E Type racing gearbox

Do the racing E Types use the factory all synchro gearbox? If not what it the box of choice?

Thanks, H

Hale, Group 44 used the EJ close ratio box that was only available in the S1 4.2 E. It’s the box most racers try to use as it has a 2.64:1 1st.
In my 4.2 E racer, I used a modified Moss CR box with a 1st gear ratio of 2.00:1.

Are you building a racer? What do the rules say, wrt which kind of 'box can be used?

I have probably asked the wrong question – I was trying to find out how much power the E Type box could take.
As this box was used in the S3 E Type it obviously would bolt up to a V12 and despite the increased displacement it seemed to “hang in”.
I haven’t had a problem with my S3 but I also don’t push it.
What this is really all about is the idea of putting a 420 box with overdrive into my 95 6L XJS which will be putting out much more hp than my S3.
I realise that everyone goes to a 5 speed which I also have but would rather retain the flavor of the original design.
The 6L will simply be a touring car but I would rather have a standard transmission and the OD would just add to it.

Many thanks for replying to my question.

Cheers, Hale

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I don’t think it will harm it: Jag gearboxes, in good nick, are incredibly durable and reliable 'boxes.

Just make sure it’s all in top shape.

The group 44 E’s made a lot more HP than your car will, but that’s not what destroys transmissions.
Transmissions are maximum Torque rated in 1st gear. That being said, the XJS manual trans was the lowest rated of all the All-synchro boxes due to it’s 3.238:1 1st gear ratio.
The highest rated trans was the E type CR trans with it’s 2.68 1st gear, that made it 20% stronger.
So in theory, if you want to use the Jag trans behind a 6L, then you definitely should be looking for an EJ gear set, as the KL gear set used in the V12 E is only 10% stronger.

Hale, I think your real problem will be the Torque rating of the OD.
Originally Jaguar was going to offer a 2 speed diff for the XJS as the OD was not considered to be adequate for the 5.3. It would be even less so for a 6L.
Your best bet would be a 5 speed, but a T5 with a 2.95:1 1st gear is only rated at 300 lb.ft., just adequate for the 5.3.
You can buy uprated gear sets for this trans that are rated at 330 lb.ft. that more than likely would survive if moderately driven in a heavy vehicle like an XJ.
I have driven a V12 E with a 6.8L with the T5 trans. but it’s real saving if driven hard, was it would spin the wheels due to the light weight of the vehicle.

Clearly many things to consider.
While the V12 has about the same hp as the 3 carb XK engine the torque is much higher.
I was thinking that the extra weight of the 420G – probably the only thing that weighed more than the XJS might offset that.
I am definitely going to open up the gearbox and try to figure out what the ratios are.

Many thanks for the replies as they have been welcome additions to my information pool.
This is a long term project and I want to get all the ducks lined up prior to taking the car off the road for the transplant.

Cheers, Hale

Hale, give me the gearbox No. and I will tell you the ratios.

I’m interested in how Hale will fool the computers to think there is still an electronic transmission fitted.

On a more fundamental note, I know more about cycling/motorcycling and clutch replacement than gearbox ratings. But doesn’t the highest torque stress and slippage/breakage risk occur when there is the highest resistance to progress - i.e. top gear not first gear?

Hence light weight reduces torque loadings and wide sticky tyres increase them.

Good question: an answer may be contained in this.


The max Torque load in the gearbox is a factor of the gear ratio. So 1st gear will produce the maximum, it’s why 1st gear is usually the one that fails the most.
If you look at a chart of Getrag or T5 transmissions that have a great range of ratios available, you will see a range of Torque Ratings, all directly related to the 1st gear ratio

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I hope to get a chance to go through the transmissions I have next week and get a number from the 420 – am I looking for the serial number or more likely some casting number on the case.
Regarding the engine management computer. To my best knowledge people don’t do anything with them when they do the change over. Then again most people are doing the swap on the earlier 5.3L cars.
Perhaps I will leave the 6L alone as it does have a 5 speed automatic (4 + lockup) and just use one of the earlier cars.
Again, thank you for your thought and contributions.

The casting No. tells you nothing as the same case was used for all gear sets.
If you use an electronic controlled trans, you will need a stand alone controller, which as far as I know, are only available for the GM and Ford trans.

