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TVS TCS Switch ASM for 1972 Riviera

Discussion in 'Buick FAQ' started by Daves72, Aug 8, 2015.

  1. Daves72

    Daves72 I get jokes.

    Has anyone seen one of these?

    [​IMG]

    The setup for the 455 GS and Stage 1 looks similar but the TCS and TVS are separate.

    [​IMG]

    I don't have either of these and my vacuum advance isn't working either. So, I'm trying decide how to handle this. This car is stock but I guess it won't hurt to set up my timing where the mechanical advance is all in no later than 2500RPM per Larry's instructions in the Buick FAQ. Would that negate the need for the TCS?

    I'm guessing the TCS is supposed to activate the vacuum advance when the transmission kickdown solenoid is activated. Is that right?

    It seems like the list of to do items on this car just keep growing....
     
    Daves72, Aug 8, 2015
    #1
  2. GSX 554

    GSX 554 Gold Level Contributor

    The TCS ( TRANSMISSION CONTROLLED SPARK ) is supposed to only allow vacuum advance in 3rd gear.

    The TVS ( THERMO VACUUM SWITCH ) send full vacuum to the distributor when the coolant reaches a certain point to speed up the engine and prevent overheating.

    You can eliminate both and run full vacuum to the distributor if you want.
     
    GSX 554, Aug 8, 2015
    #2
    72 Riviera TR likes this.
  3. Daves72

    Daves72 I get jokes.

    Thanks for the info. Currently I don't have either the TCS solenoid or the TVS but I do have the TCS solenoid connector from the engine harness laying loose. I have a replacement harness from M&H that I haven't installed yet partly because I wanted to get all the peripheral solenoids and switches in place first. The engine needs to be cleaned and painted also but that's another story.
     
    Daves72, Aug 8, 2015
    #3
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Dave,
    If you want to go for the concourse look that's fine, but understand that whole system was a performance, drive ability, and gas mileage killer. If you want the system, disable it so you have full time vacuum advance. The engine will run better.

    I don't know how original your car is, but if it has the stock original distributor (1112110), and you have it faithfully timed at 4* BTDC, that distributor only has 14-18* of mechanical advance. That means the total at WOT can only be 18-22*. That is about 10* shy of where it will make best power. If you power time it to 32*, the initial advance will be much higher, and that timing will wake the motor right up.
     
    LARRY70GS, Aug 8, 2015
    #4
  5. Daves72

    Daves72 I get jokes.

    Thanks Larry. I have no idea which distributor I have other than it's a Delco points type. Where is the part number on it?
     
    Daves72, Aug 8, 2015
    #5
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member


    Right on the circumference below where the cap contacts the base.
     
    LARRY70GS, Aug 8, 2015
    #6
  7. Daves72

    Daves72 I get jokes.

    Larry, it's 1111285 which looks to be for a 1968 400 or 430.

    [​IMG]

    [​IMG]
     
    Daves72, Aug 8, 2015
    #7
  8. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Yes, that is from a 1968 430 engine. Has 30-34* of mechanical advance. That means it needs to be timed initially closer to TDC. The 1112110 is a better distributor for performance. Pretty typical, someone replaced the distributor along the way.
     
    LARRY70GS, Aug 8, 2015
    #8
  9. Daves72

    Daves72 I get jokes.

    Thanks for the info! I've decided not to pursue adding the TCS/TVS stuff back on. I'll just have to tie wrap those connectors somewhere out of sight when I replace the harness. It would probably be just as well to cut them off but I just can't go hacking up a brand new harness.
     
    Daves72, Aug 8, 2015
    #9
  10. Nevada Boatail

    Nevada Boatail Well-Known Member

    Actually, from what I have learned, when connected properly (as per the diagram at the top of this thread) the vacuum advance will see "ported" vacuum at all times, except in the following 2 cases.

