Jeep axle swap

[nolan in blaine]

So this is just a thread im writing for reference. To give someone a bit more info on the swap if they search for it and are thinking about it.

My car is a 37 chrysler Royal 4 door. I had the 4.30 gear. It sucked bad. I bought a 3.55 rear end from a 96 Cherokee complete drum to drum. Typlicaly you find the Dana 35 but i lucked out and wound up with a Chrysler 8.25. Its a bit stronger im told. It measured about 3/4" narrower then the '37 axle. No biggie. I had to cut the shock mounts, and spring perches off. I used the perches off the '37 axle and welded them on the bottom of the jeep axle. I was able to bolt it in using the chrysler royal u-bolts. I did have to get a new drive line built. It needed to be 54 9/16" from the flange on the back of the O/D unit to the center of the u-joint on the axle. The new drive line had to have a slip yoke in place.
I cut the ebrake cables off at the backing plates and just kept the original parking brake in the 37.
I had to adapt the rear brake lines from the chrysler to the jeep, but running the newer rear brakes has made a huge difference in stopping power. Id say its partly due to the smaller diameter rear wheel cylinders taking less volume to move, and also im sure i never had the old brakes adjusted right anyway. But it stops much better!

I will say, if you're thinking about better gearing... Do it! This swap isnt hard at all if you can do some cutting and welding. I paid $100 for the axle, and another $375 for the brand new drive shaft.
Before the swap, I could do about 55-60 in overdrive and it sounded like it was wound to tight. I know it would probably do it all day but i felt it was revving too high. Now it will cruise on the freeway doing 75 and its nice and easy. And on the back roads it does 50-55 in 3rd. Im glad i got the 3.55 gears but a 3.23 would have been just a bit better. 3.73s seem a bit more common but i dont think it would have been ideal for my car.
Another benefit i to the swap, for me anyway, is the horrendous vibration i had at cruising speed is completely gone. Its super smooth now.

Now to get some seat belts in this thing so i can take the kids over the pass this summer!

 

[nolan in blaine]

just a quick note.
according to an rpm calculator i found online, with the 4.30 gear, a 26.3" tire, .70 O/D, at 70mph, it was turning 2,692 RPMs
Now it should be 2,200

If i step up to a 28" rear tire it will knock it down to 2,100 RPMs.. That will be perfect!

Dont be afraid to play with this stuff guys, totally worth it!

[pflaming]

I fully agree and experienced similar results with my B3B. Now I need an over drive so I have 2nd and over on a long pull. Also, I need to tune my truck more often, on loses a lot of torque with a poorly tuned engine. 

[Plymouthy Adams]

9 hours ago, nolan in blaine said:

Dont be afraid to play with this stuff guys, totally worth it!

 

many thread on this over the many years this forum has been online...glad you are discovering gearing , tires etc...but it is nothing new....I am glad to see  you taking the time to dial your ratios in where you want them....sometimes it is not just knowing, it is actually STARTING the job that hold many people back

[48ply1stcar]

I only wish that you have documented the conversion with pictures.

 

[nolan in blaine]

3 hours ago, Plymouthy Adams said:

 

many thread on this over the many years this forum has been online...glad you are discovering gearing , tires etc...but it is nothing new....I am glad to see  you taking the time to dial your ratios in where you want them....sometimes it is not just knowing, it is actually STARTING the job that hold many people back

Ive been doing this stuff for years. Nothing new. This post is meant to be more motivational then anything. Just one more ""gearing" thread that might just help convince someone else they should take the leap.

 

 

3 hours ago, 48ply1stcar said:

I only wish that you have documented the conversion with pictures.

 

I should have taken pictures for sure.

[pflaming]

" I only wish that you have documented the conversion with pictures."

This is not difficult to do. I put the two axles in parallel on saw bucks. Then I clamped a bar on to the perches so that the spindles were exactly at the same degree of angle. That done i reclamped the two so the could not change. I then welded on new perches on THE Cherokee axle. 

 

Finally I put the Cherokee axle on the truck. Worked out perfectly. Just duplicate!! Easy to do.