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Sluggish downshift

Discussion in 'V8 Engine' started by Richard B, Nov 12, 2017.

  1. Richard B

    Richard B New Member

    Hi All

    So I have a P6B which is becoming hesitant when pulling away. I inititially thought that it was the idle speed being too low. It was indeed too low and is now adjusted to about 650rpm.... checked with a tacho. However this hasn't really solved the problem. I now think it might be because it is not changing down into 1st at a junction. Also kickdown requires some persistence to get to work.

    Any suggestions?

    Thanks

    Richard
     
  2. harveyp6

    harveyp6 Well-Known Member

    There are 2 things you can do to check if this is the case, firstly after coming to rest, move the lever to "1" and see if that improves matters, if not you are getting the 2-1 downshift, and if you're still not sure, come to a stop in "D", and then select REVERSE, if it hasn't changed down into FIRST, you won't go backwards.


    That would cause the problem, so make sure you're getting full throttle, and that the kickdown cable is correctly adjusted.
     
  3. Richard B

    Richard B New Member

    Thanks Harvey,

    Is there a write up on the full throttle and kickdown cable adjustment?

    Sorry.... probably really basic stuff.

    Thanks

    Richard
     
  4. harveyp6

    harveyp6 Well-Known Member

    It's been covered a lot on here before, but is probably difficult to find in isolation, but you need to eliminate any play in the throttle linkage, make sure you're getting full throttle (correct adjustment, no worn bushes, and no carpet or mats wedged under the pedal), and then set the cable to the point where there isn't any slack, but it's not so tight so as to be holding the valve open in the box. Slack in the cable gives early upshifts and in the extreme a loss of kickdown, too tight and the upshifts are too late, often with the need to lift off the throttle to prompt the upshift, and there is often a clonk on the 2-1 downshift on a closed throttle. You just need to find the sweet spot in the middle, which you can then compare with the shift speeds listed in the WM.
     
    PeterZRH likes this.
  5. PeterZRH

    PeterZRH Well-Known Member

    Yes, there's a lot of slop as the linkage is frankly crap quality. I had to replace all the bushes and make a new coupling BEFORE I could adjust anything properly. The reason I got great MPG when I first had my car was indeed that I couldn't open the throttle 100%.
     
  6. Richard B

    Richard B New Member

    The Peter. Sounds like this could be the problem. Will have a look tomorrow
     
  7. Richard B

    Richard B New Member

    So I replaced the bushes and the white plastic coupling. Huge difference. Without any further adjustment the kickdown now works perfectly. Still a bit slow pulling away from junctions.

    Carburettors?

    Richard
     
    PeterZRH likes this.
  8. Penguin

    Penguin New Member

    combination of low octane fuel and retarded timing?
     
  9. PeterZRH

    PeterZRH Well-Known Member

    Result. Utterly rubbish design is it not?
     
    Richard B likes this.
  10. Richard B

    Richard B New Member

    You are right.... I've made sturdier things out of meccano!
     
  11. Richard B

    Richard B New Member

    Maybe.... but it's a new issue. Timing is 2 deg BTDC, fuel used is 97 and always has been
     
  12. classicalgreen

    classicalgreen Active Member

    2 deg? wow I have mine set at 6 and am thinking of advancing to 10 deg BTDC. ( no pinking) is sluggish but I have not changed cam yet and compressions are around 145 psi so adequate but not best. ( dry test) . kick down is rubbish .not even sure it works! have changed bushes and no play as far as I can see. i was looking at gearbox fluid level maybe ,,,have checked all spark plugs with gunson and all blue. carb balancer used too. fuel is 97 ron and have thrown the fuel enhancing metal stuff in tank.
     
  13. Richard B

    Richard B New Member

    6deg BTDC is the setting for 100 ron fuel.....will 10deg BTDC cause problems?
     
  14. PeterZRH

    PeterZRH Well-Known Member

    If it doesn't pink it's fine. 6 BTDC is very, very conservative. There are endless threads on tuning sites about this. Ultimately a worn engine will tend not to make the compression anyway and will be fairly tolerant. Each one will be different.
     
  15. Penguin

    Penguin New Member

    2 degrees is very retarded, most v8 P6's we see are happiest around 8 degrees ( vac disconnected)
     
  16. harveyp6

    harveyp6 Well-Known Member

    Removing the vac doesn't make any difference, other than increasing the idle speed a bit.
     

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