Seatbelt weight sensor in '72

[Kurt G.]

I'm a bit confused. I am in the process of getting my very early (September 13, 1971) '72 coupe ready for PV in the near future and have been reviewing the test guide. I find on page 34 of the guide the mention of a 1972 passenger seat belt weight detector. Then, in the TIM&JG I find on page 12 the mention of a alarm added about January 1 to the lap belt retractor. My interior appears to be a carry over 1971 interior, based on markings on the carpet, date codes on the seat covering and door panels (July and August 1971). In addition I have no wiring harness, etc going to the seats.

My question here is how far do I need to go to prove that the weight detector was never installed on my car, or am I just basically screwed?

[Terry M.]

Re: Seatbelt weight sensor in '72

I'm a bit confused. I am in the process of getting my very early (September 13, 1971) '72 coupe ready for PV in the near future and have been reviewing the test guide. I find on page 34 of the guide the mention of a 1972 passenger seat belt weight detector. Then, in the TIM&JG I find on page 12 the mention of a alarm added about January 1 to the lap belt retractor. My interior appears to be a carry over 1971 interior, based on markings on the carpet, date codes on the seat covering and door panels (July and August 1971). In addition I have no wiring harness, etc going to the seats.

My question here is how far do I need to go to prove that the weight detector was never installed on my car, or am I just basically screwed?

You should communicate with the 1970-72 National Team Leader, Stan Falinski. Click on the button "Contact Information" above or the inside front cover of The Restorer. Get in touch with him since he is likely to be doing your PV, and ask him. My hunch is you will only have to tell him your build date and he will know, but neither I nor anyone else can speak for him.

[Don L.]

Re: Seatbelt weight sensor in '72

Hi Kurt.

As Terry suggests, no one can speak for anyone, including Stan. I don't have my JG handy but thought that this was covered. I could be wrong.

Here's what I "think" about your posted issue:
The 1972 AIM shows how the car was built at the END of the production run, reflecting all engineering changes that were made during the run. The seat belt monitoring system shown in the AIM was in accordance with a federal regulation, effective January 1, 1972. Accordingly, model year '72 cars built prior had a different seat belt warning system. My August '71 built 1972 convertible carries instead, a 15 second timer that automatically extinguishes the warning light (no interlock). There's a thermal switch located behind the RH lower dash pad, affixed to the w/shield frame/bulkhead that drives the warning light. There's also no wiring harness/connector on the early belt assemblies or in the console either. You will find a seat belt system label posted on the LH sun visor of later cars, describing the operation of the 1972 mandated system and the decal is dated approx. November 1, 1971. One more thing comes to mind. The 1972 AIM revision blocks show "redesigned and redrawn" in numerous places where the seat belts, the console and the electric harness are involved. All this gives me confidence that seat belt systems in early 1972 cars such as yours and mine are different than later 1972's (after the engineering change to comply with FMVSS mandate).

BTW, I've had my car judged 3 times, the last one being at the national level. My "15 second warning" system has passed all 3 times.

I think/hope I am right here and I further hope this helps you in your project.

[Terry M.]

Re: Seatbelt weight sensor in '72

I am sure you are right Don, especially about this being covered in the TIM&JG. While I haven't looked at the JG, I recall lots of conversation with one 1972 owner who was in the same position as you two, and almost came to the point of trying to install the later system in his car because he thought that was what he should have. Sometimes we over think these matters.

[Kurt G.]

Re: Seatbelt weight sensor in '72

Don and Terry, thanks for the replies. I have an early AIM dated 4/21/71 and it shows no indication of the system in question. I understand it does show up in a page of the AIM dated in October '71 but I haven't seen the page yet. I've also sent Stan an email for his thoughts. I'm thinking that since our cars are early production '72's they probably don't have it. Mine just has the 15 second timer, like Don mentions. Just wanting to have all my ducks quacking the same tune when I do get the PV done. I spent enough time in the windshield washer getting it to work that my hair doesn't need to be thinned next time I have it cut. That's another story.

[Reba W.]

Re: Seatbelt weight sensor in '72

I think we have pretty well determined that the sensor began sometime in late December or early January. (The JG says "around January 1). A chapter member, who is also preparing his December car for PV, does have the weight sensor. Kurt, your car is close to mine in build date, and we have Model C14 lap belts. They should have only the timer for the light.

