Topic: Confused about gearing (Read 25726 times)

Yakko · « **on:** February 25, 2015, 10:21:33 AM »

Hi.

I'm confused about gearing, hoping someone can help me make sense of it all.

I've got a 1998 TJ 4.0 manual, according to the build sheet I got from Jeep its got 3.07 rear axle ratio in it currently (D30 front D44 rear).

I've put 31s on it, but wish I'd gone for 33s and am slowely thinking about a regear, I'd like to get back to standard speed to rpm ratio.

All the forums suggest that 4.56 is the right ratio for 33s, but if I look at a gearing calculator (e.g. http://www.jeep4x4center.com/calculators/index.htm) it looks like 4.56 is way too high and that 3.77ish is closer to factory.

This feels right as 4.56 is nearly 50% higher than 3.07, but the wheels are only 14% taller.

What have I missed?

I know I could just accept the advice of the various forums, but I'd like to understand it myself!

Thanks

Yakko · « **Reply #1 on:** February 25, 2015, 10:24:56 AM »

Ahhh, it's just hit me. Is it because 3.07 is particually tall gearing for a Jeep and that people are recommending 4.56 to get back to factory ratios for Jeeps that left the factory on shorter gearing?

In which case, why did Jeep put 3.07s in my Jeep when others are much shorter geared?

Brachunky · « **Reply #2 on:** February 25, 2015, 10:53:02 AM »

Yakko, you have just made me think to check what ratios I have on my 97

Runs well on 31's though!

Yakko · « **Reply #3 on:** February 25, 2015, 11:06:25 AM »

Mine drives ok on 31s, but is noticeably less perky than it was on the 28.8s it came out of the factory on. Most noticeable climbing hills in 4th.

JamesH · « **Reply #4 on:** February 25, 2015, 11:25:18 AM »

The diameter / circumference of the new tyres is one thing but normally on modified Jeeps there is a combination effect of bigger tyres, higher suspension, more weight and the result of more drag. This means the lower gears (higher numbers) is what works best / feels best.

As most Jeeps are great at high motorway speeds over the speed limit and the engines are actually quite happy to rev a bit then no harm really comes from going a bit low with the gears.

wildwood · « **Reply #5 on:** February 25, 2015, 11:47:11 AM »

Tis weight and drag.....
Mathematically 4.56 is OK for 35s......

I had 33s and it was great ...it did what it should, went up to 80 if you really wanted and would go down to 30 in 5th......

I then put 35s on and was a slug.....ll60 was OK any more and you knew you were just pissing fuel out the back..... Below 45 50 it was gagging fora down change.......

Was great off road though

Now I've got 40's and 5.38 in the axle .......but although mathematically correct I bet the weight would be against it if it ever went on road

Ezz · « **Reply #6 on:** February 25, 2015, 12:18:48 PM »

33s and 4.56 is the way to go but

If you've gone up to 31s but wish you went to 33s why not do a proper job and go 35s and 4.88?

I'm on 37s and 5.38 but not driven it yet, not stock axles either

Yakko · « **Reply #7 on:** February 25, 2015, 01:05:25 PM »

Thanks for all the quick replies all.

Ezz, I'd heard that the standard axles didn't really like 35s? Also, I don't really want to lift much more than 3.5 inches otherwise it looks like it becomes a bit of a ballache.

Thought 33s were a good compromise of size, ease of install and ability to keep using the car as Dog transport (which is how I justified it to the Mrs in the first place!)

Yakko · « **Reply #8 on:** February 25, 2015, 06:27:41 PM »

Hmm. This is starting to sound like it's going to be more expensive than I'd hoped.

Am I right in thinking that if I can find a 2.5L TJ, the diffs from that are 4.10s and should just drop straight into my axles? Does it matter that the 2.5s won't have Dana 44 rear axles?

Err, I guess what I'm saying is that I haven't got a clue. What's the cheapest way of getting my axles OK for 33s? I think 4.10s would be OK.

georgen · « **Reply #9 on:** February 25, 2015, 06:50:47 PM »

I thought all the TJ,s over here came with d44 rear and d30 front not just the 4.0L, if I am wrong no doubt someone will come along and shoot me

On the Gearing front I have 4.88 on 33,s, next set of tyres will be 35" but still think if you use your TJ more onroad than off 4.56 and 35" would be fine. if you can get a pair of 4.10 Cheap and could do it yourselve saving money it would make a difference and 33" would be tolerable but 33,s on 3.07 is awful, what ever you end up doing you also have to order a speedo drive cog for your gearing and tyre size to correct the speedo.
Have fun and if I have learned one thing, the words Jeep TJ and Cheap rarely end up in the same sentence.

