4L60-E hard shift from first to second gear

[Johnny Racer]

My 99 Yuk had symptoms of this late in the summer last year (like twice). All winter long it was fine. Now that the weather is warm again, happened the other day as well. Drive at a sustained "highway" speed (50-70mph) for a period of time, come to a stop, accelerate, BAM... instant shift kit. But whats weird, pull into a parking lot, shut it off, grab a soda, fire it back up nor more than 3 minutes later... no problems for the rest of the journey. Ugh... Valve Body, I figured as much. Welp the rear AC lines will have to wait. LOL

 

[juggjiggler69]

Hell i just had my tranny rebuilt back in august and it does that and everything in mine is new

Sent from my Galaxy Nexus using Xparent Red Tapatalk

 

[preshus]

i might have missunderstood but if you allready have a chip on it that could be

the cause of the problem . . . my buddy has a burban with a chip in it and didn't

program it right so it dose the exact same thing as you stated

 

[letsbangout]

My 99 Yuk had symptoms of this late in the summer last year (like twice). All winter long it was fine. Now that the weather is warm again, happened the other day as well. Drive at a sustained "highway" speed (50-70mph) for a period of time, come to a stop, accelerate, BAM... instant shift kit. But whats weird, pull into a parking lot, shut it off, grab a soda, fire it back up nor more than 3 minutes later... no problems for the rest of the journey. Ugh... Valve Body, I figured as much. Welp the rear AC lines will have to wait. LOL

Yea the problem you're describing, and probably the poster before you, is the classic valve body issue. Also could be the #8 check ball or a worn separator plate.

I found that the issue with my truck is mostly related to the 1-2 accumulator. When I did a fluid/filter change on the tranny, I dropped the accumulator, turned it over and the piston fell right out - it's not supposed to do that. The piston should be tight in there. I had a spare '93 accumulator assembly I could have replaced it with, but it was worse than mine, more "wobbled out" (the accumulator pistons like to wobble on the piston pin, causing irregularities in the piston bore, causing them to stick). Also sometimes in this series of trucks (98, 99ish from what I gather), sometimes those pistons are plastic rather than metal, so they crack easily. I resolved this by getting ahold of a stronger "big spring" (There's a big one and a little one in the piston assembly) - I was unable to get the piston and seal with only an hour's notice and I didn't wanna leave her unbuttoned for a long time. Now I simply can't make my transmission shift hard under high throttle/high torque, whereas before, gunning it from take-off would produce nail-biting shifts. It's also much calmer at lower RPM/lower torque, drives much more like a cadillac than it did before. Now the only time I have any semblance of a problem is when first starting out, before the system enters closed-loop, sometimes it likes to shift harder than necessary. I attribute this to the computer commanding more shift pressure than necessary because 1) it's open-loop and has less info about fuel mixture (as relates to engine load) at it's disposal, and 2) because the engine load is probably higher when everything is cold, if for no other reason, than because my fan stays engaged for the first minute or so after you fire it up.

I've become significantly more knowledgeable about this, and about these trucks in general, in the last 4 or 5 months.. although I'm no expert, i'll try to point you in the right direction if anyone should have other questions related to the 1-2 shift.

 

[WckedMnd]

Thanx for the info, my 95 two door just started doing this after being rear ended last week after 332,000 miles

 

[letsbangout]

Thanx for the info, my 95 two door just started doing this after being rear ended last week after 332,000 miles

Unfortunately I don't have much specific advice for you, except to check the accumulator of course. One other thing I can tell you is that issues with the valve bodies and the separator plates don't seem to be as prevalent (according to my research) with those older non-electronic trannies (I believe you have the 4L60, the non-E version). What most likely happened is that your accumulator piston has "wobbled out" on the pin. While preparing to fix mine, I bought a complete 93 accumulator, it was considerably more "wobbled" (that is, the piston was "stickier" while sliding on the pin) than my 99. You'll know you have an accumulator problem because if you drop it down (being careful when separating it from what appeared to be a paper gasket on the surface it mounts up to) and turn it over, the piston will fall out. The piston is supposed to be tight in there, to the extent that you'd need to use a light coat of vaseline to put it together. If you go after the accumulator, I recommend having an entirely new accumulator either in your hand or at your disposal in a parts depot, should you need it. In my case, the local tranny supplier only stocks the pistons and the big spring, but your accumulator also consists of a small spring, the housing with the pin, and the piston seal. The seals, btw, are usually sold as part of a complete rebuild kit so getting those might be a bear. To add some perspective to this thread, feel free to browse the pics I took of the repair: http://www.servidoresdedicados.us/yukon/

I should also add, there are other things external to the transmission that can still cause this problem (i.e. low[er] fuel pressure - replace the filter, etc). In my case, I've observed lately that my power steering pump seems to be working overtime because of the loose to extremely loose steering I have. I've read sporadic reports of the gearbox being to blame, but that makes no sense to me. More likely is the steering position sensor, present on 98 and newer trucks. It signals a pressure modulator that's built into the steering pump to control power steering pressure. Mine seems to be maximum pressure most of the time. Now it's affecting my gas milage, I've dropped from 14 - 15.5 down to 13 or less. It also affects the 1-2 shift.. when the steering is loose (what I perceive to be maximum power steering pressure), the first few shifts are always hard while it's in open-loop, and when it warms up and switches to closed-loop fuel trim, it gets better but still somewhat noticeable. I theorize that the PS pump is robbing power from the engine, making the PCM think the engine is under more load, and signaling the harder shift. The same thing has happened when I run the compressor, likely a combination of the two factors.

