M1008 transmission stuck at WOT shift points

[DTL]

Yesterday I had to merge into heavy traffic, so I floored the throttle and the truck responded normally. It shifted at the correct, later, points and everything was fine. Now, it will ONLY shift at those shift points, regardless of throttle position. ( 1-2 shift: 28mph, 2-3 shift: 39mph)

When I got the truck from GL, it was behaving in a similar way. I replaced the vacuum modulator on the transmission and ran new vacuum tubing to it, just to be safe. All was fine after that.

Does anyone have any idea why the truck would get "stuck" at the higher shift points? As of now, I'm probably going to replace the modulator again, but is there something else I should be checking? I don't want it to kill a part every time I go WOT, even as rare as that is.

Thank You!!

 

[Westech]

Vacuum pump, TPS Valve or transmission modulator. Also check all the vacuum lines.

 

[DTL]

What/where is the TPS valve?

Thanks

 

[gimpyrobb]

You didn't get the memo on the TPS report?

 

[DTL]

LOL, that's the first thing I thought of too.

 

[Westech]

Do you have any TM's or even a Chilton repair manual for the civy trucks?

If not pick them up and read up on them. way way too much info to school you over a few posts.

 

[DTL]

I have the TMs on my computer at home. Unfortunately, I'm way out on my farm and only have my iPhone right now. A little help would save me a LOT of hassle and running around.

Thanks

 

[Westech]

I could tell you what it is but if you do not know the operating system its kinda pointless. You need to do a little work for your self.

 

[DTL]

I'm a farmer. We do EVERYTHING for ourselves. Thanks for the help.

 

[Gunnar1071]

I have the TMs on my computer at home. Unfortunately, I'm way out on my farm and only have my iPhone right now. A little help would save me a LOT of hassle and running around.

Thanks

Hopefully you can see JaTonkas site.


http://www.jatonkam35s.com/CUCVTechnicalmanuals/tm9-2320-289-20.pdf


I am at work, but have been stuck out in the field (pun intended) .

Work is slow, so lemme know if I can look anything up for you.

 

[Warthog]

From the TM 9-2320-289-34 Technical Manual, Troubleshooting Section.​

56. NO UPSHIFTS, DELAYED UPSHIFTS, OR FULL THROTTLE UPSHIFTS ONLY​

Step 1. Disconnect downshift electrical connector from side of transmission. Operate truck and observe upshift performance. If upshift is normal, replace transmission downshift switch on side of accelerator bracket.​

If upshift performance is still poor, perform step 2.​

Step 2. Connect downshift electrical connector to side of transmission. Test transmission oil pressure with brakes applied, “ D“ (Drive), engine at 1000 rpm. (See paragraph 5-11)​

If oil pressure is normal; remove, disassemble, clean, and inspect governor
assembly. (See paragraph 5-5)​

If oil pressure is high, perform step 3.​

Step 3. Test transmission oil pressure with brakes applied, “N” (Neutral), engine at
1000 rpm. (See paragraph 5-11)​

If oil pressure is normal, perform step 4.​

If oil pressure is high, perform step 5.​

Step 4. Check for leaking or damaged detent solenoid.Tighten detent solenoid if loose and replace if damaged. (See paragraph 5-7)​

If detent solenoid is not loose or damaged, clean transmission control valve
assembly. (See paragraph 5-7)​

Step 5. Check for loose or damaged vacuum lines and hoses.
Connect vacuum hoses or vacuum lines if loose and replace if damaged. (See
TM 9-2320-289-20)​

Step 6. Disconnect vacuum hose from vacuum pump. Install hose and vacuum gage on vacuum pump. Start engine. Calculate proper vacuum gage reading as shown in
chart. Shut off engine. ​

If vacuum drops 1 in. Hg or more in less than 1,5 seconds, or if vacuum never reaches proper gage reading, replace vacuum Dump. (See​

TM 9-2320~289-20)

Step 7. Remove, clean, and inspect vacuum modulator assembly and modulator valve,
(See paragraph 5-3)

*********************************************
Sooooooo...remove the wire from the drivers side of the transmission and see what happens..... Sounds like the downshift switch is stuck on the accelerator pedal.

 

[Westech]

I'm a farmer. We do EVERYTHING for ourselves. Thanks for the help.

Then why post here with a question? I gave you the things to look at. I am not a over the "phone" tech.
I have been ASE master for over 10 years. I do things for my self too. Just trying to point you in the correct direction.

And thank you dug you are all ways right on top of things.

 

[cagosti]

I am not afraid to call a jackass when I see one post.

WESTECH your phone is ringing..


The vacuum pump will almost never last this long
Replace it first

Charles

 

[chicagodiesel]

If you have a vacuum gauge it would really help your efforts. They are under $20 at the store versus $150+ for a rebuilt vacuum pump or $95 for a regulator!

There are three components for the vacuum regulated shifting on the trans. They've all been named in previous posts...you got the memo.

Check vacuum at all points. After the vacuum pump (back side of the engine between right before the firewall)/before the regulator (mine has rubber hose from the pump to regulator, not sure about everyone else). Check at the beginning and end of the line to see if it is that line itself. Would suck to replace something when you could have gotten new vac line for 5 bucks. Check right before regulator (black thing on side of the IP with the two barbs sticking out and hoses connected to them on the passenger side). Make note of what hose is going where before removing. I can't remember off hand but I think top is to the trans and bottom is to the pump. Then check right after regulator. Note, the vac reading before the regulator might be jumpy because of the pump. Then check right after the metal line from regulator to the vacuum modulator on passenger side of the trans. This should tell you exactly where the problem is. Or at least keep you from completely guessing and randomly replacing parts...though they probably need it.

Good luck. Seriously though, do yourself a favor a get a cheapo vacuum gauge. If you are a total scum bag you can put a zip lock baggie over the end of the hose with a rubber band and observe what happens. I've never done it but have seen it tried. Nothing, no vacuum, bag shrinking up, you got vacuum.