My 93 Chevy truck transmission

Brian N.E Ohio · #1 04/26/06, 12:41 PM

...wont hold high gear (OD or 3rd) at normal road speeds of 50-60 mph. The transmission I have been told is a 700-4R automatic. The shifts are tight with no slipping between gear changes, it just frequently downshifts for no reason in OD and the torque converter frequently locks and unlocks when I manually use 3rd gear. The fluid has been checked and found ok. The truck has about 161,000 mostly trouble free(read that pampered) miles. There is no drag anywhere in the driveline that I can find. It coasts fine. I have owned this truck since new and it feels no different now than 10 years ago.
Anybody have any ideas what to check next?

SouthernThunder · #2 04/26/06, 02:17 PM

If it is a true 93 tranny it should be a 4L60E but a handfull of early 93's did have 700r4s. The 4l60e is the electronic version of the 700r4 (4l60). Its nearly identical internally with the electronic valve body being the main difference between the two. The easiest way to check is to see if it has a cable running from the throttle linkage to the passenger side of the transmission case. (called a throttle valve cable) If it does then it is an older 700R4. If not it is a 4L60E.

I am not sure what you mean by "wont hold high gear". Does this mean it slips out of gear or does it downshift?

If it is a 700R4 this is what I think. If it slips in 3rd and 4th then the odds are the 3-4 clutch pack is toasted. Very very common problem.

3rd and 4th gear share this clutch pack with the shift to 4th being made by a band that is shared for 2nd. So if you have 1st gear and 2nd gear but no 3rd and 4th then the 3-4 pack is bad. On the other hand if you have 1st and 3rd but no 2nd and 4th then the 2-4 band is bad. Either way it will require a full rebuild.

If it is not slipping but rather downshifting to second then it could be a simple adjustment of the TV cable and I can tell you how to do that.

Let me know exactly what its doing and which model it is and I'll try and be a little more helpfull.

Best of luck.

mtman · #3 04/26/06, 05:38 PM

this is shop talk

Brian N.E Ohio · #4 04/26/06, 09:33 PM

SouthernThunder, by "not holding high gear" I mean that it is downshifting to third gear for no aparent reason when in OD then upshifts again normally. If I manually shift to third gear I can feel the electronic torque converter locking and unlocking, also for no aparent reason. The shifting process has not changed and there is no slipage. All shifts are smooth and firm as they aways have been.
I have been called out of town for a few days and wont be able to verify the exact transmission untill I return, possibly the weekend. The 700-4R designation was what the salesman told me when I was signing the papers 13 years ago and could be incorrect.
I am sure this thread will die before I return, can I pm you?

mtman, you are correct that this is shop talk. I wasnt aware of the new forum as I have been away from this sight for a few months now. If one of the mods would like to move this post you have my blessing.

Thanks
Brian

SouthernThunder · #5 04/26/06, 10:30 PM

Torque Converter Clutch can be disabled on the 700R4 by disconnecting the 4 wire connector on the driver's side of the case. This will be the first thing to do to further diagnose the problem although driving it for a lengthy amount of time like this will eventually cause excess wear. If it is a 700R4 then it is highly likely that your TV cable is misadjusted, stretched or kinked. The proper way to adjust this cable it to have someone floor the gas pedel (with the engine off) and someone else press the little "D" shaped release tab on the TV cable and slide the adjuster back towards the firewall to remove all slack. No more, no less. If the cable is bent, or stretched it should be replaced. NEVER drive with the cable broken or disconnected as this WILL destroy this particular transmission quite quickly and thoroughly.

If, after disconnecting the TCC wire connector you still have converter issues then you likely have a 4-3 downshift switch leaking. This would bleed off the pressure to the 4th gear servo causing a downshift and possibly allow the converter to act funky because of the improper reading.

Lastly, you might have to drop the valve body and clean it out real good and also your 2-4 servo assembly. 160k miles, Im sure theres some metal powder in there...

I will send future replies to you though PM as requested. Let me know when you find out for sure what kind of tranny this is... Take care.

Red Devil TN · #6 04/27/06, 02:05 AM

I'm going to vote for old fluid and some varnish in the valve body. The 700r4 et. al. are supposed to downshift from thord to fourth when you get into the throttle a certain percentage, but not while at a cruise. Probably time to drop the pan, change the filter and install a drain plug for some upcoming drain and fills unless you can get a power drain somewhere. Either way, I make it a habit to add a drain plug to every pan that I drop.