funny rpm's

04xuv

Original poster
Member
Dec 3, 2011
94
Driving between 40 & 65 mph's, if I keep the throttle at a constant speed, my rpm's will slowly fall a couple of hundred rpm's and then jump back up to normal. It will do this consistently, with or without using cruise control. It doesn't do it at every speed in the range, but definitely not slower and not faster. Nor does it do it while accelerating or going up hills, or coasting. Any ideas?
 

chief0299

Member
Jul 1, 2013
67
It's very likely your torque converter going in an out of lockup. Is your SES light on? If you know someone with a scan tool, they can look to see if the TCC solenoid is working abnormally or if there is a pending code.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Mileage and maintenance history on the tranny?
 

04xuv

Original poster
Member
Dec 3, 2011
94
chief0299 said:
It's very likely your torque converter going in an out of lockup. Is your SES light on? If you know someone with a scan tool, they can look to see if the TCC solenoid is working abnormally or if there is a pending code.

That's what I thought it might be, after reading similar threads. No lights or codes showing.

the roadie said:
Mileage and maintenance history on the tranny?

I'm at 115,000. Just replaced tranny fluid and filter within the past 6 months.
 

Sparky

Member
Dec 4, 2011
12,927
Could be signs of the TCC valve bore starting to get worn. Seems about half the 4L60E transmissions suffer from that My old car was one of them, so I applied the fix to my Trailblazer just in case (as it also strengthens other stuff).

I installed this combo kit:

4L60E 4L65E 1996 2006 1870 P1870 Code Buster Combo Kit Corvette Servo Kit Book | eBay

No sluggish, smooshy feeling TCC lockup anymore, no RPM wavering, just a nice, crisp lock that doesn't let go unless it is supposed to. Almost feels like a gear shift.

Downside is you would have to get more trans fluid.

Note I'm not guaranteeing this is what it is. Check other causes of it coming out of lockup first, but IMO this is never a bad thing to install in a 4L60E transmission. I installed it at 120k, I have 182k now.
 

04xuv

Original poster
Member
Dec 3, 2011
94
Sparky said:
Could be signs of the TCC valve bore starting to get worn. Seems about half the 4L60E transmissions suffer from that My old car was one of them, so I applied the fix to my Trailblazer just in case (as it also strengthens other stuff).

I installed this combo kit:

4L60E 4L65E 1996 2006 1870 P1870 Code Buster Combo Kit Corvette Servo Kit Book | eBay

No sluggish, smooshy feeling TCC lockup anymore, no RPM wavering, just a nice, crisp lock that doesn't let go unless it is supposed to. Almost feels like a gear shift.

Downside is you would have to get more trans fluid.

Note I'm not guaranteeing this is what it is. Check other causes of it coming out of lockup first, but IMO this is never a bad thing to install in a 4L60E transmission. I installed it at 120k, I have 182k now.



If that is the problem, how tough of a job is it? Any specific tools needed? I don't mind doing it myself, but I also don't mind paying a pro. to do it right.
 

Sparky

Member
Dec 4, 2011
12,927
Not overly tough (the hardest part is getting to the servo on the side of the trans). Just a lot of little pieces to keep and put back in the proper order. Pretty much, if you're a little OCD and can follow directions, it isn't too bad. I think it is more nerve-wracking than anything since it is the valve body of the transmission you're messing with.

You'll need an inch-pound torque wrench for the valve body bolts and snap ring pliers. A prybar is VERY helpful when putting the 2-4 servo cover back on as it is rather tight. The rest is your typical sockets, screwdrivers, etc.
 

Scott89TTA

Member
Jul 30, 2013
11
Sparky said:
Could be signs of the TCC valve bore starting to get worn. Seems about half the 4L60E transmissions suffer from that My old car was one of them, so I applied the fix to my Trailblazer just in case (as it also strengthens other stuff).

