Help! I had the tranny in my half ton z71 (4l60E) rebuilt a few months ago (6000 miles). I know this is a forum for bigger trucks and I have those too but I thought to post here since I have been here awhile. I expected it to shift like a new truck after complete rebuild but it didn't. I thought it may not since it had 140,000 on it. Then I had 5000 lbs behind it so I used tow/haul. During the 1-2 shift it felt like a sledgehammer but a little less on the 2-3 shift. 3-4 was about normal. After unhooking the trailer, I ran the truck in tow/haul and it again shifts like a hammer. What the f***? I took it back to the shop since it is still under warranty and they are saying no codes and it drives ok. So i said no and they said we checked it out and the keys are in it so you can take it back. I haven't picked it up yet since it seems there is a problem that is not fixed. What do you guys think it could be? I had them put redline clutches in- could it be that? Sticky valve? I answered the sticky questions below.


1. Fluid level okay while running, warm, level surface. YES
1a. Fluid color and smell Red Normal
2. Speedometer reading correctly YES
3. Shifting normal/hard Hard
4. Shifting into OD okay? YES
5. Any service engine light: yes/no NO
6. If SES light on, what codes do you have?
7. Model year: 99 new body
8. Describe symptoms: 1-2 and 2-3 shift sharp, like a hammer in tow/haul
9. Does the engine come up to full temperature? YES
10. Any service work recently done that may contribute to your issues. Tranny rebuilt 6000 miles ago
11. Does the TCC lock up (or how many "shifts" do you hear?) Seems ok
12. Are you experiencing any kind of slipping? NO
13. What type of rear do you have? (Check RPO codes) 4.10/ 3.73/ 3.42 or 3.08 3.73
14. If you have an accurate tachometer, what is the RPM at 55 or 65? Normal

Sounds like they put a shift kit in it when they did it. If they did, they may have set it up to firm, but don't feel like replacing the seperator plate to get the smaller passages.

So should they fix it as part of the warranty? Will it cause future failures? Seems a little too harsh to be good (especially in tow haul) though.

I wouldn't think harsh shifts shouldn't cause an early failure. I quick firm shift does not slip.

Did you understand they were going to add a shift kit? If so, than you are stuck with it. If not than have them fix it. I understand there is technicly nothing wrong with it(otherwise you would have codes) but customer satisfaction requires it to shift like normal if thats what you want.

Another option is to never use tow/haul & it should live ok.

So should they fix it as part of the warranty? Will it cause future failures? Seems a little too harsh to be good (especially in tow haul) though.

Thanks. THe only understanding was that they were to put redline clutches in. He said today that the valve body came from some company other than GM (not new but rebuilt by some company that started with a "s") then he went on to say they changed some passages at some point but he wasn't sure to what degree. He said initially that he has never had any complaints before. After pressing him on the shift points and why they are high for my truck, he said they have had some customer issues with that! If the truck engine didn't act like it was young I'd just live with it and not use tow haul but the truck seems to have a lot of life left and I want to make sure the tranny works properly.

Where we ended was he is going to talk to the valve body supplier and I am going to talk to Chevy about programmed shift points. I am still not convinced it is only shift points since the tranny felt like it was going to be shocked from the truck when I was towing 5000 lbs in tow/haul mode.

On my gassers with a 4L60E, a sticking EGR valve would cause them to shift hard enough to rattle your teeth. With a good 2way scanner like a Snap-on or the dealer Tech II, the Electronic EGR valve can be tested from 0-100% open. The reason the for the hard shift is, GM wants to preserve the durability of your tranny, and to do so, the timing and fuel delivery are retarded along with a quick cycle of the EGR valve, all leading to an imperceptable, but important, Detune at the time of shifting. At over $100 for an EGR, I'd test it first.

All mine had no stored code or a CEL activation, just simply a "rattle your teeth" hard shift from 1-2 and firmer than normal 2-3 shifts. The 3-4 felt normal.

Just a thought...

My educated guess is the reason your 1-2 shift is hard is because of a uncured 2-4 band and/or improper 1-2 accumulator piston/spring for the valve body calibration you got sent. If they used a high performance or kevlar lined band this will amplify the problem. There are two ways to solve the band problem 1. just let it break in over time (will take about 10k miles) 2. put the truck on a lift running in manual low and pry on the 2-4 piston cover to engage the band until a little smoke comes out the vent (sound crazy but it works, I prefer to wait it out or use a good used band) Now the 2-3 shift being harsh is most likely caused by a combination of the trans builder and valve body manufacturer trying to make the 3-4 clutch pack last longer since it is a weak point in the trans. the builder may have left out the load release springs or used a z-pack or added clutch packs and the valve body is probably recalibrated to try to help the 3-4 pack live longer by firming up that shift. I would ask them the make sure your accumulators pistons and springs are matched to that valve body and that they are stacked correctly as they do change the order sometimes piston on top sometimes spring.