Diff swap or 5 speed?

I’ve been reading through the various threads on replacing a high ratio diff with a lower one and the threads on a 5 speed conversion.

What would a 5 speed conversion kit cost?

What would it cost to have a shop convert my 3.54 diff to a 2.88 or 3.07? There’s no way I have the skills to do this.

I’d be doing the removal and replacement myself.

Personally, I’m happy with the original 4 speed in terms of it’s shifting feel. I’m just looking for lower revs on the highway.

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I would imagine a shop would be willing to swap the gear set for around a grand if you can find the correct gear set. A 5er gives you the perfect solution offering speed off the line, and overdrive to keep RPMs down on highways. A diff change only gives you the latter at the sacrifice of the former.

But realistically 1st is a waste on these cars and function as stump pullers because the XK has so much torque. A 5 is a very nice thing but the problem is the cost, and the difficulty and also now the availability since the JT5 is NLA.

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I’ve done two five speed conversions through the years, neither was cheap, and neither vendor still trades today. Given the high cost and hit or miss quality of five speed conversions, I would suggest the most expeditious and simplest solution would be a 3.07 rear. You can easily pull the rear and deliver the differential to any transmission shop for installation of a Dana 44 gear set.


The ONLY reason I wanted a 5 spd in Tweety was to get rid of that gawd-awful Moss: with the 3.07, I found it perfectly adequate in all driving conditions…

My vote goes to the diff.


I’m going to try Driven Man 5 speed conversion. Cost was under 6k. When I ordered last week was told 7-10 week wait.

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Please keep us up dated Tim. I hope it’s a smooth retrofit.

What ratio are you getting for 5th?

What would it cost to have someone do it for me? Just the diff work. I’ll remove/replace.

Try a second gear start. Doable with 3.54 final gear.

1st gear with a 2.88 is in between 1st and 2nd with 3.54. (I think right in the middle.)

.80 5th. I had a sedan with .77 O.D. so this will be even better.

The cost for parts is about $500, if you use Dana 44 parts. With the diff out of the car, I would guess about 5 hours labor, anywhere from $500 to $1000 for that, depending on the shop. Make sure the shop has experience with Dana44’s, and understands the (minor) nuances of the Jag diff. This isn’t an uncommon swap, as Jag rears have been used by hot rodders for decades.

Thanks for all the input so quickly. This project, if it happens, will happen next winter.

I really hate the idea of pulling the cage off and dismantling it again but it’s definitely the least expensive option.

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Like you, I didn’t want to tear into a differential myself so I bought one professionally rebuilt with 3.058 gears from Coventry West for $1,250 plus and $300 core charge plus shipping and freight. IIRC, I was told they had a quantity of 2.88 diffs for less money, but I have also seen a notice that they have stopped selling used parts. I installed the diff myself when it arrived at the house. You might give them a call and see what they can do for you.

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Any good axle shop can do it: maybe $500-$1000, parts included?

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as most have said…a diff ratio change. there are several mph to rpm calculators on the web…easy…tire diameter needs to be known…try different numbers and make notes for what you want, say at 60 or 70mph. AS has been said the Dana 44 type is popular with hot rodders and Jeep type rock crawler crowd…they go for the super low gears (high number= low gear)…so the ratio we want should be in the spares bin. Note there are some gear/spline tooth difference: L …they should know that tho. They will LOVE LOVE that you just bring in the pumpkin. Most can put it on a bench and do it with coffee in the am, and done.


If no-one else has said it, if you change the diff ratios you will also have to change the Speedo.

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Tweety, at 75 mph, with 205/70-15s, was cranking along at ~2900 rpm. I NEVER felt the lack of acceleration…

I have bought a 5 speed Driven man gearbox for the 65 OTS I m currently restoring.
will keep the 3.54 for low speed driving in 1 gear and high speed driving in 5 gear.

I installed a 3.07 in my 69 FHC however driving at low speed in 1 gear is a pain in the butt constantly using the clutch in and out, and slipping it.

yes the DM 5 speed is kind of expensive but I hope to get the best of two worlds.

Or have one of these made up.

Speedometer Gear Ratio Adaptor installed. Was Speedometer Cable Nut Size? - E-Type - Jag-lovers Forums

It still performs flawlessly.

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I purchased a 5 speed from Driven Man for my 68 FHC. The gearbox has been sitting in my garage for a few months. It should go in the car this fall.

Sounds interesting Bill.

Please let us know what you think after driving it.
My OTS is for sure not ready before sometimes next year-------------------in the best case