Transmission intermittent hard shifting

[Peaches93Z71]

Hey guys, first post on the forum. I've got a 1993 chevy k1500 extended cab Z71 stepside silverado, TBI 350, 4l60e, np241c, 8.5 inch 10 bolt rear end. It's my DD. I think that covers everything, let me know if I missed something. Short history on the truck: I bought it in June of 2023, previouse owner owned it since like 1997. I'm the 3rd owner and i have all service/repair records on the truck since the previous owner bought it. Truck has 226k on the clock. Has a hesco parts inc. Rebuilt 350 that has~36,000 miles on it. Tranny was rebuilt by L&D transmission in Kingsland georgia at 221,855k. (Engine and tranny rebuilds were the previous owner). Everything runs strong except 1-2 shift is almost always jolting. In 1st gear, if it gets right to about 2700 rpm it shifts firm but smooth into 2nd. If your rpm is any lower or a little higher, it'll jolt pretty bad. On a rare occasion it will shift 100% normally but not often. Every shift is quick and firm nomatter what gear, speed, or rpm your at but 1-2 shift will knock you back in your seat. I'm guessing it's a pressure issue but I've got a limited knowledge of transmissions so any ideas/trouble shooting? Is it gonna cause me other issues? Also, any of yall have personal Experiance with L&D Transmission? Any questions are more than welcome. (Sorry for the long post)

 

[NickTransmissions]

Hey guys, first post on the forum. I've got a 1993 chevy k1500 extended cab Z71 stepside silverado, TBI 350, 4l60e, np241c, 8.5 inch 10 bolt rear end. It's my DD. I think that covers everything, let me know if I missed something. Short history on the truck: I bought it in June of 2023, previouse owner owned it since like 1997. I'm the 3rd owner and i have all service/repair records on the truck since the previous owner bought it. Truck has 226k on the clock. Has a hesco parts inc. Rebuilt 350 that has~36,000 miles on it. Tranny was rebuilt by L&D transmission in Kingsland georgia at 221,855k. (Engine and tranny rebuilds were the previous owner). Everything runs strong except 1-2 shift is almost always jolting. In 1st gear, if it gets right to about 2700 rpm it shifts firm but smooth into 2nd. If your rpm is any lower or a little higher, it'll jolt pretty bad. On a rare occasion it will shift 100% normally but not often. Every shift is quick and firm nomatter what gear, speed, or rpm your at but 1-2 shift will knock you back in your seat. I'm guessing it's a pressure issue but I've got a limited knowledge of transmissions so any ideas/trouble shooting? Is it gonna cause me other issues? Also, any of yall have personal Experiance with L&D Transmission? Any questions are more than welcome. (Sorry for the long post)

Check servo inboard travel...Shouldnt be more than 1/8" of an inch. If it passes that test, drop the pan and pull off the 1-2 accumulator housing to check for a broken spring...if the piston itself is plastic, replace it wih an aluminum one.

Since you have a 1993, we dont see too many issues with the TCC regulator valve in the valve body but it's worth testing if you have a Sonnax vac test machine.

Has the 1-2 shift always been harsh or harsh since the rebuild? If so, there's a couple other things you can check/remediate if so...

Lastly, harsh shifting can also be caused by a worn out rear pump stator bushing...In the 95+ units, this will trigger P1870 (or the OBD1 equivalent code for the 1995 vehicles).

 

[Peaches93Z71]

Ok, so I know the 1-2 servo is on the side right? Not sure what inboard travel is or what the accumulator is. Definitely don't have a Sonnax vac machine(not sure what that is either lol). The 1-2 shift has always been harsh since I've owned the truck which has been since the rebuild. I don't have a way to read OBD1 codes without taking it to a shop. I did this like 6 months ago and all I had was an egr code. It was shifting hard back then too.

 

[NickTransmissions]

Ok, so I know the 1-2 servo is on the side right? Not sure what inboard travel is or what the accumulator is. Definitely don't have a Sonnax vac machine(not sure what that is either lol). The 1-2 shift has always been harsh since I've owned the truck which has been since the rebuild. I don't have a way to read OBD1 codes without taking it to a shop. I did this like 6 months ago and all I had was an egr code. It was shifting hard back then too.

Correct - The servo is on the pass side of the transmission.

My video on installing a 4L60E valve body will cover the other relevant components and their locations...

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Check it out - it should give you a very good idea of the scope of the work involved, technical information and other tips/pointers relevant to what you'd be doing.

After watching, let me know if you still want to tackle the job yourself and we can go from there.

 

[Peaches93Z71]

Ok, so I watched the video (great video by the way) and I have a couple questions. Can the 1-2 accumulator be removed without pulling the valve body? If it is the problem, it should be replaced right? Also, I still don't understand 100% on adjusting the servo inboard travel. And with your knowledge and experience, will this hard shifting condition cause issues long term for other parts in the trans?

 

[NickTransmissions]

Ok, so I watched the video (great video by the way) and I have a couple questions. Can the 1-2 accumulator be removed without pulling the valve body? If it is the problem, it should be replaced right? Also, I still don't understand 100% on adjusting the servo inboard travel. And with your knowledge and experience, will this hard shifting condition cause issues long term for other parts in the trans?

Good questions.

1. You can remove/reinstall the 1-2 accumulator housing without removing the valve body

Check the spring - it should not be broken (replace it if so). Also you should have a single spring that sits in the housing on top of the piston. The piston should be installed upside down in the housing. In late 95 they changed the design to a two spring set up, different housing and smaller pin diameter / diff piston with smaller diameter pin bore

2. Check out this video for a full explanation on servo travel, band clearance and implications for excessive clearance/servo travel:

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That video is part 1; part two hasnt been filmed as of yet