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[tartanzj]

Here's one for u,

I am trying to find what gear ratios are in my diffs but the small plates attached to the diff cover with all the info are not there. I have contacted local jeep dealer.....loads of help there!!

Can any of you guys help?

[tim_aka_tim]

1996 ZJ 2.5TD

[Steve B]

Put some tape on the tyre and some tape on the drive shaft.

Then count how many turns the driveshaft does to one tyre revolution.

If you have a jeep tj and it is std it will probably be around 3 drive shaft revs to 1 tyre rev.

ie 3.07:1

[Mike Pavelin]

I think they're 3.73:1 but to be sure if you take the rear cover off you'll see the ring gear. If you look around the edge of it it'll have some numbers stamped on it. If they're 41-11 that's 41 teeth on the ring gear and 11 on the pinion. 41 divided by 11 is 3.72727272 which is a 3.73:1 diff.

[Bubba]

that makes my brain hurt

[tartanzj]

I think they're 3.73:1 but to be sure if you take the rear cover off you'll see the ring gear. If you look around the edge of it it'll have some numbers stamped on it. If they're 41-11 that's 41 teeth on the ring gear and 11 on the pinion. 41 divided by 11 is 3.72727272 which is a 3.73:1 diff.

Thanxs Mike, will the nos. be visible w/o having to dis-assemble anything? or is technical ability going to be required

[Bubba]

just go with tipex on the tyre and on the flange rotate wheel once and coun the prop turns once for the wheel 3 and a smidge =307to1 if it were 3and ahalf 354to 3nad threequarters 373to i know it sounds a bit dumb  but it works

[tartanzj]

Right guys, now I'm well confused  :?  :?
Marked up the tyre and prop, hung up the back end and rotated the wheel once...... prop rotated about 1.8 rotations.
Am I missing something, surely the ratio is not that high!!!

[tim_aka_tim]

That method sounds iffy to me. There's an LSD there that doesn't want you to do what you're doing.
Surely you would need to have either the diff locked with both wheels jacked, or both wheels on the
road somehow.

[greggmo]

are you planning a regear or rebuild then? i would say mike is right cos he usualy is

[Mike Pavelin]

Get both rears off the ground and turn 'em together (you need long arms) while someone watches the propshaft.

[tartanzj]

Sorry, bad wording. I lifted both rear wheels off the ground and rotated a single wheel (100K miles on factory LSD - got an open diff now!!).

Greggmo not planning a rebuild, I drive it and break it, someone else fixes it so a rebuild would be expensive I guess. I have a bigger lift on the way and am just trying to get my head around tire sizes and possibly re-gearing. I run with 31" at moment and it is fine both on and off road. Only time I struggle is hill start with 2+ tonnes behind on trailer, but that's not often. When I get lift on I know I'll end up looking at larger rubber again so was wanting to know my current gearing to see if anyone was running something similar with larger tyres.

Mike are you saying both wheels must be rotated forward together for me to calculate my ratio?

[greggmo]

both wheels in the same direction mate. think you will struggle with any bigger boots on mate and your fuel bill will double. go for a regear if you want bigger boots, it,s not as expensive as you might think. speak to mik on here for an idea on cost.

[Mik]

Right guys, now I'm well confused  :?  :?
Marked up the tyre and prop, hung up the back end and rotated the wheel once...... prop rotated about 1.8 rotations.
Am I missing something, surely the ratio is not that high!!!

It will be close but you need to be more accurate.

1.8 rotations x2 gives you a 3.6:1 ratio (which doesnt exist) so its either

1.775 rotations giving you a 3.55:1 ratio or more likely...

1.865 rotations giving you a 3.73:1 (What Mike said)


For greater accuracy using this simple method, count the number of wheel revolutions per single rev of the prop (or better still, 10 revs of the prop then divide it when youve done)