Rationalised Axle???

[SafeAirOne]

A couple of years ago in the middle of nowhere in Northern Baja, Mexico I did something...foolish, we'll say...and broke a tooth or two on the ring gear on the front differential of my heavily-laden SIII 109.

Being the economically-minded (cheap), handy type, I got a new ring, pinion and bearings and installed them in accordance with the SIII workshop manual (or so I thought).

Six months later, as I'm driving home from work on the highway, I sense something...a hesitation...so I exit the highway to investigate. As I'm pulling off the street, the rover makes it MOSTLY off the pavement then locks up completely--I can't go forward or backward.

To make a long story short(er), I have finally gotten around to pulling the front differential to investigate the cause of the lock-up and found that the (new) inner pinion bearing (the one farthest away from the propeller shaft) has destroyed itself. The metal cage that retains the rollers had smeared between the rollers and race and had really wedged in and locked the whole bearing up.

I don't think I got a defective bearing, so I guess that I didn't shim correctly below this bearing race or the race was installed slightly out-of-kilter.

My question (finally): What are "Rationalised" and "Pre-Rationalised" Axles? The pinion height (shim thickness) is different for these 2 axles according to the repair manual. I researched it at the time and thought I knew the difference, but my seized differential suggests otherwise.

Any help would be appreciated.

Thanks,
--Mark

[Mercedesrover]

Rationalized = 24-spline diff
Pre rationalized = 10-spline diff

As in , "it's not really rational to use a 10-spline diff in an off-road vehicle, but let's do it anyway." or "It would be rational to make a stronger diff with 24-spline side gears."

Don't put too much effort rebuilding that one...Series diffs are a dime a dozen. Find a good used one and stiff it in there. If it's not free, it will certainly be less then the cost of a rebuild kit.

jim

[SafeAirOne]

Ahh...That makes sense. I definitely have a PRE-rationalized diff then. Giant splines on the axle shaft where it mates into the differential, but 24 spline on the wheel ends.

As for rebuilding the diff again---You're right. I think I'm just going to slip in a used (proven) unit, rather than rebuild this one. It'll save me from rebuilding it AGAIN 6 months from now.

Now if I can only find a used, pre-rationalized diff for less than $200... And, perhaps a pair of 24-spline freewheeling hubs....

[Mercedesrover]

$50 at the most. Ask around the boards...Someone will have one. I've gotten rid of a bunch of them over the years. Don't think I have any good ones left.

24-spline hubs are easy. If our hosts don't have them, try George at Rovers Down South. I know he has them. Mile Marker still makes them under the "Selectro" name.

[SafeAirOne]

$50 at the most. Ask around the boards...Someone will have one. I've gotten rid of a bunch of them over the years. Don't think I have any good ones left.

I found a replacement rover-type differential locally for..well, $50 actually. When I got it home, I noticed that the housing was a bit different than my bad one.

My bad diff has a flat block cast into the bottom of the housing for oil passages to the pinion bearings. The replacement doesn't have this--just reinforcing ribs.

I don't believe there will be any interchangibility issues. Of course I've never had to address this problem before, either.

Gear ratios are the same on both differentials. Does anyone know of any problems putting an older Rover-type differential in place of a newer Rover-type differential (spline count is the same on both diffs)?

[leafsprung]

splines should be the same. Just in case . . .count them.

[Mercedesrover]

Also make sure it has a fill plug. Older diffs had the fill plug in the diff housing, later ones had it in the axle housing. If it doesn't have a fill plug you'll have to drill a hole in the axle housing and weld a pipe plug bung in.

[SafeAirOne]

Also make sure it has a fill plug. Older diffs had the fill plug in the diff housing, later ones had it in the axle housing. If it doesn't have a fill plug you'll have to drill a hole in the axle housing and weld a pipe plug bung in.

I was noticing that when I took off the bad differential...Fill plugs on BOTH the removable differential assembly AND the axle housing. Looks like I'm covered there!

[Daurie]

Mark.. sorry to dig up this dead thread but what did you ever figure out to be the problem with your pinion bearing? I'm putting together a diff with a trutrac in it. I'm not fooling with the pinion depth but want to make sure the bearing preload is good, but not looking forward to spending money on a dial type torque wrench. My first thought about your situation was possibly too much pinion preload. Let me know what you figured out if you dont mind!

Thanks!

[SafeAirOne]

Mark.. sorry to dig up this dead thread but what did you ever figure out to be the problem with your pinion bearing?

I hate to admit it, but I think I used the wrong measurements when I set up the pinion spacing. To be more precise, I think the measurements were spot-on according to the book, but my front diff was not the one depicted in the book due to a previous owner installing a later-type diff. I know they're all rover-type diffs, but there are different versions. I now think the one that failed came off a coiler originally. Here's the photo of the type I used to have before the pinion bearing failure. Note the rectangular block, on top in the photo (diff is upside down), housing the pinion bearing oil galleries:

[scott]

i blew out the spiders and snapped an axle. badvibes fronted me a pair of axles and i slapped in a rrc diff with my od r&p. it lasted about a month and then i realized that there's a reason for all that measuring and stuff. bought a trutrac and had a guy named rob of southwest rover here in albuquerque. he did great job at setting it up.

[Daurie]

Yes there is definately a good reason behind all the measuring and percision work. I bought a 3rd member completely built from RDS. I replaced the diff with trutrac and pinion depth shouldn't be an issue but I will definatley check gear lash with marking compound before I seal it back up.

My main issue will be getting the pinion preload spot on as I don't have a dial type torque wrench. It is pretty easy turning as it sits with just slight resistance lightly oiled. Everything looks to be in excellent shape so I'm gonna say it was taken care of, but is broken in. Any suggestions on how much thinner to go on the preload shims to accomodate for wear but still be safely able to say it's not too tight?

[scott]

maybe you could take it to a tranny shop and have them check it.

[SafeAirOne]

My main issue will be getting the pinion preload spot on as I don't have a dial type torque wrench. It is pretty easy turning as it sits with just slight resistance lightly oiled. Everything looks to be in excellent shape so I'm gonna say it was taken care of, but is broken in. Any suggestions on how much thinner to go on the preload shims to accomodate for wear but still be safely able to say it's not too tight?

If I'm reading this right, you have left the original pinion assembly in place and changed out the carrier housing/spider gear/ring gear assembly.

If this is the case and you didn't touch the pinion, you shouldn't have to mess with the pinion gear/shims/bearings at all. The only adjustment you need to make when you reinstall the carrier is a side-to-side adjustment to set the backlash correctly, and you can do this with a simple dial indicator.

[Daurie]

I'm not replacing the pinion. I pulled it out because it basically fell out when I went to replace the seal. Regardless pinion depth isn't an issue and doesn't need to change as far as I know. The only reason I wanted to check/set the pinion preload is because #1 The pinion bearings look great but are undoubetdly well broken in and #2 it's all out and why not make sure it's back to spec.
Pickin up what I'm puttin down? :thumb-up:

[SafeAirOne]

Pickin up what I'm puttin down? :thumb-up:

Got it! I hadn't realized that the pinion had been removed when you removed the vent...er...oil seal.