The Stovebolt Site Forums The Shop Area The HiPo Shop '58 Apache rear end/tranny replacement

I am down to the frame on my '58 Apache. Eventually, she will have a 350 chevy with what I am thinking is a 3.73 posi rear and a 4 speed manual tranny. I am wondering if anyone has any comments on this setup, and if I need to box in any parts of the frame due to the added torque that the 350 will output. Also wondering if this setup will pull too many RPM's on the engine cruising down the highway in 4th? Looking to get a new rear end soon, so I can rebuild and fit it asap. Any suggestions are appreciated. Thanks!

I'm building my 56 with a 350 and a Saganaw 4-speed (4th gear is 1:1) and a 2.73 TransAm Posi Rear. I calculated I'd be running about 61 mph at 2000 rpm with a 28" tall tire. Using the same tire you will be turning 2700 to run 61 mph.

I hope to get about 25 mpg Hiway...

Check it out here. The trans gear is one (1) for 1:1 (direct drive).

http://www.wallaceracing.com/gear-speed.php

Welcome to the Stovebolt!

Mike B

I have a 59 gmc 1/2 ton with a 447 inch pontiac motor (1959 pontiac 389 bored .030 and stroked 1/2 inch) This motor destroyed the factory rear I had with 3.38 gears. I replaced the rear with an aftermarket 9 inch with 3.70 gears. I swapped the 4 speed granny low with an NV4500 5 speed. I recently changed tire size from 28 inches to 31 inches, and plan on changing the gears to 4.10 to make up for the taller tires.

OK, I gave to much background. Bottom line my stock frame is holding up fine to the torque (about 450 lbs or more) You will likely be fine too.

3.73 gears might be too low for comfortoble cruising with a 4 speed. You might consider higher gears in the 3.08-3.38 range. Depending on tire size, 3.73 gears may be too high for an OD. The factory 3.90 ratio works really well with an OD transmission.

Mike B... The 20 mpg barrier is tough to break in our trucks. They simply push too much wind. Good luck to you in your attempt, but I suspect 17-19 mpg on the highway is closer to reality. I get about 14 mpg at 70 mph in my 1/2 ton long bed. 70 mph at 2050 rpm currently, will be 70 mph at 2270 when I change to 4.11 gears.

Yeah I thought I would be pulling pretty high RPM's. I just don't know if I want anything higher geared than a 3.73, maybe like a 3.55, but I will lose lots of low-end torque if I go to a 3.08-3.38 range. With a 3.55 and a 4 speed, I would only gain about 200 RPM's, which would put me at around 2500 for highway cruising. Maybe I would be better off with a 5 speed and a 3.73 or the 3.55?

there's certainly no need to reinforce the frame unless you intend on a lot of clutch popping drag racing with a really built engine, the added torque of a "usual" 350 over the original era 283 isn't huge .... what rear ratio you want depends entirely on what you're going to use the truck for, work, pleasure or showing off .... a 3.55 ratio is available for the stock rear and works fine for good mileage on the highway without losing a lot on the low end, an overdrive trans will do as well with the stock 3.90 rear

Bill

Thanks Bill. I mostly want to use the truck for a weekend driver, with the ability to have some HP if I want it, so yes, a little show off ability you could say! If i just changed out the rear gears in the stock rear, would the torque from the 350 v-8 tear the rear end apart? That's why I was thinking of upgrading to a later model rear, something late 60's to early 70's.

I put 3.08 gears with a 350 and TH350 in my 58 1/2 ton and it works fine.It really helps on the highway and has plenty of power.

I can chirp the tires easily with a good 283 and the stock 3.90 rear is 53 years old, and although it's used mostly for town driving and load hauling, I cruise it at 65-70 when on the highway no problems except a bit too much exhaust and road noise .... the 3.55 gears would be as much improvement as needed for more highway time, although I'd be inclined to go with an OD trans and leave the rear - my next truck will have a 700R4 with the 3.90 rear, trucks should be able to haul a load

Bill

what about posi rears? If I am going to replace the factory rear end, should I definately go with a posi, or doesn't it matter that much? How about a 3.73 with a 5 speed to get the RPM's down at highway speed? I am not too worried about mileage, but this would help the RPM issue and the mileage, as well as still give me the low end torque that the 3.73 gears would offer. I want a torquey rear end, not so conerned with the high end speed, but don't want to put extra stress (uneeded high RPM's) on the motor. I appreciated all of the comments and advice...very helpful! Also, what are you guys doing about cross members and other parts attached to the main frame by way of rivets? Just leave the old rivets, or replace with bolts?

I don't see any reason for a posi, just more things to go wrong, and if you have a transmission with an overdrive 5th, why bother with the trouble and expense of changing the rear? a 3.90 rear is plenty 'torquey' and a .7 high gear drops the rpm enough at high speed, the small blocks like rpm a lot more than lugging .... and if you have to remove/replace a crossmember, as when installing an automatic, I'd weld the new one or use grade 8 bolts, otherwise what rivets would you want to remove??

Bill

I appreciate your patience with me Bill, as I am new to this game. There are rivets that hold the rear leaf spring mounts to the frame as well, just wondering if the bolts would be a more solid way to go? Just wondering if the rivets would be more likely to come loose over time, or they may be rusted severely.
Thanks!

No need to worry about those rivits. They're actually stronger than bolting it, as the rivits conform to the shape of the holes when they are installed. Putting in bolts would require drilling the holes to the exact diameter of the bolt neck to ensure the same strength. I would only be concerned if one was actually loose or missing, in which case using a bolt would be fine.

Nothing wrong with the rivots. If your spring hangers are damaged or loose, go ahead and replace the hangers and bolt them with grade 8 bolts.

There are plenty of online gear calculators out there where you can plug in the known variables to see rpms at a particular speed.

Low gears pull a load better, and accelerate better. High gears just don't push you in the back of your seat. Generally having a final drive ratio of around 3:1 is on the economy side. Having a final drive of around 4.11:1 is on the performance side.

Using lower gears (4.11) with an OD transmission will put your final drive ratio close to 3:1. You will not lose the acceleration the lower gears offer, and you will get the economy of the higher gears. The OD transmission really is the best of all worlds.

Tire size can also affect the gearing. 31 inch tall tires with 4.11 gears are equal to 3.73 gears with 28 inch tall tires. The 4.11 gears are lower than 3.73 gears, but with taller tires, the will behave like 3.73 gears.

I am a big fan of lower gearing. In my 59, I changed the factory rear to the after market 3.38 gears. 3.55 gears are not available for the 1955-1962 1/2 ton rears. When I blew up the factory rear, I wasn't too upset because I knew I was getting posi. I went with 3.7:1 gears. Those gears worked great with 28 inch tires and OD. I went to taller tires to give the truck the stance I wanted. Now I want the 4.11 gears to give me the acceleration I lost with the taller tires.

There isn't one answer here that will work for everything. Play with the numbers with a calculator till you are satisfied. There are several trade offs that need to be considered.

The only gears available for the factory rear are 3.9:1 and 3.38:1. The factory rear should hold up to a 300hp/ 300 lb torque 350 small block. Any more power than that will rip the housing apart.

I am with red58. There isn't much advantage to change from 3.9:1 to 3.7:1. However, if you have a well built motor, you will need a stronger rearend to hold up behind it.

Thanks for all the input guys. I am planning on having a 300+ powerhouse, so I will be changing out the rear end, and believe I will now look at a 5 speed tranny to lose some highway RPM's. Thanks for all the posts guys, really helps me out!

Sorry for the previous post, 300+ hp powerhouse, if it wasn't intuitive.