1994 K2500 7.4L - Slips out of gear on hard stops

[Dark Jester]

Hi All,

I'm hoping someone can help me out. My wife has a 1994 K2500 7.4L Suburban that has been a pretty good vehicle for a lot of years and she loves it to death. Recently it's been having an issue though where if you stop suddenly, it will slip out of gear. It doesn't seem to happen when stopping slowly. But say you're doing 35 or 45 and the stop light flips yellow right in front of you and you're not quite close enough to make it through so you hit the brakes hard to stop, once you fully stop moving it slips out of gear.

You take your foot off the brake and push the accelerator and you don't go anywhere for 5 or 10 seconds, when suddenly it will slam back into gear and start rolling again. If the RPM's are high, it can be pretty violent. Almost feels like you got rear-ended. If you just lightly push the accelerator you can keep the RPM's low enough that it isn't that rough when it finally does engage.

Around the same time this started, it also began idling really rough. Well, not idling rough exactly, but vibrating the vehicle quite a bit when idling. We don't notice the vibration much when moving, just when stopped.

Anyone have an idea of what the issue might be? I'm not a professional mechanic or anything, but I do a lot of my own vehicle work. I've just never messed with anything transmission related yet so I'm kindof in the dark here and searching the net didn't turn up much information so I figured I'd ask the people most likely to know.

There has been no loss of power or anything, and other than the above issues the vehicle seems to run like a champ aside from a small power steering fluid leak I'll be fixing soon in the high pressure hose.

Any help is greatly appreciated.

-Dark Jester

 

[zora]

You make no mention of the first thing to check, the fluid level, did you check it?
Engine and trani have to be fully warmed up, engine running, momentarily place the shifter in all gears and then back into park and check fluid level.
Does the fluid smell burnt?
When is the last time the transmission fluid and filter where changed?

 

[Dark Jester]

Hi Zora,

Sorry, Yeah the fluid level looks alright. Halfway between cold and hot on the dip stick after the vehicle is warmed up, so it may need a little bit, but it's still in the operating range. The fluid is still red and doesn't smell burnt at all. The fluid was changed about 6 months ago, just before a 2500 mile road trip in December. I actually don't remember for sure if the filter was changed at that time or not, but I think it probably was.

This issue started after that road trip, maybe 6 or 7 weeks ago. It hasn't gotten any worse since it started, but not going away either.

Thanks.

 

[zora]

Did you have the transmission flushed or did you have the correct servicing consisting of dropping the pan and replacing the filter and fluid. If you only had the transmission flushed and then went on a long drive that may be the cause of your issue. Flushing disturbs sediment sitting in the bottom of the pan and spreads it throughout the transmission.

 

[Dark Jester]

I'm not positive.. We took it in to a pretty reputable shop for the tuneup, they checked/filled/replaced all of the fluids as needed. I'd assume they would have done it the right way and changed the filter and cleaned the pan as well, but I couldn't say for sure. I've been looking for the invoice to see if they had a replacement filter on there since that would be an indicator, but I haven't been able to locate it yet. Now that I know how simple it is after watching a few videos I'll be taking care of it myself in the future to make sure it's done the right way, but that won't resolve what may have already been done.

Assuming worst case and they did flush without cleaning the pan first, what would be the remedy? Am I looking at a rebuild?

 

[zora]

recommend you take it to a shop that can scan your transmission. The vehicle has either a 4LE60 or 4LE80 which are electronic. It could be a sticking shift solenoid but just a guess.

 

[Dark Jester]

Alright, thanks for the help.