transmission slips when kicking down a gear
Thread Starter
On The Tree
Joined: Mar 2011
Posts: 142
Likes: 19
From: Beaufort, SC
transmission slips when kicking down a gear Need help guys. I’m trying to get an idea of whats wrong so to see if this is something I can take care of myself or if this needs to go to a trans shop. I have a good bit of mechanical experience with diesels but I’m clueless when it comes to auto tranys.
Heres the scenario. Driving down the highway at 70mph. I go to pass someone so I press the pedal to the floor (or close to it) and the rpms jump up to almost the revlimiter for about a second. Then it jumps (not slams) into gear and takes off. Almost like a clutch dump at 70mph. it started doing this when going from 4th to 3rd but now it does this in all gears but only when down shifting. From a dead stop it upshifts through the gears just fine. any ideas?!?!
2002 z28 with 88k miles. Only mods to powertrain are ported TB, lid and Flowmaster muffler. I changed the trany filter about 2k miles ago and it didn’t change anything. Its slowly gotten worse since. Fluid was/is clean, not burnt and at correct level.
Thanks in advance
Heres the scenario. Driving down the highway at 70mph. I go to pass someone so I press the pedal to the floor (or close to it) and the rpms jump up to almost the revlimiter for about a second. Then it jumps (not slams) into gear and takes off. Almost like a clutch dump at 70mph. it started doing this when going from 4th to 3rd but now it does this in all gears but only when down shifting. From a dead stop it upshifts through the gears just fine. any ideas?!?!
2002 z28 with 88k miles. Only mods to powertrain are ported TB, lid and Flowmaster muffler. I changed the trany filter about 2k miles ago and it didn’t change anything. Its slowly gotten worse since. Fluid was/is clean, not burnt and at correct level.
Thanks in advance
Thread Starter
On The Tree
Joined: Mar 2011
Posts: 142
Likes: 19
From: Beaufort, SC
update: i now notice what seems to be the converter flaring up. if i have cruse control on and give it even just a little gas, maybe 1/4 throttle, maybe less, the rpms jump up almost 200 rpms for a second and then you feel the car move and rpms drop back down.
is this a sign the converter is going bad? i hope so because i would like to upgrade and solve an issue at the same time. then the wife cant get mad i'm buying new car parts
is this a sign the converter is going bad? i hope so because i would like to upgrade and solve an issue at the same time. then the wife cant get mad i'm buying new car parts
Thread Starter
On The Tree
Joined: Mar 2011
Posts: 142
Likes: 19
From: Beaufort, SC
thanks for the reply, i'll check out google.
i scanned it with my little handheld friday and didnt get any codes. i'm going to see a buddy with a better scan tool tomorrow. and yes every now and then it will bark 2nd but 3rd and 4th feel a mushy. did you replace your converter and solve the issue? thats what i'm hoping is the issue since thats something i can do my self.
i scanned it with my little handheld friday and didnt get any codes. i'm going to see a buddy with a better scan tool tomorrow. and yes every now and then it will bark 2nd but 3rd and 4th feel a mushy. did you replace your converter and solve the issue? thats what i'm hoping is the issue since thats something i can do my self.
Thread Starter
On The Tree
Joined: Mar 2011
Posts: 142
Likes: 19
From: Beaufort, SC
after reading up a bit on the code i found that the valve body is most likely the culprit. i guess i'll be looking for a new valve body. i was hoping to get a stall but i guess that will have to wait.
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Joined: Aug 2010
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From: Ann Arbor, MI
If your upshifts at high throttle are all good, I doubt it is a converter or internal trans problem. It does sound like a valve body related problem.
Kinda taking a guess here... but I would first replace the 3-2 downshift solenoid. I know you mention the 4-3 downshift, but this solenoid controls the pressure to the 3-4 clutch. Next, unless you enjoy repeatedly dropping the pan and replacing one piece at at time, I would at the same time replace the EPC (Pressure control solenoid). Any stickiness in these two solenoids can cause all kinds of problems with strange symptoms. Again, I am NOT sure of this advice. A sticking valve in the valve body could be the culprit too but much harder to find/fix.
If you do decide to get a "new" valve body, any '98 through '05 should work just fine. You will need new gaskets too. I have bought used (and one new) VB from ebay seller "powertrainpartsplus". They are reliable and their "condition" for parts is honest.
