Best gearbox for manual conversion

Evening all,

I’ve got myself a pre-HE V12, I’ve posted previously about my ITBs I’m designing, to go with this my engine needs a gearbox, I’m looking for a manual box. I’ve done a little abit of reading and I’m lead to believe the Getrag 260/5 box is the best option. Ideally I don’t have to design the adaptor plate myself, and there is a readily available option.

What I’m asking what’s the best box for the conversion, and if possible where can I buy the adaptor plate/kit, I’ve seen simply performance but the boxes they sell are a bit steep for me.

Many thanks,

If you are located in europe then the Getrag is probably the best option these guys can get you taken care of. : If you are located in the United States then the getrag will be hard to find and/or expensive to ship over seas. I too am doing a 5 speed swap and I am going to use the Tremec TKO 600. These guys sell through ebay or their site and offer a bellhousing that can make any Tremec fit except for the t56.
Another option using the same gearbox choice would be these guys They offer full kits but are really pricey.

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I personally prefer the T5, has a higher Torque rating, better ratios and can be configured to suit many installations.
The largest OE engine the 260 was used behind was the Jaguar 4.0L, for the T5 it was the Ford 302/ GM 305.
You can also buy uprated gear sets suitable for up to 6.0L.
Years ago I drove a S3 V12 E with a 6.8L 4V engine that used a T5, never gave any problems.
To fit the T5 into the XJS you use a Mustang 5.0L version with the 2.96:1 1st gear, and change the rear extension to one from a S10 Chev. to give you the correct gear lever position. A bell housing is available for this conversion


The bellhousing I linked will fit the T5 too

Ben, Google the 260 and the T5, you will see the 260 ratios are crap, good for people that can’t really handle a stick shift.

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Hey, I’ll see if I can find a good deal on a T5 then, Ideally I don’t want this build to roller coaster so I really am trying to find a shopping list of parts that are know to fit!

The std Mustang V8 trans is rated at 300 lb/ft., which is more than adequate for the 5,3L V12, but JEGS have a G-Force uprated version rated at 500 lb/ft.
I did purchase a couple of uprated gearsets of Ebay a few years back to use behind my 6.0L V12 engines.
Probably the same gearset that G-Force use, but they also do a stronger case for their 500 lb/ft. version.

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I would love to use the T5 but I am unsure if the gear stick will come out in the right location on a series 1 XJ. I have heard of using the S10 tailhousing to move the shifter further forward. When I was thinking of swapping my 1965 Faclon to a T5 it was recommended to use the S10 part in order to bring the shift forward. While the TKO 600 is nice as it has multiple locations for the shifter, but its also super expensive compared to a junkyard T5 out of mustang which are plentiful here in Southern California. Would you happen to know how similar to an XJS placement it would be?

Having a quick search there isn’t many T5s in the UK, I do wonder if a GS6-53DZ gearbox from a 330D would be good? I know it’ll easily handle the torque, I also don’t need to worry about gearbox selector postion as it’s not in a Jaguar.

Here’s a link:

The current model Ford Mustang uses a Getrag. What model is it, I dunno, but it can clearly handle the power. If you’re looking for something you can scrounge from a junkyard, that might be a good option. Note that the early Getrag setups had some issues that resulted in a bad reputation, but Ford rather quickly fixed all the issues, so as long as you don’t get one of the earliest versions you should be OK. Also note that the shifter is not mounted on the gearbox, it’s mounted on a structure hanging off the back, which might mean you can fiddle a bit to get the shifter right where you want it.

Others might recommend going with a Tremec. There’s a T5 5-speed and a T56 6-speed. The T56, besides having one more gear, also handles a lot more torque, weighs a bunch more, and costs a bunch more. I personally think 5 speeds is enough, the T5 can handle the torque of the Jaguar V12, and I’m cheap, so that’s the way I’d go. There are at least three different places on the top of a T5 where the shifter can be mounted, and you can usually fine-tune the shift knob location with the shape of the shift lever itself.

