Overdrive issue

Fellas, my 93 GMC 1500 2WD is giving me problems. I can't complain because I have 270K on it, all original motor and tranny. The trans is a 4L60 and overdrive is all of sudden an issue. It seems to never shift into overdrive. The RPM's go down as it does if you are shifting, but if you hit the gas the trans appears to be in drive, no overdrive. Ideas? No SES or codes shown. Shifting between all other gears is fine. Doesn't appear to be slipping or missing. New filter and fluid approximately 5K ago. Motor is 5.7. Thanks in advance.

To be sure that it is really not shifting into OD, drive the truck at freeway speed and shift from OD to D. If the RPMs remain the same, it is not shifting into OD.

Pretty sure you have a 4L60E in a 93. Also remember that the TCC will still lockup in both D and OD. When this happens the RPMs will drop 200 or 300 RPM.

Report back your findings.

//2000CAYukon

I'll be riding at 70 mph and run around 3500 rpm with the gear shifter in OD. When I let out of the gas the RPM drop back to 2-300 give or take. When I press the gas it hovers until I get it back up to 3500 and it starts to accelerate again. Don't feel like it's making into OD at all. It's like it comes out of one gear, but never goes into the next. Again though this only applies to OD. All other gears shift as they should.

At 70, what happens if you shift into D? It is not clear if you have a problem with it shifting into OD or a problem with TCC lockup.

//2000CAYukon

Sorry it took me so long to get back to you, been out of pocket. At 70 appears to shift into OD because the RPM's drop. Then if I pull the shifter down to D, the RPM's raise up to about 3500 again. Does that tell you what you need? In my opinion it's making into OD, but not locking into gear. Thoughts?

To be sure that it is really not shifting into OD, drive the truck at freeway speed and shift from OD to D. If the RPMs remain the same, it is not shifting into OD.

Pretty sure you have a 4L60E in a 93. Also remember that the TCC will still lockup in both D and OD. When this happens the RPMs will drop 200 or 300 RPM.

Report back your findings.

//2000CAYukon

I don't believe that your statement of lock up in 3rd[D] is correct...when towing it is written always use 3rd not over drive [big D],,,as this will not engage the torque converter...

when the vehicle is above 45 mph at speed the torque converter should engage when shift selector is in overdrive which will result in a drop of about 200 rpm....when braking or accelerating the torque converter should drop out...


most likely this vehicle has lost the TCC ---torque converter engagement

I don't believe that your statement of lock up in 3rd[D] is correct...when towing it is written always use 3rd not over drive [big D],,,as this will not engage the torque converter...

when the vehicle is above 45 mph at speed the torque converter should engage when shift selector is in overdrive which will result in a drop of about 200 rpm....when braking or accelerating the torque converter should drop out...


most likely this vehicle has lost the TCC ---torque converter engagement The torque converter must lock up in 3rd gear or the converter will overheat and burn the transmission up. Towing in OD is not a good idea because the gear set needed to acomlish OD will generate heat when pulling a load and will also burn up the unit. Gm transmissions comand lock up in manuel 3rd or OD. I have rebuilt many that have failed due to tcc failure. Tdetermin problem we need to know the rpm and speed to determine gear acomplished. 3500 rmp is to high for 4th gear.

I don't believe that your statement of lock up in 3rd[D] is correct...when towing it is written always use 3rd not over drive [big D],,,as this will not engage the torque converter...

when the vehicle is above 45 mph at speed the torque converter should engage when shift selector is in overdrive which will result in a drop of about 200 rpm....when braking or accelerating the torque converter should drop out...


most likely this vehicle has lost the TCC ---torque converter engagement

I have a 90 and it does lock up in 3rd (this can be verified with a test light and using the diag port). I also have the factory manuals which state that lockup occurs in both 3rd and 4th.

Towing in 3rd is recommended since the 2-4 band is not applied in 3rd and the hunting from 4 to 3 back to 4 builds up a lot of heat on the band and sun shell.

//2000CAYukon

I have a 90 and it does lock up in 3rd (this can be verified with a test light and using the diag port). I also have the factory manuals which state that lockup occurs in both 3rd and 4th.

Towing in 3rd is recommended since the 2-4 band is not applied in 3rd and the hunting from 4 to 3 back to 4 builds up a lot of heat on the band and sun shell.

//2000CAYukon

you guys are correct in 3rd and 4th gear the TCC will lock up..
with the RPM'S at 70mph @3500, that should be around 2200rpm...so its more of a lost OD 4th gear...this could be many items...some not in the transmission...
it is possible the electrical connector is corroded at the transmission...

I'm not towing with this truck. Not sure where that came into play, but no towing. This is just normal driving. What else can I tell you guys or any ideas of what to test? If I drive in D there are no indications of a problem. This is simply when I put in OD. Fluid levels are fine and fluid and filter were changed about 8 months ago. Somewhere around 5K on that filter and fluid. I'm half tempted to take it to a tranny shop, but am afraid I'll get the "rebuild" story. I'm not convinced this trans needs to be rebuilt. If I simply lose OD, I'll accept that. No more interstate driving if that's the case...

Thoughts? And thanks to all that have replied!

I'm not towing with this truck. Not sure where that came into play, but no towing. This is just normal driving. What else can I tell you guys or any ideas of what to test? If I drive in D there are no indications of a problem. This is simply when I put in OD. Fluid levels are fine and fluid and filter were changed about 8 months ago. Somewhere around 5K on that filter and fluid. I'm half tempted to take it to a tranny shop, but am afraid I'll get the "rebuild" story. I'm not convinced this trans needs to be rebuilt. If I simply lose OD, I'll accept that. No more interstate driving if that's the case...

Thoughts? And thanks to all that have replied! Sorry we caught you up in the inner operations of a transmission but your problem is serious and it will need to be replaced or rebuilt. OD assembly is usually the first thing to go in an aged transmission. These transmission are common and not that bad to rebuild.

I'm not towing with this truck. Not sure where that came into play, but no towing. This is just normal driving. What else can I tell you guys or any ideas of what to test? If I drive in D there are no indications of a problem. This is simply when I put in OD. Fluid levels are fine and fluid and filter were changed about 8 months ago. Somewhere around 5K on that filter and fluid. I'm half tempted to take it to a tranny shop, but am afraid I'll get the "rebuild" story. I'm not convinced this trans needs to be rebuilt. If I simply lose OD, I'll accept that. No more interstate driving if that's the case...

Thoughts? And thanks to all that have replied!

since this is a 93 250k++++.,2wd what is the current value...1000.00max..? drive it until it dies...If you have transmission shop fix it it , will cost more than this vehicles value...if you owned this since 93 you got your monies worth...

get a newer vehicle its time...trucks in my area are very good priced...

Looking at my 96 FSM (I know you have a 93 but the diags should be similar), a No 3-4 shift can occur due to the following:

- Valve Stuck in Valve Body (2-3 shift valve, accumulator valve, 1-2 shift valve, 3-2 control valve)
- Worn Spacer Plate
- 2-4 Servo seal missing or damaged
- 3-4 Accumulator piston, seal or worn bore
- Restricted oil passage

Most of these can be checked without removing the tranny.

//2000CAYukon