1970 TCS 3rd/4th Gear Vacuum Activation
I just got my 1970 LS5 TCS system working when the engine is cold and when it is fully warmed up. There was a fantastic article in a recent Restorer magazine on how to fix a 1970 TCS relay, and it really worked! My problem now, there is no distributer vacuum advance re-activation when put in 3rd or 4th gear! I took the trans switch out, and the continuity changes when manually moving the steel ball in and out. I even tried a second switch, same thing . I decided to look inside the hole where the trans switch screws in the trans side cover, and I did not see any machined flats on the exposed shaft when in changing from 2nd to 3rd gear! It looks the same when in 1st and 2nd gear. It is a 1969 dated trans (P9H04A) not original. What does this mean? Can this be fixed?
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White 1970 LS5 390/454 -
Re: 1970 TCS 3rd/4th Gear Vacuum Activation
Chris------
The 1969 Muncies used shifter shafts of GM #3950308. I do not think that these shafts have provisions for TCS switch activation. 1970-74 Muncies used shafts GM #3952649. These shafts do have provisions for TCS switch activation. So, you need the latter shafts which will work just fine in a 1969 transmission. The problem is finding them as they are long-since GM discontinued. They might now be available in the aftermarket. I'd contact a transmission parts source like Larry Fischer in New York.In Appreciation of John Hinckley -
Re: 1970 TCS 3rd/4th Gear Vacuum Activation
Then why does this 69 transmission have a trans side cover with a TCS mounted switch?White 1970 LS5 390/454Comment
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Re: 1970 TCS 3rd/4th Gear Vacuum Activation
Chris------
Simple-----someone has replaced it over the years. The 1970-74 sidecovers are compatible with any 63-69 Muncie. In fact, the cover with TCS fitting replaced the covers without the fitting for all 63-69 SERVICE in June, 1970. The cover was supplied with a special plug for the fitting for those applications not requiring TCS. For those with TCS the plug was removed and replaced with a switch.
If your transmission's side cover actually has the switch installed, then it was likely a cover removed from a 1970-74 transmission and transferred to yours. The switch was left installed because they lacked the special plug, so they just used the switch as a plug. However, they transferred the 1969 shifter shafts to the replacement cover. MANY Muncie transmissions are, by now, a "mix-and-match" kind of thing.
I don't know of any 1969 applications, Corvette or otherwise, that originally used TCS.In Appreciation of John HinckleyComment
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Re: 1970 TCS 3rd/4th Gear Vacuum Activation
Ok, so the big question is, IF, I find the correct 3rd/4th gear 70-74 shifter shaft to swap out, can this be done while the transmission is still on the car? How do I contact this Larry Fischer of New York? Thank so much for this information!White 1970 LS5 390/454Comment
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In Appreciation of John HinckleyComment
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Re: 1970 TCS 3rd/4th Gear Vacuum Activation
I just happen to have my trans out of my '70 Chevelle. I took some photos of the shaft you are looking for your trans. If you can't find a shaft I can post the measurements if you want to try and modify the one you have now.
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100_4912.jpgComment
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Re: 1970 TCS 3rd/4th Gear Vacuum Activation
Chris,
I'm 99% sure that you will have to remove the DVR head pipe to get the cover and shaft out. As well as swinging the 4spd control linkage up and away from the cover.
If you don't mind doing some extra work, it helps a BUNCH if you can rotate the tranny about 30-40 degrees in the direction of the DVR side.
Just allocate a Saturday day for the job.Comment
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Re: 1970 TCS 3rd/4th Gear Vacuum Activation
Thanks Erich for the a[FONT='Calibri','sans-serif']wesome pictures, that will help allot![/FONT]
[FONT='Calibri','sans-serif']Bill when you say DVR Head pipe, do you mean the driverside exhaust header pipe? Not sure what DVR is? Thanks.[/FONT]White 1970 LS5 390/454Comment
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Re: 1970 TCS 3rd/4th Gear Vacuum Activation
DVR == driver.. sorry for confusion.
and yes to the head pipe. I am reasonably sure there is not nearly enough clearance to slip the forks and cover off.Comment
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Re: 1970 TCS 3rd/4th Gear Vacuum Activation
Chris -
Put the transmission in 2nd gear before removing the side cover so the 1-2 shift fork doesn't hang up on the edge of the opening.Comment
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Re: 1970 TCS 3rd/4th Gear Vacuum Activation
Chris there is an advantage to bypassing the TCS solenoid and using a direct connection of full time advance to the vacuum advance can 100% of the time. Better gas mileage in the city driving and a cooler running engine in traffic. First modification I made to my new 70 over 40 years ago was full time advance 100% of the time.Comment
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Re: 1970 TCS 3rd/4th Gear Vacuum Activation
Jim, I am purposely getting this TCS working on my 454! I just had full vacuum running on it and it is way too much advancement with the centrifugal and vacuum. It would be backfiring or popping in a fast rpm decel and I was out of idle adjustment once the engine was fully warmed up. The idle screw was backed out all the way, and was a very difficult idle because the vacuum advance increased rpms to a point where the throttle plates were practically closed! Now, the vacuum advance cuts off before full engine warmup, and I can adjust the idle screw to a steady 700 rpms, and have an incredible sounding low rpm big block exhaust gurgle! Before this, the idle would be constantly roaming. This is the first time in years it has a steady idle! You didn't state if your 1970 is a big block or small block? I hope this makes sense. I just don't have the high speed vacuum advance right now.White 1970 LS5 390/454Comment
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Re: 1970 TCS 3rd/4th Gear Vacuum Activation
Never experienced your conditions using full time vacuum advance between the carb and vacuum advance unit. Is your centrifical advance and vacuum advance unit original? Centrifical advance pieces need to be clean to operate freely. A previously owned Corvette had a unclean centrifical advance that only retract when the engine was cold and stay in centrifical advance at operating temp. It affected idle. My 70 is a 350/300. Gas mileage improved in the city improved about 3mpg bypassing the TCS and using full time vacuum to the vacuum advance. I saw no advantage in letting the TCS remain in control of vacuum. If your engine gets to hot, the temp unit in the right cylinder head comes into play and allows full time vacuum through the TCS to reduce engine temperature. This function verifies that full time vacuum is beneficial to the engines operating temperature.Comment
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Re: 1970 TCS 3rd/4th Gear Vacuum Activation
Jim, the whole distributor is new and stock setup, but not original, I think the centrifical advance works too well added to the engine vacuum gives it too much timing advance! This 454 seems to have allot engine vacuum at idle. I have measured it, but don't remember what the number was. No engine temp problems. This is a completely restored car.White 1970 LS5 390/454Comment
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