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M46 OD questions

noz-e8tr

noz-e8tr

Well-known member
Joined
Aug 27, 2003
Location
Ocean Springs, MS
I'm trying to grasp how this OD unit works. On the 85 740t m46, its currently not running. The car was parked for 10+ years in the POs garage. I know the slave cylinder is shot. I have no clutch actuation at all at this time. But I was playing around and bumped starter with the car in gear. I was expecting for the car to move/rock, and it didn't. I can actually turn the engine over with car in gear and clutch out with no noticeable resistance. Turns over the same as when in neutral. PO has been very honest about everything, and I do not question when he says it was shifting fine when parked.

What are your thoughts on this? I'm pretty sure the OD has a pump and depends on pressure to engage. Would sitting for 10+ years cause the OD to slip this badly? (I'm assuming at this point that the flywheel is turning the clutch disk and transmission.)
 
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noz-e8tr said:
I'm trying to grasp how this OD unit works. On the 85 740t m46, its currently not running. The car was parked for 10+ years in the POs garage. I know the slave cylinder is shot. I have no clutch action at all at this time. But I was playing around and bumped starter with the car in gear. I was expecting for the car to move/rock, and it didn't. I can actually turn the engine over with car in gear and clutch out with no noticeable resistance. Turns over the same as when in neutral. PO has been very honest about everything, and I do not question when he says it was shifting fine when parked.

What are your thoughts on this? I'm pretty sure the OD has a pump and depends on pressure to engage. Would sitting for 10+ years cause the OD to slip this badly? (I'm assuming at this point that the flywheel is turning the clutch disk and transmission.)
Click to expand...

Is fluid even still in the trans? I could have leaked out. Clutch might be all rusty covered in crap.
 
I honestly don't know. If clutch was rusty, I'd expect it to not want to release, not slip. I guess that is my question. If OD is low on fluid, or just dry from sitting, will it slip like this?

And if so, would simply adding fluid fix. Will the OD need to be spun a bit for the fluid to circulate?

240240 said:
Is fluid even still in the trans? I could have leaked out. Clutch might be all rusty covered in crap.
Click to expand...
 
Does the car have a driveshaft? Is the rear end blown out? Is the clutch plate rusted on to the pressure plate? In either mode, especially in the non OD mode, the OD unit is gear driven. Lack of lube or the solenoid not engaging in fourth gear shouldn't make a difference in the car moving or not when the OD isn't engaged. I'll say that your problems , at least for right now ,lie somewhere besides the OD unit.
 
OK..Thats the info I was looking for. I just wanted to eliminate the OD before I climb under and start looking. LOL...I haven't even looked under yet, sure would feel dumb if there no drive shaft. :oops::oops:

benski said:
In either mode, especially in the non OD mode, the OD unit is gear driven. Lack of lube or the solenoid not engaging in fourth gear shouldn't make a difference in the car moving or not when the OD isn't engaged.
Click to expand...
 
No worries; just go for the easy stuff first, and work your way to more difficult. The most common problems on these Laycock de normanville OD units is electrical issues, either with connections or the OD relay. Heck, I've even had an OD button in the shifter stick in place due to some extremely poorly placed Pepsi..:omg::oops::nod:
There's tons of info out there on care and feeding of these things on this site and others.:cool:
 
On a side note, I tested all lights, windows, wipers/washers, brakes, emergency brake, fan blower and all seem to be functioning like they should. I can feel the OD relay clicking and "5" lights up on dash when i push OD button. Next is to put in up on stands, get under it to drop tank and clean. I'll look at slave cylinder and figure out why there seems to be no connection between crankshaft and wheels. :omg:
 
If you are in 4th gear, and the starter spins the engine, but the car doesn't move in a gear other than reverse, it's unlikely to be od related. The sprag clutch will catch it on acceleration in forward gears even if the cone clutch is basically completely shot.

Sprag clutches can and do fail, though usually on the 85 and earlier j type Od units, when that happens, the gearbox mainshaft snaps off where it meets the od.

