PDA

View Full Version : Differential swap/compatibility



mountainhick
11-21-2013, 08:38 AM
After checking in with TheMAN about adding a LSD to his Previa, I've been searching and searching to try to find what else could be compatible for a LSD and to possibly change final gear ratio.

Here's what I know so far:

Previa non SC final gear axle/diff code F282 which is 7.5" ring gear, 4.300 ratio 2 pinion diff

Previa SC final gear axle diff code F302 which is 7.5" ring gear 3.727 ratio, 2 pinion

The Previa rear axle from what I can tell was not used on any other model, but the diff guts were.

These codes are for the rear. Front diffs on AWD are apparently not identified on the door tag, but I suspect would be T282 and T302 with 6.7" ring gear. The T series seems to have been used in a number of models as rear diffs with independent suspensions.

Transmission gearing relativity: The Auto previas are geared for higher speed highway driving. The pertinent gears for me a low for getting started from a stand still to climb uphill, and high for highway cruising. Gear ratios are 1st @ 2.452 and OD is 0.73.

Manual trans has lower gearing for both 1st and 5th at 3.704 and 0.854 . Result in performance is that the Auto is sluggish to inadequate for climbing hills in low gear. Manual 1st gear is great for this, but at the expense of running at highway speed. I can't see driving at more than 60-65 with the manual trans to keep rpm in a reasonable range.

The ideal thing would be to just change the 5th gear ratio in the tranny, but that is not something I want to even try or pay for.

So that leaves playing with diff ratios.

I crunched some numbers and it looks like if I swap out the 4.3 for the SC 3.727, I'll still have better torque than the auto trans in 1st gear, but still will have less than the comparable top speed with auto trans gearing and 3.73. Might be worthwhile to have the highway cruising speed, but I am not sure I will still have the desired 1st gear torque I need.

It looks like there are two other gear ratios between the Previa's in different model diffs for the 7.5" F series diffs, but I can't determine whether the rings and pinions will swap into the previa's diff cases. They are 3.909 and 4.100. But i have found no love for the 6.7" ring gear size and matching these in between ratios for both front and rear axles.

(there is a very common 2.92 ratio in a bunch of models which I think is the 6.7" size, but that ratio is way out of range for the Previa)

I've been searching on part numbers to try to cross reference interchangeability with other models, and found some correlation with Celica, Camry, Supra, RAV4 old pickups, tacomas, T100, forerunners, and Lexus IS series cars. The problem in direct cross reference is in some cases, there are internal diff parts that match, while cases don't, possible different axle diameters and spline counts etc and so on. And, for a bunch of these other models, the diff coding completely changed. I am finding info that on Supras for example, the code variables are even relative to the car model and year itself and not consistent between different models. So something coded A01B in a Supra may mean something different than A01B in a Lexus IS series.

So if anyone has any insight into what Brand/Model cars diff guts, Rings/pinions and internal diff case assemblies are interchangeable, I sure want to know!

I am speculating about the possible benefits of changing final gear ratios, and it seems around 3.9 would be ideal for my purposes, but I have not yet found that ratio in other models to swap into both front and rear diffs on the Previa.

And, there are many models that used LSD or had it as an option and if possible I'd like to find more interchangeability options. I am looking at the Japan and European as well as North american market to try to source parts.

mountainhick
11-21-2013, 03:15 PM
After all that, for gear ratio, and not finding availability of the 4.1 and 3.9 for the front diff, I think it is going to come down to swapping in the SC gear sets. My numbers show a 49% difference between Automatic and manual first gear, and changing the diff ratio is only 16%, so I'd lose only 16% for low end torque (Not sure if this is a linear relationship), but still have the remaining difference of 33% better torque compared to the auto gearing. And I'd get the highest change in top end speed on the highway.

There's a rear diff on a RWD, but with a lot of miles at a nearby used part lot. If I can get a look at the internals I'll probably get it, which would leave me needing the front. Anyone know where to find a used front diff with SC ratio 3.727 or ring and pinion gear set?

LSD is a different story, probably will be a while before I sort that one out!

TheMAN
11-27-2013, 02:41 AM
more than you ever want to know: http://home.4x4wire.com/erik/diffs/
the diff codes on the ID stickers don't matter because they don't make enough sense across the entire line of cars across a wide range of years... physically looking at them is better and there's tons of information out there about toyota diffs

the previa rear end is the same as the 86-95 mini truck front ends and are the low pinion gears... there are tons of aftermarket gear sets you can get... why buy used when new is better? the 7.5" was used in many different RWD toyotas, such as celica, cressida, corolla, vans, etc

you don't even need to get a LSD if you don't want it... you can get aussie lockers or ARB lockers, they work and work good, but the 3rd member needs to be modified to control them
the S/C 3rd members are exactly the same as the non-S/C ones.... you can actually just buy the entire 3rd member off a S/C and swap it onto yours over in a day, assuming nothing goes wrong