When I placed a Supra W57 5 speed behind my S2 XJ V12, I was told by the engineer who sold me the parts that the Jaguar OD unit was not rated to take V12 torque

He was vastly experienced in these matters

OK, bear with me Norman - I suspect this could be a ‘teachable moment’ for me or others. The facts are not negotiable but I may be missing some or we may be viewing/describing the same things from opposite ends of the telescope…

Two data points:

  1. A racing cyclist with shoes locked onto the pedals can generate torque for 360 degrees of crank rotation. Maximum torque is generated when climbing steep hills and using the whole body out of the saddle including back and shoulders to work both pedals. Maximum vein-bulging torque is applied just before the rider stalls and falls, or or the chain snaps/slips. If at any point up the hill the rear tyre rides over gravel or ice, traction can instantly fail and the strain on rider and transmission suddenly reduces drastically. The lower the tyre grip the lower the torque stress that can be applied. A cyclist can do 40 km/h endlessly at practically zero torque on a warm-up bike with the back wheel off the ground. The chain never slips or breaks. Torque depends on resistant forces, right?

  2. A car with a slipping clutch can only apply a low stress to the transmission before clutch grip fails at lower than normal torque. If you need to get home in a car with a slipping clutch, it will slip worse in 4th gear than in 1st because torque stresses in the drive train are higher in the upper gears due to increased resistance.

I think of it very crudely as faster a drive spins the less stressed it is transmitting a given power output. It’s a nice shorthand for engineeringly-challenged people like me who get muddled with torque multipliers etc…

This is neatly demonstrated in motorcycles where the primary drive
(driven pinion spinning at crank speed) always uses far lighter chain than the big secondary drive spinning slower due to the primary drive reduction plus gearbox reduction, if any.

Paul Cangliosi sees more broken diffs at 2.88/3.07 than 3.54. He said:

“It seems to me that you have to look at the whole picture. Most production cars if you multiply the overall 1st ratios
(1st x axle) you end up with 8 to 10. A 6cylinder and 4 cylinder car in general tend to have an overall ratio of 9 to 10 range… Running something in the 6 to 7 range will usually kill something.”

Dick Vandermeyden, who knew his Jags, wrote:
“I could not agree more with Paul’s observations. If you want to use a 2.88 or 3.07 with an EJ gearbox, better be very gentle while accelerating from a full stop. Personally, I feel that an EJ gearbox should be used with a 3.54 or 3.31 differential only.

“For use with a 3.07 or 2.88, a KE gearbox should be used as a minimum, preferably modified for a 3.238 first gear in combination with the 2.88. That will make most premature gearbox and clutch failures go away.”

Does first gear max torque rating happen because that pair always uses the smallest pinion in any box? I am confused how the ratio that most easily causes traction breakaway (leading to lower torque loads) can stress a drive train more than the ratios that can load a transmission so hard it brings the engine to a dead stop or fries the clutch in a heartbeat.

Maybe it’s repeated lower shock loading rather than sustained highest torque?

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Peter, I bought my first E type in 1966, 54 years ago, and have basically worked on nothing but Jaguar’s since.
In all that time I have never come across a blown Jaguar diff that occurred in a Jaguar powered vehicle for any reason other than inadequate lubrication.
But i have definitely repaired a lot of transmissions with broken clusters.
If we assume that a 2.88 C&P is manufactured from the same material as the 3.54 C&P, then is mathematically impossible for the 2.88 to fail before the 3.54.
Assuming the max Torque value of 300 lb/ft. of a V12 with an EJ 1st gear of 2.68, then the max diff load would be 804 lb/ft. regardless of diff ratio.
That means because the 2.88 has a larger pinion than the 3,54 it has an 18% lower tooth load, therefore a much less chance of breakage.

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Ditto: saw worn ones, but never broken ones.

No worries (I’m practising my Strine, ETA 9 April)

I’ve never seen a ‘broken’ diff either, and the bigger the pinion the more abuse you’d expect it to stand (which is presumably why Ist gear is the weakest as well as being normally the most used. The gearbox thing’s a slightly different issue but life’s too short to type that much. It’s quicker done verbally some day.

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Let know itinerary and will try to arrange a meet.