1986 th400 Not Shifting Up/Late Shifting

[dom1986ck30]

Aloha, My Truck is not shifting up until 35+ for 2nd and 50+ for 3rd. Not good for Tranny. I have opened up and checked shift relay/down shift switch. I have checked governor. Both good. took them to a few shops. Replaced Modulator. 4 times, due to the fact that I don't care for aftermarket parts, nor trust them. I have replaced Vacuum Pump. I have a steady 24 at the gauge. I also have a steady 12 at the Modulator rubber connection. All rubber is new. The only part that I am wondering is the Vacuum Regulator at the Vacuum Pump to Modulator connecting/transfer point. I know there is a procedure to adjust and set the Regulator to the Fuel. I suppose the question that I have is... Can the regulator be bad if it is transferring the Vacuum Pumps 24 on the gauge to giving/delivering 12 on the gauge to the Modulator??? If there is any other hints to my situation of resolving my late shifting, please LMK... Mahalo, Dom.

 

[NDT]

Welcome to the forum. Does the vacuum at the VRV (device on the IP) vary the vacuum going to the modulator? It's purpose it to duplicate the vacuum levels that a gas engine would generate at various throttle positions. Low vacuum= harsh shifts at high RPM. 12 is kinda low.

 

[dom1986ck30]

Mahalo for getting back to me NDT, and Happy New Year!!! So I have 24in.hg at the Vacuum Pump. 12in.hg coming out the VRV. Is it sounding like a bad VRV? Adjustment necessary to the throttle? Because if I connect straight from the Vacuum Pump to the Modulator (Which is not advised), it shifts better but not how it should. Maybe the vacuum VRV is not changing or converting as I throttle on down the road. Maybe a consistent 12in.hg is not how it works. It needs to change vacuum as the throttle changes. Which is something I am not sure of.

 

[dom1986ck30]

Also, I have played with the VRV by moving towards the firewall and towards the radiator. I have played with (2) turns at a time with the Modulator. Again, I went through a few Modulators as to not let that be the $20 problem.

 

[dom1986ck30]

How should I check if vacuum is "Varying" at the VRV? By moving it while it is running and hooked up to a gauge? Attach gauge after the VRV(On the way to Modulator)?

 

[rustystud]

First off I would disconnect the vacuum modulator hose and run the truck and see how it shifts. It should shift like "right now !" . BAM, BAM, BAM. If it doesn't then the problem is in the transmission. If it does (shift right away) then your getting "to much" vacuum to the modulator valve. Then you need to check the "VRV" for proper function.

 

[dom1986ck30]

Cheers rustystud, Iwill give this a try, right now. A bit of hope. Trouble shooting.

 

[dom1986ck30]

Okay. I disconnected the Modulator and took it for a spin. Doesn't shift "Right Now". It still shifts late and hard. I am realizing that tranny removal is necessary but I don't understand how it can shift even when the Modulator is disconnected. Seems like Modulator is not as important for functionality. Cause it still drove the same.

 

[NDT]

Rusty, I thought disconnecting the modulator would result in high rpm hard shifts, or no shifts st all. Full vacuum to the modulator should result in shifts at low rpm.

 

[dom1986ck30]

Aloha Rusty and Happy New Year... So with that being said... should I try to check for "Variance" in VRV? Do I hook to Vacuum "Out" to Modulator while engine running and VRV loose? With VRV loose, I can move forward and back and watch in.hg? Just thinking...

 

[dom1986ck30]

If I do full vacuum at Modulator, it shifts quickly. (Vacuum Pump straight to Modulator, bypassing VRV.)

 

[NDT]

So that tells me the transmission is fine, the VRV is not VRVing or is way out of adjustment.

 

[dom1986ck30]

NDT, I like the sound of that. I mean its not a big deal to me to replace/rebuild tranny... just down time. Wanna have fun... and use the truck. So should I focus my energy on the Throttle and VRV synchronizing etc...? #TM... .646 spacing at the Throttle with the advised in.hg at the VRV?

 

[dom1986ck30]

Also, does the VRV change vacuum when the truck is running by moving toward the firewall and the radiator?

 

[rustystud]

Rusty, I thought disconnecting the modulator would result in high rpm hard shifts, or no shifts st all. Full vacuum to the modulator should result in shifts at low rpm.

Yes your correct. When the vacuum modulator receives no or low vacuum it thinks the engine is at WOT (wide open throttle) . The governor weights then controls all upshifts. I must have been having a "fuzzy brain" moment ! Probably just took my pain pills.

 

[rustystud]

Another thing to look at is the modulator itself. Is it an "adjustable" unit ? You can see a small slotted screw inside the hose connection (remove hose and look inside) . If it is adjustable then try and screw in or out the adjuster. Moving the screw in will increase modulator pressure. Moving the screw out will decrease the modulator pressure. Experiment with it and see if the shift points don't get better.

 

[rustystud]

If I do full vacuum at Modulator, it shifts quickly. (Vacuum Pump straight to Modulator, bypassing VRV.)

I should have read all the posts before posting ! I see the VRV pump is out of wack. I agree with NDT and try and adjust it.
I also see your in the "Northshore" area. I have family living in the "Waimanalo" area. My wife was born there.

 

[dom1986ck30]

Yep I live Haleiwa, North Shore Oahu, I am in Waimanalo all the time... Small Island... Small World...

 

[dom1986ck30]

Well I am in the adjustment of the VRV stage. I have played with it. I have (2) Gages. One for pulling vacuum from bottom port of VRV and one reading for 8"hg from Top To Modulator/Transmission. I am still in confusion. I am thinking other possible issues. Shifting still not right. Something just popped out of placement when I was driving one day. Problems getting it back. I have proper vacuum at the sources. Dumbfounded... Tranny? But I still have gears... Timing Chain? But I don't feel or hear anything. It still drives fine... Just won't shift properly... ****!!!

 

[rustystud]

Well I am in the adjustment of the VRV stage. I have played with it. I have (2) Gages. One for pulling vacuum from bottom port of VRV and one reading for 8"hg from Top To Modulator/Transmission. I am still in confusion. I am thinking other possible issues. Shifting still not right. Something just popped out of placement when I was driving one day. Problems getting it back. I have proper vacuum at the sources. Dumbfounded... Tranny? But I still have gears... Timing Chain? But I don't feel or hear anything. It still drives fine... Just won't shift properly... ****!!!

Did you try and adjust the modulator on the transmission ?