Torque Converter Lockup???

[fulcrum]

Help!

I am having a problem with the transmission in my '94 Suburban that I have not seen described in any previous posts that I can find, and would appreciate some help, hopefully before it causes something really expensive to happen...

 

It is a two wheel drive, 5.7 liter engine with 225,000 miles. Sometimes, at speeds over 50 mph or so the transmission will shift in and out of lockup (I think), increasing the engine RPM's about 300 RPM or so, every few seconds. My cousin thinks it is the torque converter locking up and then unlocking repeatedly. It will only do this about half the times it is started and driven. The other other half of the time it shifts normally. I did have it rebuilt at about 175,000 with no problems until a short time ago. In general, the transmission seems fine otherwise, good, positive shifts with no slipping between gears that I can tell. I put it into third (from drive) the other day and it seemed to do the same thing, locking up and unlocking. Does anyone have any idea on what the cause of this could be?

 

This is my first post here, so if I am in the wrong place, let me know and I will try another part of the forum.

 

One other symptom that may be related. When it is acting up, it seems that the engine has less power and winds to higher RPM's before shifting, like it was under a load (only it is not).

 

Thanks for any ideas!

[ChevyTech007]

You need to have it scanned for codes. One thing that can cause this is the brake switch.

[mcreyaufmiller]

I believe it is a 4l60, if it is an E (4l60E) there is a lock-up selonoid in the transmission, or you could have a problem with the converter itself. I had a problem with my tranny and it did not want to come out of lock-up. My fix was removing the tranny and rebuilding the entire thing, but at the least, you may want to check the lock-up valve and converter.

[fulcrum]

Thanks ChevyTechooy and mcreyaufmiller. I will see if I can read any codes tomorrow to get more information. I do not know what transmission model it is, but hope I do not have to get it rebuilt again! I will post back if I find any codes.

Thanks!

[fulcrum]

Well, I jumpered out the DCL and got a code of 12. I think that this means only "diagnostic mode" according to the trouble code site that I looked at. I guess that I will need to go to AutoZone or someplace to have it scanned...