Volvo 760 turbo gearbox

[Aubergine S70]

Hi, over the past few months I’ve been doing a light restoration on my D reg 760 turbo estate B230ET. After a turbo and engine rebuilt the car is running great, very smooth and powerful but the gearbox. It has a ZF22 box, which from what I have read isn’t the best, at 70MPH its revving at 3000RPM and doing 23-24.5 mpg. I know that these old Volvos aren’t built for economy and that’s not the reason why I bought it, but I’d like it to be quieter at these speeds making more comfortable at these speeds. I’ve read people changing this to a AW box. Also mine is leaking where the bell housing meets to the gearbox, which is also common.
Is the AW box a lockable torque converter and would this be a good idea on a turbo car?

If so has anyone done a ZF to AW conversion and what parts do I need as this would be greatly appreciated.
Thanks

[tofufi]

I've got no knowledge of the auto gearboxes... but if your main priority is to reduce RPM at motorway speeds you may find a new rear axle ratio is an easier route to do this.

The auto gearboxes typically have higher back axle ratios than manual cars, so if you can find a back axle from a manual car it's easily done in under a day. Autos typically have 3.73 or 3.91 ratios, I've got a 3.54 axle in the garage waiting for me to find time to sell it.

Going from 3.91 to 3.54 would give ~2700rpm instead of 3000rpm - around 10%.

My diesel went from 3.54 to 3.31 which gave less of a drop in RPM (around 7%) and seems to have given me around 3 more MPG (from 44 to 47, but that's only on around 400 miles).

[Laird Scooby]

Originally Posted by tofufi

I've got no knowledge of the auto gearboxes... but if your main priority is to reduce RPM at motorway speeds you may find a new rear axle ratio is an easier route to do this.

The auto gearboxes typically have higher back axle ratios than manual cars, so if you can find a back axle from a manual car it's easily done in under a day. Autos typically have 3.73 or 3.91 ratios, I've got a 3.54 axle in the garage waiting for me to find time to sell it.

Going from 3.91 to 3.54 would give ~2700rpm instead of 3000rpm - around 10%.

My diesel went from 3.54 to 3.31 which gave less of a drop in RPM (around 7%) and seems to have given me around 3 more MPG (from 44 to 47, but that's only on around 400 miles).

Axle ratios quoted from my 760 handbook Jim :

3.91:1 - 760GLE with auto trans (that's the B280E/F engines)
3.73:1 - 760 Turbo and Turbodiesel with auto trans
3.54:1 - Manual transmission.

This is where it gets interesting, the M46 overdrive has a ratio of 0.78:1 for overdrive, the AW71 is 0.69:1 (highest out of all 3 options) and the ZF4HP22 is 0.73:1 but i find that 4th can be a bit tall on the motorway for a good overtake and 3rd is just that little bit too low for a nice overtake. On the autos, 4th is an overdrive ratio with 3rd being 1:1 like 4th is on manuals.

With a diesel, you probably wouldn't noice it so much but i suspect on a petrol, raising the axle ratio to 3.54:1 on mine for example would have the box going up and down between 3rd and 4th to cope with supply and demand of the road vs the engine.
I think Volvo got it right first time with the ratios, some are a tad high on the overdrive ratios but on a good clear road, they work well.

I'd like to fit a higher ratio if i ever have to change the axle and just use the overdrive lock-out button a bit more if needed so give me a shout if you ever decide to sell that 3.54:1 axle.

Meanwhile i'm enjoying the fruits of todays labour - fitting a rear ARB from a later 940, vast improvement and i haven't driven it in anger round a bend yet!

[rwdkev]

Originally Posted by tofufi

My diesel went from 3.54 to 3.31 which gave less of a drop in RPM (around 7%) and seems to have given me around 3 more MPG (from 44 to 47, but that's only on around 400 miles)

Results speak for themselves Jim. Where did you manage to get a 3.31 diff from? What's it like to drive now? There are a few on here who seem to think this high ratio would ruin performance but you can actually speak from experience.....

[Laird Scooby]

Originally Posted by rwdkev

Results speak for themselves Jim. Where did you manage to get a 3.31 diff from? What's it like to drive now? There are a few on here who seem to think this high ratio would ruin performance but you can actually speak from experience.....

I'd say there's an argument for and against the taller diff gearing ruining performance Kev.

