WTT - MT 4.30 differential for 3.90 AT differential + PRO wheels

Kind of gauging interest and all the guys in the MT thread tell me I’m nuts for even considering this...but I’d be willing to give it a shot. If you just bought a PRO and are going to upgrade your wheels and tires anyway, I’d be willing to swap front & rear differentials with you IF you throw in your pro wheels / tires with it. You get a diff with 4.30 gears from a manual, I get your 3.90 gears+ your wheels and tires. PM me if interested

 

If it’s 4X4 the front and rear gears have to be the same, as far as I know

 

Nah, he just needs different sized tires in the front and he'll be good.

 

Thought the autos came with 3.90’s

 

Yeah, I guess you’re right...would get a bit of a surprise as soon as i tried 4wd! Edited to say swap front and rear diffs

 

Yeah, you’re right. Was going from memory. Edited...

 

What's your motivation for this?

 

Stock truck and gearing just seems a little low geared for my use. I’m not a huge off roader and doubt I will ever tow anything of substance (or anything at all really). I find myself wondering if I forgot to shift out of 4th gear when I am rolling down the highway at ~2500 rpm

First gear also strikes me as being very low. I get it if you tow a lot or haul heavy loads often, but that’s not me.

Swapping with someone who wants the lower gearing would seem to be a win -win. Asking for the wheels to sweeten the pot slightly for myself in case this doesn’t go quite as well as I’m thinking

Anyway, I was initially thinking of just the rear diff, but a previous poster educated me that I would need to do the front as well...that obviously makes it quite a bit more involved, but I’d still consider it.

 

Someone correct me if I'm wrong, this is going off memory of the other models. You can swap the rear gear set with only the TRD OR AT. The manual OR and Sport have the larger rear end, I believe the AT OR is the only AT with the 8.75" rear. You could do a full axle swap to get around this though. Either way, are you planning to do labor yourself?

You could consider lifting the truck and running larger tires, or without a lift, just running 255/85r16 on the stock wheels or a 275/70r17 on a 17". Swapping to a 33 will effectively bring that 4.3 ratio to a 4.1ish ratio. The highway RPMs at 60 in 6th should be right at 2k instead of 2.2k. You're definitely in the minority here though most complain that the truck is too sluggish and go to a 4.56, 4.88 or 5.29.

Also, there's a big difference in gearing in the trans as well. You'll likely never be able to get close to the ATs 6th ratio. If I remember correctly it was 6th at .58 ratio and the MT is 6th at .71. That puts the AT at like 1600 rpm at 60, to get that in a MT you'd have to run close to a 3.0 gear set.

Basically swapping your gears to the AT will net you 200ish less rpm at 60 in 6th. 1st gear is like 3.98(mt) to 3.6(at), so again even with the AT ring and pinion you'll still be at higher rpm than an auto.

Wish you luck though, in whatever you decide.

 

Yeah your OR transmission is geared lower. So it's not a direct swap as if it's an auto final.

I'd double check those numbers to see what you're working with

 

The only diffs that will swap over correctly would be from an automatic PRO or Off Road.

Why not just get bigger tires?

 

Yep...looking for an AT pro owner...

Don’t really want bigger tires, but maybe I’ll do that if the diff doesn’t do the trick for me

 

Just go 265/75/r16

 

I can sell you my 3.9s off my 3rd gen OR.... PM me. I think I have the ad up some where here

Edit: https://www.tacomaworld.com/threads...-stock-front-and-rear-ring-and-pinion.589683/

 

Thanks for offer, but not really the deal I’m looking for.

 

Bump

 

I’m over the hill by Reno, and will swap with you. But no way I’m throwing in wheels since there is no price difference in differentials.

 

@ThatsExactlyWhy

DO NOT RUN 3.91’s IN YOUR MT!

You will be lugging the shit out of the motor. These engines like to be in the higher RPM range and by going to a higher gear ratio you are in turn reducing RPMs. Lugging this engine is the fastest way to burn a valve bank or shit a cylinder. Ask me how I know.

 

Ok...HOW DO YOU KNOW?

 

Reduced RPM due to higher gear set or larger tires cause the engine to work harder at lower RPMs outside of the normal power band. By running 3.91 gears on the MT you should be running a 26” tire (265/50R16) to keep it in the proper power band.

I was running 35” tires on the stock 4.30’s for almost 20k miles before I regeared to 4.88’s. At 70mph, I was running at 1800RPM when I should have been around 2600RPM. I noticed an excessive amount of valve tap and rod knock after the fact that never settled down. When I took it in to have it looked at, it was determined that I had burnt a valve bank. I got a second opinion by my buddy who is the head mechanic for a NHRA pro-stock team and he said the same thing.

DON’T PUT 3.91’s IN YOUR MT!