Kinda taking a guess here... but I would first replace the 3-2 downshift solenoid. I know you mention the 4-3 downshift, but this solenoid controls the pressure to the 3-4 clutch. Next, unless you enjoy repeatedly dropping the pan and replacing one piece at at time, I would at the same time replace the EPC (Pressure control solenoid). Any stickiness in these two solenoids can cause all kinds of problems with strange symptoms. Again, I am NOT sure of this advice. A sticking valve in the valve body could be the culprit too but much harder to find/fix.
If you do decide to get a "new" valve body, any '98 through '05 should work just fine. You will need new gaskets too. I have bought used (and one new) VB from ebay seller "powertrainpartsplus". They are reliable and their "condition" for parts is honest.
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On The Tree
Joined: Mar 2011
Posts: 142
Likes: 19
From: Beaufort, SC
thanks for the response mrvedit. i have seen you post a lot on transmission issues and you seem to know your stuff so i value your opinion.
after reading more about the PWM valve i thought that might be issue but i was just kind of taking a shot in the dark and it seemed simple enough to change. where is the EPC located?
after reading more about the PWM valve i thought that might be issue but i was just kind of taking a shot in the dark and it seemed simple enough to change. where is the EPC located?
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Joined: Aug 2010
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From: Ann Arbor, MI
In this picture the EPC is on the bottom slightly right of center; it held in place with a 8mm bolt, but you also have to remove the 1-2 accumulator housing which is held with thre 10mm bolts.
The 3-2 is in the upper left corner; it is held in with a little clip.
The TCC PWM is in the lower left corner.
Again, I want to say that I am not sure of my suggestions, but they are relatively easy to cheap to test.
The 3-2 is in the upper left corner; it is held in with a little clip.
The TCC PWM is in the lower left corner.
Again, I want to say that I am not sure of my suggestions, but they are relatively easy to cheap to test.
Thread Starter
On The Tree
Joined: Mar 2011
Posts: 142
Likes: 19
From: Beaufort, SC
thats great, thanks for the pic. i have read that with some (maybe all) PWM replacements you have to use a reamer. i dont think thats the case with this one but since you recommended it on another thread i thought maybe you would know if its just a straight swap?
http://www.transmissionpartsusa.com/...-0a74741qa.htm
http://www.transmissionpartsusa.com/...-0a74741qa.htm
Last edited by Zac28; Nov 24, 2013 at 05:01 PM. Reason: forgot link
Moderator
Joined: Aug 2010
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From: Ann Arbor, MI
thats great, thanks for the pic. i have read that with some (maybe all) PWM replacements you have to use a reamer. i dont think thats the case with this one but since you recommended it on another thread i thought maybe you would know if its just a straight swap?
http://www.transmissionpartsusa.com/...-0a74741qa.htm
http://www.transmissionpartsusa.com/...-0a74741qa.htm
The Fitzall valve is usually used to fix the mentioned P1870 code. I'm not sure that is your problem.
Thread Starter
On The Tree
Joined: Mar 2011
Posts: 142
Likes: 19
From: Beaufort, SC
That is the Fitzall valve which replaces the PWM valve with a simpler and more reliable on/off valve. No reamer is used; the o-rings seal a worn bore. Most aftermarket converters prefer an on/off valve anyway.
The Fitzall valve is usually used to fix the mentioned P1870 code. I'm not sure that is your problem.
The Fitzall valve is usually used to fix the mentioned P1870 code. I'm not sure that is your problem.
since its easy to replace, i'll be in there anyway and converters like it better i'll probably go ahead and do it. if i didnt replace the stock converter with a stall would it negatively affect the stock converter? would i need to tune any codes out?
thanks again for all your help and being patient with me. for 4 years i worked at a diesel shop where i pretty much did nothing but rebuild International 466E engines. i work very meticulously and (knock on wood) the only issue i ever had was rocker arm nut backing out. i just dont know squat about automatics
Edit: while looking up part the number to order the 3-2 downshift solenoid i came across this http://www.ebay.com/itm/4L60E-Transmission-TCC-PWM-LOCK-UP-3-2-DOWNSHIFT-SOLENOID-1993-Up-OEM-GM-/251214777701?pt=Motors_Car_Truck_Parts_Accessories&hash=item3a7d914d65&vxp=mtr
is this the TCC, PWM or 3-2 downshift? or they all the same part number. i just want to make sure i order the correct part.
