Diff strength..

KingSlug

Observer
I usually a Land Rover driver, but since I am upgrading to toyota diffs I have just a quick question. How much stronger is the 9.25" diff than the 8" diff? I don't need a total engineering explanation, just some quick reasons? Do others swap the 9.25" in to places the 8" was? I think I will just have room to put the 9.25" in a rover axle housing.

I already have 2 8" e-lockers waiting to be put in my abulance, but if the 9.25" is stronger I will swap that in my 109 ambulance and put the 8"s in the 88" I just got.

Thanks

Jared
 

Grim Reaper

Expedition Leader
Really the 8's are pretty strong. If you put a set of Longs http://longfieldsuperaxles.com/ in the front it would be pretty tough up till about 5.29's. After that the pinion becomes very small.

That said the 9.25 are wider and the housing is stronger in addition to the bigger ring. In the 90's the rear axle was a full floater. In japan they really concider them more of a 3/4-1 ton.

Ambulance sounds heavy.....I think I would go with the 9.25's myself especially with the stability of a little extra width.
 

KingSlug

Observer
Actually

I am just swapping in the toy diff into the factory trussed rover housing, I just have enough room to mount it. Gearing really isnt a worry I would like to get below 3.70 for stock tires but might go with 9x16s and 4.10 gearing. I will be having a low reving 4bt powering the amby coupled to a NP435/rover xfer case combo. I already purchased the axles and only recently someone suggested the 9.25 instead of the 8, the lasthing I would want is to break a diff overlanding.

Thanks

Jared
 

Brian894x4

Explorer
How much weight are we talking?

The 8" rear diffs are found on Toyota trucks overseas with a gross weight of up to about 6000lbs or a little more.

If you're talking much over that, then the larger diff would probably be beneficial. But under that weight, then the 8" should be fine. I'm not sure how much torque the 4TB puts out, but that should taken into consideration too.

There are two kinds of Toyota 8" diffs though. There's the 2 pinion and the 4 pinion diff. You want the 4 pinion diff as it's stronger. If you have electric locker diffs, then you should be fine.
 

KingSlug

Observer
I figure my ambulance will be between 6500-6700 GVW. The 4bta will put out around 130hp and 355 lb-ft of torque, still getting around 30 MPG. I have a lead on a series 80 LC high pinion front and a 9.25 rear both with e-lockers. I think I will feel safer with the 9.25 diff.

Jared
 

Brian894x4

Explorer
I agree. The 6700lbs combined with 355ft/lbs of torque probably won't overwhelm an 8", at least on the highway, but you're getting close.

However with either diff, the weak point is still probably going to be the axles, since they are the same size. If you can run full floaters, you'd be set. At least a broken axle won't leave you completely stranded where you sit.
 

Dirty Harry

Adventurer
Andre (dieselcruiserhead on here) ran an 8" rear axle in his 4BT powered FJ55 with a springover and 35" tires. I was skeptical when he first told me this but he never had any breakage issues.
 

KingSlug

Observer
My rover axles are full floaters. I think all rovers from S1 upto the Disco2 have been full floating axles. I have custom axles from SeriesTrek http://www.seriestrek.com/axles.html , I think they should hold up fine even if the front axles have u-joints. I have thought about running Michelin XZL 9x16 https://www.expeditionexchange.com/michelin/ , they would fit nicely under my amby although they would affect turning radius. I have a few pics of LR ambulances in europe fitted with 9x16s, they are tall but thin.

Thanks for all the info.

Jared
 

cruiseroutfit

Supporting Sponsor: Cruiser Outfitters
Dirty Harry said:
Andre (dieselcruiserhead on here) ran an 8" rear axle in his 4BT powered FJ55 with a springover and 35" tires. I was skeptical when he first told me this but he never had any breakage issues.
He never had R&P issues... but he did rip the perches off the housing a couple times. They were literally ripping the housing. :chowtime: After a good "patch" I think it was troublefree.




When it comes to the actual failure mode of the 8" versus the Cruiser 9.5" there are the same. The usual failure is the pinion, right at the splines of the pinion flange. The 9.5" and the 8" are 100% identical at that point (assuming your running the fine spline Cruiser stuff). The next line of failure is most likely ring gear deflection in the 8", the 9.5" doesn't fall victim to this failure. There are V6/turbo differential housings that will increase stength in this area. Ulimately, if the width of a Tacoma axle works, the non-TRD 8.4 (as its called) axle is like on of the stonger diff. designs your going to find in light duty axles. The integrated carrier bearing caps really eliminates deflection!
 
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