not use a gasket behind the bearing retainer plate, hope this wasn't a factor.

[Joe L.]

Re: Changing The Ratio In The Rear ?

Thanks Joe I have a 350 in it at the moment, it has give or take 1 hp per cube. The original 283 is out of the car in resto.
I changed another car of mine to 2.75 (Ford Mustang) and drove 30 hours in a road tour and worked magic. I changed it when I got back and put the 3.55's back in it, 9 inch diffs are a dime a dozen over here so I did what you said would be a good idea and I now have a spare rear for the Mustang when I go for these crazy long hauls to car shows.
I know the car would pull a 3.08 easy in my Vette and would be much easier on the car for these massive road trips.
The only problem I can see is finding a spare case I can change to 3.08 for the long trips. I haven't started pricing them yet but being a C1 it is going to be pricey.
I figured that changing the rear myself would be tricky and best left for the differential shops over here.
The 3.36 would be a good all round gear but I do love the 3.70 and when I put the little slug back in with all the stock bits I think I will need a 3.70 to make it come alive. Stewy

Stewy-----


With a 350, I think the 3.08:1 will be just fine.

[Wes S.]

Re: Changing The Ratio In The Rear ?

One more note to be careful of. If you buy a rearend with big gears 4.11 and decide to put in 3.08 there is a big difference in thr carrier and you'll need a spacer or the other carrier.
Wes

[Tom P.]

Re: Changing The Ratio In The Rear ?

One more note to be careful of. If you buy a rearend with big gears 4.11 and decide to put in 3.08 there is a big difference in thr carrier and you'll need a spacer or the other carrier.
Wes

You CANNOT, repeat, CANNOT put a 3-series ring gear on a 4-series carrier!
You CAN put a 4-series ring gear on a 3-series carrier----------by using a spacer.

[Stewart A.]

Re: Changing The Ratio In The Rear ?

I plan on putting a 3.70 posi in the car at a later date. I need to buy a case with 3.08's in it, I have seen a couple for around $500 and will slow boat one over here. That way I can swap them around when I do the big trips. Thanks guys for the help.