Changing diff ratio

[skodajag]

I'm sure this must have been addressed before but a quick search didn't throw up an answer to my question, which is: how costly and difficult is it to change the rear diff ratio on the E Type (series 2)?

[mgcjag]

Hi...whats your name...please try to put it with your car model in the signature area.....two options..rebuild your existing diff or replace with another......second hand diffs are around £500....plus around £500 for a professional to rebuild it....depending what ratio you want prices vary....re how difficult to replace depends on your ability..first you have to remove the IRS ratio can only be changed by changing the internals..Full details in the service manual.......for just refurbing the diff have a word with Universal Axels in Kidderminster...run by two guys..old school....Steve

[politeperson]

I did it and it was pretty easy. Well worth it IMHO.

I put a 2.88 in and it was very successful. I have been all over Europe now keeping the 4 speed Jaguar gearbox.

It was from an XJS and was £400.

It turned smoothly with little backlash. I had the flange and output seals changed prior to fitting as they were the originals. The unit did not seem to need rebuilding at the time.

It has been as quiet as a mouse since.

James

http://forum.etypeuk.com/viewtopic.php? ... &hilit=xjs

[Tom W]

I’ve just rebuilt my IRS and swapped the 3.54 LSD diff for a 2.88 LSD. I took the back cover off the new diff,nothing seemed worn, so I fitted it as is after repainting the outside and cleaning up the threads. So far, it’s quiet and leak free. I think most of these 2.88 diffs come from autos, so probably lead an easier life.

I paid about £500 for my diff. 2.88s seem to be a bit more affordable than the ratios that were originally fitted to E-types. The alternative is to get your original diff professionally rebuilt with a new crown wheel and pinion for the ratio you want.

The most expensive part of my swap was rebuilding everything else in the IRS that I found to be worn whilst it was apart.

[PeterCrespin]

The alternative is to get your original diff professionally rebuilt with a new crown wheel and pinion for the ratio you want.

You can't just fit a crownwheel and pinion to go from 3.54 to 2.88 - the LSD carrier has the flange in a different place to accommodate the bigger pinion. There are three carriers; one for the very low ratios, one for mid-range group and one for the tallest ratios. You can fudge it with spacers and longer bolts sometimes but I wouldn't fancy it. Ideally, buy the whole diff in the ratio you want so it's built right.

[abowie]

I drove a 2.88 and found it a trifle long for my taste and ended up fitting a 3.07 which I'm very happy with. I just used a diff centre from an XJ.

[Tom W]

You can fudge it with spacers and longer bolts sometimes but I wouldn't fancy it. Ideally, buy the whole diff in the ratio you want so it's built right.

You can only go from higher to lower ratios this way, but as you say, not an ideal solution.

I should have elaborated in my reply that not every diff can be rebuilt to every ratio. I thought it was only the 2.88 that has the high range carrier though, and every other E-type diff can be rebuilt to any other E-type ratio between 3.54 and 3.07?

Unless you’re going to do as I did and risk fitting a diff that’s an unknown quantity, then there’s the cost of rebuilding a diff involved. In which case why not have the original professionally rebuilt with a new crown wheel and pinion to swap the ratio, rather than rebuild a 2nd hand diff? Unless the OP specifically wants a 2.88.

I went for a 2.88 as it was the cheap option, thankfully the risk paid off. I have to say it’s really transformed the car. Motorway cruising is far more refined. It doesn’t really seem to have made that much difference to in gear acceleration either, the car still feels very fast, though the gears are held onto a lot longer, so it’s less frantic. For low speed manoeuvres starting up hill in first it possibly feels a bit high, but there aren’t many steep hills where I live so this isn’t an issue.

It’s made the car a lot faster in real terms. If you like accelerating to the redline each time, 1st and 2nd are now the only options, with 3rd now taking you way over the speed limit. Roughly, changing from 3.54 to 2.88 seems to be a 15% increase in speed for the same revs.

[mgcjag]

Just to add that changing the diff ratio will cause you speedo to read incorrect so will need re calibrating..also if you actually change the diff you will need to keep your existing diff mount brackets.... Steve

[PeterCrespin]

"You can only go from higher to lower ratios this way, but as you say, not an ideal solution."

Agree totally, which is why I said 'sometimes' rather than spell out you can't make a crown wheel 'thinner' by adding spacers etc.

"I should have elaborated in my reply that not every diff can be rebuilt to every ratio."

Nah, it was fine. Same as above - you can't put every detail in every post.

"I thought it was only the 2.88 that has the high range carrier though, and every other E-type diff can be rebuilt to any other E-type ratio between 3.54 and 3.07?"

Correct-ish, since only short-circuit E-Type racers would want to go below 3.54 (although 3.54 is technically in the middle of the options). I have a pic somewhere from a time I had all three LSD carriers in front of me and lined them up with the flanges like three steps. There is a ratio taller than 2.88 (2.69?) but I've never seen one so 2.88 is the only one for that carrier. The other one is used on cars like the 2.4/3.4 Mk2 and 2.8 XJ IIRC. Commonest ratios are 3.77 and 4.10 .

With a 1.88 first and 0.77 fourth, I had to use a 4.10 axle on the D, as 3.54 would be a bit hard on the clutch, being good for 70 mph at 5500 rpm with the huge 6.50 x 16" Blockleys.

"I went for a 2.88 as it was the cheap option, thankfully the risk paid off. ...For low speed manoeuvres starting up hill in first it possibly feels a bit high, but there aren’t many steep hills where I live so this isn’t an issue."

Exactly. Lake District or Alpine hairpins can abuse the clutch a bit two-up, but not everyone lives in Windermere or Winterthur.

"Roughly, changing from 3.54 to 2.88 seems to be a 15% increase in speed for the same revs."

And the same reduction in torque, but there's plenty more where that came from

[mark10337]

Winterthur is bloody flat. but wonderful to see the reference and linguistically it worked very well

[Lost Horizon]

I drove a 2.88 and found it a trifle long for my taste and ended up fitting a 3.07 which I'm very happy with. I just used a diff centre from an XJ.

I felt the same, and settled on 3.07 for my restoration. Have approx. 2,000 miles on it now, and it's just right for the city, on the highways and in the mountains Link below:

http://forum.etypeuk.com/viewtopic.php? ... =40#p98280