Axle swap help

[nikbristow]

Disclaimer. I'm new to Scouts but a fast learner. Be specific with your responses as I don't really know much of anything. But hey, at least I can admit it. Also, parts of this post are slightly Skunkwerksish but I posted it here as it deals with swapping Scout parts for Scout parts. I want to keep her as stock as possible but Frankenstein just a few things with parts from other Scouts. Hope that's okay. If not, bump me to the Skunks.

Here's the scoop. I just got an '80 Scout II with the SD-33T about a month ago. Promised myself I wouldn't start working on her until I sold my other car and for once, I was able to resist the temptation of a new project until the funding was ready.

Long term plans are for a well-done restoration by amateur standards. To keep the diesel's crack-prone pistons safe on the highway I've heard that 30" or 31" tires with 3.07s are a good set-up after an EGT probe, elbow elimator and larger exhaust. (that's the skunky part, sorry). I've found a set at a good price from a guy up in North Carolina and if you guys give the okay I think I'll take them off his hands.

I'm fairly mechanically inclined but I've never done final gear/axle stuff. So I have a few questions. Hopefully some of you can help me out.

1. Can you mix axle ratios? Meaning can I leave the front axle alone and just swap out the rear even with different gear ratios?

2. Can you swap just the gears and not the entire axle?

3. Caster. Pre-80 Scouts had zero caster. The '80 had like two or three degrees. This is why I was wondering about just swapping the gears and not the whole axle. I've heard that I'll miss the caster if I go with earlier axle. I'm not even really sure why. Steering?

4. If I go ahead with an axle/gear swap, what else should I do while I'm at it? Bearings, brakes, shocks, springs etc? Want to do the job right.

Thanks in advance. I've already learned a lot from you guys and I can't wait to learn more.

[Steve Jackson]

Originally Posted by nikbristow

1. Can you mix axle ratios? Meaning can I leave the front axle alone and just swap out the rear even with different gear ratios?

You can as long as you're not going to EVER use 4WD. Go ahead and do it right the first time. Make the ratios match.

Originally Posted by nikbristow

2. Can you swap just the gears and not the entire axle?

Sure. You can just take the carrier with ring gear and the pinion gear and put it in another housing assuming they are the same housing. If the axles are in good shape, it might be just as easy to swap the axles as it is to redo the gears (especially if you've never set gears before).

Originally Posted by nikbristow

3. Caster. Pre-80 Scouts had zero caster. The '80 had like two or three degrees. This is why I was wondering about just swapping the gears and not the whole axle. I've heard that I'll miss the caster if I go with earlier axle. I'm not even really sure why. Steering?

A negative caster gives the wheels a tendancy to track straight and stay straight. Search here on the BB for more information. Yes, you want some negative caster. Keep the '80 axles or use a caster shim with older axles.

Originally Posted by nikbristow

4. If I go ahead with an axle/gear swap, what else should I do while I'm at it? Bearings, brakes, shocks, springs etc? Want to do the job right.

I like to do things once. Change the spring bushings, if you break into the axles then change the bearings and such, change the shocks, are the springs ok or saggy?

What's the ratio of the current axles? No reason to change from stock.

[nikbristow]

Well then, it sounds like I want to keep the '80 axles for the caster. I guess that means I should just swap in the gears instead of the entire axle. So what all is entailed in lining up the gears?

[Steve Jackson]

What are the current gears, and why do you want to change them?

Search on google for tutorials on setting up ring and pinion gears. It's not *hard*, but it can be done wrong very easily.

Maybe a mod can move this to the main TechTalk forum for more exposure.

