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740 M46 Seals

bmdubya1198

Active member
Joined
Aug 24, 2016
Location
Charlotte, NC
Just picked up an M46 for my 740 Turbo, and now I'm trying to figure out where it's leaking and what to replace before putting in my car. The front seal below the input shaft is definitely leaking, but which seal is that? On the parts diagram, it only shows "input shaft seal," which I don't think exists on the actual input shaft. It seems that the bearing is just covered by a ring that's held in by the bell housing. Maybe I'm missing something, but I don't see how there is a seal there.

Then it appears to have a leak where the overdrive unit is mated to the gear box. I already ordered the front overdrive gasket, but it seems the leak is forward of that (the front side of the plate above the cross member shown in the diagram below).

I'd rather not rebuild the overdrive right now (although it probably needs it, I'm told it didn't work and the solenoid and 4th gear switch are functional), so what is my solution here to get gaskets? What's the deal with the front seals? I found the input shaft seal on FCP, but I'm confused as to whether it goes on the actual input shaft on on the lower shaft.

I'm driving myself nuts looking at this diagram and finding leaks on this grease-caked transmission. I'd rather not put this tranny in my car just for it to pour out all the fluid in a week.

M46 Diagram: http://volvopartslisle.com/assembly/56201771/Manual-Transmission
 
The input shaft seal seats into the bell housing. You have to remove the bell housing and drive the seal into the hole there for the input shaft. Then reinstall the bell housing. You will need the front trans gasket as well.

With it all out now. give it a good cleaning and reseal everywhere you can get to. It really is the time to service or repair the overdrive now and a gasket set for that isn't too bad.
 
I have the bell housing off right now, and I just see the input shaft bearing and a ring that covers it and holds against the bell housing. I don't see how there's a seal that goes in there.
I have the front trans gasket on the way now.

Pic: https://photos.app.goo.gl/NwwMtBpZH9wT8UF38
https://photos.app.goo.gl/bvXMdanPA9Ww77XE6

I'm going to clean the heck out of it today, because it's nasty. Hopefully that will clearly reveal the leaks.
I'd like to pull the OD and repair it, but my worry is that the rest of the transmission won't last. The more I read about the M46's durability (or lack thereof) the more I feel like just running it as-is until it blows, then T5 swap.

Then, I have this car's original M46 (that is no good) but I believe when the PO told me it was rebuilt, I think he meant the OD was rebuilt (visible sealant instead of the correct paper gasket between the OD and trans). I want to swap that over to my good M46, but I'm wary of that because there were bits of gear in the fluid, not to mention that fluid was nasty and milky. I don't want to take the risk that a piece of gear got lodged somewhere it shouldn't and it turn out that this OD needs a rebuild too. Or if that bit gets into the transmission and blows this M46 too.

If I end up repairing it, is there any source for the P type OD repair kit other than iPd? Otherwise, how necessary is the overdrive, really? This car isn't going to be a daily.
 
I guess how necessary the OD is up to you. I use mine just about every time i drive the car. Gives a nice relaxed cruising gear over 45-50 mph.
 
You don't see the input shaft seal because you are looking at the transmission. The seal is located inside the hole in the bell housing. Look in the bell housing.
 
many times OD issues are just wiring related. Clean up the harness and connections first. I completely replaced the old worn out connector with 4 prong waterproof one from ebay.
 
I figured that could be a possibility too, that his wiring was bad. I'll make sure everything is clean before I put it back in the car.

I pulled the OD unit off my old M46, and I noticed it has writing on the top (presumably the name of the junkyard from which it was sourced) along with "OK." I'm pretty sure it was rebuilt, like the PO of the car claimed.

Now my only worry about swapping this unit over to my newer M46 is should I worry about any metal particles that could have gotten into it from the damaged gears? The fluid that came out of it looked nasty (as with the rest of the fluid in that transmission) but I didn't notice any particles in the overdrive when I took it off.
My main worry is something that is possibly lodged in the OD unit flowing through the fluid and between gears in my new-to-me M46 and rendering that another paperweight.

If I have to take the transmission down again eventually to repair if, it's not a huge deal but do you guys think it would be safe to use it?

I know, not a great picture, but it's something. The front looks pretty clean at least. https://photos.app.goo.gl/DkWeqHX6faEmTuHZA
 
My main worry is something that is possibly lodged in the OD unit flowing through the fluid and between gears in my new-to-me M46 and rendering that another paperweight.
The OD has two filters: the pan course screen filter and a cylindrical fine cartridge filter under the largest pinwrench cap.

You could take a look at those to get a good idea of what the OD has seen as far as particles but I would suspect that those filters would have trapped any dangerous pieces.
 
The OD has two filters: the pan course screen filter and a cylindrical fine cartridge filter under the largest pinwrench cap.

You could take a look at those to get a good idea of what the OD has seen as far as particles but I would suspect that those filters would have trapped any dangerous pieces.

Cool, that makes me feel much better. I thought there was at least one filter in there.

I'm going to go ahead and order a gasket/seal kit (the Volvo dealer I ordered from initially had to order them from Sweden, and I'm not waiting for that) and get everything all cleaned up. Hopefully it will go smoothly and I can get this transmission in within the next week or so.
 
Okay... bit of a plot twist... this is what the inside of the overdrive looks like... https://photos.app.goo.gl/AwQQ1w3a84Wz8Ajo8

Now I don't know for sure that those pieces are from the overdrive, but being the way they were in there (and the ring piece was lodged between the housing and the filter, as seen in one of the pics) I'd rather not bother swapping the OD.

I've decided to just run it as it is for now and hope the issue with the OD was with the wiring or something in the M46's previous owner's car.
 
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