XJ6 & XJ12 Series I, II & III 1968-1992

Diff question

 
  #1  
Old 08-06-2014, 10:30 PM
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Is it possible to change the rear gearing from 2.88(i think its around this stock, may be mistaken) to something higher? 4.10? Maybe?
1984 xj6 btw
 
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Old 08-06-2014, 11:09 PM
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Originally Posted by sunchip View Post
Is it possible to change the rear gearing from 2.88(i think its around this stock, may be mistaken) to something higher? 4.10? Maybe?
1984 xj6 btw
Why in the World do you want 4.10?? That's a truck diff! Are you drag racing it? Mine is 3.31 and that's plenty behind a 700R4.
(';')
 
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Old 08-07-2014, 08:18 AM
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Ya i was planning on racing it, ive built up a 400hp 350sbc and id rather not replace the entire rear end if i can.

Id just like to know is it possible to change just the rear gears with replacing the diff
 
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Old 08-07-2014, 08:26 AM
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The usual Jag ratios for the older diffs are 2.88 3.07 3.31 3.54 3.77 4.09

Other possibilities are out there as the diff is apparently a kissin' cousin to the well known Dana 44.

I would contact Icsamerica as he has a good handle on this subject

There's some info in this thread that might help

https://www.jaguarforums.com/forum/x...f-head-123057/


Cheers
DD
 
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Old 08-07-2014, 09:00 AM
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Originally Posted by sunchip View Post
Ya i was planning on racing it, ive built up a 400hp 350sbc and id rather not replace the entire rear end if i can.

Id just like to know is it possible to change just the rear gears with replacing the diff
A few thoughts. The diff carrier you have is spaced for tall gear ratios. All numerically lower gears, aftermarket or OE use a carrier with a different offset so you can not install a new ring and pinion on to the carrier you have, unless you use a "thick gear".

Since you're racing I'd avoid the thick gear science project. The best thing to do is purchase a new 19 spline Auburn locker, Dana 44 gear set, Dana 44 side bearings. Then install a standard dana 44 yoke and matching drive shaft, this can get you any Dana 44 ratio you want and you'll have a modern system for solid launches.

You'll also need to manage cage roll. The rear IRS will rotate and cause wheel hop / Axle tramp and loss of traction when approximately 350HP is applied.
https://www.jaguarforums.com/forum/x...shings-119418/

The largest rear tire you can fit in the rear wheel well with clearance is a 235 series. That's not enough for a hard launch with a tall diff. A larger tire can be fitted but flaring the rear wheel well is required.
 
The following 2 users liked this post by icsamerica:
Calhale (08-07-2014), sunchip (08-07-2014)
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Old 08-07-2014, 06:24 PM
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add to isca; i have seen the entire rear subframe ripped out of XJ-XJS jags, when adding big power and big tires, especially with old and rusty mounts.
 
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Old 08-09-2014, 03:12 PM
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my rear sub-frame ?mount? has snapped at one side so when its on the hoist the drivers side is about 4-5 inches lower. I'm going to try and figure out a way to fix this up, but is there any other way to secure the sub-frame if the old mounts are too far gone?
 
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Old 08-10-2014, 02:42 PM
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mount it solid to the car(no rubber mounts), makes for a rough ride and hear all types of road noise, but if its a race car be alright!

there are stories about the actual cage twisting ,and the outer aluminum hubs cracking.

Jag type rear suspension was never designed for hard accelleration with hi-grip tyres.
 
 
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