Gear Swap Info

[kpaske]

I read in a couple of other threads about how some folks (Spazz?) have swapped out gears to regain some pep after adding bigger tires and possibly improve gas mileage. I'm considering this mod but need some more information. For those who've done it, are these claims true? Are there any drawbacks? What all is entailed in the swap? What are the part numbers and where can I get them?

[SPAZZ]

your stock rear axle is a Corporate 12 bolt 26 spline and you will need 456 gears at least or 477's or 488's...you probably don't want to go any larger as the front axle has to be the same ratio and it is too much for it to handle.

your stock front axle is a Corporate 10 bolt 17 spline ..... if you do this work...you might as well install lockers...unless you don't care.

front ratio has to match rear ratio...so you will need the gears, and all the stuff necessary to set up your 3rd members.

the rear axle is a breeze to replace 3rd members..probably like an hour. but, the front axle has to be practically removed and is a pain to undo everything and work it around the steering linkage.

easiest way is to find some cheep 3rd members or just the housings and then buy all the stuffing separate...then all you have to do is take it all to a gear shop and drop it off for them to do all the dirty work.....this is also ALOT less expensive bill for you and easier for them.... then once you pick up your 3rd members all set up ...they are ready to drop in.

[MrCrowley]

The only gears I know of that are available to us are 4.30, 4.56, and the 5.38. You might want to do more hunting on some of the Trooper forums as they do alot of heavy modifications including drivetrain. There are 4.77's but I think they only fit the old generation troopers, and ours is basically a new generation trooper platform. I also agree with Spazz- do at least a front ARB locker if you can. No driveability issues, but push the dash button and you will be locked front, and the rear limited slip is about the best available minus some extreme rockcrawling but it can hold its own.

The good news is if you want 33" tires, the 5.38's will put you back to stock gearing and your speedo wont be off.

If anyone has found any different gear ratios- please share

[Nazrat]

The 4.77:1 gears will fit 88-97 Troopers, 89-94 Amigos, and pickups with disc brakes. It also appears that they will fit the Vehicross. Externally the rear axle appears to be the "older" Isuzu 12-bolt axle. 98+ Troopers have a newer 12-bolt that isn't compatible.

Dan R's Vehicross rear axle:
http://tad.grosvenor.org/gallery/Mis...ation/IMG_0517

Conway's 2001 Trooper rear axle:
http://tad.grosvenor.org/gallery/Mis...01_trooper_dif

88 Trooper diff: (sorry for the mud) http://tad.grosvenor.org/gallery/MiscInstalls/slider9

88 Trooper diff again:
http://tad.grosvenor.org/gallery/KYSep01/IMAG0024

Does anyone have a VX rear axle that looks like the 2001 Trooper axle and not like Dan's VX axle? Mine looks like the older 12-bolt. (like Dan's).

If you find a set of the 4.77s, they are quite rare. I got my set out of an 89 RS Trooper. 1st Gen Troopers with the wide tire option apparently came with the 4.77 gears, and no other Trooper did.

Some 4cyl 98+ amigos or rodeos came with 4.77s, but that doesn't matter to this forum because they have a dana-44 rear axle and the gears don't interchange.

-Tad

[kpaske]

Wow, this sounds like a major project. So the 5.38's sound like the ideal ratio for those of us with 33" tires, but Spazz says it might be too much for the front axle to handle. Does everyone agree with this? The last thing I want to do is spend a lot of time and money on a crazy mod only to end up breaking a bunch of other stuff.

Also, I'm not familiar with all the parts we're talking about here. What are the "3rd members" and what would ARB lockers do for me?

[SPAZZ]

the big PUmpkin removable thingy from the axles... the type of axle you have depends on the bolt count ON THE RING gear and not the housing of the 3rd member.

Our front axles should be compatible with any Corporate 10 bolt that Isuzu offered... evn some Honda Passports and some other cars. The rear is Compatible with any Corporate 12 bolt that Isuzu offered. Our front and rear axles are Modified 12 bolts and 10 bolts. By "MODIFIED" that means a thicker ring gear.

A while back my rear 3rd member went out. I at the time could only afford a 456 3rd from a 90 PUP... my front is going out and I can only afford a 90 456 3rd from a 90 Trooper.

you do NOT want to go with 538's as your front cv shafts will twist off unless you just do highway soccer mom curb hopping driving such as H2's. 577 or 588 Ring and Pinions will work as long as they are from a Corporate 12 bolt axle rear and Corporate 10 bolt axle front...as long as inner spline count the same..but all my and Swordy's research comes up with is that their usually is no change.

[MrCrowley]

Come on now- its not too much wear if you can actually try to have less than two tires in the air. The term is 4 wheeling... you guys make it more like 3 or even 2 wheeling sometimes! ;Dp; ;Dr;


Oh yeah, the ARB air locker is a type of limited slip device. A "locker" will make both tires on an axle turn the same even if one is in the air or one has more or less traction. Although some units have additional built in compromises including clutches. This is for great offroad, and is horrible onroad due to binding. This is when on tire is trying to rotate more revolutions than the other. This is called "binding". Its the same reason your TOD is not engaged under about 5 mph unless you slip and then it will engage.

