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-   -   1988 Chevy k2500 transmission won't shift...sometimes (https://chevroletforum.com/forum/1988-1998-gmt400-106/1988-chevy-k2500-transmission-wont-shift-sometimes-58164/)

Mugglemage May 10th, 2013 7:46 PM

1988 Chevy k2500 transmission won't shift...sometimes
 
Hello all, first time poster, I've been a Dodge guy for a long time until I saw this beauty on Craigslist :P

Anyway, quick details:

1988 Chevrolet K2500 4x4
261k Miles
350 V-8
Looks cool

Anyway, I got it for 1000 dollars as the belt that goes around the power steering pump and alternator would slip off all the time and the guy who owned the truck could not find a bracket for it. I got that fixed. Then my Dodge (Shadow) died, making this behemoth my daily driver, and.... I can't go back. I won't.

Anyway, before I start hugging my truck awkwardly outside... AGAIN...

The transmission is acting weird. It has a Jasper transmission in it, it has a 4x4 but needs the 4x4 solenoid (I will get to that later), but when you start the truck up, you have to let it warm up past 1/4 mark before it will shift correctly.

What I mean by that, is if I go out right now and start the truck up and try to take off, it will go, but will shift VERY hard at 20-25 MPH. If I let it warm up a LOT, it will shift smoothly and easily at 10-15MPH or so. I don't know a lot about trucks, but this doesn't seem to me to be a "you need a new tranny" issue. I asked at work if maybe there was some pump or something that was old and almost out?

Last note: Even warm, when it shifts into 2nd, it halfshifts, revs a little high, then finishes shifting into 2nd. I looked around a bit on the forums here and saw something about a TPS? What is that? Is that something I could easily replace? I can do basic maintenance, but nothing fancy.

Last LAST part: One time, some jackass in a little Honda was talking on his phone and driving 15 under the speed limit. To show him he is less than me, I gunned the truck up around him, and almost messed my pants as that throaty V8 smoothly and easily accepted it and took off like a shot. As I was laughing about it, I slowed to a stop and took off. The truck would NOT come out of first. I babied it home, let it sit, tried taking off after letting it warm up, it's been fine.

It does NOT leak fluid, ANY kind of fluid.

It does NOT have issues starting.

Any help would be appreciated. Sorry for being so wordy, I get to talking about that truck and I get excited :)

Allan In NE May 10th, 2013 8:45 PM

First ya gotta tell us what you're working on. Is this a three speed or a 4 speed automatic?

Forget the tps for now; that isn't your problem. Is the check engine light on?

Oh, and another thing, there is no 4x4 solenoid. ;)

Allan

Mugglemage May 16th, 2013 2:06 PM

Lol
 

Originally Posted by Allan In NE (Post 247929)
First ya gotta tell us what you're working on. Is this a three speed or a 4 speed automatic?

Forget the tps for now; that isn't your problem. Is the check engine light on?

Oh, and another thing, there is no 4x4 solenoid. ;)

Allan

That should point you to how little I know about this :P I just idiotically repeat what the ad said when I bought it.

Its a 4 speed automatic. The check engine light is on, I thought since for the most part the engine checked out that it was a bad fuse or something... the brake light on the speedometer comes on and turns off all the time like there's a loose connection, and under the steering column the little wire shield fell off, gonna put that back on this weekend.

As an update, the truck will no longer shift into second. It goes from first, and then shifts at 30 to third I'm guessing. I have been letting it sit for a few days until I can figure out what's wrong with it. I have heard it might be a vacuum hose, but that sounds like more bull pucky :)

Thanks for the response Allan, I appreciate it

kevinkpk May 16th, 2013 2:17 PM

I'd replace this first.
1988-1988 Chevrolet C1500 Automatic Transmission Modulator Valve Standard, OE

Mugglemage May 16th, 2013 4:04 PM

Sweet thanks!
 

Originally Posted by kevinkpk (Post 248379)

That looks like it goes between a couple hoses... so shouldn't be incredibly tough to find (I hope?) I will try that out this weekend, and hopefully be clogging KC roadways by Monday again!

Allan In NE May 16th, 2013 7:53 PM

First off, your transmission doesn't even have a vacuum modulator, so don't waste your time looking for it. :)

Secondly, the transmission is just a reactionary device; it does what it's "told to do" depending on the load placed on the engine. Further, if the engine isn't running right, the transmission cannot operate correctly.

Engine load information is relayed to the transmission thru the lower cable attached to the throttle body. Make sure it is clean and moves thru it's travel smoothly.

NEXT, remove the positive battery cable for a few seconds, then hook it back up. This is to clear the ECM's memory of any stored codes (We don't want to be chasing something that happened 6 months ago).

**Now, the absolute #1 ailment of this transmission is a plugged fuel filter. If I had sold a transmission for every one of these outfits I've cured with a new filter, I'd be rich instead of so darned good lookin'. :D

You think the engine is running fine. It's not; it's actually starving for fuel and for any given road speed you are applying more force to the accelerator pedal...............this pulls further on the transmission cable and heightens the transmission's line pressure which in turn produces harsh shifts and shifts held out

Since you just bought the truck, I'd crawl under there and replace this guy; it's inside the driver's side frame rail.

Then, after doing these two chores, drive the truck to see how it now acts, note if the check engine light is still coming on, and if necessary holler back if it's still not right and we'll go from there.

Allan

kevinkpk May 16th, 2013 8:22 PM

[QUOTE=Allan In NE;248406]First off, your transmission doesn't even have a vacuum modulator, so don't waste your time looking for it. :)



QUOTE]
Ok

kevinkpk May 16th, 2013 8:27 PM


Originally Posted by Allan In NE (Post 248406)
First off, your transmission doesn't even have a vacuum modulator, so don't waste your time looking for it. :)

Secondly, the transmission is just a reactionary device; it does what it's "told to do" depending on the load placed on the engine. Further, if the engine isn't running right, the transmission cannot operate correctly.

Engine load information is relayed to the transmission thru the lower cable attached to the throttle body. Make sure it is clean and moves thru it's travel smoothly.

NEXT, remove the positive battery cable for a few seconds, then hook it back up. This is to clear the ECM's memory of any stored codes (We don't want to be chasing something that happened 6 months ago).

**Now, the absolute #1 ailment of this transmission is a plugged fuel filter. If I had sold a transmission for every one of these outfits I've cured with a new filter, I'd be rich instead of so darned good lookin'. :D

You think the engine is running fine. It's not; it's actually starving for fuel and for any given road speed you are applying more force to the accelerator pedal...............this pulls further on the transmission cable and heightens the transmission's line pressure which in turn produces harsh shifts and shifts held out

Since you just bought the truck, I'd crawl under there and replace this guy; it's inside the driver's side frame rail.

Then, after doing these two chores, drive the truck to see how it now acts, note if the check engine light is still coming on, and if necessary holler back if it's still not right and we'll go from there.

Allan

I'll leave this to Allen's expertise.

kevinkpk May 16th, 2013 8:38 PM

Well, thought I'd help with posting exchanges from these boards, guess it's time to say good bye.

Mugglemage May 16th, 2013 11:12 PM

thanks for all the replies
 
I will try to check all of this tomorrow... Hoping to take the truck camping next week and when I called the transmission place before getting on these forums the guy got all excited.

I will get a Chilton and see what I can do, I can figure out instructions if nothing else ;)


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