While rereading a R&T mag from 1979 I came across a test of the then-new XJS: V12, 5.3L, low compression, smog, all the normal stuff of that era.

The transmission is the GM Turbo Hydramatic 400 with, apparently, 2 first gears. I thought it was a fluke but the Mercedes 450SL several pages further in seems to have a similar setup.
XJS: 450SL:
1st (2.48 x 2.4) 19.70:1 ratio 1st (2.31 x 2.0) 14.18:1 ratio
1st (2.48) 8.21:1 1st (2.31) 7.09:1
2nd (1.48) 4.90:1 2nd (1.46) 4.48:1
3rd (1.00) 3.31:1 3rd (1.00) 3.07:1
Final drive 3.31:1 Final drive 3.07:1

I've never seen this before. Anyone have a similar XJS with this setup? Does it really have a low gear for starting off the line? Ideas?

 

Okay, I had arranged the Jag and MB specs side by side and the forum condensed everything into a mess. Don't see any way to edit this but you can see the mag clip.

 

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Thank you!

 

Not two first gears. The "x2.4" is torque converter multiplication

Cheers
DD

 

Interesting, so does this indicate that the torque converter locks up at some point in first gear?

 

It doesn't lock up in the sense that convertors did on later transmission; not a solid coupling. But it does reach a point of reduced slippage.

Anyhow, here's some info from ....

https://www.ihra.com.au/TD-Torque-Co...20acceleration.

A typical torque converter will have a torque multiplication ratio in the area of 2.5:1. The main point to remember is that all properly functioning torque converters do indeed multiply torque doing initial acceleration. the more drastic the change in fluid path caused by the stator from its "natural: return path, the higher the torque multiplication ratio, a given converter will have. Torque multiplication does not occur with a manual transmission, clutch and pressure plate; hence the need for a heavy flywheel, very high numerical gear ratios, and high launch RPM. A more detailed discussion of torque multiplication can be very confusing to the layman as high multiplication ratios can be easily considered the best choice when in fact more variables must be included in the decision. Remember, the ratio is still a factor of the engine torque in the relevant range of the torque converter stall speed, i.e.: a converter with a multiplication ratio of 2.5:1 that stalls 3000rpm will produce 500 ft/lbs of torque in the instance of full throttle acceleration if its coupled to an engine producing 200 ft/lbs of torque at 3000rpm. However, if this same engine produces 300 ft/lbs of torque at 4000 rpm, we would be better off with a converter that stalled 4000 rpm with only 2.0:1 torque multiplication ratio, i.e.: 300 x 2.0 = 600 ft/lbs at initial acceleration. Of course it would be better yet to have a 2.5:1 ratio with a 4000rpm in this example (provided this combination still allows the suspension to work and the tyres don't spin). This is just a brief overview as the actual scenarios are endless.

Cheers
DD