YAY! Another regear question, but this one is different!

[Fergie]

Okay, so I have a 1995 XJ with the RC-D30 and 8.25" axles:

1. I don't want 4.10s or anything that high(numerically)
2. I don't plan to run anything but 30s(*MIGHT* got to 31s eventually, but not for a *LONG* time).
3. I do some light/moderate towing.

So here are the questions:

Where do I find 3.91s for my RC-D30(obligatory "where do I..." question)?
Has anyone regeared to 3.91s(obligatory "has anyone..." question)?
Are 3.91s THAT much better than 3.73s?(3.73s are much easier to find)
Will 3.91s work with a factory TracLoc, or a TrueTrac(<--I think that is the gear driven LSD)?

I'll edit this if I have more questions, but I would really appreciate some input on these questions. Thanks for helping.

Fergie

 

[RCP Phx]

Sorry but I dont know of anyone w/ the 3.9 series gears for the D30.Go with the 3.73's.

 

[ChuckD]

And if you could find 3.90, then you might as well go 4.10.

 

[Kejtar]

One big question:
is your XJ stick or auto?

If stick.. then definately think about 4.11's. I have my stick with 4.11's and for about 8 months I drove with 235's on... and except it ran high rpms' at 80mpg (about 3K or so, but it's well within tolerable range) I loved it!!!

Kejtar

 

[Fergie]

It is an auto. I REALLY dont want to go into the 4.XX range because I dont need to. I am going to run 30s for a very long time.

I have been looking though, and it looks as though 3.73s are the only way to go(unless someone knows something I dont)

Fergie

 

[Bronco]

If you want to look at the numbers, I set up a spreadsheet that lets you put up to three setups side by side and graph them speed over RPM. If you want to send me your Email on a PM I’ll send it to you.

 

[XJFREK]

I was also going to go to the 3.93's but the shop then discovered I had a 8.25 in the rear(no tag and I bought it used). I am planning on going to 31's this year but I also tow a 3500lb camper often. I have an auto and was thinking of going up to the 4.11's but the shop said I should be running at least 33's before doing that. Yet I have seen charts which list the 4.11's as being in an acceptable range. I tow pretty long distances but it's also my daily driver and I don't want to run high rpm's every day. I have a 94 sport and am currently running 235/75R 15's. On mild hills while towing the stock gearing is adequate at best. But on steep hills I can't even hold my speed. Anybody out there have a similar situation? Any input or advice would be greatly appreciated.

 

[Beezil]

if yours is auto, then you have 3.55's....

going to 3.73 or 3.9 IMHO is not worth it.

You will probably NOT feel the difference on such a small jump.

At 65MPH in overdrive(.71), and 30" tires (30.0 used in equation) your rpms will be:

3.55-1835
3.73-1928
3.92-2026

I'd save your money. I think it would be more important to dial in your gearing on a stick, since you have a "direct hook up", but you are lucky to have a torque convertor working for you....

 

[Matt]

Beez hit the nail on the head - don't bother jumping up a single increment - you will not notice much difference and your auto will be very forgiving...

I held out and ran 33" boggers with 3.55 gears and an auto - it still cruised down the freeway fine (was a little lacking on the hills) but my next jump was up to 4.88's - which I loved with the 33's but are just ok with 38's

6.5:1 would be what I would run now if the RC could accept it but unfortunately 4.88 is as deep as the RC30 can go - perhaps when I get bored down the line I will add a 9" center section to the tubes and outers I have now... probably not; but who knows

 

[woody]

Plus with the D30, a different carrier is required beyond the 3.55 you likely have with your auto. The 8.25 carrier is good for all available ratios (3.92 may be avail in Dodge p/u?)

