72 Big Block Questions

[John Lejsal #32021]

First question:On the drivers side of the engine is a temperature sensor on the head. When I got the car in July 1999 the wires that go on this sensor were disconnected and taped up in a ball. I untaped the wires and found that the plastic holder/connector is gone. What exactly does this control? Is there a plastic holder/connector available? Does it matter which way the wires go on the sensor?

Second question: The automatic transmssion will not downshift(kick down) when the gas pedal is depressed to the floor. My research tells me that it is probably the detent switch. How do you check this switch to see if it is bad? The transmission works great and downshifts manually.

[Terry M.]

[John L.]

Re: 72 Big Block Questions

Terry,

I cannot believe I said drivers side. I ment passenger side as you suspected. Can you tell me about this sensor?

[Terry M.]

Re: 72 TCS - Joe or Bill Carpenter help this guy

Yes I can, but it is a looooooong story. I'll try to make it brief and suggest you wade through the archives. One of the posters here Bill Carpenter recently purchased one from Chevrolet and successfully replaced it, so maybe he will help you. Brief story: It operates a part of the emissions system that controls vacuum to the distributor by means of a solenoid on the intake, right in front of the distributor in your case. There is also a relay on the firewall that is involved and a pick-up on the transmission.

The Chevrolet Service Manual gives a description and troubleshooting guide. Check it out for this and a thousand other reasons.

The system (when working properly) basically only provides vacuum to the distributor: 1) When engine temperature is below 70 or so degrees (for faster idle on start up) or over 270 or so degrees (to help prevent overheating due to prolonged operation with ignition retarded). This is what that sensor on the passenger side controls. 2) In 4 th gear in manual transmission or high with TurboHydro transmission.

There should be a green wire with two connectors that has a little jumper between the two connectors. If plastic is melted use a plastic connector from turn signal flasher of any GM car of '60 to '90 give or take a few years.

Joe or Bill will help with the current GM part number for the sensor if yours needs replacement. I have heard horror stories about how hard it is to replace, but Bill tells me he had no problems. Key is right size socket - long bar and plenty of room, he says.

Do you need this system for the car to run - no. It might accelerate marginally better without it, but if you have the stock carburetor and stock distributor curve you may have to put up with minor idle problems without it. It would take a much longer post to explain why, but with vacuum to distributor all the time throttle plates will be in the wrong position to pick up the carburetor idle circuits without it.

Terry

[Joe L.]

Re: 72 TCS - Joe or Bill Carpenter help this guy

Terry and John-----

The current GM part number for the 70-72 TCS cylinder head-mounted switch is GM #25036519. Available at your GM dealer for about 16 bucks list. This will be a special order part.

[Bill C.]

Re: 72 TCS - Joe or Bill Carpenter help this guy

I just purchased this sensor from my local Chevrolet dealer, list @ $18.12. The new number is 12322552. The wiring harness is available from Dr. Rebuilt @ $15.00 and is his part #2515291. Now you have all the pieces, let the fun begin!!! You need to remove the oil dipstick, using a 6 point 24MM socket (when we are dealing in larger sizes, they run very close to our 15/16) and a 18" or 24" strong bar. Making sure that you have a good fit, with STEADY presure it should come out. DON'T jerk on the bar, this tends to round off the brass fitting. You should do this to a COLD engine only. Have the new unit ready with alittle grease on the threads do not use thread tape. If your real quick, you will only lose about a cup of coolant since the sensor goes into the cooling jacket on the head. I put my thumb over the hole temporarily till I could get the new sensor in place. I used a 15/16 box wrench to firmly snug the new one in place. Take your time, have fun and GOOD LUCK! Bill #20328

[Terry M.]

Re: Thanks Joe and Bill

And now John you have the whole story about that sensor.

Now don't tell me you want to make the TCS system work???

Terry

[John L.]

Re: Thanks Joe, Bill and Terry

Hey guys thanks for the information.

Terry - I only need it to work if I need it for a Performance Verification.

John