The Stovebolt Site Forums The Shop Area Engine Shop I found a rear axle but is it too much gear?

Looking for oinions from the experts once again. I found a rear axle which will work great in my 50 and the price couldn't be better--free! Its a GM 10 bolt and measures 61" where the wheels bolt on. Don't know what it came out of and frankly don't care, it'll fit! Now, I will have to have the axles drilled to my 6 bolt pattern as I have wheels I want to use but I can get that done pretty cheap. That brings me to my big question and the one I would like your opinions on. The gearset is a 2.73/1 ratio and I am going to be running a Camaro T5 with .063 OD behind a basically stock (headers and possibly 2 1bbls only) 1957 235 cu. in. six. Do I need a little more gear or can the 235 handle this without lugging constantly or slipping the clutch halfway down the block to the next light? Sure hate to pass on it cause the price is so right! Once again I await your expert advice.

Thanks, Chuck

The 2.73 gears will not work behind any OD transmission. A 235 simply can not push it. I would think that it would be tough for a 235 6 banger to pull a .63 OD at all. You would almost have to run 4.57 gears behind it to give you a final drive ratio of 2.87:1. Realistically for economy and performance the final drive should be close to 3:1, with about 2.73:1 being the highest final drive ratio. Others will disagree with me.

Final drive ratio equals the (rear end ratio) X (transmission ratio in top gear)

In my opinion, the perfect ratio for a 235 would be 3.73 gears with a .72 overdrive and tires with a 26-28 inch diameter.

Hope that helps.
John

A 235 can easily handle the gear. I have run a stock 235 with 3.08 rear end and .70 overdrive, making an overall ratio of 2.15. Of course that is only on flat ground, you will have to downshift on the slightest hill, but it will work fine. My '54 GMC with a 248 is running a 3.36 rear end and a .70 overdrive, makes a great freeway gear I can run with the best of them now.

CayoRV,
I suggest calculating an ideal using knowns and unknowns.
For instance cruising speed (mine was calced on 70 mph), tire height (mine 31"), optimum engine RPM (about 3200 as a guess - someone will chime in on this for your 235), O.D. ratio of .63 (this is a given and won't change). Unknown or variable will be rear gear ratio. Plug in the 2.73 to start and change tire heights (usually the cheapest and easiest change for the buck)and gear ratios to get the opimum engine RPM at top speed (i.e. 70 mph).
There is a link to a calulator on the links page of this site.
My guess - 2.73 will lug her down. Mine calculated to 3:90.
Cavebull

Sure can bring a guy down from a free parts high!
I kinda knew that would be the case though when I pulled the cover and counted out the teeth on the gears. I got the T5 from a friend who wants some paint work done on his Harley so I kinda got it for free and the rear was just layin behind a buddies garage (he took it out of a project but it was not original to the project so we don't know the origins of it). The engine was one from one of my previous projects that was such a good runner I couldn't part with it. I haven't given up though, I'll just keep looking for a rear axle for the 50 and keep the highway geared rear for my 46 project which is more of a hot rod and will have a 364 nailhead Buick with enough torque to pull them 2.73's!
Thanks for keeping me straight though.
Chuck

To me it's not all that complicated. You've got a T-5, you've got a 2:73 axle, run 'em. Worse case - you've got a nice synchro 4-speed you can use all the time with an extra gear for those down hill, tailwind roads! Besides, one of the complaints I hear from guys running T-5's with lower rear gears is that 1st gear becomes useless because it's too low. Yours should be just right IMHO.

One issue I can see that hasn't come up besides the gear ratio. The axle flanges may not be large enough to redrill safely to the 6x5 1/2" bolt pattern. Without knowing which 10 bolt it is and what it came from, this could be an issue. If the flange isn't large enough, you may end up with a comprimised wheel mounting surface.

I have 2.79 gears in my 37 and I also have a t-5 behind the 235,on flat ground I can put it in 5th but as soon as I hit a hill it has to go into 4th. I did notice a drop in gas mileage due to lugging it too much and will be putting in 3.25 to 3.50 gears this winter,with the trans I have it takes off great from a stop but 5th is useless. Jeff

Gear ratios in my T5 are listed as follows:
Rev 2.76, 1st 2.95, 2nd 1.94, 3rd 1.34, 4th 1.00, and 5th 0.63.
I did find the calculators that I was referred to by Cavebull and after plugging in the #'s I realized that, no matter how smooth or torquey or well designed the stovebolt is, I would need at least 2 more cylinders or ALOT of expensive modifications for this to all work well. I will continue the search for another rear axle and just keep this 2.73 for the next project.
The late 70's and 80's Japanese import PU's rears all were 3.90 to 4.11 or so and most all were 6 on 5.5 so thats where I'll be lookin next. I hate to put something together only to have to take it apart again and change something so it will work. I'd much rather ask ? and do the research and hopefully get it right the first time. Heck sometimes I even learn something new!

Also for those looking for some good info on the many different T5 variants this site may be of use

http://www.britishv8.org/Articles/Borg-Warner-T5-ID-Tags.htm

Thanks again,
Chuck

Gotta be carefull with those import trucks, especially the late '70s-early '80s Toyotas. Many of those have 4.30 gears in them. Mitsubishi P'Ups and Dodge D 50s are bad about that, too.

Thanks for the headsup Longbox55. I'll keep my eyes open when I'm out scroungin.

Chuck

Is the 55 first series a open driveshaft design?.

Yes, first year for it on 1/2 ton.

Do a search on this as well. A lot of good info and links to pics and how too's.
How free is the rear if you have to pay to get axles drilled for bolt patterns and new drive shaft gonna cost you about 100 buck as well.
What worked for me: Had the closed rear in my 46. Bought a 55 rear with 3:90's for 55 bucks. Changed from a closed to open rear by swapping punkin and saddles and building me a new drive shaft. Got to keep my original axels, bolt patterns, knee shocks, etc. The 10 bolt punkin and spider gears spline the same from 46'ish to 61 I believe. Poor mans quick change.
I assume you're starting with no rear, correct?
Cavebull

Cavebull, I have the original 1950 rear in the truck now but as you said it is a closed drive and I want to switch to open drive shaft. That being the case I knew I would have to spend the $ for the driveshaft and I'm OK with that however I wasn't aware that a later punkin would work with the housing I have. The 3.90 gear would be great I think and changing saddles is a piece of cake. As long as I don't have to look for a 55 1st series to get it (I would think that would be a pretty rare piece) and can look for something up through 61. Gives me alot more to look for anyway. Thanks for the info.
Chuck

Anyone close to S.W. Michigan have a punkin they keep stumblin over?

Give the link to my Flikr pictures a look if interested. I have a full pictured documentation of the closed to open rear swap. Steppenwood has the pict I modeled all my pics off of.
Like I said I had a 55 rear for 55 bucks and it was a piece of cake.
Cavebull