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LateApex
10-14-2022, 12:18 PM
I have the standard Moser 8.8" 3-link rear on my coupe. How much noise is "normal" for this gear on gear design?

I have a grand total of 450 miles on the coupe since getting some tags. I am babying the car, or "breaking it in", tweaking alignment etc, and running up and down some of the local canyons. Very impressed with handling and balance, ..., etc.

Yesterday I am running down a concrete road, with the usual seams every 20' and the typical pitching like a carnival ride that comes with concrete roads over expansive clay soils. I starting noticing a serious clanging (over the sound of the exhaust. ) To the extent I pulled over to make sure I wasn't bouncing a side pipe down the road. The sound appears to be coming from the rear. Can't find a thing. I ease onto a black top road and head for home and shop. On that black top, the racket disappears.

Hmmm ... Up on the stands, everything is tight, from suspension fasteners to to U-joint bolts and brake calipers. The only thing I notice is what seems like excessive axle lash and end-play. I contact Moser for good measure this morning. And the basic answer I get is "Some end play is normal (maybe 3/32" in my case?), the gear on gear design comes with some gear noise, and measuring lash is challenging." When I was looking at play, with the car on the stands, I can dither one wheel and guestimate how far I can rotate before other components, like the other wheel and driveshaft move. That too is about 3/32", as measured at brake disc rim, which is about 1/4" at tire diameter.

I am guessing that this amount of play is pretty typical.

I am at a bit of a loss to explain how a pumpkin full of gear oil can clash gears enough to sound like one is dropping metal on the highway. So this is probably a red herring. Have others had this experience though?

And yes, there is a slight weep through the cover gasket too (yep, seen those threads ;-)

Back to crawling around on the shop floor. Going to check exhaust inserts next ....

Papa
10-14-2022, 12:29 PM
Does the Coupe use that same fuel tank setup as the Roadster? If so, be sure the straps are fully tightened. I had a lot of "metalic" noise when I first got my roadster on the road that turned out to be the fuel tank moving around.

I do also hear a bit off gear noise at cruising speed, but that is a much different sound.

Dave

LateApex
10-14-2022, 12:41 PM
Yes it does (I believe). The straps seem quite tight and I can't get any movement pushing from below. I'll add looking above the tank - maybe something is slapping around ....

LateApex
10-14-2022, 01:15 PM
Note to self (1): Re-tighten header ball joints at 450 miles. Matter of fact, it is a great time to go through the FFR Race checklist (and your own checklist). Not convinced this was the source of my "noise", but it DID sound like I was dragging a side-pipe (even though no dragging was involved ...)

Note to self (2): Next time I build a car, it will be AFTER I install a lift system. A year of rolling around on the floor, while a modest ab workout, is getting a little tired :-)

It is interesting (to me anyway) how ripping up and down mountain canyon roads in a new build is just lovely, and trundling up and down city streets not only irritates me, but the Coupe as well :-)

Still crawling around on the floor ....

drewr
10-14-2022, 01:24 PM
Can't imagine "clanging" is coming from the rear end gears. Maybe suspension, like the panhard bar mounts, banana mount, etc. Maybe the heim joints? Drive shaft touching the frame/safety loop when going over a bump?

LateApex
10-14-2022, 02:18 PM
Can't imagine "clanging" is coming from the rear end gears. Maybe suspension, like the panhard bar mounts, banana mount, etc. Maybe the heim joints? Drive shaft touching the frame/safety loop when going over a bump?

Yep, and Nope - Everything is tight and good clearance. There is not a whole lot of suspension movement unless one is "getting air". It is more like a skate board :-)

My current working theory is that the side pipes were "checking", that is the ball joint fasteners had loosened substantially during thermal cycles of break-in (despite bona fide lock nuts), and the side pipes were moving.

Another run this afternoon should confirm (or refute) this theory :-)

Thx!

sread
10-15-2022, 01:38 PM
I have a Moser 3 link rear axle on the hot rod and recently noticed what seemed to be excess rotational play at the left rear wheel. Made a noticeable clunk when rocking it back and forth and sounded like it was coming from the diff as excess back lash. I was just about to open the cover to look for a cause and discovered it was actually caused by one of the bolts in the lower control arm, which had loosened just enough to allow some slight movement of the heim joint.
Probably not the cause of your clunking over expansion joints but definitely something to look at if it seems like you have extra rotational play in the rear.