stumped so far

[DUCOTI]

Hi, When I drive my 96 Tahoe over 55, a check engine light comes on after a minute or sometimes 10 minutes. If you come to a stop then and start going,

you get a klunk between 1st and second gears. The rest of the gearing is smooth.

Stop again, and start up...same thing. If you pull over and turn off the engine for about 10 seconds, start up and go, no klunk. Go over 55 mpg and you start all over again. You can go under 55 mph for ever and it won't happen.

I drove 66 mph for 30 miles on the highway using the cruise control and the problem didn't occur.

Any ideas ??

[71GMC_3/4T]

Locking torque converter going out?

 

Check the fluid. Smell it to be sure it isn't burnt.

 

Change the fluid or better yet, have it flushed.

 

Maybe you can prolong it before it dies for good.

 

I'd be worried about it shelling and running bits of junk through the rest of the tranny. A new torque converter might be a lot cheaper in the long run.

[DUCOTI]

Locking torque converter going out?

 

Check the fluid.  Smell it to be sure it isn't burnt.

 

Change the fluid or better yet, have it flushed.

 

Maybe you can prolong it before it dies for good.

 

I'd be worried about it shelling and running bits of junk through the rest of the tranny.  A new torque converter might be a lot cheaper in the long run.

 

<{POST_SNAPBACK}>

 

 

Thanks...have you heard of this one before...I've been told it's a crankshaft to camshaft corralation fault to a shfting sensor for 1st an 2nd gear. I've had the timing done, line check on the tranny etc.

I am no mechanic...but why does the problem go away after shutting the engine off.?

[GM-Tech]

This sounds like a classic case of a P1870 DTC setting (TCC slip). When this code sets, the PCM commands full trans line pressure. You don't notice that driving along, but as soon as you come to a stop and take off again, 1-2 shifts are neck snapping hard. Cycling the ign. key off will clear this condition until you once again drive on the highway, the PCM sees the problem again and the problem repeats. That's why it goes away when you shut the engine off.

 

There are several common causes for this in those older ones. Valve body (and if you search for P1870, you'll probably find some aftermarket kits to fix this) or input shaft/pump bushing. If you pull the pan down and find a pile of brass filings, it's the bushing.

[DUCOTI]

This sounds like a classic case of a P1870 DTC setting (TCC slip).  When this code sets, the PCM commands full trans line pressure.  You don't notice that driving along, but as soon as you come to a stop and take off again, 1-2 shifts are neck snapping hard.  Cycling the ign. key off will clear this condition until you once again drive on the highway, the PCM sees the problem again and the problem repeats.    That's why it goes away when you shut the engine off.

 

There are several common causes for this in those older ones.  Valve body (and if you search for P1870, you'll probably find some aftermarket kits to fix this) or input shaft/pump bushing.  If you pull the pan down and find a pile of brass filings, it's the bushing.

 

<{POST_SNAPBACK}>

 

 

Thanks!