Volvo 760 turbo gearbox

[Laird Scooby]

Originally Posted by rwdkev

Hi Dave,

Yes, I know what you are saying here and agree with just about all of it.

The reason I asked the question was because at while back Will (willvg95) was looking to replace a 3.54 with a 3.31 in a 940 TDIC. See this thread:

https://www.volvoforums.org.uk/showthread.php?t=243147

It was suggested that a 3.31 would be "a bridge too far"!! and blunt performance but some of us know only too well that the D24 cars are torquey and undergeared.

And I specifically asked Jim because not only has he now done that very ratio swap but also done it on a D24.



The traffic lights grand prix has never been my thing and 0-60 times don't show the whole picture. For me, mid-range pick-up for overtaking is more important (eg. 50-70 time).

Ironically, at one time, Volvo actually used to market their cars on this principle........

Very valid points there Kev and while i agree on it all, the 0-60 times are a very useful indicator of how it'll perform on overtaking.

Funnily enough, in the early to mid 80s, several manufactures used the overtaking flexibility as part of their advertising campaigns, Austin-Rover Group launched the Ital 1.7 with an advert claiming it was faster than a Mercedes 200 (for overtaking - can't remember the exact speed range), Citroen did a spoof advert for the 2CV saying it was faster than a Porsche (top speed of a 2CV was 71mph so faster than a Porsche at the legal limit of 70mph) for both top speed and overtaking.
Can't remember the overtaking bit but it was basically thrashing the 2CV through the gears over a smaller than usual overtaking range compared to the Porsche in 5th gear only. Think it was 30-60kmh or something silly, may have been 30-50kmh so even tighter parameters.

I actually have my own comparisons, the 760 is 170bhp from the factory, 2.8 V6 in 90 degree formation. My other beast, Rover 827 Sterling is also a 90 deg V6 but is a 24v and produced 169bhp from the factory. Both are auto, have similar 4th/overdrive ratios but very different diff ratios.
The Volvo is 3.91:1 and the Rover is 4.2666:1 and i expect you're probably thinking the tyre size is different. Well it is and it isn't. The Volvo is on 195/65/15 and the Rover is 205/55/16 (but can also use 195/65/15) and the rolling circumference is within a few mm of each other. Both similar weights so you'd expect the performance and economy to be similar.
Driven gently i can achieve similar economy from both and driven hard (and i mean hard!) there is a difference - the Rover is quicker in all areas.
Is it purely down to the slightly lower diff in the Rover? Maybe. Maybe not as it has a higher (official) top speed.
Two very different cars with very similar credentials - the Rover is FWD and the Volvo is RWD so maybe the big difference here is down to that. Maybe it's the gearbox, the AW71 in the Volvo is a traditional auto box with brakebands and planetary gear sets. The Rovers is an electronically controlled, hydraulically shifted manual connected to a torque converter with a 2-stage lock-up clutch on the torque converter.

Bottom line out of that lot is that while on paper they are very similar, the one with the lower final drive is quicker in all areas (0-60, overtaking and top speed), the economy is similar so the final drive doesn't necessarily make a difference to performance and economy - it's as much about what powers the car as it is everything else. Also gearbox ratios, aerodynamics - the whole package.

With all that said, i know Jim is getting better economy, doesn't seem to think the acceleration suffers so he's proved the higher final drive works on the D24TIC. I'm seriously thinking of having his old 3.54:1 axle for my beastie to replace the 3.91:1 seeing as it seems to be a bit noisy and worn after 224k miles and an apparent lack of oil changes.

[tofufi]

Originally Posted by Laird Scooby

With all that said, i know Jim is getting better economy, doesn't seem to think the acceleration suffers so he's proved the higher final drive works on the D24TIC. I'm seriously thinking of having his old 3.54:1 axle for my beastie to replace the 3.91:1 seeing as it seems to be a bit noisy and worn after 224k miles and an apparent lack of oil changes.

The acceleration in lower gears appears slightly improved.

The acceleration in overdrive/at higher speeds appears slightly slower, but that doesn't greatly bother me. It's not a large difference, to my mind, and is counteracted by the reduced noise, smoke and improved fuel economy

[rwdkev]

Originally Posted by tofufi

From a '96 (I think) 940 petrol turbo saloon. The tone ring for the speedometer is the same on all '90-on cars I believe, so mine worked without a hitch (48 tooth tone ring).

I do pretty much all motorway miles.....I don't drive mine hard... but it'll sit happily at 70 on cruise control - both with the 3.54 and 3.31 diffs I've never come across a hill where I've needed to downshift at that speed, but I'm rarely in anything other than overdrive 4th from 40mph up.

Mine is manual so I've not much experience of the auto boxes. I briefly owned a 940 diesel auto and there was no chance of it needing to downshift at motorway speeds.

Originally Posted by tofufi

Forgot to mention - the reduction in engine RPM, only by 250 or so at 70mph, made a big difference in cabin noise too.

Thanks for all that feedback from your experiences Jim.

Originally Posted by tofufi

Mine is a TDIC and actually feels a bit more sprightly off the line, probably because most of the acceleration is on engine torque rather than power.

Yes, when these engines are set up properly they're surprisingly brisk. When the D24TIC became available in the 940 with a manual gearbox (that engine variant was first seen back in the 760 mk2 in 1987 but with auto gearbox only) it was the fastest diesel on the UK market in the early 90's.

Originally Posted by tofufi

Both the diesel auto and manual were geared to give approx 3000rpm at 70, which is a bit high to my taste for a straight 6 diesel

Yes, my thoughts entirely. My V90 3.0 turns over at around only 2500rpm at 70mph and that's obviously petrol.

[Aubergine S70]

Thanks for the replies. I’d like to know something about the gearboxes from the brochure.
My car has the ZF box, Is this a lock up torque converter?
In the brochure, the 760 turbos came with a 4 speed auto with a lock up torque converter (overdrive) is this the Zf box or the better AW box.

Thanks

[Laird Scooby]

Originally Posted by Aubergine S70

Thanks for the replies. I’d like to know something about the gearboxes from the brochure.
My car has the ZF box, Is this a lock up torque converter?
In the brochure, the 760 turbos came with a 4 speed auto with a lock up torque converter (overdrive) is this the Zf box or the better AW box.

Thanks

Easy way to tell is look at your gear lever. If there is a button on the side this is the overdrive defeat button, presssing it while in "D" will bring an orange arrow up on the instrument cluster on the right hand side - this is the AW7x box.

If there is no button and the shift positions (from rear to front) are marked 1-2-3-D-N-R-P then it's the ZF4HP22 box.

Either way, under moderate throttle opening, you should feel the lock-up engage almost as if it's an extra gear.