Rear Differential Info
11-22-16, 08:22 AM
#1
Driver School Candidate
Thread Starter
Rear Differential Info
Can anyone help point me to some type of guide on rear differentials for lexus models? I'm putting together parts for a custom offroad buggy and I've always been a Toyota guy so I'd like to keep this build mostly toyota parts. I have a solid axle rock crawler on 40" tires - so this is kind of going a different route. The idea is ultra light. Like side by side ATV light. Probably a Yaris/Echo 1.5L engine with a turbo and IFS/IRS. And I need some differentials. I'm struggling to sort out which Lexus models have rear differentials that would be useable for custom IFS/IRS. I'd go with a current model tacoma/4runner front 8" IFS or Tundra's 8.7" front diff, except the housing has a long side shaft and I need as narrow of a diff as I can for maximizing suspension travel. What I'd love to find is a rear Lexus differential that is interchangeable with either the standard Toyota 8" diff parts or possibly the standard 7.5" diff. The reason is that locking differentials is a must have for any serious offroading - LSD doesn't work well offroad. I intend to use selectable lockers in both diffs. The interchangeability the differential internals is most important - I can probably design around most gear ratios by using a wide ratio transmission, but ideally I'd love to be in the 4:1 range.
I've searched quite a bit and haven't found any comprehensive guide of any sort or even a good idea of what's interchangeable between the Lexus rear diffs and the truck parts.
So - can anyone point me to a source of info on differentials in various models? I'd really love some help here. Thanks!
I've searched quite a bit and haven't found any comprehensive guide of any sort or even a good idea of what's interchangeable between the Lexus rear diffs and the truck parts.
So - can anyone point me to a source of info on differentials in various models? I'd really love some help here. Thanks!
11-22-16, 09:03 PM
#2
Well this is certainly a question that has never been asked in the 3GS forum before! I doubt anyone here can answer your differential questions – the only Lexus with locking diffs that I know of is the LX, so you might want to check the LX forum
As for info on the diffs across the Lexus model range, the only place I can think of that would have all the specs is the Toyota technical info service (techinfo.toyota.com). You'll have to make an account and pay for access ($15 for 2 days, $60 for a month, $400 for a year)
As for info on the diffs across the Lexus model range, the only place I can think of that would have all the specs is the Toyota technical info service (techinfo.toyota.com). You'll have to make an account and pay for access ($15 for 2 days, $60 for a month, $400 for a year)
11-23-16, 06:16 AM
#3
Why not just run a Ford differential say from an explorer, those are common diff to mod for high hp, but in your case 40" tires. Youll also find it easier to find gearing and lockers for that differential. 2007-to newer explorers, those IRS differentials are stout and can handle power, also there was a factory option of lockers. Explorers diffs are slightly heavier but you will need a beefy diff for serious crawling.
What crawl box do you plan on running?
What crawl box do you plan on running?
11-28-16, 04:53 PM
#4
Driver School Candidate
Thread Starter
The LX diffs are solid axles. I actually have a version of the toyota 9.5 diffs with lockers in both axles of my FJ40. But they won't work well for this project.
I was hoping to use a lexus rear diff because they might be interchangeable with all the usual Toyota stuff for offroading. The big desire I'm looking for is to use Toyota front IFS axle parts - namely the CV joints. The new 30 spline birfield joints are amazingly strong - and cheaply available. I already know they'll hold up to 40's without a problem after seeing some modified and installed into an earlier 4runner on 37's. They should be adaptable pretty easily to any of the toyota family rear diffs. Plus the Toyota design is strong and light. And the Toy 8" has a huge range of gear ratios and lockers.
My intention would be to retain the full auto transmission from the Yaris and mount the engine longitudinally. I'd lock the differential set inside the transaxle then use the axle shafts from the transaxle to run directly into the flanges on the IFS differentials. The result would be about the same as running a typical setup in 4lo. Because the shaft that would be going to the tire goes through another gear reduction. If I use a transaxle from a Scion XB it has a 3.54:1 1st gear and a 4.31 final drive ratio. With 4:10 gearing in the diffs the final crawl ratio would be 62:1 with 5.29 gears it would be as low as 80:1. For comparison my daily driver 4runner only has a max crawl ratio in 4lo of 47:1, and my FJ40 has a crawl ratio of around 60:1 but with a manual transmission. With 40" tires it's low enough, but could be lower. I think 62:1 would be a nice sweet spot, but 80:1 may be better. I don't know for sure. The wide gear range with a .8 overdrive would also allow for moderately high speeds. In 4lo in the FJ40 for example my minimum gear reduction is 14.3:1 with no overdrive and a 4500rpm redline. With a higher revving little 4cyl and an overdrive, I think I'd be fine without an extra gear box. Even at 14:1 with 40" tires (assuming 5th gear in the XB transmission) I'd be able to get up to around 50mph at 6000rpms. If I used a 3.5ish ratio final drive in a yaris 5 speed instead of the XB I'd give up crawl ratio but still be around 55:1 and then 6k rpms would give me more like 60mph. In a perfect world a 6 speed auto with a double over drive .5 6th gear would give me a top end speed of more like 100mph.
I'm not really looking for max top end speed. Just a fun toy to zip around the desert in like a side by side but can still handle 90% of where my FJ40 goes, but also is easier to tow, cheap, and easy to let a friend get behind the wheel. The side by sides are great fun, but just a bit too limited on the harder stuff because they have really small tires and weak drivelines relative to most rock crawlers. The light weight goes a long way though and they really are pretty darn capable. I'd be just taking the concept up a notch, but trying to keep the weight around 2000lbs. Starting with 800lbs of wheels and tires makes that goal pretty hard to get to. A 170lbs Yaris engine is a big help in that regard.
I was hoping to use a lexus rear diff because they might be interchangeable with all the usual Toyota stuff for offroading. The big desire I'm looking for is to use Toyota front IFS axle parts - namely the CV joints. The new 30 spline birfield joints are amazingly strong - and cheaply available. I already know they'll hold up to 40's without a problem after seeing some modified and installed into an earlier 4runner on 37's. They should be adaptable pretty easily to any of the toyota family rear diffs. Plus the Toyota design is strong and light. And the Toy 8" has a huge range of gear ratios and lockers.
My intention would be to retain the full auto transmission from the Yaris and mount the engine longitudinally. I'd lock the differential set inside the transaxle then use the axle shafts from the transaxle to run directly into the flanges on the IFS differentials. The result would be about the same as running a typical setup in 4lo. Because the shaft that would be going to the tire goes through another gear reduction. If I use a transaxle from a Scion XB it has a 3.54:1 1st gear and a 4.31 final drive ratio. With 4:10 gearing in the diffs the final crawl ratio would be 62:1 with 5.29 gears it would be as low as 80:1. For comparison my daily driver 4runner only has a max crawl ratio in 4lo of 47:1, and my FJ40 has a crawl ratio of around 60:1 but with a manual transmission. With 40" tires it's low enough, but could be lower. I think 62:1 would be a nice sweet spot, but 80:1 may be better. I don't know for sure. The wide gear range with a .8 overdrive would also allow for moderately high speeds. In 4lo in the FJ40 for example my minimum gear reduction is 14.3:1 with no overdrive and a 4500rpm redline. With a higher revving little 4cyl and an overdrive, I think I'd be fine without an extra gear box. Even at 14:1 with 40" tires (assuming 5th gear in the XB transmission) I'd be able to get up to around 50mph at 6000rpms. If I used a 3.5ish ratio final drive in a yaris 5 speed instead of the XB I'd give up crawl ratio but still be around 55:1 and then 6k rpms would give me more like 60mph. In a perfect world a 6 speed auto with a double over drive .5 6th gear would give me a top end speed of more like 100mph.
I'm not really looking for max top end speed. Just a fun toy to zip around the desert in like a side by side but can still handle 90% of where my FJ40 goes, but also is easier to tow, cheap, and easy to let a friend get behind the wheel. The side by sides are great fun, but just a bit too limited on the harder stuff because they have really small tires and weak drivelines relative to most rock crawlers. The light weight goes a long way though and they really are pretty darn capable. I'd be just taking the concept up a notch, but trying to keep the weight around 2000lbs. Starting with 800lbs of wheels and tires makes that goal pretty hard to get to. A 170lbs Yaris engine is a big help in that regard.
11-29-16, 02:08 AM
#5
Im a big fan of the J40's and the 70's!
I dont know your budget but some Polaris rzr differentials may work aswell, they have nice long travel suspension great for sand. The diffs are super light and can be built up or fully modded billet to accept the huge tires. You would have to get creative with the driveshafts.
Have you tried posting a post on pirate4x4.com? Those guys are very knowledgeable in swaps like these.
I dont know your budget but some Polaris rzr differentials may work aswell, they have nice long travel suspension great for sand. The diffs are super light and can be built up or fully modded billet to accept the huge tires. You would have to get creative with the driveshafts.
Have you tried posting a post on pirate4x4.com? Those guys are very knowledgeable in swaps like these.
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