A "limited slip" is similar except it will take the power from a spinning wheel and transfer it to the opposite wheel. Also known generically as a "posi" as in positraction. An antique domestic muscle car term. Rally cars and most hybrid offroad vehicles (ours included) have these. They are good for everything up to rockcrawling, although it is better to have a limited slip than not. Our unit happens to be one of the best (thanks Isuzu) and will hold up very well, but in extreme situations like wheels in the air a locker would be better. A limited slip is better offroad than a locker is onroad so like life- its all compromises.


The ARB is the best compromise. It is a true "locker" that uses an inflatable o-ring. It will drive as your front diff does now which is why you will notice if you ever get stuck only one tire will spin. Once 1 wheel reaches a breakaway point, all power will follow the path of least resistance. The ABR unit has a small air compressor mounted under your rig, and when you push the dash button, it will power on. This will inflate the o-ring in the diff and will force a set of gears together and act as a true offroad locker. Both tires will spin together even if one is on ice, and the other on asphalt. The fact that you have a limited slip rear will greatly help also. Then you can turn it off and drive once again stock. Usually if you are locked front and rear, there isnt many places you cannot go or get out of. The yin-You can have limited slips front and rear, but you would have to be in a true "rally" situation to appreciate it, and your tires would wear faster when cornering due to some binding. Some times in loose mud, snow, or ice you can turn the wheel and the vehicle will "shovel "straight. This can be precarious, but if you drive balls to the wall anyways it will get up and go with more traction. The Yang- You could also have ARB units front and rear, but you wouldnt have the onroad traction the stock limited slip gives when onroad, and you could leave it on, and you would probably break something with all the binding. This is why the addition of a front ARB to our already good setup enhances performance. Usually you will need the front axle to crawl over obstacles with less weight on them, and the weight is on the rear where the limited slip can distrubute it efficiently. When you are done, power off and it will drive stock. The only down side is BE EASY ON IT AS THE ARB WILL PUT ALOT OF FORCE ON YOUR FRONT CV JOINTS. An easy driver will win in this case.

[SPAZZ]

part numbers are RD44 and RD94

but with bigger taires, bigger gears, and a locker you will break your cv's offroad guarenteed!!!

[AlaskaVX]

From my research I only see 4.56 or 5.38 as upgrades (we have 4.30's stock). 5.38's is meant for 36"+ tires, 4.77 or 4.88's would be perfect for 33" tires. 4.77's would be pretty much stock and 4.88's I think would give you a bit more pep. You need the front and rear gears to match. As far as a locker in the front 10 bolt, I think Grandpa bob has that and has broken many CV's. If you get your front spinning and hopping, or need to take a hard turn at the top of a hill you will easily break our CV's. That is where the ARB locker comes in where you can turn it off for these maneuvers. A locker is only for offroad, and really only for going straight or close to it with an independant front end and 17 spline 10 bolt (weak axle for offroad). Lockers are not meant for someone who enjoys using the gas to get over stuff, more for crawling up and over things.

4 wheel drive cars are really only 2 wheel drive, without a traction device like a limited slip or locker.

There is a lot of work to put gears in, and I would highly suggest you get a gearing guru to do the work.

So anyone feel like going in on a group buy for 4.88 gears?

[Cyrk]

What would 4.88 gears do for none lifted VXs, I would love to add some more off the line pep to my SC VX... Would these gears kill top end?

[AlaskaVX]

Yes thats exactly what it would do. It gives you more power to the tire (more revs per tie rotation). Your top end suffers but you become quicker. I would not suggest putting 4.88's in a stock sized vx. Maybe 4.56's? Not sure how much of an improvement it would be though? You will have a higher rpm when on the highway so gas will suffer. I would say Isuzu put a lot of work into selecting the 4.30 gears for it, but when you mod it to make it bigger the gears need to change to keep the stock acceleration.

Here is a gear table scroll to bottom

[t2p]

I thought the VX was equipped with 4.30 ... or 4.33 gear ratio .....
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hmmm ......... gotta take a look .......

[lttlbddy]

Available gear ratios are 4.30, 4.55, 4.77 or 5.38.

My Amigo came with the 4.55. I ran 31s, 32s then 33s. While I had the 33s in, I switched to the 5.38 gears. Around town this combo was amazing as far as acceleration goes. Top end did suffer but that is not what my Amigo with the 2.6I4 is all about.

Shortly after the gear install, I switched to 35s. This combo is pretty good. Speedo error is around 8%. When the speedo says 75, true speed is 68-69 based on my GPS.

As for mileage, I was getting 15-16 with the 33/4.55 combo. I now get 16-18 with the 35/5.38 combo. The engine doesn't have to work as hard with the lower gearing, hence better mileage.

As for breaking axles, well, I broke one with the 33/4.55 combo and haven't broken one yet with the 35/5.38 combo. I think driving style has a lot to do with breaking axles.

Having run 4 different sized tires and 2 different gear sets, my opinion is the the 5.38s with the 35s is better than the stock 4.55 and 31s.

Bear in mind that the Amigo now has 185,000 miles on it.

Steve G

[AlaskaVX]

hey lttlbddy, where did you see 4.77's? will they work with our 10 and 12 bolt combo?

[t2p]

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The VX *IS* equipped with 4.30 axle ratio .....