Transmission Question

[Old77]

So 90% of the time the transmission in my '98 shifts smooth and all is wonderful. However, there is the rare occasion (that I've yet to be able to recreate at will) where for some reason is starts to have very firm shifts and I'm not sure why. During this time, if I pull away from a stoplight or stop sign aggressively it likes that and shifts great but if I drive normal it's like I have a shift kit or something and the shifts are very firm and very noticeable. Any ideas as to why this would happen and why it's so sporadic?

 

[Eskimomann209]

What year?

Does it have a lockdown cable?

I had this issue and it was timing

But mine was if I took off at normal pace it kicked
If I blasted off the line it was smooth

 

[SwampHound]

Just ran into this thread. My truck does the exact same thing. Not sure as to why though

 

[poncho62]

Are you getting any codes, engine light on?

Sounds to me like there is slippage in the trans (usually causes a p1870 code)...which puts the trans into high pressure mode.

 

[98_k1500]

^^ usually caused by a TCC malfunction.

 

[SkyHighColorado]

replace shift solenoids.

 

[Old77]

Are you getting any codes, engine light on?

Sounds to me like there is slippage in the trans (usually causes a p1870 code)...which puts the trans into high pressure mode.

No codes for me at all I can't even make it do it at will. Just randomly and not very often

 

[Old77]

replace shift solenoids.

This is probably a stupid question so bear with me LOL.......Are the shift solenoids internal or external to the trans? I'm asking because if they are external I can probably just replace those in my driveway. If internal I'd probably just have the thing rebuilt and beefed up while it was out anyway at that point.

 

[GMFORLIFE]

I experience the same type of shifts in my 99 nbs Silverado Z71 (4L60e) but have yet to figure it out. It may do it a couple times a week or it could be months before it does it just once. I usually have to pull over and turn my truck off and wait a min or 2. Then when I start it up and drive away its back to normal again.

 

[96Z71ECSB]

This is probably a stupid question so bear with me LOL.......Are the shift solenoids internal or external to the trans? I'm asking because if they are external I can probably just replace those in my driveway. If internal I'd probably just have the thing rebuilt and beefed up while it was out anyway at that point.

Shift solenoids are internal but they are attached to the valve body.
Remove the pan and they are right there.