OC-3 Transmission/Differential (Clark unit) Rattling Noise in Neutral

GlenT · October 29, 2014, 12:41:19 AM

I have been doing repairs on an OC-3 (Serial no. 1WH384) since July and finally got it running for more than a few minutes. The Transmission/differential unit (Clark unit) Main shaft bearings are new, the clutch shaft bearings and the propeller shaft are new. There is no play in any direction on the Clark Main shaft or clutch shaft. The noise is noticeable in neutral and is like a rattle and is more apparent at some RPMs than others. It is like something is loose in the Clark unit. I ran it without the propeller shaft and it was quiet. I thought it might be slop in the spline shaft to propeller shaft where the cotter pin goes so put in a 7/32 roll pin and there is no slop in the connection there and the noise does seem to come from the Clark unit.

When in neutral, is there anything moving in the Clark unit other than the Main shaft and Main shaft bearings? I did replace the spacer in the Clark unit transmission that seperates 1st and 2nd gear because I wrecked the original driving out the bearings. Were there different length spacers and I got a shorter one and two gears are rubbing? I took it for a ride and everything seems to work well but the noise in neutral is going to drive me more nuts than I am now!

Any ideas would be appreciated.

Doug424 · October 29, 2014, 01:14:49 AM

The universal joints might be making the noise. If the have any play at all, they will rattle until you put them under load. I doubt there is anything in the transmission that would make the noise, unless something is badly worn. I can't really say about the spacer, but I doubt there were different sizes. Assuming you put the transmission together properly, it's hard think there would be a rattle coming from it.

GlenT · October 29, 2014, 12:22:45 PM

Doug, you got me thinking about the drive train. There is slop between the clutch shaft and the new clutch disc. The splines on the clutch shaft were very good. I put in a cheap disk I found on ebay and I don't think it had the dampening springs on it. Do you or anyone else think the slop between the clutch shaft and the clutch disk could transfer noise so that it seems like it is from the Clark unit and should the clutch disk have the springs on it?

Doug424 · October 29, 2014, 01:29:50 PM

They don't have dampening springs, that's the correct clutch plate. Do you feel any play in the universal joints themselves? They are dry joints, metal on metal and will rattle.

GlenT · October 29, 2014, 05:17:44 PM

I did lots of listening and the rattle is definitely from the Clark unit. I replaced both bearings on the Main shaft before I got it running.

Doug424 · October 29, 2014, 11:31:10 PM

Has me puzzled to. Most every one I ever ran had some rattle, but it was always in the joints, but all that I had were with old joints.

GlenT · October 30, 2014, 11:37:44 PM

I have a Vega clutch disk on order. The Vega disc has 6 springs which should help dampen the disk to clutch shaft spline play. The new disk I had on, the possible rattle maker, didn't have springs and there was more slop between it and the clutch shaft than with the old disc.

I did some googles on "clutch disc rattle" and found this to be a common problem and the springs help dampen the rattle. There can be a problem also where loose springs can cause a different kind of rattle but I'll take a chance on the Vega disk (made by Sachs).

I'll post on the results when I get the Vega disk installed. It is getting cold here in MN and the fingers don't work to well then.

lsamuels · October 30, 2014, 11:57:10 PM

When you have the clutch out check the flywheel bolts. A loose flywheel will rattle in neutral but not so much in gear.

Blake Malkamaki · October 31, 2014, 12:29:15 AM

I have a dual disc clutch in my Cummins/Dodge Ram and it can rattle pretty good while in neutral. Push the pedal in and it stops. Let it out and sometimes it's quiet. Under load and in gear it is fine. I think it's just a bunch of little sloppy places between the parts that add up and rattle.

GlenT · November 05, 2014, 01:06:57 AM

The Vega clutch with springs is much quieter than the no-name disc I put in a couple months ago. The Vega clutch has 6 springs, is made by Sachs, and fits much tighter on the clutch shaft splines. There is still a little rattle but I guess that is normal according to what I have read and my bro-in-laws OC-3 rattles a little at slow idle also. My OC-3 needs a carb. overhaul, Mag. overhaul, rings, etc. I'm thinking if I can get it to run smoother there will be less rattle.