One other thing about the premise of this thread - decreasing shift pressure via programming. This can absolutely be done with software like EFIlive or HPtuners. Given that HPtuners is only $650 for the complete package, that it has a complete scantool including the ability to do bi-directional communications like a crankshaft relearn, and the ability to make the PCM forget about the Passlock system completely, I'm inclined to buy it one of these days.

 

[bigkahuna2]

Heres the fix

I have found the fix for my 2002 Chevy Tahoe 5.3L, 4l60 transmission hard shift from 1st to 2nd!! For those of you who just want the fix, scroll down to “Here’s The Fix”. All others read on!
I bought a 2002 Tahoe with 75,000 miles on it. It ran pretty good for about 20,000 miles then the hard shift from 1st to 2nd. Usually after the transmission had warmed up. Before I decided to rebuild it, I replaced the valve body assembly with a new one. No help. At 120,000 mile, I had a good friend rebuild it for me. He said the transmission was exceptionally clean. He did find a valve at the end of the wiring harness that had a small hairline crack in it that was along the line of where the two plastic pieces were molded together. The name of the valve/coil is the TCC (torque converter clutch) lockup solenoid and is soldered to the end of the wiring harness. He said this could have cause the torque converter to slip and lose pressure. After the rebuild, it ran better, but not perfect. I thought a rebuild would have fixed it. Well, 65,000 miles later, the 1-2 shift solenoid went bad. There was no clunk because it was not shifting from first to second. It was starting out in second gear. So I called my friend and he gave me a new 1-2 shift coil. (both 1-2 and 2-3 shift coils are about $40) I told him that it still clunked between 1st and 2nd. He told me that after replacing the 1-2 shift coil, to remove the accumulator and remove the piston and inspected the o-ring and wall of the accumulator. If you have a plastic piston, replace it with a new aluminum one. Mine was already replaced. Both looked good.
Here’s the Fix!!
He told me to adjust the Force motor (pressure solenoid). The accumulator must be removed to adjust or remove the force motor. As you look at the end of the force motor, there is a torx socket there that adjust the pressure. There is also a ring around the torx socket that might need to be held as you adjust the screw. He told me to turn the screw ¼ turn clockwise. (or from 12:00 to 3 o’clock) My outer ring did not turn as I adjusted the screw. If yours does, use a pair of right angle snap ring pliers to hold it. This force motor engages the 1-2 band. If there is not enough pressure, the band slips and hence the clunk. OMG!!! You would think I have a brand new Tahoe!!! It is SOOOO SMOOTHHHH! I have searched everywhere on the internet and not found this fix. I hope that this easy low cost fix works for you. If you can view the pictures, the accumulator is in the lower right hand corner and the force motor is directly to the left of the accumulator.

 

[bigkahuna2]

Picture of force motor

 

[bigkahuna2]

picture of transmission and valve body. Accumulator is lower right hand corner. Force motor is to the left of accumulator.

 

[letsbangout]

Thanks for chiming in. I've heard that about the force motor before, although I've always been under the impression that my problem was caused by excessive pressure, not a lack of it. Still good info. I think most people simply replace the force motor, not knowing they can be adjusted. I wonder if this adjustment is only present on certain years...

In my own case, my problem improved significantly when I replaced the big spring in the 1-2 accumulator. It improved further when I removed the AC controls, because I had a vacuum leak in the heater control valve and the vacuum actuator was kicking in while the AC controls were connected. I made additional improvements by replacing the Steering Control Module, responsible for speed-sensitive steering. The last two things, I surmise, were throwing off the load calculations for the engine, causing it to exert more pressure during the shifts, hence my commentary above. Additional items on my to-do list are to replace the entire accumulator piston with the Sonnax pinless accumulator, and to get rid of the PCV system. PCV on the 5.7 uses an inlet tube between the air intake plumbing and the passenger valve cover, then on the opposite valve cover is the PCV valve. I intend to replace the whole system with something called En-Valve which keeps the crankcase in a state of perpetual vacuum. It supposedly eliminates a lot of blow-by and dirty oil issues. In my particular case, I surmise that the whole system is leaking, causing inmetered air to enter the intake.

Thanks again for chiming in.