940 m46 to m90 conversion

[knuckledragger]

Hello all
I have two 940s. One is a scuffy, off-the-road 1995 940 2.3 LPT with an M90 box. The other is much cleaner, a 1991 940 2.3 HPT with an M46 box. I want to put the m90 in the HPT. Do I need to swap the rear axles too i.e do the final drive ratios differ between the two?

[classicswede]

No need to swap axles.

You will need a clutch to fit the M90 as I doubt you will also want to transplant the tired out DMF

[knuckledragger]

Whoa that's a relief. I gather retaining the M46's solid dog-dish flywheel is the best thing. Is there a definitive list of clutch and flywheels parts available for this conversion. Pressure plate, clutch disc etc? I gather the 20 vs 22 spline count of the M90 vs the M46 is the principle stumbling block.
Both cars are currently alongside one another and complete. Presumably the HPT' M46 flywheel can stay put, but I need to use a new 940TDi cover and 228mm pressure plate to mate the M90 gearbox?

[knuckledragger]

Originally Posted by classicswede

No need to swap axles.

You will need a clutch to fit the M90 as I doubt you will also want to transplant the tired out DMF

Classicswede, will this clutch kit you list as Sachs HDM90 mate the M46 dog-dish flywheel to the M90 box without any need to get into swapping separate covers and friction plates etc?

[classicswede]

Yes that clutch will just bolt in. It is for M90's using the dished flywheel you have

[knuckledragger]

Ah ok. And just to be sure, the axle is fine to leave, ie the speedometer reading will still be correct with the different box? I know the m90 equipped cars have their speedometer sensor run off the back of the diff, whereas I thought m46 was cable driven?

[classicswede]

all 900 series are driven off the axle.

some very early 700 series might be cable

[Laird Scooby]

Originally Posted by classicswede

all 900 series are driven off the axle.

some very early 700 series might be cable

To the best of my knowledge, all 700 cars had electronic speedos driven by a sensor from the back axle. Early 7xx had a 12 tooth reluctor ring except for those with ABS from ~1988 on which had a 96 tooth ring and a speedo converter. In (i believe) 1991, Volvo standardised to 48 tooth reluctor rings changing the ABS ECU to cope, in 1992 they switched to the Bosch ABS-2E system that had 48 tooth rings.

The ABS sensor in the back axle also supplied the speedo so if the back axle is retained, it will still read the same as it previously did.

I understand the 240 had cable driven speedos up to about 1987 give or take (not sure on the exact year) then switched to the electronic variety, again with a sensor in the back axle.

[natmargetts]

Laird- my 1985 740GL speedo isnt driven from the back axle as the plug point on it is blanked off- so I assume it must be from the gearbox.

[Laird Scooby]

Originally Posted by natmargetts

Laird- my 1985 740GL speedo isnt driven from the back axle as the plug point on it is blanked off- so I assume it must be from the gearbox.

I'm glad i said "To the best of my knowledge" - had a feeling there would be at least one early survivor that might just possibly, conceivably, maybe have a cable driven speedo!

You're not confusing the filler plug for the axle level by any chacne? Some of the speedo/ABS sensors were mounted really high on the diff cover and can't easily be seen from underneath, even when looking for them!