So...since gearing up to 4.xx isn't in the cards...maximize what you have 'around' those factory gears. Having a shop regear both ends is a fairly expensive upgrade, but if you could get ahold of used 3.73 gears & a front carrier at low cost, did the swap yourself etc...it wouldn't be a 'stupid' upgrade...just not a lot of 'bang.' With that in mind:

In 12-2000 Petersens 4W&OR mag did a bolt on upgrade for a (stock 96, AW4 3.55:1) HO 4.0 Using Turbo City parts. They did a cat-back, airtube/K&N, bored TB, MAP adjustor (A $635 kit, but the MAP cost 8 HP so it was deleted for the final test...without it it would be a $550 kit)

Rear wheel HP/Torque peak #s:
Stock HP: 135 @ 4200-4400; Torque: 193 @ 3000
Modded HP: 158 @ 4400; Torque: 216 @ 3000
Stock HP at the torque peak rpm: 110 @ 3000
Modded HP " " : 127 @ 3000
Using $544, thats $24 per extra peak HP and LB/FT (pretty cheap really)

I'd suspect that adding a 'good' header like a Borla, a free flowing head pipe, hi-flow cat would add a bit more oomph, though maybe not where you need it in the RPM band. A higher performance cam ICW those other goodies should help too, but remember that you aren't really after top-end HP. It seems that the torque #s down low increase along with the peak HP, which is good

A 'nut' could take all of the above, then clean up the head/manifolds (gasket match) for more flow, and have a pretty healthy 4.0l but at what point ya want to quit $pending and/or sinking hours of labor/downtime into your Jeep is a question.

 

[Fergie]

DAMN!!! I hate it when resonable people speak up. J\K though, thanks for all the input, as you will prolly end up saving me some money.

I already have a custom cat-back form the local muffler shop, and willl have an ARB snorkel soon...($150 brand new...hahahaha). I want to keep the engine as basic as possible, not doing anything that will decrease its longevity, but adding a little power.

The reason I ask about the *small* regear, is that I noticed a difference going from the 225s I had, to the 30s on there now. I am semi-concerned about gas-mileage, but buying gas is necessary, and I am no leadfoot. Hell, I drive at 68mph on the interstates(drives my gf crazy, shes from MD).

My concern is lugging the engine, or putting too much stress/strain on drivetrain and parts. I want my XJ to last a VERY long time. And I figure a regear will solve this dilemma.

Thanks for reading so much, and keep the comments coming.

Fergie

 

[xjmike]

I have a 2000 with 31's running 3.55's....I added some of the above mentioned power adds and noticed a BIG differance......on hills that made my jeep down shift before were no problem.......I wouldn't waste the time to re-gear in your situation....just my 2 cents

 

[macgyvr]

Dodge Dakotas and Durangos came with a 3.91 or maybe it was 3.92 gear ratio. Some of them I know have a six lug 8.25 rear axle, that would get the rear gear ratio. The front is IFS, I can't confirm it but it sure looks like a D30 center section, it wouldn't be reverse cut, but it might be something to check out.

mac '4.10s are the answer to everything' gyvr

 

[XJFREK]

Well, I recently added a high flow intake and a Gibson stainless header. I will hopefully get a bored out throttle body here in a month or 2. I put a custom 2 3/4 in cat-back on about a year ago but I still have the stock cat. I haven't towed the trailer yet since adding those mods so I will evaluate the situation then. The cat might be going soon anyway, there's somethin rattlin under there somewhere. Gonna hit the exhaust shop tuesday to have them give it a look. Thanks for the info and opinions. Further ideas or views are welcome as well. I love these new forums.

 

[Super mud]

Find a d30/d44 out of a 80s xj with towing package (3.73s I beleive) would be the only way I would.
I'm on 31s and actually regearing soon cause I have a very cheap oppurtunity to do it. I was planning to stay on 3.55s cause it runs awesome with them (87 renix + motor mods) has no problem keeping up with traffic on the hills and can hit most of them in OD. Even though it does run awesome I suppose theres room for improvement so I'll give it a try
I'm putting a built lsd in my 8.8 and better springs so while I'm at it found brand new mustang 4.10s for 100$. Then found a non CAD D30 out of a 86 2.8l xj with factory 4.10s which I will build to my liking maybe even finding a used ARB locker for it in time. So like 200$ to regear in my case plus a better front axle and maybe some extra goodies which won't take much extra effort to do while I'm at it.

 

[Johnnie Walker]

8 year old thread back at the top.. right on..