The Stovebolt Site Forums The Shop Area Engine Shop 59 Fleetside rear axle swap? 4/5-speed options?

This may come off as the dumbest, or the greatest questions ever-ok I admit, the latter was just wishful thinking but here goes anyway:

First question: The guy helping me with my truck recommended looking into swapping out the rear axle on my truck to get a better gear ratio and eliminate some of the issues I'm having with the one on it (needs a rebuild at the least). He thought that some of the late 70's/early 80's axles might swap without needing additional parts like a brake booster etc.

Is there a specific axle I should look for that would give me a better gear ratio and would be a virtually direct swap? I searched a good deal on this site but haven't had much luck finding swap info for anything but the AD trucks.

Not sure if any other info is necessary, but I've got a 1959 Chevy fleetside longbed (3200) with the stock 235, a 4 speed (including granny gear) on the floor and 2wd.

Second question: The transmission is making a good amount of noise, it works, but it's pretty loud. I understand the 5 speed from the s-10 can be swapped after checking the tech section, but I was wondering if there were any other 4 speeds that would have more cruising friendly gears and would place the shifter closer or in the same spot as the factory floor location that mine currently has.

Thanks!
Alden

2 answers: any 4 speed will have a 1:1 high gear [and be noisey], same as you already have, an original type overdrive trans [55-70] would give you better highway cruising, or the 3.38 gearset from Patricks with the installation package, which would be much better than trying to find a newer year rear the proper configuration - easy to move to column shift and change the floor pan

Bill

Price was the reason to avoid the gears kits. The local pull-a-part charges $65 for an entire rear axle and has a pretty wide selection vs $200-400 for a 3.38 ring and pin from the places I've checked online.

Just out of curiosity, what's wrong the original axle? Just needs refreshing, or is there some sort of parts failure, like damaged gears or broken axle shafts? The stock axle from the '55-'62 trucks is very strong, the Gassers from the '60s (like Stone, Woods, & Cooks Swindler Willys) used them with well over 800 hp regularly. As far as gearing, you most liley have the 3.90 ggear, which works very well with an overdrive trans. I just had mine out on the highway not too long ago, ran 75-80 mph all day long. I'm running the original style Borg-Warner overdrive, which is a 3 speed with an auxiliary trans, but the T5 would give you similar results. About the only 4 speed in the game that would help on the gear ratios would be the MY6, which was a Chevrolet version of the Chrysler A833 4 speed. Used mostly in early '80s 1/2 tons. Good trans, and should fit in your truck nicely. I do beleive there might be some alterations needed to the front bearing retainer for it to fit. You might try searching "T5 swap" and "MY6 transmission", should be able to get the exact information.

X2 on the MY6, however the shifter will be moved toward the rear about 9 inches. An NV4500 5 speed swap will not move the shifter back as far, but is probably overkill.

OK, Transmissions with overdrive work great with the stock gears. If you replace your rearend with something in the 2.73:1 to 3.38:1, the OD transmission will not be necessary. In fact that sm420 4 speed is likely the best transmission available to use ig you put freeway gears in, as you can now use that granny low to get you going.

Either figure out which rearend you are going to use and select a transmission to match, or figure out which transmission you will use and select a rear to match. By the way, I'm not sure by what you mean a "better gear ratio". The better gear ratio depends on how you are using your truck. If you want to pull some loads, lower gears will be better. If you want to cruise the highway, higher gears will be better. If you want to do both, the factory gears with an OD transmission will be the best. It really depends on how you want to use your truck.

On the HO33 rear axle housing... I believe that axle is plenty strong for a 235. I would not put one behind any engine that makes over 300 HP, as this cast housing will not withstand heavy torque forces. I wrecked a completely overhauled HO33 in my 59 gmc with a 300+ HP motor in less than 30 miles. The axle perches were ripped right off the axle tubes, causing the tubes to shatter. Expensive mistake, but now I have posi!

Some '55-59 GMCs had 3.07 spicers in them. I put one under my '56 Chevy. Almost a bolt in job.

Longbox55,
I'm quite ignorant when it comes to cars (I'm trying to learn, but I'm not there yet) and so I can only try to repeat the guy's explanation - he said something to the extent of that he noticed that the pinion was worn to the point where it was nearly all the way out when he changed my u-joint and thought that might be the cause of my noise issues (it makes a pretty bad grinding noise when you let off the gas at any speed). That and the engine is pretty much screaming once you get it up to any of the local speed limits (45-55 in most of my area) so a gear change would be really nice for the sake of keeping the engine going.

Sorry I should have clarified, I'm looking for something that will allow the engine to comfortably cruise at the 45-75 range. I plan on hauling various things in the bed of my truck, but nothing too big and I don't need gobs of low end.

3.07:1 rear as found in the 57-59 gmc 1/2 ton 3 speeds will be a bolt in deal, however any 50 year old rear end will likely need a refresh.

Now for the numbers... your rear end currently should have 3.90:1 ratio. You can go to any online gear calculator and use this information + tire diameter to figure out the rpm at any given speed. A 235 can spin up to 3200 rpm all day long, however 22- 2400 rpm should be about ideal at 65 mph. The calculators will solve for desired gears if you put the rpm and the speed in and leve the gears blank.

Are the rears from the 1960's models different?

I might have a line on a 57-59 rear end though, just to clarify that I understand correctly: if it came from the factory with the 3 speed it's most likely got the 3.07:1?

if it's a 55-59 Chevy, 3 speed or 4, it came with a 3.90, with an OD trans the original ratio would have been 4.11 - it's the GMCs that might have had the 3.07 .... and yes, the 60's rears were different, although still 3.90 ratio

Bill

The nice thing about the '55-'62 rear is that you won't need to change the entire differential housing, only the 3rd member, which is the part that the gears actually ride in, would need to be changed. As far as the cruising rpm, an overdrive trans would be the best bet, as it would give you the better gearing for city driving and towing, but then also have the overdrive gearing for highway driving and feul economy, as well as reduced engine rpm.