Mike Pavelin · « **Reply #10 on:** February 25, 2015, 06:52:45 PM »

All UK spec TJs have D44 rear axles. 4.11 is OK for 33s, to be honest, I find 4.56 is a liitle low for street use anyway. If you can find a decent pair from a 2.5TJ, it's a good low cost option.

Yakko · « **Reply #11 on:** February 25, 2015, 07:02:42 PM »

OK, thanks chaps, that's really useful.

Awaiting a quote from someone to fit 4.56s. In the meantime, someone sell me some 4.10 diffs!

isle of man · « **Reply #12 on:** February 25, 2015, 07:20:31 PM »

33" tyres and 4.56 gears work in manual gear box - one must also consider automatic, so 4.11 works equally well...END OF !!!

gazjeep · « **Reply #13 on:** February 25, 2015, 09:04:31 PM »

Got 4.10 on 31's in an Auto TJ, its only 3 speed & needs it for downhill control

Yakko · « **Reply #14 on:** February 25, 2015, 09:54:54 PM »

Don't know why I didn't consider 4.10s before, just done the gearing calculator (http://www.grimmjeeper.com/gears.html - bloody good) and that looks like it'll be spot on.

Anybody got a bottomless pile of 4.10 diffs? Or know where I could get hold of some?

Yakko · « **Reply #15 on:** February 26, 2015, 12:34:38 PM »

Might have found some complete axles off a 2.5 TJ. Are the axles a straight swap? Assume the swap is pretty easy? Basically had the axles off to fit my lift anyway.

wildwood · « **Reply #16 on:** February 26, 2015, 01:01:40 PM »

TJ to TJ should be a straight swap.....

You'll also end up with useful trail spares like the rear half shafts and the front drive shafts with the UJs already there for when you have an Offroad redmist moment.

bisleywrangler · « **Reply #17 on:** February 26, 2015, 01:17:47 PM »

I have a TJ with 33's on it was awful on the standard 3.07, I couldn't use 5th at all. I went for a Cherokee 2.5 hpd30 in the front and changed the rear diff and r&p to match, so it's now running 4.1 ratio. I love it, will do 80 on the motorway no problem and will pull 30 in 5th now. It's the cheapest way to change gearing I could find.

Yakko · « **Reply #18 on:** February 26, 2015, 02:50:46 PM »

Thanks for your continuing advice all.

Now I just have to justify to myself that its worth it all to go from 31s to 33s.

wildwood · « **Reply #19 on:** February 26, 2015, 03:27:09 PM »

With 33s you have a wide choice.....

Apart from the many tread patterns......some suitable only for road and some only for mud and Off road, you then have the choice of width...... Super skinny 9.50 that used to be popular with mud lovers and the staple of the Jeep community the 12.50
Add to that the 10.50 that's been around a few years that allows fitment without the need for wider arches and is lighter so giving better acceleration and mpg

So much choice

JamesH · « **Reply #20 on:** February 26, 2015, 05:40:51 PM »

Even 16s / 17s and metric tyres as there are quite a few 32/33" ones to choose from.

Yakko · « **Reply #21 on:** February 27, 2015, 09:27:05 AM »

Right, pair of 2.5 TJ axles on their way.

I've also bought a pair of Aussie Lockers, they were surprisingly cheap and I figured it'd be easier to put them in while I had the axles off the car. They seem a little marmite on the forums, but I've experience driving rear wheel drive cars with brutal LSDs, so I'll see how it goes. Can always take the rear out if it's a pain.

Getting them delivered when the Mrs is out as the honeymoon fund just took a hit.

JamesH · « **Reply #22 on:** February 27, 2015, 09:48:45 AM »

Good work

neilh · « **Reply #23 on:** February 27, 2015, 10:23:25 AM »

Sounds like fun - I'd be interested how you get on in case we go down that route

Might have to pop over and take a look some time

bisleywrangler · « **Reply #24 on:** February 27, 2015, 11:37:22 AM »

Want to sell me your d44 rear?

Author Topic: Confused about gearing (Read 25726 times)

Yakko

Yakko

Yakko

Yakko

Yakko

georgen

Mike Pavelin

Yakko

Yakko

Yakko

Yakko

Yakko

neilh