Trans help

[luke0011]

So I'm a new owner of a 07 Yukon xl. I've read a lot of the threads on trans. I have 170k in the truck and it's in decent shape. I've noticed when driving the truck it will shift smooth if I throttle gently. I do get a thunk going from 1st to second and down shifting from 3rd. It doesn't always happen and I am not sure what to check. I did check motor mounts and they are good. There is a lot of rust on the rest drive shaft. I was thinking to pull it and sand-paint it. I tried shaking the drive shaft to check the u-joints but they seem tight. Is there a way to check those?

Thanks

 

[thompsoj22]

just my opinion, im about 6 months into our 08 denali xl1500 at 131k miles and love the vehicle! if you search around youll find alot of info in relation to the "clunk", shift confusion in some situations accellerating. the six speed is a great trans so take some time to learn to drive it, it is new to you and you will learn to use the throttle in way that limits the issues you are describing."OR" you could start throwing cash at trans flushes, tunes, driveshaft yokes,u joints, tail housing bushings and the list go's on. i would not remove the driveshaft to paint it. it is possible that it is still in it's factory installed dynamically balanced position and you dont want to move it just to paint it. the rust means nothing.

 

[swathdiver]

Hey Lewis. Welcome! If your 2007 XL is not a Denali it will have the 4-speed transmission. The shifts are supposed to firm up as the throttle is increased. How does the fluid look?

@kbuskill @Doubeleive @Scottydoggs and others will chime in soon enough.

 

[Doubeleive]

i have the 6l80e & awd my slip yoke clanks more than I like had it lubed about 6 months ago I think it needs to be done again but I have a heavy foot so a normal driver might not notice it as much, mine will mostly clank if I jump on the pedal either from a stand still or just cruising and then accelerating fast, I can also feel it if I lift off the pedal real fast also.

 

[luke0011]

The color looks good. It looks red and smells normal. It seems to go away after driving it a bit. I did still notice the clunk mostly 2-3rd up and down. Funny wasn't as bad when I accelerated faster.

 

[luke0011]

I definitely have a smooth shift 1-2 but 2-3 and 3-2 have a good thunk. I tried manually shifting it with the shifter and it clunked up and down in 2-3 everytime.

Any idea?

 

[swathdiver]

I definitely have a smooth shift 1-2 but 2-3 and 3-2 have a good thunk. I tried manually shifting it with the shifter and it clunked up and down in 2-3 everytime.

Any idea?

Is this a Denali with a 6-speed or a 5.3 with a 4-speed? I can then see what the troubleshooting guide might say.

 

[luke0011]

5.3 - 4 speed.

 

[swathdiver]

5.3 - 4 speed.

I'm no transmission guy but I did just read through the shop manual quickly. The only thing both symptoms have in common is that they are part of the valve body and have fluid running through them. I would change the fluid and see if the problems go away and if not, consider rebuilding or replacing with new OE valve body.

A transmission shop is very likely going to suggest rebuilding the whole thing, which is not necessarily a bad thing but if all you needed was a new check ball, well, you get the idea.

 

[thompsoj22]

I definitely have a smooth shift 1-2 but 2-3 and 3-2 have a good thunk. I tried manually shifting it with the shifter and it clunked up and down in 2-3 everytime.

Any idea?

as other post mentioned valve body most likely as it is the "fluid pressure brain" and components within it determine shift smooth/firm feel. it isnt slipping so maybe just do a good flush/filter change and see what happens. although when you drop the pan to change the filter you will be staring at the valvebody and it is "somewhat" of a straight forward R&R there are linkages,gaskets,programing plates,check balls that all require exact reassembly location and tq specs. flush/filter $75 your cost and see what happens?

this opinion is based upon no mechanical looseness in mounts, u joints/tail housing/differential.