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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: markzepp820 on March 02, 2006, 01:15:00 am

Title: tranny question
Post by: markzepp820 on March 02, 2006, 01:15:00 am

I have a 79' C20 with a 350 motor, th400, and 3.73 rear end. When accelorating normaly, my truck shifts into second at 10mph then 3rd at 20mph, from there on the rpms just slowly get higher. I wanted to now, are these the normal shift points???

Title: tranny question
Post by: Lt.Del on March 02, 2006, 07:10:00 am

If that seems like it is too slow, just adjust the modulator.  Or replace it.  Take the vacuum line off of it, where it meets the trans and take a very small screwdriver and turn the screw inside the modulator.  I forget if it is clockwise to delay shift or counterclockwise, it's been a while.

Title: Re: tranny question
Post by: VileZambonie on March 04, 2006, 08:43:00 am

Yeah sounds like the modulator diaphragm is probably toast. They're cheap and easy (like my ex wife) and also make sure that your detent solenoid is receiving 12V from the switch on the gas pedal.

Title: another question
Post by: markzepp820 on March 05, 2006, 03:35:00 am

I noticed there is an orange wire coming off my tranny that leads to my inner fender and its not hooked up to anything. Is this the detent solenoid? Does the modulator control the shift points? Any help is appreciated. thanks

Title: another question
Post by: Lt.Del on March 05, 2006, 12:44:00 pm

The modulator uses vacuum from the engine to signify changing gears.  So, Yes, the modulator controls shifting points.

The first thing i'd do is get another modulator. They are very cheap. Get one that you can adjust.  By turning a tiny screw inside the vacuum tip, you can control shifting points to a certain degree.

The detent "cable", comes from where your tranny cooler lines meet the housing, atleast on a th350, i guess the 400 is the same.  It should go up to your accelerator mounting bracket behind your carb.  As far as any "wire" from the tranny, my 79, which i am sure is like your 79,  has no wire from it...that is until i put one on it when i put in a th350c lockup torque converter...i ran a hot wire that when switched activates the lockup feature.  A 79 didn't have one of these stock.  Your th400 may be a little different, but i still dont think a wire is stock.  



my new th350c that i put a wire to -to control the lockup converter.....

 




SgtDel

Edited by: SgtDel at: 3/5/06 12:54 pm

Title: tranny question
Post by: markzepp820 on March 05, 2006, 04:35:00 pm

thank you sgtdel.

Title: detent
Post by: markzepp820 on March 05, 2006, 04:38:00 pm

from what i hear, the th400 uses a detent solenoid to control the kickdown. Its a wire that leads from the tranny to the gas pedal with a 12 volt current. Does the detent just control kickdown passing gear only, or do the modualtor and detent work together?

Title: Re: detent
Post by: DnStClr on March 11, 2006, 10:22:00 am

On the TH400, the electric signal to the detent solenoid controls the kickdown.(detent) It replaced the cable found on the TH350. The wire hooks up to a self-adjustable switch under the gas pedal.
I'm gonna go out on a limb here and say that the solenoid inside the tranny probably works to change the angle of the stator blades in the torque converter. When that happens, you have a torque multiplier, and passing gear. So you need the 12 volts.
(now somebody with his saw will come along an straighten this out... )

Title: kickdown
Post by: markzepp820 on March 11, 2006, 07:36:00 pm

Thank you DnStClr, My detent was not hooked up at the gas pedal. So I hooked it up and it works great. When i floor it, i get this huge surge of power and then it kicks down like it should. Thanks again for the comments and help. Mark