The Stovebolt Site Forums The Shop Area Engine Shop 1953 3/4 ton rearend swap

I know there has been a lot of posts on this but I have not been able to get specific information for what I want to do
(I need remedial help)

I have a 53 3600.

I would like to:

swap the rearend for something with a better gear ratio maybe 411. Will that do?

not change the tranny or engine

keep the 8 lug hubs

do as little as possible to the driveline to install the new rearend.

What model and year truck is best for me to start looking at for a donor? I plan on visiting some salvage yards over the summer to start searching. I don't mind changing spring perches and such. What measurements are most critical?

also it doesn't have to be posi

Thanks
Rich

I've put a set of 4:11s in my 53 3600, ran a wanted ad here on the bolt and got a nice complete pumpkin. I think this was out of a 69 or so 3/4 ton Chevy that came from the factory with an automatic trans, which came with 4:11s. It's a direct bolt in JOB. And it is really great on the top end but mostly I was surprized how nice it goes through all the gears vs the crawl.

4.11 is one of the factory ratios available for your stock rear.

Will it do is a much more difficult question. How are you going to use the truck? With the stock motor you aren't going to be able to haul much with anything much more highway friendly.

Attn OldSub,
I'm a little bit confused by your statement above

"With the stock motor you aren't going to be able to haul much with anything much more highway friendly."

Do you mean that if he changes to a higher gear, he will no longer be able to haul much ?

When I was a teenager, I hauled plenty with my 54 Chevy Handyman Station Wagon, I don't remember what year end it had, but it cruised comfortably at speeds over 70 with it's stock 235 and 3sp. I pulled trailers etc. No problem.

Rich, I would say put in whatever gears you want, if you decide that you want lower gears afterward, you can always switch back.

Chris

The ratio that we are talking about here is 4.10. They were available in some 3/4 Ton trucks from 67 to 72, with the front loading "pumpkin". I did this to my truck and I can cruise at 60 mph but I usually don't push it over 55.

Rich -

The stock rearend in your 3600 should be an Eaton HO52. There is also an Eaton HO72 available whihc is essentially identical. Chevy/GMC 3/4-ton trucks from 1967 thru 1972 used the same Eaton rearend except that some had 4.10 gears. I agree with JiMerit that it's a straight, simple, "2 beer" swap. You should be able to find a complete pumpkin with 4.10 gears for a reasonable price at: www.67-72chevytrucks.com . You will pay more for the "No Spin" posi-traction setup.

Good Luck!
Dan M.
1949 Chevy 3600 5-Window

Minor correction, GMCs used Spicer axles, as do some variants of the Camper Special Chevrolets.

Yeah that is exactly what I mean. His truck is heavier than your car was, and his motor is a 216. While the 4.10 swap will likely work, going much higher could mean trouble. Not that it won't do it, but that it will be painful.

I once bought a truck with a 216 and a 3.42 rear axle from a guy who learned the hard way that the motor was not strong enough to move the loads any more.

GM didn't put 4.57 and 5.14 gears in these trucks because they wanted people to drive slow. They did it because these motors needed the torque multiplication to start and carry a load.

I've got a '55 1st 1/2-ton with 3.08 gears and a GMC 270. It will run 70+ on the freeway but don't put a trailer behind it.

Thanks for all the advise.

I am a real novice when it comes read ends and gear ratios.
My intent is to have a truck that I can drive on the highway ocasionally. 55 to 60 mph is plenty I just don't want to be killing it to get stay at this speed for longer drives.

I will likely not carry heavy loads with this truck. The occasional shrub from the nursery. A little lumber now and then and of course a few little leaguers in a parade or 2.

Again I am a novice...When you say pumpkin you mean the center differential in the rear end. And I assume that I can swap the ring and pinion gears from one to the other with regular tools and basic skills?

Again many thanks for all the help.
Rich

RB 53,

Reqular tools and basic skills are relative.

The average guy can change the complete differential, which is what you can do to get the higher gear ratio, but to change the ring and pinion gears is beyond the scope of most home garage builders.

The suggestion given for using the later diff is only using the center section, not the whole assembly. easy swap, no setup on the gears needed. Should be able to swap it without even jacking the truck up (advantage of the full floating axle).
As far as the ratio goes, with the stock 216, the load capacity will suffer, as the engine won't pull it. That's not to say it can't still pull a decent load, just not as much as it would with the 4.56 gears that are factory.

Pictorial from another site about the pumpkin swap that you are considering.

http://www.oldgmctrucks.com/page0276.html

The most important thing about the pictorial is the jig that they made to hold the pumpkin on the jack. They are quite heavy and they need to be mated very carefully if the thin gasket is to survive.

Randy,

That pictorial is like a light going on for me! now I get it!

Thanks a million.

thanks everyone esle as well!

I will let you know how it goes.
Rich

When I did my pumpkin swap I rolled the entire rear end out as I was having the rear springs re-built at the same time, made things much easier. Also, you can just imagine how many worn parts I discovered during this spring job. Found ALL the shackels, pins etc at a local spring shop btw and with prices a fraction of the LMC boys.

And just like rustbucket, my truck may get to haul a load of fire wood once a year and maybe a few loads to the dump, NOT a real working truck. Great attention getter at the swapmeets too. It's 'retired' like I want to be.

JiMerit

I replaced all my bushings and shackles on my truck when I did the frame work. But I agree this truck did its work now it should just cruise and have fun like I want to.

Rich