What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

97 GMC wont kick down shifts at 2k

rfda_454

rfda_454

1/2 ton status
GMOTM Winner
Joined
Jan 29, 2005
Posts
647
Reaction score
1
Location
Gillette Wyoming
Hey guys i just got this 97 GMC 1500 Z71 from my buddy, had a blown up engine so i put one in, now it shifts at 2000 RPM ot lower no matter what unless you hold the gear with the shifter, also there is no kick down whats so ever, im sure somthing is hooked up wrong or somthing but not sure, i checked all the plugs at the trans they are fine, what els controls the trans shifting and down shifting?
 
If it has the 700R4, or the other name for the same tranny, DO NOT drive it another inch until you set the TV cable!!

You WILL burn it up really quick.

Gonna post this now, to maybe save things, more later.
 
OK, hopefully you saw that and parked it. Gonna assume you have that transmission. Others here will know for sure. If you do, here is what you need to know.

The TV cable looks like the kickdown cable you might be used to. Small steel cable in a sleeve that hooks to the throttle linkage and is pulled out as you give it gas.

But, it IS NOT a kickdown cable per se. It controls hydraulic pressure inside the transmission.
Normally it is real easy to set. But in your case, you might have a problem. The way to set a factory setup, is to release the clip on the end of the sleeve by pushing a small button and move the sleeve all the way back towards the firewall.

Then, slowly open the throttle wide open with the engine off. As you do, you will reach the end of the cable.
Keep pushing the throttle open, and the sleeve will ratchet out. When you reach wide open throttle, it will lock at that point and be correctly set.

However, that is with a factory setup. In your case, you have changed engines. The geometry of the throttle linkage is critical. Yours might not be right.

The TV cable needs to be all the way back when the throttle is at idle. All the way out at WOT.
But, it is critical that it start to move the instant the throttle starts to move. If there is any slack, you will burn up the transmission.
If the geometry is off, you might have it correct at WOT, but have slack in the cable at idle.
When the engine is at idle, the TV cable causes the internal pressures that hold the clutches and brake bands locked to drop to a low value.
This is OK, since there is no load on them.
I suspect its a fuel saving measure so that there is not as much load on the pump.

If you start to drive off with it that low, the clutches and brake bands will slip and burn.
So, it is designed to increase the pressure the instant the throttle moves by detecting the cable movement.
If there is slack, the tranny will slip until the slack is taken out.

There are lots of threads about this, some of them have links to sites that do a better job of explaining all this than I do.

I linked to some of them myself.
You might try searching for threads I have posted in involving TV cables. If you do not have any luck, post and I will see what I can find.
 
rfda_454 said:
4l60e does not use a TV Cable its electronic.
Click to expand...
Ah well, wasn't sure, and figured better safe than sorry. Does that one still have the governor on the side?

Also, does the engine bog any at throttle up? About the only way other than a TV cable that the computer can tell you have moved the throttle is with the TPS. If it were bad, the engine would bog badly.

And, the 4L60 without the E is the other model designation I could not remember.
 
it seems to run just fine except the shifting, not a noticable bog, sometimes it wants to die if you gas it then let off at slow speed, other than that i cant think of anything. no check engine light the guy said it didnt do that with the old engine, thran has about 60k miles on it. im kind of stumped on this one
 
Well, if its fully electronic, then it has to be getting its shifting instructions from the computer.
Assuming that the computer is not bad, not likely, then something is lying to the computer.
When you punch the throttle, the only inputs the computer sees, is the throttle position sensor, and maybe a vacuum signal.

Any chance the new engine and the old computer are not compatable? Was there a big year difference, or engine size difference?
 
Always a possibility.
Somebody is going to chime in here in a minute to tell us how it knows to downshift, and that should give us a clue.
 
Greg Ducato said:
Check your throttle position sensor and speed sensor output
Click to expand...

There's the guy I was waiting to hear from!

And I had forgotten about the VSS. I figured the TPS would tell it when the throttle had moved, but I was wondering where it got its speed data.

I had never made the move all the way up to full electronic in my head.

That VSS signal goes several places, and its possible that the speedometer could read just fine, but the data not getting everywhere its needed.
 
If the speed signal shows to be much faster than the vehicle is actually moving it will dump the trans into the next gear too soon and prevent a forced downshift, but my first hunch is the TPS
 
Its been a while since I delved into the whole VSS signal path thingy, but what would the transmisson do if the computer did not get the VSS? I vaguely remember there are two or three VSS signals that are for different things, and I was wondering if one of them could be missing and putting the transmission into some kind of limp home mode.

Problem is, I seem to remember that limp home is locked in second. Not sure, got a bunch of other stuff going on right now.
 
Yep, you're right. I need to either start paying attention to what I am doing here, or what I am doing elsewhere.

I can't multitask very well today seems like.
 
You must log in or register to reply here.

Latest Posts

Top Bottom