The 'E' Type Forum

Ok Guys and Gals. I am looking into 5 speed options, and have looked at the 5th gear ratio on the Jaguar Classic (JLR) 5 speed and it has a ratio of .63, vs a few other offerings in the region of .75. My rear diff is a 3.07. I am considering a 5th gear ratio as a future proofing of my car as the Moss Box is really not drivable by the average younger generation. I also have had enough of the Moss experience. I know I can put a 4 speed synchro box into the car and that is an option. But for the purpose of this request, I am purely asking am I correct in thinking , all other factors remaining even, that a .63 5th gear will reduce my revs at a fixed speed by 37%? JLR don't offer different 5th gear ratios sadly. Thank you in advance. Andrew

Hi Andrew...try this calculator https://spicerparts.com/calculators/tra ... calculator

0.63 with a 3.07 looks to me much too low revs, especially for the 3.8 engine.
That would be ok with a 3.54 rear diff

thank you Steve. I had tried a couple of these calculators but they didnt seem to work, that one does. At 3300 rpm the car would be doing 135 mph, which I may hazard sounds a bit high. WIth a 3.31 it would be doing 125 which seems a lot more sensible. Nothing is ever easy is it ?! I cannot see me stripping my rear IRS down to replace a new 3.07 with the 3.31 after just 4000 miles tbh

Thanks Serge, our posts crossed. I agree

Both my FHC and OTS have a 3.31 with the Moss box.

When I purchased my first E-Type, fearing too high revs at speed, I thought I would replace that 3.31 by a 3.07 or possibly replacing the Moss box by a 5-speed.

I became however used to the Moss box, especially after having replaced the oil with Redline MTL.
And the replacement options looked to me quite expensive (installing a 5-speed or buying/restoring a 3.07)...

Years later, I observe that I only drive my E-Types on small roads and that I rarely explore speeds beyond 130 km/h on highways.
In these conditions, the 3.31 is perfect, and the Moss box is part of the adventure

Future proofing....Will the average younger person even want an E type

If any car is going to remain desirable its sure to be an E type. But in essence, if I want to leave the car to one of my children they will need to drive it and the Moss is not for the inexperience at Double de clutching.

Perhaps the sensible real world analysis is to ask what revs do I want to be running when cruising long distance on a motorway, a big A road or along the empty French roads and purchase accordingly? Everything else is lower gear "fun" or gear changing stop-start built up area driving.

kind regards
Marek

andrewh Wrote:

I am purely asking am I correct in thinking , all other factors remaining even, that a .63 5th gear will reduce my revs at a fixed speed by 37%?

Hello Andrew,
The reduction in input RPM (Motor Revs) will be 0.37 per rev when compared to a 1:1 top gear ratio. Accordingly, simply multiply 0.37 by engine RPM.

Regards,

Bill

Thank you for your replies Guys. I need to drive my car down the motorway when the weather improves and assess its happy place. At least I now know the calculations for any chosen set up. Thank you

Can’t remember where I found this info, but it has worked perfectly for me:

I have found that the 3.8 and 4.2 Jag engines like a combined OD and final drive to work out around 2.5.
example: 3.54 x .73OD = 2.5842
3.08 x .83OD = 2.5564
4.09 x .63OD = 2.5767 ( used in XK 150 type kits)

I have a 0.8 5th gear, so my 3.31 x 0.8 = 2.648, perfect!
3.31 x 0.63 = 2.085 way too high!

Thanks Simon. That’s a great rule of thumb. I have a 3.08 so with a 0.63 it’s anyone s guess . Must feel very tall indeed. Why JLR Classic built the gearbox with that ratio is beyond me. Maybe appealing to US 3.54 owners ?

Yes, typically for the 3.54 US owners liking to cruise on the highway