[Dennis Bernth]

I don't know that you'll be happy with 3.07's on a diesel. The reason the diesels are geared a little lower (higher numbers) is because of a lack of 'guts' compared to a gas engine. With taller tires and taller gears, you're going to find yourself doing a lot of shifting on grades and hills that you might not have to do with the factory gears. As far as the 'crack prone pistons', I'd check out the diesel forum; seems to me somebody found some aftermarket Aussie pistons that were not crack prone, and were cheaper than the Nissan stuff sold here. And, with the EGT and larger exhaust, too much heat shouldn't be a huge problem anyway. In fact, I'd be more worried about excess heat with the taller gears and tires; you're going to be lugging the engine more, and into the turbo more on hills and acceleration to make up for the lack of RPM's.
If you ABSOLUTELY have to swap gears, unless your axles have just recently been completely gone through I'd go the route of trading somebody with a gasser. LOTS of 1980 Scout II gassers came with 3.07 gears factory, they were looking for gas mileage. I'm sure somebody would be happy to do a straight up swap, axle assemblies for axle assemblies, to get your 3.54's or 3.73's (most common ratios with diesels). I'd not even be afraid to go to an older axle; in my opinion, the added caster really doesn't make a noticeable difference, and as mentioned earlier, a set of steel caster shims is an easy addition when you trade axles. Dunno where you're at, but I've got an 80 Scout II parts truck that I'd almost bet has 3.07's....it's gonna be for sale here shortly

[CareyWeber]

Originally Posted by Dennis Bernth

I don't know that you'll be happy with 3.07's on a diesel. The reason the diesels are geared a little lower (higher numbers) is because of a lack of 'guts' compared to a gas engine. With taller tires and taller gears, you're going to find yourself doing a lot of shifting on grades and hills that you might not have to do with the factory gears. As far as the 'crack prone pistons', I'd check out the diesel forum; seems to me somebody found some aftermarket Aussie pistons that were not crack prone, and were cheaper than the Nissan stuff sold here. And, with the EGT and larger exhaust, too much heat shouldn't be a huge problem anyway. In fact, I'd be more worried about excess heat with the taller gears and tires; you're going to be lugging the engine more, and into the turbo more on hills and acceleration to make up for the lack of RPM's.
If you ABSOLUTELY have to swap gears, unless your axles have just recently been completely gone through I'd go the route of trading somebody with a gasser. LOTS of 1980 Scout II gassers came with 3.07 gears factory, they were looking for gas mileage. I'm sure somebody would be happy to do a straight up swap, axle assemblies for axle assemblies, to get your 3.54's or 3.73's (most common ratios with diesels). I'd not even be afraid to go to an older axle; in my opinion, the added caster really doesn't make a noticeable difference, and as mentioned earlier, a set of steel caster shims is an easy addition when you trade axles. Dunno where you're at, but I've got an 80 Scout II parts truck that I'd almost bet has 3.07's....it's gonna be for sale here shortly

FWIW I think that 3.07's might be a good thing although on hills you are going to use 3rd gear more. If you want to keep the low range performance then maybe get a 4 to 1 gear set for the transfer case.

John Donnely posted some good info on 3.07's in the diesel forum.

Carey

[Bruce A. Frank]

Originally Posted by Steve Jackson

A negative caster gives the wheels a tendency to track straight and stay straight. Search here on the BB for more information.

I know that this thread is 6 years old, but many who come to the site glean the old posts for what they need to know at the moment. Steve has the information on caster angle exactly opposite the the fact. Positive caster improves stability, reducing the vehicle's tendency to wander and can eliminate a shimmy even when parts are worn to the point that they would allow violent shimmy. Positive caster CAN increase the apparent effort to steer the vehicle with manual steering, but I have not found it to be a problem.


Here is a short article from a track-racing site: http://www.thedirtforum.com/castersimplified.htm

[WRENCH MAN]

Reading the description under "Positive Caster" "GREATLY reduces the chance of shimmy" this is not always true!, to much will make it shimmy in a corner at speed (clover leafs on the Interstate), not exactly our trucks but we've had a serious problems with this in the Isuzu NPR's when we jack up the caster to normal specs.

[Bruce A. Frank]

Originally Posted by WRENCH MAN

Reading the description under "Positive Caster" "GREATLY reduces the chance of shimmy" this is not always true!, to much will make it shimmy in a corner at speed (clover leafs on the Interstate), not exactly our trucks but we've had a serious problems with this in the Isuzu NPR's when we jack up the caster to normal specs.

Could be the drop axle. But, I have worked on several IHC 4X4s over the years. I have not run into shimmy with straight axles when positive caster is increased.

[WRENCH MAN]

NO drop axles on Isuzu's.