    1. The engine temp rises to 220. (The thermo part)
    2. The transmission is in 3rd gear (The electrical part)

    If either of these occur, then full manifold vacuum is applied to the advance. The theory is that if the engine gets too warm, advancing the timing helps cool it down. Also, when cruising in third, your pedal is light enough that full manifold vacuum exists and by aplying this to the advance, it advances the timing further and provides better economy at cruising speeds. A lot of people have disconnected/bypassed this item and just run full manifold vacuum. Which, at the end of the day, it's up to you. In my own experience, I found that by running full manifold vacuum AND with the timing setup correctly (right amount of mechanical and all in by 2500) my engine wouldn't idle smoothly. I finally went back to ported vacuum and it idles super smooth now, runs strong and the timing is set where I want it. Also, with full manifold vacuum, the moment you push the accelorator, the timing retards because you lose vacuum. With the ported, it increases. This also created a slight hesitation for me when connected to full manifold vacuum only. Now, with ported, the hesitation is gone and it's silky smooth off the line at a normal acceleration rate. Your mileage may vary, just my 2 cents.
     
    Nevada Boatail, Aug 20, 2015
    #10
    72 Riviera TR likes this.
  11. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member


    Actually, the ONLY time the switch supplies manifold vacuum is when the coolant temperatures rise above 220*. In 3rd gear, it supplies ported vacuum. There is no vacuum advance at all in 1st and 2nd gear. At part throttle, there will no difference between ported vacuum and manifold vacuum. Ported is sourced above the throttle blades, manifold vacuum, below the throttle blades. They will both go towards 0 at WOT. Manifold vacuum may respond a little bit quicker to throttle openings because the advance is already there as opposed to ported going from 0 at closed throttle to maximum as the throttle opens.

    Whenever you bring in the mechanical advance in early (2500 or earlier), it is necessary to limit the AMOUNT of vacuum advance. The reason for this is with stock springs, only part of the mechanical advance is in at cruise speeds. The 14-18* of vacuum advance brings the cruise total to about 40*. Bringing in the mechanical advance earlier results in all of your mechanical advance being in at cruise RPM. In this case, adding the 14-18* of vacuum advance can result in 50* total timing at cruise, and that can result in surge. I like to limit the vacuum advance to 8-10* maximum.

    [​IMG]
     
    LARRY70GS, Aug 20, 2015
    #11
  12. tommieboy

    tommieboy Well-Known Member

    I am reviving this old thread...

    In reference to the diagrams posted in the first post, does anyone understand the logic behind having two different TCS/TVS implementations on effectively the same engine in the same year? I realize that one implementation was for the GS and Stage 1 engine, but still, the logic defies me as both implementations seem to accomplish the same goal in the same manner.

    Thanks,

    Tommy
     
    tommieboy, Nov 16, 2024
    #12
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    They are both the same system. What you are looking at is the TCS, (Transmission Control Spark). The two diagrams are from the 350 and 455. They appear different, but work the same. They eliminate vacuum advance in 1st and 2nd gear, and enable it in high gear. It's all for emissions. It decreases response, performance, and gas mileage. The thermovacuum portion of it is there because the system uses relatively retarded timing at idle, with ported vacuum advance (none at idle). Engines are prone to running hot with the system, and when engine coolant temperatures reach 220*, the thermovacuum switch switches over to manifold vacuum. That immediately gives the engine 14-20* of ignition advance. The advanced timing and increased idle speed cools the engine down. So the TVS is a band aid for the TCS system. If you want to run it for originality's sake, fine, but the engine will run better and cooler without it.
     
    LARRY70GS, Nov 17, 2024
    #13
  14. tommieboy

    tommieboy Well-Known Member

    Hi Larry,

    Thanks for the reply. I should have been clearer with my question. Since they accomplished the same thing, I wondered why Buick didn't stick with one of the implementations for all the engines.

    Tommy

    [EDIT]

    I just checked some of the old service manuals and it seems that in 1971 they did exactly that; one style of TCS implementation for all 455 engines. So that makes sense to me.

    Also, it seems that the 1972 TCS/TVS combination switch assembly was a one-year deal.

    So it's becoming a little clearer on the hows and whys of this.
     
    Last edited: Nov 17, 2024
    tommieboy, Nov 17, 2024
    #14
  15. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Who knows? Just inefficiency? Two teams of engineers working on different engines, 350 and 455? Your guess is as good as mine.
     
    Last edited: Nov 19, 2024
    LARRY70GS, Nov 19, 2024
    #15

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