Maybe something nasty happened to it when towing it? Or maybe a tow guy removed the rear half of the driveline cautiously like you are supposed to on the automatic cars (unless it's an early bw35 double pumper or technically a zf auto with rear pump), not wanting to chance it or knowing it would be "fine" on a stick one if all was in more or less ok repair/intact.

It's definitely more common to see the clutch rusted together on cars that sit s real long time (like 10+ years), parking brake rusted up and stuck, and od orings shrunken and brit-ish od leaking worse than ever when put back into service.
 
So far I've been amazed how well things are preserved. Parking brakes and brake calipers are all functioning. And I really do believe the PO when he tells me it was shifting fine when he parked it. It was inside his nice garage and covered as well. I'll know more about it soon. This weekend I'll be auto crossing so no chance to mess with it. But after that, I'll really look into whats going on. It may be something as simple as the drive-shaft disconnected.

Kjets On a Plane said:
If you are in 4th gear, and the starter spins the engine, but the car doesn't move in a gear other than reverse, it's unlikely to be od related. The sprag clutch will catch it on acceleration in forward gears even if the cone clutch is basically completely shot.

Sprag clutches can and do fail, though usually on the 85 and earlier j type Od units, when that happens, the gearbox mainshaft snaps off where it meets the od.

Maybe something nasty happened to it when towing it? Or maybe a tow guy removed the rear half of the driveline cautiously like you are supposed to on the automatic cars (unless it's an early bw35 double pumper or technically a zf auto with rear pump), not wanting to chance it or knowing it would be "fine" on a stick one if all was in more or less ok repair/intact.

It's definitely more common to see the clutch rusted together on cars that sit s real long time (like 10+ years), parking brake rusted up and stuck, and od orings shrunken and brit-ish od leaking worse than ever when put back into service.
Click to expand...
 
Kjets On a Plane said:
Maybe something nasty happened to it when towing it? Or maybe a tow guy removed the rear half of the driveline cautiously like you are supposed to on the automatic cars (unless it's an early bw35 double pumper or technically a zf auto with rear pump), not wanting to chance it or knowing it would be "fine" on a stick one if all was in more or less ok repair/intact.
Click to expand...


You HAVE TO remove the drive shaft when towing a manual transmission ! The way they are oiled is the counter or layshaft turns and brings the oil up from the bottom of the case.
Idiots do this all the time just put it in nutral and go.
When you do that with the motor off only the output shaft turns. But the gears are connected to the input shaft and that ain't turning. The only lube there is whatever gear oil is on the bearings at the time. Not much. Tow it far enough and it's tost.

Worst one I heard of was a Dodge PU with a Cummins. Moron tow truck driver in Montana pulled it untill the bearings sized up and started turning the engine. That took out the injector pump. (they don't like running dry either)
That was a friend of my dad's truck and of course Inbred Hillbilly Redneck Towing didn't have insurance. So not only did he have to fix whatever was wrong in the first place he needed a tranny and a new injector pump.
 
^while this is true, the speed gear bushings have some friction, probably more than the needle bearing trans in the dodge or whatever, I'd guess that the countershaft still turns on the volvo trans and oil splashes around even in neutral. I've never heard of anyone roasting one.
 
Never worked on a transmisisson have you? When you get one on the bench pop the top off with it in nutral. Hold the input shaft still while turning the output shaft. You won't see anything turning inside because the output shaft isn't engaged to any of the gears.
Pretty simple math there's whatever oil in those bearings it's only going to lube it so long before it gets hot and burns out.
Now how far you have to pull it before that happens depends on the gear oil and how long it's been sitting there dripping back into the bottom of the case.
 
Well to my knowledge the PO did not tow the car at all. It was intermittently running when he tore the fuel pump out 10 years ago. I had it moved to my place on a flatbed, so I'm good there. I'll post what the issue was as soon as I get a chance to dig into it.
 
Issue solved.... When the clutch was depressed it blew the seal out of the slave cylinder. The seal is lodged not allowing the slave cylinder to release. So the clutch is stuck engaged. First time I've ever seen that.
 
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