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I am also planning a 5-speed conversion for my S2 XJ12. Vintage Jag Works in Idaho has kits from which they will apparently sell the individual bits. They offer a bellhousing-engine adapter with the bellhousing presumably a direct fit to a T5. My car came with a “bonus” T5 and adapter plate but the plate looks to be for an E-type bellhousing. I don’t know if an E-type setup offers any advantage. In any event, has anyone else dealt with Vintage Jag Works in this area?

I have had a Supra W57 5 speed behind a Daimler vanden pas Double six for many years.

The clutch is a rare XJS Borg & Beck

Bellhousing by Dellows Engineering in Sydney Australia

I had to cobble various bits together myself, including machined flywheel centre

There are plenty of Series 3 Etypes with 5 speed conversions - most are based on the T5. Some also have the Supra box and the Getrag but most are T5.

The gear lever position on the T5 can be moved to one of three positions with different housings so something will fit an XJ.

Look at the XJC V12 on Harry’s Garage Youtube channel as his car is a 5 speed.

Also look at the UK Etype Club forum for heaps of information on 5 speed conversions.

The biggest bang per buck (i.e. cheapest and most compatible) if to fit a complete EType bell & flywheel setup and the XJS or XJ four speed. The benefit of spending several thou extra on a 5th ratio is far smaller than the transformation from dumping the auto and going manual. The V12 revs to 6500 unlike 5000/5500 for 4.2/3.8 sixes, so cruising issues are a mental thing more than pushing the engine ‘too hard’ mechanically.

The Jag box option means everything stays workshop manual-stock and parts are off the shelf. Same propshaft, transmission mounts, gear lever position, speedo. With a 2.88 diff which many V12s have, the cruising revs are the same in 4th as they would be in 0.75 overdrive fifth with a 3.54 diff. It’s the factory manual XJS spec from 75-76 until they dropped the manual option.

Yes, I’ve got a couple of those V12 4-speeds surplus to requirements ideal for any Series XJ6 or 12, or any V12 E or 2+2 6cyl…

So, working with what I have (T5 and adapter), is the simplest path to get a V12 manual bell and flywheel? Do I need to specify the source vehicle, or are these the same across all V12 manual trans equipped cars? For example S3 e-type bellhousing and steel flywheel are available new from SNG -would that work in my XJ? They’re pricey, but searching the used market, these parts seem scarce –or maybe I’m just looking in the wrong places?

Yes, all standard JagV12 manual (XJ-S same as S3 E-type). All parts as shown in S3 or XJS parts book except your GM box means you need GM dowel positions for the bell-to-block joint. These are slightly different to the BW trans dowels but easy to change (see forum). Either keep GM dowels and drill two bell holes, or fit BW dowels to bell and drill block.

Try Fidanza (or SNGB) for an alloy flywheel. It is probably cheaper. Not ideal in a heavier car IMO because you want a bit of flywheel energy to avoid stalling on move-off without feathering the clutch too much. What diff does it have? 3.54 would be ideal for acceleration with a 5-speed and is usually the cheapest ratio to buy used because all the E-type guys prefer 2.88 or 3.07 for cruising. You don’t need that benefit as the V12 revs higher than a 6 and your 5-speed already has low rev cruising from overdrive 5th. Compared to a six there’s lots of spinning hardware anyhow, so it’s your call on alloy vs steel.

I have a manual console trim and gaiter and stick, although the stick would need to be clamped differently on the T5. You will love the transformation.

3.31, which may be close enough to do the job.

Agree. I will probably go with steel. I think the flywheel is the biggest contributor to rotational momentum. Reducing that with an aluminum part would seem to upset the balance with the braking effect from ring-cylinder wall friction. -more friction with the V12 than say, an equal displacement and stroke V8.
I’ll contact you offline about those console bits.
BTW, a BIG assumption I am making is that this conversion can be done without removing the engine -or am I dreaming?

Happy New Year!

Most of an engine’s braking effect is from compression/pumping losses, not ring friction.

No, it’s doable on a lift or multiple large axle stands. A friend just swapped out his T5 from his S2 XJ in my shop last summer. V12 is more work but still doable.

You will be disappointed.