In the smaller engines with not much torque, it could easily turn them into a damp squib but the high torque engines (i mean n/asp or diesel) will lap it up and just use the higher ratio.

The turbo petrols will take a short time longer to build boost then use the higher ratio.

If someone is going for all-out acceleration, no matter what engine size/aspiration the higher diff ratio is likely to squash it somewhat although could still make it quicker on o-60 time by reducing the gearchanges needed to one from two - in other words the higher diff ratio would allow 60mph to be reached in second gear, rather thanhaving to change into third to reach 60mph on the lower ratio diff.

If economy is the goal, a taller diff usually pays dividends but sometimes will mean dropping from 5th to 4th for motorway inclines because the engine doesn't have the torque to keep going. Again, bigger engines/diesels and/or turbos are less likely to suffer this way.

[TonyS9]

The autos are aweful mpg in my experience, low rpms are not going to help you much. The main problem is the drag when slowing down and idle. The auto's actually go through back brakes alot faster than manuals because of this.

Either get a manual or just live with it.

[tofufi]

Originally Posted by rwdkev

Results speak for themselves Jim. Where did you manage to get a 3.31 diff from? What's it like to drive now? There are a few on here who seem to think this high ratio would ruin performance but you can actually speak from experience.....

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. 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. 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.

As an added bonus, the lower RPMs mean I get a lot less engine soot up the back end of the car - probably only an issue on the diesels

Originally Posted by Laird Scooby

Axle ratios quoted from my 760 handbook Jim :

3.91:1 - 760GLE with auto trans (that's the B280E/F engines)
3.73:1 - 760 Turbo and Turbodiesel with auto trans
3.54:1 - Manual transmission.

This is where it gets interesting, the M46 overdrive has a ratio of 0.78:1 for overdrive, the AW71 is 0.69:1 (highest out of all 3 options) and the ZF4HP22 is 0.73:1 but i find that 4th can be a bit tall on the motorway for a good overtake and 3rd is just that little bit too low for a nice overtake. On the autos, 4th is an overdrive ratio with 3rd being 1:1 like 4th is on manuals.

With a diesel, you probably wouldn't noice it so much but i suspect on a petrol, raising the axle ratio to 3.54:1 on mine for example would have the box going up and down between 3rd and 4th to cope with supply and demand of the road vs the engine.
I think Volvo got it right first time with the ratios, some are a tad high on the overdrive ratios but on a good clear road, they work well.

I'd like to fit a higher ratio if i ever have to change the axle and just use the overdrive lock-out button a bit more if needed so give me a shout if you ever decide to sell that 3.54:1 axle.

Meanwhile i'm enjoying the fruits of todays labour - fitting a rear ARB from a later 940, vast improvement and i haven't driven it in anger round a bend yet!

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.

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

You're welcome to buy the 3.54 diff if we can sort out collection/delivery - drop me a PM and we can see what we can do

[Laird Scooby]

Originally Posted by tofufi

You're welcome to buy the 3.54 diff if we can sort out collection/delivery - drop me a PM and we can see what we can do

PM sent Jim!

[tofufi]

Originally Posted by rwdkev

Results speak for themselves Jim. Where did you manage to get a 3.31 diff from? What's it like to drive now? There are a few on here who seem to think this high ratio would ruin performance but you can actually speak from experience.....

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

[rwdkev]

Originally Posted by Laird Scooby

I'd say there's an argument for and against the taller diff gearing ruining performance Kev.

In the smaller engines with not much torque, it could easily turn them into a damp squib but the high torque engines (i mean n/asp or diesel) will lap it up and just use the higher ratio.

The turbo petrols will take a short time longer to build boost then use the higher ratio.

If economy is the goal, a taller diff usually pays dividends but sometimes will mean dropping from 5th to 4th for motorway inclines because the engine doesn't have the torque to keep going. Again, bigger engines/diesels and/or turbos are less likely to suffer this way.

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.

Originally Posted by Laird Scooby

If someone is going for all-out acceleration, no matter what engine size/aspiration the higher diff ratio is likely to squash it somewhat although could still make it quicker on o-60 time by reducing the gearchanges needed to one from two - in other words the higher diff ratio would allow 60mph to be reached in second gear, rather thanhaving to change into third to reach 60mph on the lower ratio diff.

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........