I installed this combo kit:

4L60E 4L65E 1996 2006 1870 P1870 Code Buster Combo Kit Corvette Servo Kit Book | eBay

No sluggish, smooshy feeling TCC lockup anymore, no RPM wavering, just a nice, crisp lock that doesn't let go unless it is supposed to. Almost feels like a gear shift.

Downside is you would have to get more trans fluid.

Note I'm not guaranteeing this is what it is. Check other causes of it coming out of lockup first, but IMO this is never a bad thing to install in a 4L60E transmission. I installed it at 120k, I have 182k now.

My 03 Trailblazer has 120K on it and definitely has something going on with the trans. I did a AIRAID CAI and PCMforless tune a couple years ago with 50% torque management removed and stage II trans mod basically for towing. Just prior to had both the trans and transfer case flushed, fluids and filter changed. Trans has a slight clunk pulling away on light acceleration and sometimes on the 1-2 shift plus sometimes in reverse. Lightly letting on and off the accelerator and lock up may be acting up a little. When the trans guy did the flush, filter and fluid change he said everything looked fine but he did not remove the valve body so these failing parts everyone is speaking of is quite possible especially at 120K. Shifts are not what I would call firm at all or what I expected after reading posts from others with the PCMfoless tune?

Does this kit come with the filter and pan gasket as well?

Thanks,
Scott
 

DocBrown

Member
Dec 8, 2011
501
Check for low fluid also, but I assume you already did that. I had the same symptoms and this was my issue. However, I'm bought all the parts and am doing the 4L60E upgrades, probably sometime next week since I'm due for a fluid change. I ordered all my parts from Transmission parts USA. Good prices, and fast delivery. Here's a couple of really helpful threads.

http://gmtnation.com/f24/built-4l60e-replacement-4894/

http://gmtnation.com/f93/how-remove-4l60e-valve-body-replace-plastic-accumulator-pistons-4972/
 

Sparky

Member
Dec 4, 2011
12,927
Scott89TTA said:
My 03 Trailblazer has 120K on it and definitely has something going on with the trans. I did a AIRAID CAI and PCMforless tune a couple years ago with 50% torque management removed and stage II trans mod basically for towing. Just prior to had both the trans and transfer case flushed, fluids and filter changed. Trans has a slight clunk pulling away on light acceleration and sometimes on the 1-2 shift plus sometimes in reverse. Lightly letting on and off the accelerator and lock up may be acting up a little. When the trans guy did the flush, filter and fluid change he said everything looked fine but he did not remove the valve body so these failing parts everyone is speaking of is quite possible especially at 120K. Shifts are not what I would call firm at all or what I expected after reading posts from others with the PCMfoless tune?

Does this kit come with the filter and pan gasket as well?

Thanks,
Scott

You still need a filter and gasket since there are two filters depending on whether you have a deep or shallow pan (most of these trucks have deep but always check).
 

CaptainXL

Member
Dec 4, 2011
2,445
04xuv said:
Driving between 40 & 65 mph's, if I keep the throttle at a constant speed, my rpm's will slowly fall a couple of hundred rpm's and then jump back up to normal.

Would a slow fall indicated a bad TCC solenoid? Doesn't sound like it. To me this sounds like you have an exhaust leak or something and the O2 sensor is compensating.
 

04xuv

Original poster
Member
Dec 3, 2011
94
CaptainXL said:
Would a slow fall indicated a bad TCC solenoid? Doesn't sound like it. To me this sounds like you have an exhaust leak or something and the O2 sensor is compensating.

been pretty busy lately. i'll update when I get a chance to have a shop check it out. thanks for the extra opinion. i'd be super happy if it had nothing to do with the tcc. well, as long as its cheaper.
 

04xuv

Original poster
Member
Dec 3, 2011
94
fixed my transmission issues. had it rebuilt. I was 4.5 hours away from home towing a uhaul when the tranny went out. good times. got some recommendations on a reputable shop and had them do the work. drives great now. solid rpm's, solid shifts.
 

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