If the engine is out, check the scavenger pump!

I was given a 1983 engine a while back.

When I first installed it the clutch dragged very bad. By drag I mean it wouldnt completely release when the clutch was pulled in.
This made it impossible to get into neutral and shifting was very difficult.

I tried a flush with MMO with no improvement. Maybe it helped slightly but I contributed that to the thinning effect MMO has on the oil.

I pulled the rear cover to inspect for something out of place and tried a different cover which has a earlier actuating mechanism.
No improvement.
Next I swapped clutch plates and hardware from a known good working clutch.
Still no improvement.
What was really throwing me was the clutch and shifts worked beautifully for the first 3 miles and 4-5 stops and starts.
The exact same symptoms happened after 3 first runs, 2 times opening of the rear cover and the first run after installing the engine.

This is what clued me into the drag must have something to do with some kind of change taking place and led me to the problem and solution.

What I thought was odd was I'd get at least a 1/2 quart oil out when taking the rear cover off.
Looking at another engine I have I couldnt see any way for that oil to drain into the engine when it was sitting like during a oil change so that would mean at least a 1/2 quart of old oil would stay in the engine during an oil change. That didnt seem right.

With these 2 clues, drag starts after a time and oil remains in the rear cover, the drag had to be too much oil around the clutch assembly.
After pulling the engine for the 3rd time, I found the scavenger pump was plugged with debris.



Apparently these clutches, though wet in design, arent designed to be immersed in oil.
From what I can gather on the net, oil is there to cool the clutch and has very little to do with it's operation.
Evidently what was happening was the scavenger pump was not removing the "excess" oil surrounding the clutch and the oil was "hydraulically" causing the drag.

After cleaning the debris out the clutch has worked great.
Some have argued the debris was getting in between the clutch plates. I disagree with that theory because the rear cover design and oil flow path would prevent debris sitting below the scavenger pump from getting up around the clutch area.

After 400 miles shifts are still very smooth and going into first at a stop is just a click instead of the usual clunk and jerk.
Getting into neutral is usually easy. Sometimes it wont quite go in but letting the clutch out slightly then pulling it in it will go right into neutral. That has something to do with getting the gears and cogs to line up.

So if you have the larger rear engine cover off anyway, remove the scavenger pump, wipe out any debris sitting there on the engine case, and make sure you can see into the impeller thru the pickup tube that there isnt any junk plugging it up.

Otay...so what the heck IS that stuff? Looks like a couple of tree leaves, and some buttons off of a shirt! :shock:

A "wet" clutch isn't supposed to be bathed in oil all the time. The oil is basically a friction cooling fluid, and it helps with the longevity of the friction. A multi-plate, dry clutch in that capacity would engage waaay to harshly for normal applications. The oil is a cushion, but it has to have an "escape route" when the clutch pac is applied. Some clutches have grooves in them for this, some clutches are "wavy". All need some way to exhaust the excess fluid from the apply surfaces.
On some of the later model GM automatic transmissions, the steel plates have slotted holes in them, called "turbolators". The idea is to give the fluid more escape routes, plus the holes also "scrape" the fluid off of the clutches to keep them from dragging. :mrgreen:

Dan, do you have to pull the clutch basket to check the pump? I pulled the back cover off the '81 and I cannot see where to check for a clog.

Yes, clutch basket has to come out.
The pump location is circled in red.



The pump is chain driven by the back side of the clutch basket.
Look under the basket and to the left you'll see a hex bolt, 10 mm I think.
Going off memory, that bolt has to come off then the clutch basket, pump sprocket and chain needs to come off as a unit.

I think then 3 bolts have to come off to get the pump out.

I decided to post some pics of how to get to the pump and check it:
To remove the clutch basket, there is a circlip on the shaft that is pryed off gently. I used a small flathead screw driver.




Be careful of the thin gasket in the pump cover. The inlet is at the bottom of the pump. You do not have to remove the cover to remove the pump. I am only illustrating the inside of the pump for inquiring minds!






You can see in this picture that the inlet hole (the square hole) is pretty small.

Great post! Thanks for the pics.

yeah gerry good pics this is going to help me for sure soon ive never been there before :mrgreen: