I question the thrid and fourth gear rpm speed up and would like to find out what year it changed. On my 73's with four speeds they speed up in fourth gear only. I just bench tested a new trans. pollak switch #3996286 mounted on the trans. and it only completes the circut in fourth gear so the system can't work in third.My question is my transmission shift rod in the trans. installed wrong or was their a change to fourth gear operation only.
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Lyle
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Re: C-3 TCS switch#3996286 operation
Lyle,
1970 and 1971 had both the 3rd ad 4th gear "speed ups". 1972 had 4th gar only. Can't say for sure about 1973 up, but it is likely it is 4th gear only. -
Re: C-3 TCS switch#3996286 operation
Do you know if the 72 TIJG has it correct as I am geting facts to try to change the 73-74 TIJG. I would think that the rod the switch rides on has a flat spot on it different than when it would if third and fourth both make the speed up. In my limited libray I could find only one part number for the arm and rod the switch rides on.Lyle
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Re: C-3 TCS switch#3996286 operation
You can expect to find a wealth of knowledge in the appropriate Chevrolet Chassis Service Manual. Expect to find a section dedicated to emissions control (which is what the 'feature' you're asking about falls under) and this generally starts with good narrative text giving theory of operation. Then, they proceed to walk through each functional sub-system and recite differences (and similarities) between specific models of Chevy along with the impact any specific configuration option brings (BB, A/C, Etc.). I think I'd go look there for the answer to your question.Comment
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Re: C-3 TCS switch#3996286 operation
Lyle,
I can only speak for 70 and 71 as I've been through the TCS operations for each. Someone with more 72 knowledge than I will have to chime in.Comment
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70-72 TCS write-up *TL*
Lyle, The "judging manual" preceding the one you are working on is 1970-72 TIM&JG, but it will not have the info you seek. What you want is in the 1968-72 Corvette Operations Manual & Performance Verification Test Guide. The current 1970-72 TIM&JG does not have any operations information in it. Pulling the 1972 only information from that manual that covers five years will be no mean feat. Good luck.
You are correct that the shift rod has two flats for those years that operate in third AND fourth gear, and only one flat for fourth gear operation only.
TerryComment
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Re: C-3 TCS switch#3996286 operation
I found in the text of the transmisson switch that it works in high forward gear and now think that 73 four speeds should not speed up in third gear.I will advise the team leader of my findings as both theTIM&JG ops check and OM&PVTG both say 3rd gear also.Lyle
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Re: 70-72 TCS write-up
Terry I thank you for the information on the flats and I will get with Marvin on this item so he can check on this information. LyleLyle
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Re: 70-72 TCS write-up *TL*
Let's put this on the agenda for our spare time at Seven Springs.
I expect to be traveling with Marvin tomorrow (really today now) so he and I should have ample opportunity to cover it. Perhaps we can all get together on the subject while we are there.
TerryComment
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Re: 70-72 TCS write-up
Terry's information is correct. Just about everything you wanted to know about the TCS system in your 73 is in your appropriate Service Manual. Terry helped me, a while back, understand and then troubleshoot my TCS. From personal knowledge, my 35000 mile 72 and my friend's 44000 mile 73 have the same fourth gear only operation of the TCS.
GaryComment
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Re: 70-72 TCS write-up
I have made the TCS system work for my corvettes and also helped others but had a question on just the one item. I was trying to pin down when and if the third gear operation stoped and with your help and others 72 is the year most people agree on . If one is getting ready to do a PV he would maybe spend time trying to fix something that never was. I know passing a PV is hard enough without added stress.Lyle
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