3.54 differential with 0.63 overdrive

[LeffeBrune]

Does a 0.63 5th gear overdrive work well with a 3.54 differential or should one better take a 0.73 5ht gear? The car is a 4.2 S1 OTS. I want the 5th gear mainly for motorway cruising. However, I concerned that with the .63 the drop in RPM from 4th to 5th gear is too significant. The car would do 112 km/h (or 70 miles/h) in 4th at 3000 RPM and then drop to 2000RPM in 5th. With the .73 5th gear, the drop would be to about 2200 RPM. Also, with the .73 5th, I would still do more than 150 km/h @3000 RPM (which is likely more than my wife would tolerate) and almost 180 km/h at 3500 RPM (which may be more than I would tolerate).

Thanks for the advice.

Georg

[andrewh]

one for those with direct experience, but I would have thought that you may be better to switch the diff ratio at the same time to a 3.31 or even a 3.07. I am currently having a differential rebuilt to 3.07 but keeping the 4 speed. My experience of a 3.07 , particularly in a 4.2 with a little extra torque from factory, is that the ratios work very well indeed. A fifth gear overdrive would keep the desirable aspects of the 3.07 , for me anyway, whilst providing the relaxed option for motorway use.

[Moeregaard]

I'm with Andrew on this one. The 3.54 gearing is absolutely worthless, since the first three gears on the standard gearbox get "used up" more quickly than you can shift it. I never got around to installing 3.07 gears in either of my E-Types, and the only positive thing I can say is that they probably saved my driver's license when we had the dreadful 55-MPH speed limit here in the states.

I think either the 3.31 or 3.07 gears would be ideal with the .73 5th on an E-Type I've driven a Healey 3000 with 3.54 gears (original for non-OD cars) that had been retrofitted with a Toyota Supra five-speed 'box, and it had no trouble dealing with the .73 OD.

[LeffeBrune]

Thanks. I drove the car last summer (picked it up in July). I agree that the first three gears are close with the 3.45 but would not call them useless. One of the reasons why I am leaning towards the .73 5th is indeed the option to change the rear differential to a 3.31 or 3.07, for which the .63 5th may be too much.

[abowie]

The 3.54 gearing is absolutely worthless,

I disagree.

The standard gearing works very well with the 3.54 and is complemented by the overdrive in 5th. This is particularly true of the 3.8 with less torque.

WRT 06.3 vs 0.73, I was advised against the 0.63 by the manufacturer. This has turned out to be correct.

My 3.8 has a 3.54 diff with 0.73 OD.

My speedo is inaccurate; the car is travelling at 100kph by GPS.

[Tferrer@gmail.com]

Dick Maury told me finding 3.07 ratios was very difficult so I went with a 2.88 and kept my 4 speed....perhaps its just a US shortage ;-)

[christopher storey]

I agree absolutely that the 3.54 final drive spoils the gear ratios , leaving 2nd in particular far too low for overtaking purposes ( particularly if you have the later KE or KJS box), whereas with 3.07 it becomes a wonderful overtaking gear, with a maximum of 120 kph achievable if it is an EJ box . Furthermore, if you are never going to cruise at more than 150kph , a 3.07 or 2.88 will provide you with the cruising gear you need without going to all the trouble of having the engine out and making the necessary structural changes to fit a 5 speed . Final drives are readily available secondhand in the UK , usually from XJ6 scrap cars

[PeterCrespin]

Agreed, although XJ12 or V12 XJ-S are better, as they are always limited-slip and almost always 2.88.

[Heuer]

Avoid the 2.88 as it makes town driving or uphill hairpin bends a real pain. The 3.07 is the sweet spot IMHO, having driven 55,000 miles with the 2.88.

[abowie]

I agree absolutely that the 3.54 final drive spoils the gear ratios , leaving 2nd in particular far too low for overtaking purposes ( particularly if you have the later KE or KJS box), whereas with 3.07 it becomes a wonderful overtaking gear, with a maximum of 120 kph achievable if it is an EJ box

Just took the 3.8 out for an "Italian tuneup". At 5000 rpm in second I'm moving at about 90kph. If I can't overtake with that, there's always 3 more gears

Man the angry bee sounds good at 5k!

[Jagboi]

I have a 1966 S Type 3.8 with a 3.77 ratio. Originally I had the 0.63 overdrive and it was too tall. I have also put on EDIS and EFI on this engine, it feels like it has much more torque than a standard engine.

I changed the ratio to 0.73 and was much happier. It produces relaxed cruising without lugging and always having to drop out of overdrive. With 0.63 I found I was always shifting down. 0.63 to 1:1 is a fairly big jump too.

I also had a stock 3.8 E Type with a 2.88 and all syncro box. It was a nice combination too, I didn't think the low end performance suffered, it was plenty quick enough for me. 70 mph was 2700 rpm, whereas in the S Type with OD it's 2300.

In the S Type I can get 30 mpg at 70 mph, so I'm very happy with that.