I started a thread last week on the TCS problem on my 1970 BB with M-21. On a warmed up car in idle, the RPM should kick up to about 1100 rpm when put into 3rd or 4th gear. Mine was not. I checked the solenoid that distributes vacuum to the distributor by testing the continuity and that was ok.
I traced the wiring from the TCS solenoid to the TCS relay on the firewall. This relay had three connections to it. A continuity test on the prongs extending from the relay showed that one (upper, on engine side) was open. I ordered a new TCS relay (GM#3961573, now discontinued) from a dealer which still happened to have one in stock and it arrived in today's mail. Once installed, the new relay solved the problem. A continuity check on each of these prongs showed they are all closed circuits.
The new TCS Relay was still manufactured by the same company (LITTELFUSE, INC.) and looked identical from a judging point of view with the exception of the date code. Also, the origianl mounting tab has two holes while the new replacement has one hole and a slot for the other hole. However, once properly mounted, this mounting tab is not visible as it resides between the firewall and the oval mounting plate. The relay is held in place by two small black bolts that I fastened using a 5/16" nut driver.
The date code on my original relay is "6-0" which I interpret as June 1970. My car was built at the end of July 1970. The date code that is stamped on the new relay is "7262" which I guess is a Julian code representing the 262nd day of 19x7 (1977, 1987, or 1997). I do not know when the Julian date code replaced the month-year code that I observed on the original relay. I would be interested if someone had more information on this aspect of the relays.
Thanks for all those who were able to lend a hand and help with this minor project. Hope this post will help others with their troubleshooting of their TCS system in the future.
I traced the wiring from the TCS solenoid to the TCS relay on the firewall. This relay had three connections to it. A continuity test on the prongs extending from the relay showed that one (upper, on engine side) was open. I ordered a new TCS relay (GM#3961573, now discontinued) from a dealer which still happened to have one in stock and it arrived in today's mail. Once installed, the new relay solved the problem. A continuity check on each of these prongs showed they are all closed circuits.
The new TCS Relay was still manufactured by the same company (LITTELFUSE, INC.) and looked identical from a judging point of view with the exception of the date code. Also, the origianl mounting tab has two holes while the new replacement has one hole and a slot for the other hole. However, once properly mounted, this mounting tab is not visible as it resides between the firewall and the oval mounting plate. The relay is held in place by two small black bolts that I fastened using a 5/16" nut driver.
The date code on my original relay is "6-0" which I interpret as June 1970. My car was built at the end of July 1970. The date code that is stamped on the new relay is "7262" which I guess is a Julian code representing the 262nd day of 19x7 (1977, 1987, or 1997). I do not know when the Julian date code replaced the month-year code that I observed on the original relay. I would be interested if someone had more information on this aspect of the relays.
Thanks for all those who were able to lend a hand and help with this minor project. Hope this post will help others with their troubleshooting of their TCS system in the future.
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