Transmission "bump" after shifting into OD

[Phishin]

1990 Chevy K1500 350TBI with 700R4 transmission.

Today was the first time I noticed that my transmissions gave me a "bump" right after the truck shifted in OD under light acceleration, which was around 40-45mph.

When I got home, this was bugging me, so I just took the truck back out down the road, and I got it to do it again. Both times it happened, I was barely accelerating.

Is this "bump" I'm feeling a transmission slip? Or is it the TC locking up? Perhaps the TC was locked up in 3rd, and once it was shifting into OD, it unlocked, and then shifted and the TC re-locked causing it to give me this "bump"? I don't know, this is all a guess.

Anyone ever feel this "bump" right after their truck shifts into OD under light acceleration?

 

[SteveSRT8]

Sounds like shift flare. never a good sign.

Service it soon, start with a pan drop and a filter.

 

[Phishin]

Originally Posted By: SteveSRT8
Sounds like shift flare. never a good sign.

Service it soon, start with a pan drop and a filter.


About 8k miles ago, it had a pan drop. Replaced 3-4 quarts of fluid. Filter was clean. But replaced. No crud in bottom of pan.

Going in for a flush this week. Gonna add a bottle or two of LubeGard Red as well. She will get Valvoline MaxLife Dex III ATF.

She didn't do the "bump" this morning going to work.

Now I have to look up what a shift flare is...never heard of that term.

 

[Phishin]

I understand what a flare is now. I have no tach in my truck, but for sure there is a "slip" when it shifts...perhaps a raise in RPM's when it's happening. But this is an old truck and I don't press down very hard on the gas pedal.

HOWEVER, this weekend, after rebuilding the TBI, I decided to "water steam" the combustion chambers...by spraying water down the TBI from a squirt bottle. When I was done, I took the truck down some back roads and flogged on it a bit. One time when I was at WOT from a dead stop, it rev'ed very high and as it shifted into 2nd, there was a hesitation/bump. That kinda freaked me out. Since then, I've experienced this "bump" right after it shifts into OD.

 

[[email protected]]

My 4L60E ALWAYS did the little bump after going into OD. Actually I thought it was the torque converter going into lockup.

Sold the truck 2 weeks ago with 162,000 miles on it and the trans was all original, never opened and exhibited that bump since the day I bought it.

 

[Gotch]

Have you tried adjusting the T.V. cable? There is a "push" button on the end of the cable near the throttle connection to the TBI. Push the button in, pull the cable all the way towards the firewall, let go of the push button. Jump in your truck and push the throttle pedal all the way to the floor (ENGINE OFF). This will reset the T.V. cable, you may here some clicking and some extra resistance while ajusting the T.V. cable.

The TV sets shift point and shift feel based on this. Give it a try first, it's free.

 

[Gotch]

Here's a really good explaination of TV and how its works.

http://www.cpttransmission.com/tech_tvcable.htm

 

[mechtech2]

Your projected flush and Lubeguard are your best bets.

We have to consider that in 2 years it will be eligible for antique license plates.

 

[Phishin]

So I disconnected my TV cable. I held the intake at WOT. The TV cable will JUST pull tight enough so it lines up with the linkage it hooks to.

Meaning, at WOT, the TV cable is extended to it's maximum.

This it's correctly adjusted, right?

 

[ms21043]

Try cruising in high gear and then pressing the brake pedal a bit. Just enough to activate the switch on the pedal but not enough to brake. You should be able to feel the converter unlock and then lock up again when you release the pedal. If it's the same bump you're feeling than that's what it probably is.

 

[Gotch]

Taken from Art Carrs page.There are pictures in the link I posted.

1. Stop the engine.
2. Depress the adjusting tab and move the slider back through the fitting away from the carburetor until it stops.
3. Release the adjustment tab.
4. Move the throttle linkage to rest against the full throttle stop, then release it .
5. Check the cable to insure that it is not sticking or binding.
6. Road test the vehicle.
7. If the problem still exists, refer to the cable diagnosis section.

 

[Gotch]

To reset the TV you have to press the tab and move the cable away (as far as it can go) from the throttle linkage. Let go and either open the throttle by hand or depress the accelerator pedal all the way. You should hear at least 1 click. If not, then there is something wrong with the linkage or cable.

 

[Phishin]

Thanks Gotch.

But I think I found the problem. And it wasn't the transmission.

Today on my lunch break, the truck stumbled when I put into reverse and back out of my drive way. Same feeling as before. When I put it in drive and move forward, it stumbled once or twice. I think it's an ignition problem.

Probably just needs new plugs. This oil burner probably has them trashed. I changed them 12k miles ago, but with the amount of oil this thing can burn under load, it wouldn't suprise me they are toast. 12k miles ago, it also got a new dizzy, cap, rotor, and plug wires. I thin I'll just install new plugs....and wait and see.

So, it stumbled when it shifted into OD the other night. Now it stumbled back out of my drive way....low RPM's seem to trigger it. Does this seem to indicate a spark plug problem? Dizzy problem? Or who knows?

 

[Phishin]

Last night when good and hot... ..she was stumbling like crazy. She even stumbled in park with it revved up. So no drive train issue. Definitely fuel or ignition issue.

Gonna check cap, rotor, and ICM. It's not the EGR. Unplugged EGR source, no change in stumble. Manually opened EGR, she stumbled like she should too.

 

[Phishin]

Last night when good and hot... ..she was stumbling like crazy. She even stumbled in park with it revved up. So no drive train issue. Definitely fuel or ignition issue.

Gonna check cap, rotor, and ICM. It's not the EGR. Unplugged EGR vacuum source, no change in stumble. Manually opened EGR, she stumbled like she should too.

 

[Gotch]

Are your injectors still dripping after the TBI rebuild?

 

[Phishin]

Originally Posted By: Gotch
Are your injectors still dripping after the TBI rebuild?


Injectors looks much better. Fine mist spray on both sides.

Supposedly these engines are prone to burn up caps and rotors. So glad it's not my transmission going. With the fact that it "gets worse as the truck gets more warmed up/hotter, I'm leaning towards the top of the distributor or the Ignition Control Module....they are known to act up when they get warm.