The JG states that Model 15 (although it does not say it has the sensor, something for an update) began around December or January. The PV manual lists both systems (time and sensor) but not the dates. I believe at the time it was written we were still determining what was different about C14 and C15. The first edition of the 1972 owner's manual has no mention of the sensor, but the second does.

[Tom L.]

Re: Seatbelt weight sensor in '72

That timer is a unique piece. When I bought my oct. '71 build 6 years ago it worked fine. About three years ago it died. It's not reproduced and the two used ones I've found don't work either. While it's not fun to get at I might disconnect it and re-connect it whan I need it to work, if I had one anyway. Still looking for a solution to my problem.

Good luck with the PV!

[Don L.]

Re: Seatbelt weight sensor in '72

That timer is a unique piece. When I bought my oct. '71 build 6 years ago it worked fine. About three years ago it died. It's not reproduced and the two used ones I've found don't work either. While it's not fun to get at I might disconnect it and re-connect it whan I need it to work, if I had one anyway. Still looking for a solution to my problem.

Good luck with the PV!

Excellent point, and bang on Lynn!

My timer functioned just fine when I bought the car - then it didn't. That's when I began to learn just how dear these things are. Although used in many GM vehicles (not just Corvettes), it appears that they were only used for the first/early part of model year 1972. I found a guy to "rebuild" my original timer. What he ended up doing is removing all the guts from it and installing a mini circuit board that timed the circuit for 15 seconds. It was GREAT! No larger than 1/2" X 1/2 X 1/8", the board/timer fit inside the original can and was, therefore, completely discreet. This piece worked for approx 1 year then failed. I believe it failed due to heat build up in the board and no heat sink to handle the heat.

I began to investigate what would be needed to fix the circuit board, when one day I happened to GOOGLE the GM part number and found that there was a NOS part on ebay live. I bid and won the thing for about $7. I swapped out the new for the old timer and have been good since. Learning that these things are so hard to find, when I happened across another one in an ebay lot of various elctronic parts, I bought the lot for spare parts.

In the end, junk yards that have early 1972 GM cars left may be our best source for this hard-to-find part. there's probably opportunity to re-build them too - just find a way to protect against destructive heat generation.

[John H.]

Re: Seatbelt weight sensor in '72

I still clearly remember living through the nightmares of that seat belt/start/interlock system in production at Lordstown, from the testing machine at the end of the front seat assembly line in the Cushion Room that "sat" on the seat to make sure that the "membrane" seat sensor embedded in the foam worked within the specified weight limits (at 103 cars per hour), to the day when Congress finally reacted to the public outcry and repealed the requirement, and we mobilized repairmen to cut off the ground wires on the seat switch harness on every completed car still on the property.

[Tom L.]

Re: Seatbelt weight sensor in '72

Don, I hate you... I've been looking for a while, guess I missed that one. I did find a timer, with the help on an engineer firend, that might work. Won't fit in the can and should do the job but I challange anyone to see it if they wanted to. It ain't exactly in view.

It's a task on my "to do" list. Might get to it soon, I'll see. Seems that list gets longer, not shorter. Have fun!!

[Kurt G.]

Re: Seatbelt weight sensor in '72

Thanks Don, Terry and Reba. Horse beaten and done. I can now concentrate on the blasted windshield washer, which I think I have handled, and the A/C that isn't quite cooling.

[James B.]

Re: Seatbelt weight sensor in '72

I think we have pretty well determined that the sensor began sometime in late December or early January. (The JG says "around January 1). A chapter member, who is also preparing his December car for PV, does have the weight sensor. Kurt, your car is close to mine in build date, and we have Model C14 lap belts. They should have only the timer for the light.

The JG states that Model 15 (although it does not say it has the sensor, something for an update) began around December or January. The PV manual lists both systems (time and sensor) but not the dates. I believe at the time it was written we were still determining what was different about C14 and C15. The first edition of the 1972 owner's manual has no mention of the sensor, but the second does.

To confirm Reba's comments, my January 31st, 1972 build car has the seat sensor. It also has the Second Edition owner's manual (with the seat sensor reference).

James