1999 Yukon Hard Shifting When Hot

[Blaine]

Just bought a 1999 Yukon SLT and I have fallen in love with it. Before making the deal the owner said that the transmission shifts hard after a long drive. After driving for more than 40 minutes it shifts very hard from first to second.
I have ask several people about this and I get mixed responses, from just change the transmission fluid to transmission rebuild.
Before making any decisions I figure I would see if anyone here has experienced the same problem and may have a solution.

 

[roadrageror]

i don't know but they make shift kits for our tranny.maybe add a tranny cooler,or get the tranny flushed and new ATF..just some suggestions.

 

[04SS99Denali]

as your trans gets hot your pcm reduces Torque Management to reduce slip during shifts. this will make your shifts firmer so it will make less heat while shifting. more than likely your tranny is getting hotter than it normally should. i would start by changing the fluid and possibly adding a bigger trans cooler.

 

[nimrodcs]

My 'Hoe is doing the same thing. It's really hard between 1-2 and kinda hard bewteen 2-3. Once I have the $, I'm gonna do fluid & filter change, shift kit, corvette servo, deeper pan and e-fan cooler. If that doesn't help, I guess a new tranny will. Let us know if you get this fixed, will ya?

 

[Blaine]

Ok, just returned from a local transmission shop that has a very good reputation in this area. He took my Yukon for a drive with a computer. Later he returned and I thought I was in for bad news. He said that a valve body update would be necessary to cure the problem and not a transmission rebuild. He quoted me out the door in 1 full day at $350
As soon as I can find a loaner, my Yukon will be parked on his lot. I will let you know how it goes.

 

[99COOP]

Its all in the valve body, the TCC bore wears out and lets fluid slip past. In return the trans gets put into "limp" mode and hards shift. They have updated kits with new sleeves along with a fresh bore on the valve it self to correct the problem. This is not only very common but it is a service bulletin from GM, so it is a well known issue. 350 sounds a little high, but the person who quoted me was a friend so i guess that makes a difference.

 

[Blaine]

Sorry it has taken me a while to reply.
Anyway, I thought I would follow up on this post so it may help others wit the same problem. The valve body kit done the trick. The truck shifts perfectly now. Watching the engine rpm at 60 mph, there is more than a 500 rpm decrease with more of a “solid” in gear feel. I didn’t even know the transmission was slipping when I first got the truck.
Runs like a top now.