Securing ECU mounting tray

[BladeBronson]

I found today that some loud clunking that I hear when going over rough roads is the ECU mounting tray jumping up and down. It looks like there's a screw holding the inside corner down, but the outside edge flops up and down. How is this supposed to be secured, or what is the best way to secure it?

[bigmac]

Pretty sure it's 2 screws that screw into rivnuts.


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[David T]

Are you talking about the one in front above the steering column or the ones behind the driver's seat?

[jwrayth]

The ECU tray is indeed mounted into the tub via two rivnuts. I recently replaced mine whilst doing some other modifications;

http://i.imgur.com/uh0E4PNh.jpg

There is one at the top of the bracket not visible in my photo, and one at the bottom visible in the bottom left. I'd recommend replacing the foam underneath the bracket if you really want to reduce the rattling as in my case the old foam had mostly disintegrated so it meant the ECU tray did not have even support. New foam, new bolts into the rivnuts and tightened down and you should be good.

[DMCMW Dave]

Add another screw at the outside edge. Keep in mind that the other end of the screw will be sticking into the area above the tire, so use a rivnut and sealant.

[David T]

Add another screw at the outside edge. Keep in mind that the other end of the screw will be sticking into the area above the tire, so use a rivnut and sealant.

Instead of the usual riv-nut there is an alternative. Later Lotus's used a brass nut in a rubber sleeve instead of aluminum riv-nuts. If you can get them it is a nicer solution. The steel screws eventually rot to the aluminum riv-nuts and when you try to remove them they spin so you have to cut or grind them out. If you stay with the aluminum riv-nuts at least use some Never-Seize.

[PJ Grady Inc.]

Instead of the usual riv-nut there is an alternative. Later Lotus's used a brass nut in a rubber sleeve instead of aluminum riv-nuts. If you can get them it is a nicer solution. The steel screws eventually rot to the aluminum riv-nuts and when you try to remove them they spin so you have to cut or grind them out. If you stay with the aluminum riv-nuts at least use some Never-Seize.


Those are known as well-nuts. While they don't rust they are not particularly strong. The better solution is a stainless 5mm bolt with a stainless or plated steel riv-nut. In either case either Tef-gel or anti-seize should be used on the threads.This riv-nut suggestion is rather complicated as you must remove the tray and computers completely to install the riv-nut. The whole process can easily take an hour to do.

There is an even better fix IMHO. It's common for the driver side computer tray to bounce over bumps on the fiberglass.

When I get this complaint I've found a much easier solution is to put a piece of double-sided tape between the tray and the body. To do this remove the wooden inspection cover over the tray behind the seat. Remove the locking stowage box cover with the ignition key. From inside the stowage compartment push up on the tray and use a cloth saturated with solvent to clean the contact faces of the tray and F.G. body ledge it is resting on. Install a 2" x 1/2" piece of 3M tape or equivalent between the cleaned surfaces and reinstall both covers. This is just as effective, less invasive, and takes just 5 or 10 minutes. You can substitute thin doubled sided foam tape to equal effect....no more noises.
Rob

[BladeBronson]

Cool, I think I've got it now. The mounting tray is screwed down both at the top and the inside corner. I pulled up and down on the tray tonight to try to figure out where the loud clacking noise was coming from. In the cubby behind the driver's seat, the Jetronic lambda ECU has a slotted metal tab at the bottom that was slapping on the fiberglass rear of the cubby. I lifted the tray a bit and cleaned beneath it with alcohol and jammed a piece of industrial strength double sided tape between the tray and maybe a piece of rubber. More importantly, I put another piece between that slotted tab and the fiberglass wall. The tray doesn't really move now.

Thanks everyone.