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Automatic transmission shifts hard

I

Isotep

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I have a 1990 k5 w/5.7 350. Runs great, but reverse & 1st gear seem to shift hard, not incredibly drastic, but More like 'thunk' when it shifts. The rest of the gears seem to shift smooth. The fluid is great condition and been regularly maintained.
thank you.
 
Do I check that by turning the drive shaft by hand and seeing how much play there is? Other than the tons of great knowledge I'm gaining from the ck forums I'm a noob to DIY on this truck, but doing my own work on it is partially why I bought it.
 
The flexplate on the One piece rear main seal blocks (1986 I think, and newer), Likes to crack around the bolt holes.
 
check your motor mount's also....with the hood up, see how much the motor moves when shifting from reverse to drive.......
 
Isotep said:
Do I check that by turning the drive shaft by hand and seeing how much play there is? Other than the tons of great knowledge I'm gaining from the ck forums I'm a noob to DIY on this truck, but doing my own work on it is partially why I bought it.
Click to expand...

Truck in park, push/pull the truck back and forth while watching the U-joint.

I got a short vid of when one of my U-joints went bad...give you an idea anyways.

 
Last edited by a moderator:
Isotep said:
I have a 1990 k5 w/5.7 350. Runs great, but reverse & 1st gear seem to shift hard, not incredibly drastic, but More like 'thunk' when it shifts. The rest of the gears seem to shift smooth. The fluid is great condition and been regularly maintained.
thank you.
Click to expand...

Before we go too far, is your idle a little high?
If it is, it's what causes this.
If your idle is normal, then look for the stuff mentionned already.
 
With a good U-joint I don't get a clunk or bang into D or R even at 1200-1500 rpm idle...
 
Thank you all for the great advice. I'll give the Truck a good push/pull tomorrow. My idle is good and motor mounts are good too.
 
It could be excess play in the spider gears or cross pin ,or worn side gears,or too much backlash in the ring & pinion in the diff causing the clunk when you put it in gear--check the splines on the drive shaft slip yoke too,if they are sloppy or have no grease,that can cause similar noises...
 
Ok, I apologize in advance for being a complete idiot in my description. I have now had a decent amount of time to drive around in the truck, and from reading more on the forums here, have much better description of issue. I now think the issue is TV cable adjustment, here's why... I need to be clarified on the issue though.

The truck shifts fine from Park > Drive.
From 1st > 2nd... thats when it had a 'Thunk' but not ALL the time.
2nd > 3rd... seems like it slips during the shift, engine will rev up as it changes gear, almost like it has a split second of neutral during the shift. But this again, not ALL the time.
3 > 4th, Seems like I do NOT have a 4th gear. Truck will be revved pretty high and wont shift, even if I tap Off the gas to coax it. I am to chicken to keep going to see at which RPM it does shift. 4th seems gone. Good thing this truck doesn't really get highway time. (I do not have a Tac on the truck, dash is all stock)
This is an OD transmission. 174K Miles, dunno if its original transmission or not. Fluid is clean, smells pretty and at proper level. No drips on the ground from anything ever. (so far). U-joints are pretty. Motor idles really really smooth. hardly feel it running. Mounts are good.
TO: diesel4me--- I'l have to take it to a shop to have the things you recommended checked, I have no clue what that stuff is. I just know very basics right now, but I am really mechanically inclined and can learn quickly once I have all the tools and more importantly... time. Once summer hits, I'm not afraid to tear the truck apart... LOL!
 
If its the TV cable, stop driving it!!

The adjustment is way too critical for the survival of the transmission.

Stupid design in my opinion. You can burn one up in just a few miles.

They are stupid easy to set. And as easy to check. With the engine off, open the throttle all the way. The TV cable should just be at the limit of its travel. If you can pull it out any amount farther, then its not set right and your transmission's life is in danger.

There are lots of threads here that tell how to set it, just do a quick search, or post back here and someone will be glad to help.
 
Ok, I just went out and had my boy Floor the gas peddle. I checked the cable while floored and it was tight like a piano string...
 
The cable should not be piano string tight.

If the transmission shifts too early, then the cable is too lose.

If the transmission hangs or shifts late, then the cable is too tight. This will also cause a hard thunk when slowing down or coming to a stop as it downshifts.

I'll try to find the link for adjustment.
 
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