Where is the vacume modulator on the transmission

a vacum modulator does not prevent a car from shifting into gear. Usually when a car fails to move, internal parts of the transmission break and sometimes shatter prevent the clutch pack from functioning. The purpose of a vacum modulator is to allow the transmission to shift smoothly from one gear to the next, but now on allot of cars these days transmissions are solely controlled by the computer. If you transmission does have a vacum modulator then your will find a steel vacum line from the engine going to your transmission with short pieces of hose connecting the lines together.

I don't know about a 1996 modle, but older chevys had a vacume modulator right side of transmission ,above pan some where between frount corner, and middle of transmission.
if the vacume line came of motor would rev extreamly high before a shift,(if it ever did)
my 1988 GMC with 700R4 trans does't use the modulator valve. yours may not either, but it's worth a look.
I hope this is helpfull

I would check the operation of the idle speed control valve, it is what changes the idle speed when a load like the transmission is put on the engine, without it the engine will idle slow and stall out, this is even more apparent when reverse gear is selected or drive or the AC is tuned on. The ISC valve is located on the side of the throttle body top of upper intake manifold. Below is a picture of the ISC (idle speed control valve)

Your transmission is failing. Your clutches are burnt. Your check engine light should be on by now. By now you should be experiencing rough gear shifts amongst other things.

These are mounted towards the back of the transmission. usaully on the passenger side. They are about 3" in diameter. only thing with a vacuum hose on it. easy to replace. I haven't done one of these in years.

it may be a bad transmission modulator valve located on the side of your transmission,vacum operated. a sudden downshift or forward shift when unexpected is sign of a bad modulator valve or a vacum leak to the transmission.best to shop around for a garage w/references when it comes to transmission work though. check all the vacum lines to your transmision,you need to look on the underneath side of your truck on the side of transmission for a loose or disconnected vacum line on the side of the transmission. when you feel the vacum line,follow it to the top of engine,the vacum line is about 3/8th line,and may be disconnected or losing air. to make this short,when you drive the car,start out in low gear and shift the transmission,manually from 1st to 2nd to 3rd does it do right with no slipping? if it does this right and shifts great manually,the modulator valve on the side of the transmissions bad,or a bad vacum leak in-between.thank you for choosing fixya.com

check for a bad vacum to the modulator valve on your transmission,or a bad vacum to the modulator valve on the transmission. the modulator valve to the trans. works off of vacum from the engine,look for loose or disconnected vacum lines around the carb. or the air induction system. look for cracked vacum lines that seem to be sucking air when engine running at idle speed. in park. the modulator valve [usually] located on the drivers side,of the transmission,is the main cause of shifting failure. if the valve itself is bad, it will need replacement. thank you for choosing fixya.com!

Check the vacuum line at the transmission modulator for a broken rubber hose at the transmission or up on the engine where the line connects at the intake manifold. also check the throttle cable to see if it is broken or stuck.

Check the vacuum modulator on the transmission if it has one. If you pull the vacuum hose off and see any fluid, change it. Make sure you are getting vacuum from the hose. Change the fluid and filter and add 2 bottles of Lucas "Stop Slip." It could help and it can't hurt.

Hello Friend:
Your Vacum Modulator is on the Side of your Transmission, You'll see a Vacum Line Running to it. From your Intake Manifold.

Theres a Retaining Clamp with 1-Bolt Holding it in the Transmission ,Remove the Bolt and Don't Loose the Clamp or Bracket. NOTE: On some vehicles the Modulator Screws in, You'll know By Either Seeing the Retaining Clamp and Bolt.

When you remove the Vacum Modulator theres a Acuating Pin ,Sometimes more than Not it will Fall out DON'T Loose This You'll need to Put it back in Before you Install your New Modulator.

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