2020 - Manual Transmission Conversion in Houston

There are lots five to 15-year-old posts on this. A few from 2017. I assume the market has changed in three to 10 years.

Anyone have any recent experience in a conversion?

Anyone have parts to sell?

I am looking to do a T-5, Muncie or Super T-10 conversion for my '84. I have a parts '77 which should have a 3.XX differential. A ring and pinion to any ratio under the sun is not too expensive.

Prices around $7k are not realistic for what our cars are worth. I would like to hit $3k.

I would sincerely appreciate current recommendations and leads. Another whole car is an option for the right parts.


Houston, TX

Check eBay UK on regular basis. Not long ago there was v12 XJS 85’ manual advertised for £3k. Full of brownie, probably it would snap in a half if lifted. Definitely went cheaper to the breaker or person with your interests. If breaker was a winner - it will reappear on eBay shortly - just let them know what you want, with overseas freight still should be much much cheaper than $3k

Many thanks for the lead. I don’t think this is as hard as it appears…


Sounds like you wan to DIY it instead of a conversion kit
. The only place in USA I know that still sells bits instead of a kit is: http://www.vintagejag.com/Parts/Transmission_Conversions.html. From them, you’d get just a bellhousing.

5speeds.com may still sell a bellhousing but it appears not. There’s a place in UK too but you need a transmission not cheap and common in USA (Gertag), and another in Australia called Dellow but it’s the same problem with obscure-in-USA Aussie market tranny.

Then for a conversion of pedal box from just brake to two pedal, call this guy (but be prepared to wait). http://www.oldjaguarparts.net/ If you’re an iron monger and machinist you could DIY it? For $500 I wouldn’t bother.

Then find a used or new tremec TKO, figure out a clutch and flywheel (Fidanza seems popular), have the driveshaft shortened…

And then you’ll find out it stalls, so the ECU has to be sent to Roger Bywater … http://aj6engineering.co.uk/

Good luck! I’ve got a pile of bits from another enthusiasts abandoned project and will be on a similar path. I think I have the 5speeds bell housing and a factory LHD pedal box but the rest is still vague.


You might contact Dellow Conversions; they offer adapters (and possibly bell housings) for the V12. They have an adapter to fit a Chevy pattern auto to the V12…maybe use a GM bell and T5.
They are in Australia so shipping is going to be high.

Take a look at Simply Performance in the UK, they do loads of conversion kits and I am waiting for mine to arrive. Still looking around £4k with the tax though…

Simply Performance is another Gertag based kit. $5300+shipping! Even if you could buy the adapter ring separately, that’d be a tough transmission to get in USA.

The big benefit is dropping the slush box. The big cost is going to five speeds. The best option for bang per buck is factory four speed which I have. The factory bell and flywheel are available new or used No change to gearbox mount or drive shaft, all stock, as per the XJS manual. Should come in under three grand.

If you definitely want 5-sp I have an adapter to fit a BMW or earlier Jag Getrag 265 to a stock bell, or a repairable John’s Cars quarterbreed adapter and hydraulic throw-out to fit a T5 to the back of a Borg Warner auto bell. Both very cheap to get you started but lots more work than stock.

The Ford Mustang uses a Getrag. Different?

The Getrag (wow I’ve been spelling that wrong for years) they use in XJS is a 265, so you have to trash an M3 to get one in USA. I think the mustang uses an MT82 if Google is correct :slight_smile: Probably different enough?

Didn’t your XJS have a Tremec or Borg Warner T5 out of a Mustang? That’s basically the TKO without later updates.

I think it was fairly common on period BMW sixes but don’t know if BMW were like Jag and hardly sold any manuals in the US.

The short 265 needs a linkage to bring the lever forward for E-types (I fitted one to mine) and the later ones had no cable speedo drive, but at least with the small adapter ring you can use a stock Bell/Flywheel/Clutch. Unless you get it cheap from a breakers yard I wouldn’t struggle to do this conversion as it’s not a great box anyway. Value-wise, you really can’t do much better than the cheapest option: 4-speed factory using all stock parts.

True, a five speed can give you an overdrive fifth, but you can adjust the diff ratio later if you feel the need. ANY manual V12 is a transformed car at any ratios but the diff can be adjusted for preferred mode [cruising with a 2.88 or 3.07, or acceleration with a 3.54 or 3.31].

American 4.2 E-type guys like to swap to 2.88 as their 3.54s make the car a bit busy at illegal speeds and first gear is over very quickly. Many V12s have the 2.88 so they are great for fast cruising. But a V12 has an extra 1500 rpm to play with so swapping to 3.54 gives great acceleration and the engine stays relaxed at speed.

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Why? The Coyote engine is considerably more powerful than the Jaguar V12, so whatever is used in the Mustang should work. The XJ-S V12 didn’t come with any Getrag, so it’s not as though you have to stick with originality.

I meant the Getrag they use in the Getrag kits is the 265. If you made your own adapter ring like I believe you did, I certainly don’t know a reason you couldn’t use the Mustang Getrag.

Which you might wanna do well ahead of time.

Last time I sent an ECU to Roger (two years ago, maybe?) he had a several-months-long backlog of work. And I just gotta think he’ll be retiring more sooner than later.



Many thanks for the great responses on the transmission conversion. I am looking at all of them and trying to absorb all the information.

Vintage Jag bellhousing seems a viable path. Are flywheels open? Would the dimensions of a stock flywheel work with a Centerforce clutch in a Muncie?

Information hunting will be a fun project the next few days.



Like all the others, thank you for the time to respond.

I was not aware that a manual was available. All-knowing Wiki implies only the earliest XJS had it available.

Aware of any other model cars I should be looking for?

I am more interested in a 4-speed or 70’s-era 5-speed. I have a parts '77 with a complete differential which I need to count revolutions to check its ratio, so 5-speed is still open. No interest in a 6-speed or Getrag.


Thanks for all the information you share on the forum. I enjoy reading your thoughts.

John’s comment that the ECU will need an update makes sense, but I am not sure why. I suppose it is because of the advance curve not keeping pace with the new transmission’s RPM changes. That correct?


Thank you

I think the main issue has to do with engine stalling as a result of the ECU killing the injectors on closed throttle.

Others who have BTDT will chime in with a more thorough answer


Good morning. My Sunday flurry of activity continues…

FYI - the '77 parts car has a 3.31 differential.

With my current understanding of how all this works, I believe I am in the gray area of 4- or 5-speed and could go either way. Brute acceleration would be better with a 3.5X and 80+ motoring better with the 2.88.

My guess is that for vintage racing, those guys use a 3.5x and a 4-speed.


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The V12 got a manual trans from launch in 1971 to 76 after the second year of the XJS. Not surprisingly, since the US was the biggest market and new buyers here preferred slush-boxes, the option was eventually deleted. The full system is covered in Jaguar shop manual and spares books, as well as in Haynes manuals etc. You can certainly assume that you more than cover the outlay on a 4-speed by the increased value of the car.

If you are going racing, do NOT go for a 2.88 or even 3.07 thinking they will give you a higher top speed - they won’t. The Bonneville flats or Mulsanne straight are the exception and for the vast majority of short circuits you likely won’t max out in 3.54 top gear, let alone 3.07. For the D-Type, which had a red line 1000 rpm lower than the V12, 3.54 was the middle option, not the lowest-geared.

I’ve lost track slightly but if this is the thread where there was a budget of $3000 then I just don’t see another option, let alone a better one.