shift point in th350

Discussion in 'The Garage' started by nerraw117, Mar 6, 2005.

  1. nerraw117

    nerraw117 1/2 ton status

    Jan 5, 2005
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    charlotte, NC
    Hey all, I just bought my blazer a few weeks ago, havent had time to mess with it really, but I noticed on the drive home, that it is shifting really high in the rpm band. O btw, it is a th350 backed by a np203, with a 350tbi motor. Anyway, the previous owner told me it had a shift kit, but is there any way I can adjust the shift rpm down? Does the th350 have a kickdown cable like the 700r4, or is it electric like the th400? Also, can I adjust the vacuum modulator to change the shift rpm, and which way do I turn the modulator to bring the shift rpm down? Long post, but thanks for any help. Steve
  2. diesel4me

    diesel4me 1 ton status Premium Member

    Jul 24, 2003
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    Fine tuning tranny shift points..

    The first thing to check is the detent cable adjustment,its important for it to be correct,also the vacuum modulator itself,make sure the diaphram isnt ruptured and allowing tranny fluid to be sucked into and burned in the engine,and that it has a good vacuum at the hose,no leaks or cracks(it goes to manifold vacuum,not "ported")and if that all checks out,the govenor is what really controls the shift points,the springs and weights in it determine the speed it will shift at--the detent cable and modulator do affect(up) shifting too,but not to the degree the govenor does..

    You can make it shift later and harder by turning the small screw inside the hose fitting on the modulator--it only changes the speed the shift occurs by 5-10mph at most--if it still seems to wait too long to upshift it could be the govenor was reworked with stiffer springs,or might be defective,the detent cable adjustment being too "tight" can make it take too long to upshift too--(most likely cause,especially if the carb has been changed to a different one other than the original Q-jet)also a pressure problem in the tranny can cause hard or late shifts too.( a partly clogged filter can cause pressure problems,among other things..)

    ..its usually the detent cable adjustment or the modulator thats the problem--usually it wont upshift out of first gear if the govenor fails,or its nylon drive gear strips,and pressure problems usually result in short life and or tranny failure in a short time--might not hurt to change the filter,fluid,and modulator (cost you less than fifty bucks if you do it yourself)and check the detent cable--good luck..

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