Hey there guys and gals, i was curious if there is any common rear diff upgrades to get a little higher ratios and top end speed in the larger trucks? Like is there a certain year or model of diff to look for, that bolts right in place?

I would like to keep dual wheels on the back if possible, and I was also curious if any of you guys know of any front wheel upgrades a guy can do (to get into a radial tire, and away from the suicide rims)?

I was hoping there was maybe some kind of swaps out there where a guy wouldnt have to swap the whole front end out. (like swap a jag front end in, I dont want to do something like that on the large truck I have)

 

I've been on the look out for the same thing. 70's to 80 or 81 class A motor homes I think, the big ones are what we are looking for. Some that I found only had 17 inch wheels with lock ring rims. Lock rings aren't so bad but 17's.Tiny for our trucks. Ford and Dodge motorhomes with 19.5 or 22 inch wheels. Stu is the man on this issue along with some of the other fellas. He might be along tomorrow. There was a guy awhile back called Danbear, that swapped a front end from a more modern dodge motorhome, but I think he had to do a few mods to get it to work.

 

There have been several threads on this subject, and remedies advocated for. To me the solution that is best allows you to retain the stock 5 lug x 8" bolt pattern front and rear. The way to achieve that is to find a 1970s/80s era Dodge RM400/500 motor home to donate its Dana 70HD rear axle and its Budd #89340 one piece tubeless 19.5" x 6" wide wheels.

The wheels, and perhaps even their 8R19.5" radial tires if in good shape, are a bolt on fix front and rear. We've had dozens and dozens of guys make this swap even on stock rear axles. The 8R19.5" tires are shorter than your stock 20s, 33.5" vs about 37" for a 7.50 x 20", but they work well. Combining this swap with the Dana 70HD is so ideal because the stock axle ratio is 4.56/1.

I had one of these axles intending to do what you are doing, but ended up selling all the pieces when I faced it wasn't getting done. The axle is a near bolt in. The spring perches are about 1/8" off on each side. I was intending to shim the small difference. Others have talked about moving the perches. I sold my axle to a guy who put it under an F-500 iirc. I also know of it being done on a comparable Studebaker. Below is a pic of my former axle. Stu

 

Thanks for the reply. I wouldnt be opposed to smaller tires at all for myself. Im planning on just shortening the truck and driving it like it is, not going to be using it for anything but puttering around the farm and backroads, occasional trip to town on the highway.

Ill keep my eyes out for old motorhomes, that might be tough to find around where i live. Ive read a few threads, and read the advice to call chucks trucks (or whatever the name is) but I live in Canada, and that isnt an option for me either.

I used to work as a tire guy, and ive done hundreds of split/suicide rims, and I know the ins and outs of them, but would still rather upgrade to a newer style that has nothing to do with any rings haha.

On edit: Stu I must have posted at the same time as you, but thank you for that info and pic as well, especially with the rear ratio info. I guess im on the lookout for an old motorhome!

 

Toby mentioned the option of using tubeless 22.5s, which would need to be fitted with 9R22.5" tires. If you call Chuck I think he will advocate for them over the 19.5s. They are the true/correct replacement for the 20s, but are really hard to find. Old Class A derelict motor homes are generally common in yards. As Toby said you don't want the 17" locking side ring style wheels if you find them, but they'd work too. And be safer than your widow maker 20s. But they won't fit your stock rear axle. Stu

 

One additional thought to save you some grief. You will find some old Class A motor homes with 5 lug pattern on the front, but 10 lug on the rear. Avoid them, they are GM. Their wheels are all 10 x 7.25" pattern with blanking plates covering the odd holes on the front axle. And while I cited Dodges as the target donors, there were also some Fords from that era used as motor home platforms. Dodges just seem to be more common. Stu