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/MiscCarDocumentation/IMG_0517

Conway's 2001 Trooper rear axle:
http://tad.grosvenor.org/gallery/MiscCarDocumentation/2001_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!;Db; ;Db; ;Do; ;Dp; ;Dr; ;Dy;


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 (http://www.highriders.ca/documents/4x4calc.htm#Gear Ratio / Tire Size Table) scroll to bottom

[t2p]

I thought the VX was equipped with 4.30 ... or 4.33 gear ratio .....
.
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]

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

[AlaskaVX]

I have no idea how I got 4.11's in my head? 4.30 it is:mbrasd:

will edit other posts so noone gets confused

[SPAZZ]

477's came rare in Trooper's with Wide Tire OPtion... and yes there are 488's... I would be in for a group buy for the 488's if price was decent...will that be for new or used ring and pinions???

and yes..even with slow crawling 538's, larger tires, and a front locker will break the stock week cv's. better to replace cv's with high angle drivelines or just change out front axle for a way beefier one or SAS.

[kpaske]

From the looks of that chart, putting 33" tires on without changing the gears should give you better gas mileage. Why does this not seem to be the case? I believe my gas mileage has gone down (accounting for the 10% change in speedo/odo readings).

It seems that the 4.88 gears with 33" tires would be the combination closest to stock. I only occassionally offroad, so I'm mostly interested in on road characteristics, though I don't want to do anything to decrease the VX's stock offroading capabilities.

I would also consider mods that would make my VX peppier. I'm planning to purchase a supercharger within the next 6 months or so. Would the 4.88's be the best option for a SC VX with 33's?

[AlaskaVX]

I am just seeing if anyone is interested, because if we come up with a buch of people (20+) we can see if we could organize another group buy like the one for 5.38's on the 4x4wire board.

Is there 4.88's out there for the 12 bolt? or the 10 bolt? If not then this could get spendy ($500) But I really want them and am definately willing to throw that much cash at it.

kpaske, Yes I have 33" tires and am SCed

[kpaske]

I'm interested, but we'll have to see the final price tag. What would this include, and what else would need to be purchased?

[SPAZZ]

gear ratio means what Ring and Pinions you have. Usually when you buy gears it means you just get a front Ring and Pinion and a rear Ring and Pinion. Then you have to get the bearings, races, seals, and shims, pinion nuts, pinion seals, etc...necessary to set up your Ring and Pinions with your ratio choice up in your 3rd members. Yes, 488's are out there. each 3rd member costs around $250 for the parts to set up and then on top of that whatever $ the gear shop charges to set them up.

it is less expensive for you if you already have the 3rd members removed and you just drop them off at the gear shop, then pick them up and install them yourself. rear axle takes about an hour if every thing goes smooth...meaning no problems unforseen, such as in my case where your pinion welds itself to the outer bearing and race and will not come out:mad:

[Nazrat]

Originally posted by SPAZZ
gear ratio means what Ring and Pinions you have. Usually when you buy gears it means you just get a front Ring and Pinion and a rear Ring and Pinion. Then you have to get the bearings, races, seals, and shims, pinion nuts, pinion seals, etc...necessary to set up your Ring and Pinions with your ratio choice up in your 3rd members. Yes, 488's are out there. each 3rd member costs around $250 for the parts to set up and then on top of that whatever $ the gear shop charges to set them up.

it is less expensive for you if you already have the 3rd members removed and you just drop them off at the gear shop, then pick them up and install them yourself. rear axle takes about an hour if every thing goes smooth...meaning no problems unforseen, such as in my case where your pinion welds itself to the outer bearing and race and will not come out:mad:

You can't keep is in suspense here Spazz. What axles are you planning on swapping in for the 4.88s? Personally on my Trooper (My offroad vehicle) I'd like a low SAS with coil springs and a Toyota axle. That would let me run 4.88s up front. Then probably a matching rear Toy axle, or a Dana 44 or 9".

-Tad

[kpaske]

So should I consider an axle swap also, if I don't plan on doing much off roading? Would it give any advantages for street driving?

