Volvo 940 gearbox issue?

[tom13]

Hi guys,

Went to have a look at a Volvo 940se last night. I though it had a 5speed box but it has a m46 box, 4 speed with electronic overdrive. The seller has said it is jumping out of the overdrive though and from what I have read people say the box is then goosed. Has anyone had this problem and if so, whats its like just running the 4 speed and what are the chances of the rest of the box eating itself.

I have thought about the idea of buying a m47 or m50 5 speed box. How big a job would it be and what parts are needed. The guy did say the clutch that is m46 is not very old too.

Cheers

Tom

[rich745]

The overdrive is attached to the back of the box and shares the same lubricant. I've not had one with that box personally but the most common issue I've heard of with it by far is relay and switch failures. the rest of the box tends to be fairly bomb proof. Personally I can't think of a time when I've heard of mechanical failure of the overdrive and I've been active on the Volvo forums for about six years now at least.

Only information I can find about common failures of the lay cook denormanville overdrives relate to the earlier a type units in triumphs and Austin healeys which suffer from low oil pressure causing slow engagement and disengagements. Apparently this is caused by worn springs inside the unit. Whether laycock remedied this in the later j type units fitted to Volvos is something you could look into, but they fitted over a million of them in Volvos so a spare should be available if necessary. I scraped two last month!

The M90 box which was fitted to later 940s is a good one and reliably, but expensive to acquire. Conversion would need a box, clutch, crossmember and propshaft.

Don't bother fitting the m47 if it's a turbo engine as it won't stand up to the torque. It was built for the lower torque engines by cramming a five speed gear set into the m46 casing meaning all the gears are smaller and weaker than the m46.

Hope this helps



Richard

[mylittletony]

Sept 17, 2015 8:24:57 GMT rich745 said:

Don't bother fitting the m47 if it's a turbo engine as it won't stand up to the torque. It was built for the lower torque engines by cramming a five speed gear set into the m46 casing meaning all the gears are smaller and weaker than the m46.

That's a bit misleading, although probably a correct conclusion.

The M47 has an additional casing on the back containing the 5th speed, it looks like an M45 (4-speed) with a bit bolted on, in a similar way that an M46 looks like an M45 with an overdrive bolted on.

M45:



M46 (overdrive):



M47 (5-speed):



The first 4 ratios are the same between M45, M46 and M47. The overdrive of the M46 is a slightly taller ratio than the 5th of an M47. The overall lengths and therefore propshaft lengths also differ.

From what I've read, the M47 can handle ~200hp, but they're not the strongest. If you're planning on high power, go for an M90. If standard-ish a replacement M46 or M47 should be suitable

[rich745]

Aah, thanks for putting me right! Sorry, hadn't looked at the two side by side and my m47 was that covered in oil that I hadn't noticed the extra casing in the back! apologies for relaying not entirely correct information then and thanks for putting me right.

Strength issues point was based on the tired feeling of mine after 200000 behind a b200e which was hardly making a lot of torque, but as you say they might be strong enough to take power but probably not for long!

Personally I'd still be thinking that relay or switch failure is most likely?



Rich

[steveg]

Check the wiring. My Triumph 2000 overdrive had a few moments and all it was was the wires running up the gearstick.
If you fit the M90 box you will need a diesel clutch, this allows you to use the original flywheel and not the dual mass one Volvo fitted as standard. You need to make the clutch pivot ball a little longer and this is normally done by using a couple of washers. You might need the M90 crossmember and I think the propshaft will be different.
Make sure you get a petrol gearbox, the bellhousings are integral and the diesel one is different.

[ChasR]

When my MGB used to jump out of overdrive it was down to a faulty solenoid. The filter looked fine at the time but it was replaced as a matter of course.

[tom13]

These are all great responses and very much appreciated guy. Nice to known it wont be all doom and gloom. I am going to have another look at it I think and then see how I'm feeling from there. Put a cheeky bid in maybe.