Need GM# for TCS Relay on 71

[Ralph A.]

Need the GM part # for the TCS relay mounted on the firewall drivers side engine compartment. Reference made to it on Asm manual UPC 12 A16.
Thanks
RA

[Mike H.]

Re: Need GM# for TCS Relay on 71

Ralph,
I believe 3990842 is the original GM number for that relay.

[Gary S.]

Re: Need GM# for TCS Relay on 71

Ralph, a while back I was looking for a TCS relay and finally figured out that I think the only place to pick one up is used from a Corvette salvage yard. If you find another source, please post and let us know.
Gary

[Bernard S.]

Re: Need GM# for TCS Relay on 71

Ralph:
When I restored my 71, the relay was available from GM dealer-this was a while back. I also replaced the new cover with the old cover with the numbers and logo on it.

[Patrick H.]

Re: Need GM# for TCS Relay on 71

Gary,

They're frequently on eBay in NOS form.

Patrick

[Joe L.]

Re: Need GM# for TCS Relay on 71

Patrick-----

Yes, they do. I think that's because these things ended up "languishing" on the shelves of Chevrolet dealer parts departments and many came into the "surplus" inventories being auctioned off by individuals who purchased "bulk lots" of these parts. For the most part, the TCS systems were rendered inoperative by many owners. For the rest, they'd never really know when one of these relays failed, so one was VERY unlikely to ever get replaced (and, consequently, purchased).

They were, roughly, the old-time equivalent of the "skip shift" solenoid on 1989-05 Corvette manual transmissions, ZF, Borg-Warner, and Tremec. This solenoid, GM #1015404 (1989), 10140541 (1990-96), and 12523292 (1997-05) carries a GM list price of, respectively, $230.35, $779.49, and $128.90.

I wonder how many of these that GM sells, especially the 90-96 version? I'll bet not too many dealers stock these parts, either (just those that got "stuck" with one that someone ordered and didn't pick up). With respect to stocking, maybe they learned their lesson from those TCS relays?

[Gary S.]

Re: Need GM# for TCS Relay on 71

Thanks Patrck, but I picked one up at Carlisle from a wrecked 72 that had been burned. $2 and I had to remove it!

Gary

[Ralph A.]

Thanks ALL, found 2 resources claming they have

WIll make a post if they come up with the part.
Thanks again
Ralph

[Jack H.]

Doesn't exist, technically speaking....

The emissions system used in 1970 then again in 1972 was called TCS (transmission controlled spark). For one year only, in 1971, the Corvette emission system was known as CEC (combined emissions control), so you can't be looking for a 'TCS relay' for a '71 since they didn't exist/weren't used...

To be factory concours correct, you need a PAIR of CEC relays consisting of 3990842, reversing relay, and 3990843, delay relay. The delay relay has long been GM discontinued and your universe is whatever old stock might be here/there. The reversing relay is still available from GM, but it's appearance is detectably different from those used in factory original production (expect a 40% originality deduction from a knowledgeable judge based on lack of the Date and Configuration axis components of a correct factory original relay).

The two relays were mounted 'back to back' on the L-bracket of the firewall just ahead of the drivers seat roughly one foot from the WSW motor. The engine harness provided input/output connectors and a discrete ground line to make the relays electrically functional.

These relay controlled the carb mounted CEC solenoid (all Corvettes, base engine to LS-6) taking inputs from the engine temp switch (RH cylinder head) and the TCS switch mounted on the transmission. The position of the CEC solenoid (energized or non-energized) was dependent on:

(1) How long had it been since the engine was initially fired?
(2) Is engine coolant temp low, normal, or above normal?
(3) What gear is the transmission in?