[t2p]

Absolutely not.
.
The gearing - 4.30 ratio - is already *very* low.
.
Oops ...... forget that .......
.
You did install large tires .... not sure why you installed the large tires if you don't plan on going off roading frequently .......... but that is just me ....... I'm a conservative one ........ and my opinion is about as high on the scale as plankton .....
.
33's ? - OUCH ....... you may need lower gears to compensate for those monsters .... your acceleration - on the road/wherever - will suffer with 33's installed ....... lower gearing will help to reduce this .....
.
some might actually prefer the effect of the taller tires ....... I would rather cruise on the highway at 2000 rpm than 2700 ...

[MrCrowley]

I just towed a trailer twice this weekend and have an interesting observation. I had a chance to get firewood from a buddy's farm from a HUGE oak tree that fell over. The first trip was the VX pulling about 3000 lbs (trailer towing capacity). It was on a backwoods Tennessee state hwy with plenty of long grades- same route for both trucks. Of course it pulled fine. On the second trip, I needed the Trooper due to the carrying of passengers and just to balance out the miles between the two. Knowing now that the troop has 4.56 diff gears now, and the VX 4.30, I have to say that even though the troop has more weight, it did seem to maintain the edge when towing uphill. Not that it toted it uphill faster, but the tranny seemed to not have to downshift as soon and seemed to be "easier" on the vehicle. I did play around in both with the power mode on and off. The only thing I could think was what the VX would have been like with 4.56 AND lower vehicle weight. Now I know why there wasnt as much acceleration difference between the two as I expected when I first test drove the VX. Of course I was blown away by the handling! Hell, I ought to just use the diff gears between the two because it sure wold be cheap. Maybe Ill buy 4.88 for the troop, and put my troop's 4.56 in the VX. Cheap mod! If someone wants to do a 4.56 swap the advantage is that every salvaged trooper has the 3rd member and gears already in it! If you want a minor change and want it cheap thats probably the way to go.

[Maugan_VX]

Maybe Ill buy 4.88 for the troop, and put my troop's 4.56 in the VX. Cheap mod!

Theoretically, if 4.88 gears existed for our vehicles, this would be possible. It would hardly be cheap though.

4.88 gearing does not exist for our rigs, and even if it did, that little difference in ratio is not worth the cost of buying and installing a whole new gearset.

[kpaske]

Originally posted by SPAZZ
part numbers are RD44 and RD94

SPAZZ - What are these the part numbers to?

I'm seriously considering doing a gear swap in the near future, along with a supercharger in the next 6-12 months. I'm currently running 33's with stock gears and want some more power and pep, but don't want to lose too much fuel efficiency or top end power (or break my CV's) so I don't think the 5.38's are the way to go. According to the chart posted elsewhere in this thread, it seems that the 4.88 ratio would compensate for my larger tires, and possibly give me a hair more power. At least it would return the ratio back to near stock.

From my research, the 4.88's look ideal. Some say they exist, others think they don't. If they DO exist, what did they come off of and/or where could I get them from?

[lttlbddy]

1) Those are ARB Locker part numbers.

2) 4.88 gear do NOT exist for Isuzu differentials. Your choices are 4.30, 4.55, 4.77, 5.38

Steve G

[kpaske]

Well, it seems the 4.77's are extremely rare. Even if I could find them, would it be a noticable improvement over the stock 4.30? Maybe I just need to go with 5.38's and 35" tires. ;Db; ;Db; ;Db;

Any thoughts on what else would need to be upgraded to make this combination possible?

[CIATexan]

Well if 4 30 gears is the highest gear ratio, is there anything greater (or less than that) Say like a 4:10. I need to suck some more gas milage outa this thing. What kinda milage are people getting around town and on the highway with their VX?

[Nazrat]

4.10s are available. There is a 2wd pickup with 4.10 gears in the 12-bolt rear diff, and the mid-90s Rodeos have 4.10s in the front 10-bolt diff.

-Tad

[CIATexan]

has anyone actually tried this???? Any thoughts on if id actually save gas??? or would the weight of the vehicle overpower the loss of power to teh wheels?

[kpaske]

The 4.10's should give you a slight increase in gas mileage, but I wouldn't expect much. Check out this web site and scroll to the bottom to see a chart of gear size vs. tire diameter: http://www.highriders.ca/documents/4x4calc.htm#Gear%20Ratio%20/%20Tire%20Size%20Table

[CIATexan]

Do you think it'd be more plausable to just get some 31's or 33' all terrains?