knocking, at about 1/8 note time

[Ed Fisher]

As you may or may not remember my car is a 1964 230sl with a 280 block and head that is nicely sorted now and running/shifting really well thanks to y'all.  I have just replaced engine mounts, engine support arms, transmission mount, and rear diff pivot mount.  The latest issue is that immediately after hitting a bump I get a trailing knock for about 3-4 1/8th note strokes and it sounds a bit like an engine part against body part.  Perhaps on the passenger side near the header.  However, at the local muffler shop we had her on the lift and the exhaust manifold and all related exhaust parts have plenty of clearance (the suspension was loaded as the car was resting on it's wheels on the rack).  I was able to see under the entire car and didn't really see anything else amiss either, that is no parts that looked dangerously close to touching.  Does anyone have any idea what could be rocking/transmitting immediately AFTER a bump is hit for 3-4 knocks?

Thanks for any and all help.

Ed Fisher
Dallas, Tx

[rwmastel]

The car's suspension was under a load, but was the exhaust?  It is hanging by rubber mounts, so it will bounce up/down.  Did you push the exhaust up firmly to see if you got enough movement to make contact?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Ed Fisher]

Rodd:

We did push and pull the exhaust and did not see any interference at all.  

Ed

[graphic66]

My car had a broken bottom mount on the radiator tank that mounts to the firewall. It was a real rascal to find. I just had to resolder the bracket. It would rattle after bumps.

[RBurg]

Ed: I had a very similar experience. I would get this clunk when I drove slow over the expansion joint which had a rather wide gap. After changing the totale rear suspension bushing - sub frame was alreay done and the motor mounts were check when we did the sub frame.

I fround the problem when I did a greasing with my new air greese gun. When the two upper fitting on the king Pin were greased I could see movement back and forth when I squirted grease into the fitting.

Being the king pin is under tension from the coil spring it is rather hard to tell if the bushing is woren.

The winter project will be to replace both r & l bushing and threaded supports.  You can replace just the outside cups but I feel the it may be worn on the thread support also. I don't have the part numbers or diagram. - maybe some one else can help on that. I know all three
parts run about $250.00 per side. The caps are around  $100 or so for eache set of 2.

Good luck with you project

Ron - Minnesota
71 280SL Tobacco "O GIGI"
97 E420 Silver Mist

[Ed Fisher]

Whoa, both of these (radiator lower support and king pin bushings) are great suggestions and places that I would not have gone right away, if at all.  Thanks fellas.  These are both salient points for my car as well since I have had the radiator out and one of my zerks on the driver's side king pin (upper) refuses to take grease.  It sure seemes like the problem occured after the motor/tranny/diff mount changes, but I could be mistaken.

Anybody else out there have a spot that they found that knocked after a bump?

Ed

[ja17]

Hello Ed,

The rear transmission mount is sometimes shimmed with a spacer to insure that the driveshaft does clear the bottom of the tunnel. If it is too close you may be bouncing the driveshaft of the bottom of the tunnel right behind the transmission.

Joe Alexander
Blacklick, Ohio

[Ed Fisher]

Joe:

This sounds likely, especially since I have noted that the gear shift lever actually has a little rocking motion to it now (since the mount is rubber instead of the petrified substance that came out in pieces).  The driveshaft on tunnel would be the right frequency and location.  Do you have any pictures of the stack-up, or can you give me a description of the placement of the shim, its thickness, etc?  Thanks a bunch Joe, I have a feeling that this may be indeed the culprit.

Ed Fisher

[Ben]

quote:My car had a broken bottom mount on the radiator tank that mounts to the firewall. It was a real rascal to find. I just had to resolder the bracket. It would rattle after bumps.

........yep good call I had this and it took me ages to locate it. Felt really silly when I did eventually !

Also I have seen the air pipe fron the WRD to the CSV hitting as it runs behind the block. There should be a little bracket to hold it but it is often missing !

I like Joe's idea too and must look out for that one !

Regards,
Ben in Ireland.
'64 230SL 4sp.