vc88runner

Hi Guys, in need of some help.
I have an 88 4runner v6, automatic 4x4.
Went offroading this past weekend and my truck wouldn't go into 4wd.
Had it checked by a mechanic, and was told that my front differential is bad. Also recommends changing both front hubs.
That's the easy part. Found the front diff for $200 with a 3 month warranty. and the front hubs won't run me over $100.
Here's the problem. The mechanic is telling me that the gear ratio of the rear diff on my truck is 3.10. This just doesn't make sense to me. From my understanding 80's runners either have 4.10 or 4.30 gear ratios. All the ones that I found in junkyards are 4.10.
Does the guy not know what he is talking about? Or is it possible that a previous owner installed a rear diff with a 3.10 ratio.
His solution is to either find a front diff with a 3.10 gear ratio or to change both diffs with matching gear ratios.

akwheeler

check the gear ratio yourself, count how many driveshaft rotations with one full turn of the rear wheels. use some tape or chalk on the tire and driveshaft to mark and count. just over 3 rotations would be a 3.10, just over 4 = 4.10

vc88runner

Thanks for the reply akwheeler. We actually checked the gears using your exact same method you described. So, it looks like the rear diff is 3.10. I'm thinking it might be best to change both diff's and improve the gear ratios. As opposed to matching the front to 3.10. Are the differentials from early 90's runners compatible with the 1st gen?

akwheeler

I'm not sure if all IFS front diffs are created equal. I do know you should stay away from stock 4.88 gears since the rear diff will have an offset pinion and will not accept aftermarket lockers and gears.

vc88runner

So I'm hoping for some help. I changed my differentials this weekend. Installed a pair of diffs from a 93 v6, 4x4 automatic 4runner, gear ratios are 4.88 and front diff has ADD. The reason i changed them was because my front diff was shot and my 4x4 would not engage. I also changed my front axles, installed a "new" set of aisin hubs, and put new ome leafs and rear shocks. Anyway, after all that work, my 4x4 still doesn't engage. I did nothing to adress the ADD on the new diff and suspect that i need to something with the vaccum system. I don't know what the solution is. Does anybody know how to fix this? Thank you

millball

If your original front diff was not ADD you can easily transfer its long axle and tube to your new diff and do away with the ADD..

I think all you'll need is to install a seal into the cast iron diff housing.

vc88runner

Thanks for the reply. So i fixed my 4x4. Ended up hooking up direct vacuum to the add from the engine. When i have more time i will do the modification from 4x4wire.com to have a more reliable solution or just eliminate the add altogether as suggested by millball. Setting up vacuum took less than 10 minutes, so i highly recomend this solution to anyone short on time. Truck runs great with the new 4.88 diffs, but i have some vibration-rattling from front end when accelerating. Will check when i find sometime.

vc88runner

So I'm struggling with issues related to this diff swap. It turns out the vibration-rattling is not from the front end, but from the rear end. The sound seems to originate from the area of the rear differential or where the differential hooks up to the driveshaft. I'm hoping someone on here just straight tells me I f---d up somewhere. I am not a mechanic, but my 2 brothers and I did all the work ourselves. I would say my youngest brother is the most capable, and I'm an amateur at best. A loud rattling/ vibration metallic sound comes from the rear end when I accelerate or decelarate. The sound gets louder the faster the vehicle is going, but the sound is not constant. It happens when I press the gas or let off the gas, but not while cruising at a constant speed. We did not replace the entire rear axle, but only changed the rear differential(pumpkin) and put 75w-90 gear oil. We reused the same driveshaft that was on my truck. Did we miss a step? I saw a few post on other forums mentioning maybe having to change the differential pinion flange, others saying you need to change the driveshaft and others mentioning changing the carrier bearing? Thanks