Fluid Drive Unit

[alan32433]

I bought a NOS mopar fluid drive unit for my 48 Desoto about 8 years ago when I first bought the car. It's been a long process as it's a frame off restoration and I am really slow. Long story short, I re-installed the engine and tranny today to make sure everything is running right before I install fenders etc. I wanted to adjust the valves running also. The engine and Tip-Toe transmission have been completely rebuilt. After fixing a plugged gas tank filter, the car started right up, but it has a vibration that seems to be a balance problem. I've double checked all the electrical, distributor is in correctly, wires have the correct firing order. The points are set correctly and the engine was timed statically at 0 TDC (spec). My big concern is that the NOS fluid drive unit could be for a Chrysler 8 cylinder and not be balanced correctly for my engine. Does anyone know if a fluid drive unit for a 8 cylinder car will actually bolt up to a 6 cylinder car? Just in case you are thinking I need to unbolt the fluid drive and rotate it to the correct balance, it will only go on one way as the studs are slightly offset to prevent installing it wrong. Again, question is, will a fluid drive unit from a 8 cylinder mopar install on a 6 cylinder engine, or will the bolt pattern prevent it.

Thanks - Alan

[alan32433]

Actually the car is not being driven and doesn't have a driveshaft installed. I just re-installed the engine and got it running in the shop. The fluid drive does have the correct 10W oil in it.

[greg g]

are your motor mounts new, how about the condition of you harmonic damper??

Edited August 2, 2009 by greg g

[Don Coatney]

Actually the car is not being driven and doesn't have a driveshaft installed. I just re-installed the engine and got it running in the shop. The fluid drive does have the correct 10W oil in it.

Unless I am mistaken the fluid drive coupling takes tractor hudraulic fluid and the transmission takes 10W oil. They are two seporate units.

[Frank M.]

As Greg says, check the left rear motor mount. There was a factory bulletin issued on tightness of the bolt,and in some cases --adding a washer to the bottom so as to get the right tension. I have come across this problem several times. Some unit housings have balancing weights welded on,and can possibly be knocked off during installation,or even being moved around. Frank M.

[Don Coatney]

I really dont think the rear motor mount would have any effect on an engine bolted to the frame and not being driven. I ran my engine when it was bolted to a piece of wood with no rubber mount and it did not vibrate. I believe there is an engine vibration issue here not an engine mount issue.

Is the engine running on all 6 cylinders? If there is a dead cylinder it could be misconstrued as a vibration.

[alan32433]

I read all the posts and thanks for the help. Here is some more to the story. My rear motor mounts are new but were not tight. I torqued them down and it did relieve some of the vibration, but it's still there. I can't find my timing light darn it, so I rotated the distributor a little either way and it had no effect on the vibration. Then I disconnected wires from the spark plugs one at a time while the engine was running. Number 3 and 5 seemed to make no difference and the spark seemed weak when I disconnected them, the rest of the plugs had a noticable effect on the engine and sparks were brighter. I already have new wires, rotor, cap, points and condensor installed. The plugs in the car are old ones, but it ran fine several years ago and it's been sitting in doors since then. None the less, I have some NOS A5 auto-lites I'm going to try later this afternoon. As far as the weak spark I have no idea. I have a NOS coil in the box, I might try that while I'm at it. Someone asked about my harmonic balancer. It seems to be fine and doesn't appear as though it has rotated. I do know when #1 is at top dead center on the compression stroke, my marker is dead on TDC and the rotor is at 7 O'clock with 153624 clockwise. Both my fluid drive and transmission have 10W oil in them like the mopar repair manual says. I checked the weights that are spot welded to the NOS fluid drive, the same number of weights appear on the NOS one as the two other old units I have. While I was rotating the fluid drive, I tried to find part number stampings, and there are none.

[48mirage]

I've got to challenge the 10w oil in the fluid drive unit. There are later versions ('51 and later) that are actually torque coverters that are full pressurized systems that are completely full. But my knowledge of the "fluid drive" units is that they called for a hydraulic fluid of 10weight. Not the same as 10w motor oil. I don't know if this could cause vibration problems but if the fluid in there foamed up it sure wouldn't transfer much power.

[Don Coatney]

Does the engine mis-fire? Your posting is not clear on this?

[James_Douglas]

The input shaft of the Chrysler 8 is MUCH larger than the six. The pilot bushing and roller bearing are larger as well. If you put in a six input shaft into and eight fluid coupling the driver in the fluid coupling would wallow around. It may hit the housing and/or it could vibrate like hell.

You would have noticed that the transmission input shat "fell" into place without any pressure at all. So I doubt that is the problem.

The second thing I would suggest is to send a set of motor mounts to Steele to be re-vulcanized. His mounts came back much better than a NOS set I had been using.

Make sure that the engine to frame bolts on the front are as far back in the holes as possible. I think that it is possible that I had a vibration issue that had the mount at a slight angle (base forward a bit) and the frame mount (the big "U") rubbed the block side mount.

On the subject of fluid, please read this post:

http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=14203&highlight=fluid+drive

and this post:

http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=14433&highlight=mobile

Best, James

Edited August 2, 2009 by James_Douglas

[alan32433]

You are correct on the fluid type for a 48 Desoto, I didn't say I used a motor oil in it. I just mentioned 10W oil and didn't specify what type. The fluid drive has 10W hydraulic fluid, the transmission according to my Desoto factory manual uses 10W motor oil. As far as the engine missing, it's not a real distinctive miss like I have experienced in the past. Remember, it's not on the road it's just running in the shop because it's not roadworthy. Like I mentioned earlier, the spark on cylinders 3 and 5 are noticably weak compared to the other cylinders. I'm getting ready to go out and change all 6plugs along with a new coil and see what happens. I have my fingers crossed.

[james curl]

Make sure all of the wires are seated all the way in the distributer towers.

[Niel Hoback]

Since 3 and 5 towers are next to each other, look inside for carbon tracks between the tips. That would explain the weak spark in both cylinders and a vibration when running.

[alan32433]

I replaced the spark plugs and reseated the electrodes on the ends of #3 and #5 cylinder spark plug wires. That fixed my problem. I was able to get the engine to idle down to about 450 rpm or so with no vibration and it purred like a kitten. Now I can tell I need to adjust the valves hot as the cold settings of .010 intake and .012 exhaust is resulting in a little tappet noise. The carburetor is leaking a little so I ordered a rebuild kit from NAPA. After I get that fixed, I'll pull out my long welding gloves and adjust the valves hot. Thanks for all the help from everyone.

[RobertKB]

Glad you found your problem. When adjusting your valves it is always better to have a little noise than none at all. If the engine is silent if means the valves are adjusted too tightly and you will likely burn a valve.

[greg g]

were it me I would lerave the valves alone foor a few miles, and where is the carb leaking?? If it at the trottle plate pivot, that usually indicated a to high float level.

[alan32433]

I had the engine runnings several different times for 30 minutes or so at a time with no problem, but the leak started suddenly. It overflowed the bowl so for some reason the float stuck open. Actually I have another carburetor so I am going to rebuild it and swap it out. I agree the valve adjustment should be loose and that there will be some tappet noise under normal conditions. What I was hearing was a little excessive. The manual calls for .008 IN and .010 EX hot. I will probably set the EX at .012 since most of what I will be doing is highway driving. Thanks for the suggestions.