Diff Swap

[TallKDR]

Hi. I tried to search for this toppic but didnt come up with anything.

I just noticed the Autos have a higher numericly diff, than the 5spds.

Has anyone done the swap between the two? Is it just bolt in? I would think so, why wouldnt it.

However, the difference seems pretty small in the gearing. Is there a better donor car than an SC300 ?

And if the auto diff into the 5spd is the way to go, how much do these usually run for a lexus? I know i was able to pick up 280Z diffs for $50. Dont think ill get that lucky here haha.

Thanks in advance!

Paul

PS - here are the gears: final drive - 4.08:1 manual, 4.27:1 auto

[TallKDR]

Damn it just realized the auto wont be LSD, no chance.

Im pretty sure i have an LSD one right now, havent checked, but it sure does leave two skid marks behind itself.

I think my plan went to hell unless theres a cheap Supra LSD diff with a better gear.

[AWJ]

That is a cloudy subject there. If I were going to change the diffy, I would want some sort of limited slip. Apperently, the supra TT diffy's are torsen. The supra TT diffy(s) is rumored to fit into the (x)zz3(x) models. There are two types, the auto and the manual. The auto is rumored to bolt right in pumpkin and all. But I have heard unconfirmed that there is difficulty with the shafts on one end or the other. Possibly difficulty with mounts as well. I don't know. The TT manual diffy will work but will require the driveshaft flange to be modified some how. I think the half's will also need some sort of modification/fabrication. Then there are other units like the TRD piece made for the soarer. I think it can be found through one of the links in the faq. This is just the gears, so there would need to be alittle operation there and if things are not lined up or shimmed properly - there could be problems. I've never done anything like that so I have no clue to the details. I hear Kaaz might make something also. 50$??? Not for the SC. Sorry. Expect about 200$ or so for a used unit somewhere and up to 1500$ for a new one from somewhere like Qauife or the sort.

[TallKDR]

Thanks for that info. $200 is acceptable. I dont know how much people here know about these kinds of things, because with newer cars part swaps become more rare, but I think people should know that diff swaps are some of the best ways to make a car faster for cheapest amount of dollars. Only thing that happens it you run a little higher rpm on the highway. But overall, the kick in 1st and second is impressive and worth the money.

If anyone has any more info, please post !

[Lextech2k3]

ok i know a little about this stuff but i haven't personally done one....i know at the dealer i work at we were putting sc300 rear ends if sc400 because of a lack of pickup in the 400....as far as trying to swap supra to soarer....hmm that most definately is a grey area...you may be better to pose as a supra owner on supra forum page and ask around there...as it is more common for those guys to modify there cars....just a though sorry i couldn't be of more help....also you don't want to try to change the gears yourself...unless you have a torque wrench that's about 4 feet long...the pinion nut takes about 200+ ft-lbs of torque...that's why we don't rebuild them at the shop.

[AWJ]

You guys don't have an impact wrench? The higher the ratio, the slower the car is going to be out of the whole. The torque kick lunge feeling comes with the lower ratio. Low ratio - more seat slam lower top speed. Higher ratio - less seat slam higher top speed. If you go changing the differential - you will also have speedometer accuracy problems. But that can be dealt with as well with some kind of sensor trick using the TT sensor or something. I forgot the details. I would definitely pay a reputable performance shop to do this job if I wanted it done right.

A stall torque converter is also worth considering - for the automatic guys. Info on the supra diffy can be found at supraforums. I'll see if I can dig some up later.

[TallKDR]

Low ratio higher acceleration? Im not sure what the words actually mean, but to make it clear for those that might not understand (me) low, high, tall, short, it is clear that a 4.5:1 ratio would accelerate MUCH quicker than a 3.5:1.

And if you are having trouble unbolting it because you dont have an impact gun, or the strength to use a smaller torque wrench, i bet youll problem will be setting the clearences correctly instead of just unbolting something :P And also, Im guessing you better have a dang good vice to hold that rear when youre trying to untorque 200 ft-lbs. To change gears out you have to take it to a prof. shop that does that kind of stuff. The only DIY part of all this would just be a straight swap from one car to another.

Do any Supras have better gears than our ~4.1:1?

[SPORTcoupe300]

Low ratio - more seat slam lower top speed. Higher ratio - less seat slam higher top speed.

I think he's right AJ....

A higher gear ratio means the engine spins faster/tire rotaion = more torque.

In my opinion 5spds have plenty of torque.....want more...just rev a bit higher and get a double disc clutch.

[AWJ]

you sure about that? The lower the ratio, the quicker the response - the quicker the inertial limit is met yes? The higher the ratio - the slower the response but the longer the it takes to meet the limit. That is why the Supra's have a higher top speed but I'll jump him on the line. (If he's just your average bpu and not a better driver than me.) Ratio is x turns to make y turns yes? So if the shaft takes three times to turn the wheels 1 it will happen sooner than 4 times to turn 1. Thus the higher the ratio, the less torque. I'm not saying it is significant, but it will be affected. And it will be seen at the top end as well.

I could have it backwards though. I've been doing that lately. It took me a while to figure out air fuel ratio too. For some reason that stuff screws with my head. And you guys are making it hard on my head... I'm gonna go to bed and think about it.

[TallKDR]

Think if it was a bike. When you drop down to a smaller shaft in the rear, you make more revolutions per YOUR one foot rev.

So if you make it so that your engine has to spin more to move you the same distance, it will do it much easier.

This can be clearly seen that your car moves much quicker in first gear where the ratio is 3:1 lets say, and much slower in 4th where it is 1:1.

The diff is just like that kind of gear, except its not adjustable.

If you could have a 5:1 rear end, your top speed would go down to maybe 100 before you hit the rev limiter, but youd be flying in 1st (or burning rubber).

[SPORTcoupe300]

http://www.csgnetwork.com/gearratcalc.html

It's ok AJ....we all get confused sometimes.

The link above is to a calculator for end gear ratios.

Put in a few Top Speeds and hit calculate and notice how the gear ratio changes.

;)

[AWJ]

I had it backwards.

[K9crew]

AWJ,

Don't worry about it ... even the experts make mistakes. I personally intalled 4.57 gears in my Wrangler (front and back) and it's got way more power off the line compared to the factory 3.07 gears but now I wish I had a 6-speed manual instead of the AX-15 that's in there. The Dana 30 and 35 diffs require 350 lb-ft of torque on the pinion nut in order to crush the collar (required to set the bearing pre-load to about 15 lb-in). I haven't worked on a Lexus diff yet but the high torque required may be for the same reason. If you're really good you could check the pinion bearing pre-load while tightening the pinion nut with an impact ....

:)

[Masubi]

I just ordered a cusco LSD, I will let you know how that goes if you like.

[AWJ]

I just ordered a cusco LSD, I will let you know how that goes if you like.

OOOOOOOOOO......

Nice. B)

[Masubi]

I just got my LSD, I will take pics to show the install and let you know how easy or not it is...