My trans is driving me crazy!

[fox3344]

Hi everyone, I'm working on a 86 M1009 with a hard shifting problem. I searched the many posts and have tried several of the suggestions given, there's lots of knowledge here.

This is where I'm at so far.

-vacuum lines are all new, double checked the hard line to the modulator, even ran a new vacuum hose to eliminate it for a test.
-I eliminated the rubber block at the vacuum regulator and hooked the two lines up direct, top port to the trans lower to the vac pump.
-vacuum pump seems to have sufficient pressure (no gauge as of yet)
-adjusted the vacuum regulator all the way back towards the firewall
-has a new red stripe modulator, adjusted out.
-I ran a hose directly from the vacuum pump to the modulator, plugged the port on the regulator, just for a test to see if it would shift any sooner.

All of which made no change, the truck shifts hard and at high rpm. If I let off the gas it just hangs in gear. The fluid is clean and full, and all tests were at operating temp.

I haven't taken apart the vacuum regulator to clean it because I figured by hooking a line directly to the vacuum pump it would eliminate that as a potential issue.

Hopefully I'm missing something else here. Any info would be appreciated.

--I'm still going thru the manuals as well!

Thanks, Andy.

 

[Warthog]

The vacuum pump pulls 20" and the transmission is looking for 8". The regulator should be adjusted for 8". It is covered in the TM 9-2320-289-20 manuals and I posted a thread on how to adjust it.

http://www.steelsoldiers.com/cucv/50568-cucv-throttle-vacuum-valve-adjustment.html

Are you sure you are getting vacuum at the pump?

 

[raiburn]

Search M1009 Transmission Solenoid on here.
Check the solenoid, and the peddle switch.

 

[chevymike]

I agree with Warthog, if you don't have a vacuum gauge to verify what you are getting at the trans modulator, you will be chasing your tail. Test gauges are cheap, buy one and check.

Mine was a combo of bad vacuum lines and modulator. After replacing the lines and it not working, I checked the vacuum with a gauge and got the numbers Warthog says so I new it was a modulator issue. Replaced that with one from NAPA and it worked perfect. I was set to replace the vacuum pump until I checked and found it working correctly.

 

[fox3344]

I'll pick up a vacuum gauge tomorrow hopefully. I agree I need to verify the actual pressure at the vacuum pump then go from there. It's an expensive part to just go by "feel"! The modulator is new, but you never know, it wouldn't be the first time a new part didn't work.

Thanks for the ideas, I will let you know.

Andy

 

[SPECIALTYLC]

Likely problem is with the throttle position switch on the injection pump. They are still available from Chevy dealers, but not cheap.

 

[fox3344]

I thought that to, but I figured by running a direct vacuum line to the modulator from the vac pump it should eliminate that as a possible problem..?

 

[chevymike]

I thought that to, but I figured by running a direct vacuum line to the modulator from the vac pump it should eliminate that as a possible problem..?

Problem with that is the vacuum pump is pulling about 20" of vacuum and the modulator should only be seeing about 8". It is very possible you could have damaged the modulator going direct. Also, the vacuum switch regulates a variable signal to the modulator. Directly from the pump, there is no variable signal. Also I found when I had a gauge directly to the pump, it would actually pulse a vacuum but after going thru all the correct lines, when I test at the modulator, I got a steady 8" of vacuum.

Also, in the rubber block that attaches to the vacuum switch, there should be two "reducers" (orange I think) that help drop the vacuum down to 8". I found this block was dried and cracked and would not allow a vacuum to be held. I removed it, cut a couple short pieces of line and attached them to the vacuum switch. I put those reducers into those short pieces and then new line to the pump and hardline to the modulator. Something else to check.

 

[lnnayers]

you might check the govenor. it has a plastic gear that will wear out and cause a no or late harsh shift. the gear is available seperate from the govenor and is not difficult to replace. drive out the roll pin, remove the old gear, the new gear will not have a hole in it, after the new gear is installed in the govenor body drill a hole through the plastic and reinstall the roll pin. the gear being worn out is sometimes caused by a worn center support, so you might pick up a couple extra gears

 

[Dave Kay]

Search M1009 Transmission Solenoid on here.
Check the solenoid, and the peddle switch.

To ANDY--- Have not verified this same condition will exsist on our CUCV's--- but I'm sayin' ditto on that solenoid thing. Had very similar probs with my civi 1-ton w/TH400 trans and a guy reccomended I disconnect the SINGLE wire leading out of trans body on the driver's side--- then do a test drive.

This wire connects to a solenoid inside of trans oil pan and it makes for smooth up-shifts and kick-downs for acceleration... you gotta' crawl under there to find it--- it should be visable about frame-level. If it is in fact there--- disconnect it and go test drive. Your results may give you a big clue.

After unplugging this wire on my trans it still did hard shifts but went thru all 3 gears up-n-down w/no-problemo... in fact, I've read where the switch under-dash may also be a culprit. Either way, replacing these solenoid/switches is fairly easy AND MAY solve your problem for relatively cheap. Otherwise, AAMCO will happily replace your entire transmission for this same simple problem and charge you a grand-or-more... (honk, honk, double-A, RIP YOU HARD)

It's too cold right now to go outside and crawl around under vehicles to verify this fix for CUCV's, so feel free to rip me if I'm wrong.

BTW; I have a great book by Ron Sessions on TH400's and it's helped me a lot. PM me if you got anymore Q's on this and I'll see what I can find.

Good luck!

 

[fox3344]

I was finally able to test the actual vacuum at the pump, it fluctuates of course, but it only produced about 5" of vacuum. Hopefully I've zeroed in on the problem...with you tips of course.

I've removed the pump for repair/replacement, and I want to say I remember reading that these pumps can be rebuilt, but I can't find exactly where.

Has anyone rebuilt the vacuum pump or is it strictly replacement?

Thanks
Andy

 

[chevymike]

Great, you at least found a major problem so hopefully fixing that, all will be good.

As for rebuilding, I don't know but I do remember when I was searching, I could buy just the vacuum can pod part and not the whole assembly. Seemed to cut the price down about $100 over a whole assembly.

Post up once you get it fixed. Hope all works fine after that!

 

[fox3344]

I installed a new to me vacuum pump, now were producing 20" of vacuum.

So I've fixed one problem only to find the vacuum pressure is not going thru the switch on the IP. There is no vacuum pressure at the top port of the switch, but a good 20" coming in directly from the vacuum pump.

Can the tps be cleaned, or am I looking at a bad switch? I did a search but haven't found anything just yet.

Andy

 

[Warthog]

Glad you figured out the vacuum issue.

I have never heard of anyone cleaning the TPS but it is worth a try. WD-40, PB Blaster, etc

If all else fails, Doghead has a bunch of new ones listed in the classifieds.