vacume modulator problems again? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

86C10 · 11-24-2005, 02:37 PM

installed new vacume modulator. my truck is shifting gears now. however the tranny is shifting prematurely. it does'nt even feel like a full shift either it's not a jerking feeling it's more like a tiny push--don't know how else to explain it.i was told to take hose off of modulator and try turning the end of the modulator one way or the other. i've tried both ways and nothing seems to make the shifting right.

86C10 · 11-24-2005, 02:55 PM

i can shift from 1st to 2nd then into drive by the colum shifter.for now can i use this method to drive around with safetly untill i diagnose the problem further?

MylilBowTie · 11-24-2005, 04:43 PM

They where talking about an adjustable modulator valve. You might have one but I doubt it. If you do there will be a small screw inside where the vacuum line goes on. You will need a small standard screwdriver (flat head). You can turn it to the right(CW) to hold shifts a little longer and left to make it shift sooner (CCW).

I would also now try to adjust your detent cable and see if that helps. I would probably do that first and finer tuning with the modulator valve if its adjustable.

86C10 · 11-24-2005, 05:05 PM

I Did Get An Adjustable Vacume Modulator---i Have Tried To Turn It Both Ways-- I Will Try Turning It More To The Right.
Would It Be Okay To Use The Column Shifter And Shift Manually For Now?
I Can't Quiet Figure Out How To Adjust The Detent Cable. The Manual Says How , But It Still Looks Intimidating.

piecesparts · 11-24-2005, 05:37 PM

Odds are the detent cable is part of your problem. I take it that you are working on a 350 turbo or a 350C tranny. Have you connected the detent cabel? If so then depress the lock assembly (Up at the carb mounting bracket) and slide the cable ratchet assembly all of the way into the bracket (towards the firewall). Now take your throttle linkage and manually take it all of the way open on the carb (simulate that you have the pedal to the floor). That should (in most cases) slide the detent cable to the point that it will shift the tranny like you want it. To fine tune, slide the ratchet assembly back towards the firewall to get the tranny to shift sooner and firmer.

11-24-2005, 02:37 PM	#1
86C10 Registered User Join Date: Nov 2005 Location: NORMAN ,OKLAHOMA Posts: 6	vacume modulator problems again? installed new vacume modulator. my truck is shifting gears now. however the tranny is shifting prematurely. it does'nt even feel like a full shift either it's not a jerking feeling it's more like a tiny push--don't know how else to explain it.i was told to take hose off of modulator and try turning the end of the modulator one way or the other. i've tried both ways and nothing seems to make the shifting right.

11-24-2005, 02:55 PM	#2
86C10 Registered User Join Date: Nov 2005 Location: NORMAN ,OKLAHOMA Posts: 6	Re: vacume modulator problems again? i can shift from 1st to 2nd then into drive by the colum shifter.for now can i use this method to drive around with safetly untill i diagnose the problem further?

11-24-2005, 04:43 PM	#3
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	Re: vacume modulator problems again? They where talking about an adjustable modulator valve. You might have one but I doubt it. If you do there will be a small screw inside where the vacuum line goes on. You will need a small standard screwdriver (flat head). You can turn it to the right(CW) to hold shifts a little longer and left to make it shift sooner (CCW). I would also now try to adjust your detent cable and see if that helps. I would probably do that first and finer tuning with the modulator valve if its adjustable. __________________ 1974 C25 LWB: 454 4bbl Carb / TH400 / 3.73 1992 Camaro RS 305 TBI

11-24-2005, 05:05 PM	#4
86C10 Registered User Join Date: Nov 2005 Location: NORMAN ,OKLAHOMA Posts: 6	Re: vacume modulator problems again? I Did Get An Adjustable Vacume Modulator---i Have Tried To Turn It Both Ways-- I Will Try Turning It More To The Right. Would It Be Okay To Use The Column Shifter And Shift Manually For Now? I Can't Quiet Figure Out How To Adjust The Detent Cable. The Manual Says How , But It Still Looks Intimidating.

11-24-2005, 05:37 PM	#5
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: vacume modulator problems again? Odds are the detent cable is part of your problem. I take it that you are working on a 350 turbo or a 350C tranny. Have you connected the detent cabel? If so then depress the lock assembly (Up at the carb mounting bracket) and slide the cable ratchet assembly all of the way into the bracket (towards the firewall). Now take your throttle linkage and manually take it all of the way open on the carb (simulate that you have the pedal to the floor). That should (in most cases) slide the detent cable to the point that it will shift the tranny like you want it. To fine tune, slide the ratchet assembly back towards the firewall to get the tranny to shift sooner and firmer.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.