VCCA Home Forums TECHNICAL - GENERAL Trucks and Vans Is 3:38 differential too tall?

So I want to replace the differential in my truck. Based on my previous post and research, I currently have a 3:90 in my truck.

I've talked with others that have a 3:55 and they like it fine.

I just spoke with a local differential place, and they only have a 3:38. Will this work or will I just stall out my truck. My gut feeling is the former, but my husband is nagging me to check. :eek:

Thanks for your help.

The difference is only 5 percent.....the 3.38 was the economy option for the 1/2 ton trucks up to 1962.
If you are running tires no larger than the original 6.00X16, not pulling a heavy load, not used for going up steep hills and mountains, there should be no problem. If you do get on steep grades you will find that you can easily maintain 40 MPH in 2nd gear with the 3.36.

Boy, 3.90, 3.55, 3.38, you guys are spoiled. Ya orta try living with this d&%$ 4.57 that we unfortunate Stovebolt lovers have in our 3/4 ton’s.
The standard solution I get from just about everybody I talk to is, “just put a Camaro rear end in it and get over it.”
I’m about 93% purist and I absolutely refuse to change the axle housing so the only acceptable option for me and my fellow 3600 and 3800 series truckers is to find one of those elusive 4.10’s out of a 60’s-70’s Burb. In the last two years I’ve literally called and scoured a hundred junkyards, Crag’s list, evilBay, emailed dozens of dead ends, asked everyone that I run into and I just can’t find one.
I’ve contacted Randy’s Ring & Pinion, Drive Line Service, and on and on asking the possibility of their running a batch of gears for the Eaton HO52 and have never gotten as much as a yes, no or maybe back from even one of them. With the tens of thousands of 3600-3800 trucks that are still running out there, one would think that they would be able to sell a 3.90 ring & pinion sets by the thousand. An after market gear for these would sell much better than the 1/2 ton gears because the 3100 guys have a lot of stock options available to them.
So, conceder you’re self a VERY lucky individual if you have a 3.90 in you vintage Chevy. That 4.10 would at least allow me to run 55 mph instead of holding up traffic topped out at 45 like I am now.
Denny Graham
Sandwich, IL

Denny,
Te 4.10 was used in more than just Suburbans. Many of the later 3/4 ton and 1 ton trucks had the 4.10 and some even a 3.90. Would be most common in a V8 with an automatic.
The 1974 1 ton Step Van tool truck I had even ahd a 4.10 ( V8 automatic).
If your truck has the 7.00X15 tires and the 4.57 ratio the engine is turning over only slightly faster than a 1/2 ton with a 4.11 and .00X16 tires. If you have the larger 7.00X17 tires its turning over slower than the 1//2 ton......So with a 4.10 and the larger tires (7.00X15) would be about equal to a 1/2 ton with a 3.70 rear end.
To reduce the cab engine noise install a passenger car fan blade. Will make a big difference and not affect cooling under normal driving conditions.

It’s not the cab noise that’s bothering me Gene, I strapped one of those JC Whitney $30 SunPro tachs on the mast jacket just to see what kind of revs I really was turning. All is stock 3/4 plumbing in my driveline so the only variable is the tire size. I have a new set of 7.00 x 15 bias plies mounted on the original restored split rims for the purists and for my regular driving I use a new set of 8.75 x 16.5 tubeless radials. Both are the same height as the original stock tires. The engine feels real nice at 45mph and runs roughly at about 2400 r’s. at 55mph I’m looking at about 2700 plus a few and she is really screaming at that speed. I don’t think that 216 babbit pounder was meant to run at the rpm for very long.

I could be wrong but I don’t think the Eaton HO52 was used past 1972 and the other rear end assemblies you see listed were not Eaton units. I’m almost positive that the 3.90 was never available for the Eaton HO52 rear end.

As I said earlier, I’ve really put a lot of effort into this search and from what all of my sources (mostly at the Stovebolt forum and other Chevy Truck sites) all claim is that the only one that had the 4.10 pumpkin that will interchange with the stock 4.57 was ’67-’72 3/4 ton Suburban V8, automatic. And they are durn near impossible, or in my case, down right impossible to find.

If you have any information, specs, personal experience that can dispel this legend Gene, I sure would welcome it with open arms and maybe even some sort of finders fee or bonus. Man I’m desperate, can ya tell???

As far as the fan goes, I would like to replace my original fan blade any way because the PO had done some bending or straightening on it and it does wobble a bit and I’m sure the pitch is not the same on all four blade. I don’t like that because it can cause uneven loading on the blade and eventual failure. If I could find a decent new blade I would probably buy it whether it was for a truck or car. And I would bet that the truck is probably pitched a little more to help with cooling under a load.

Any way, thanks for responding, and I hope I dint steal the thread again like I have a habit of doing.

Denny Graham
Sandwich, IL

Chev Nut - What an excellent response!! Thanks. I'm poppin' that punkin' out tonight!! (I'ts not actually pumpkin, technically it is a dropout because it comes out the front - the alliteration was irresistible.)

I had a 67 C20 with the 4.10s.

Sorry, I don't know what this means. Can you explain a little more?

Lyn,

Essentially Jeff is just chiming in that he had a sort of similar pick-up, including 'similiar' gear ratio.

His was a 1967 model.

C-20 is 3/4 ton. (C-10 was the 1/2 ton)

And his ratio was 4.10. 'Similar' to your 3.90.

Hope this helps....

Bill.

Ok, so I had the diff redone last week. 44 teeth in the ring gear, lucky 13 in the pinion equals 3.38. I popped it in yesterday, but didn't have the right tool to replace the wheel bearings and seals, so no test drive as of yet. Stay tuned for the update.

-L

test drove the truck with the new diff in it, and it WORKS and works well!! I didn't get it out on the highway, just a few doughnuts in the backyard. When I did it with the old differential, I was in second, now I did it only in first, never touched second. I am very happy. I think this ratio will work out very well.