Last edited by Zac28; Nov 25, 2013 at 06:48 AM.
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Joined: Aug 2010
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From: Ann Arbor, MI
I don't know the pre-'98 transmissions very well, but IIRC pre-96 the TCC solenoid was on/off and the 3-2 downshift was PWM. For '96+ it is the opposite - the TCC is PWM and the 3-2 downshift is on/off.
Therefore I don't think that is the right 3-2 downshift solenoid for your '02. The right one is:
http://www.transmissionpartsusa.com/...-00035394b.htm
For your trans, the TCC solenoid has a Grey connector, the 3-2 Downshift has a White connector.
Some of this is explained on Page 48 of the ATSG Update Manual.
Therefore I don't think that is the right 3-2 downshift solenoid for your '02. The right one is:
http://www.transmissionpartsusa.com/...-00035394b.htm
For your trans, the TCC solenoid has a Grey connector, the 3-2 Downshift has a White connector.
Some of this is explained on Page 48 of the ATSG Update Manual.
Thread Starter
On The Tree
Joined: Mar 2011
Posts: 142
Likes: 19
From: Beaufort, SC
I don't know the pre-'98 transmissions very well, but IIRC pre-96 the TCC solenoid was on/off and the 3-2 downshift was PWM. For '96+ it is the opposite - the TCC is PWM and the 3-2 downshift is on/off.
Therefore I don't think that is the right 3-2 downshift solenoid for your '02. The right one is:
http://www.transmissionpartsusa.com/...-00035394b.htm
For your trans, the TCC solenoid has a Grey connector, the 3-2 Downshift has a White connector.
Some of this is explained on Page 48 of the ATSG Update Manual.
Therefore I don't think that is the right 3-2 downshift solenoid for your '02. The right one is:
http://www.transmissionpartsusa.com/...-00035394b.htm
For your trans, the TCC solenoid has a Grey connector, the 3-2 Downshift has a White connector.
Some of this is explained on Page 48 of the ATSG Update Manual.
thanks. i finally got a hold of someone at the local dealership and got a part number for it. the one on ebay is an incorrect part, at least for my year it is. i'm going to get the 3-2 solenoid in the link you posted and the EPC from them as well. i'm also going with the transgo HD2 kit which has the PWM replacement valve in it and an FTI stall. in the next few weeks i'll be pulling the tranny out to address a rear main/oil pan leak so while i was in there i figured i might as well do the HD2 and stall. thanks again
You need to get a tune to lower pwm duty, or you won't have firmer shifts.
Just one question - are you sure this is a flare and
not a double-downshift, immediately upshifted again?
Depending on shift tables you can make that kind of
thing happen. Might try using the scan tool to determine
whether you're seeing frictions slipping, or just a brief
flirtation with a lower gear.
not a double-downshift, immediately upshifted again?
Depending on shift tables you can make that kind of
thing happen. Might try using the scan tool to determine
whether you're seeing frictions slipping, or just a brief
flirtation with a lower gear.
Moderator
Joined: Aug 2010
Posts: 7,323
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From: Ann Arbor, MI
The only PWM in the '96+ 4L60E is the TCC lockup. You can tune out the PWM portion by setting the minimum and maximum duty cycle to 100%.
Also, after installing the Transgo or Sonnax shift kits, or Fitzall valve, the TCC is replaced with an on/off valve and I don't think the duty cycle tune matters (although I keep it at 100).
Thread Starter
On The Tree
Joined: Mar 2011
Posts: 142
Likes: 19
From: Beaufort, SC
Thread Starter
On The Tree
Joined: Mar 2011
Posts: 142
Likes: 19
From: Beaufort, SC
Just one question - are you sure this is a flare and
not a double-downshift, immediately upshifted again?
Depending on shift tables you can make that kind of
thing happen. Might try using the scan tool to determine
whether you're seeing frictions slipping, or just a brief
flirtation with a lower gear.
not a double-downshift, immediately upshifted again?
Depending on shift tables you can make that kind of
thing happen. Might try using the scan tool to determine
whether you're seeing frictions slipping, or just a brief
flirtation with a lower gear.