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08 Avalanche 5.3 4x4, 175k on engine. P.O. had trans rebuild about 20k miles ago. Today on highway out of blue at 70 mph started revving in 4th. 1st &2nd fine, 3rd slips a lot but finally shifts in to 4th, 4th also slips a lot. 2500 rpm at 45 mph. I had my HPTuners so ran a scan.
I am well aware the 3-4 clutch pack is a frequent failure point. Seems to slip less in 4th than 3rd. Wondering where to start diagnosing. Will do a pressure test once I get home. Is there a way to test the 3-4 apply piston for leakage from the VB? Could the spool in the VB be stuck or leaking? Anything else to look at before dropping the trans?
The key phrase is: "P.O. had trans rebuilt about 20k miles ago". Very few shops properly address the many areas where the 3/4 circuit can leak or where the AFL control pressure can leak after many miles of usage. As a result, many of these rebuilds barely last 5K miles; you might have been lucky to get 20K. There have been dozens of threads over the years that started exactly like yours. Those shops claims of rebuilding a 4L60E for under $2000 (and there are MANY, MANY, MANY) will not give you a long lasting trans.
Last edited by mrvedit; 05-16-2024 at 05:30 PM.
Reason: Missing word
Fluid was burnt when I got the truck but it shifted fine, I replaced it with full synthetic about 200 miles ago when I installed external cooler, so maybe that flushed the clutch plates. I watched the temperature the entire time and never got above 220, mostly at 205 until I got to destination. Did drive about 40 miles at 45 mph (figured damage was already done).
Having found the ATF to have been burned, it was already to late!
The ATF Temperature has to been in excess for such a result to have occurred.
Why ignore such scenarios.
Expectations from that point on should have been to be prepared for a failure if not going in the direction of making corrections/ repairs to the Transmission.
If you started having acute cardiac pain, chest/ shoulder/ arm/ peripheral neuropathy/ pain, hypertensive retinopathy and auditory neuropathy...
Would you just wait for Cardiac Crisis and/ or Trans-Ischemic Attack???
No.
You would react to such signs and appropriately take action.
Well as somebody mentioned it was rebuilt by a local shop and I figured they probably did a **** job but thought I would give it a try with a fluid change and a cooler on it to see if I can keep it going a little while. still doesn't act like it's the clutches, it acts like it just doesn't have enough pressure to engage them fully. Has to rev to 4,000 RPM for third piston to apply and pretty quickly shifts to fourth, feels more like pressure loss.
Well, you could put a pressure gauge on the trans and report back to us what the pressure is at Idle, Reverse and when you blip the throttle.
Some chance a very low pressure could be fixed without removing trans, but as mentioned, it would already be too late. You have been on this forum for 21 years! (Congrats!) You have likely seen posts that when the 3/4 clutch slips, the trans is toast. Its the #1 (!!) reported fault with these transmissions and cheapo rebuilds only delay a repeat by a few thousand miles.
How long do you think a clutch pack is going to last when it is slipping at a rate of 2000 rpms. One more time I will be more specific this time, have you checked for burnt fluid once you got your vehicle home from driving it at 45 mph and 4000 rpms?
Well, you could put a pressure gauge on the trans and report back to us what the pressure is at Idle, Reverse and when you blip the throttle.
Some chance a very low pressure could be fixed without removing trans, but as mentioned, it would already be too late. You have been on this forum for 21 years! (Congrats!) You have likely seen posts that when the 3/4 clutch slips, the trans is toast. Its the #1 (!!) reported fault with these transmissions and cheapo rebuilds only delay a repeat by a few thousand miles.
Yeah, have been around the forum a while, still have the original vehicle that got me on the forum - 2002 35th Anniversary SS - ordered new. Now has about 39k on the clock, six speed in it. Basically stock except for Jordan Musser's Sam Strano setup (some of you old timers might recognize those names). Did 12.58 with the 4.30's, need to get back to getting it going again.
Anyway, about 15 years ago rebuilt the 4L60 in my sons 99 Tahoe - 3rd clutch packs completely gone. Drove home in 2nd on that one too but once it went in to 3rd there was no pull at all. This one is an 08 Avalanche with 175k, only had it about 6 months and have put very little miles on it. It should be dropped back at home in the next day or two and I am definitely going to put a pressure gauge on it first thing. As we have all see sometimes you get a hyd leak and 3rd won't apply and sometimes it slips so bad it burns up everything and sometimes they just wear out and there is no fiber material left. This one def feels like not enough pressure to get full application because you can finally feel it apply third and then shift in to fourth.
How long do you think a clutch pack is going to last when it is slipping at a rate of 2000 rpms. One more time I will be more specific this time, have you checked for burnt fluid once you got your vehicle home from driving it at 45 mph and 4000 rpms?
Honestly I was shocked it made it the 40 miles to my destination. Fluid did not burn on the final 40 miles, but as I said #1 it is full syn so very burn resistant and #2 I managed the temps to keep them under 220 - mostly in the 205-210 range - by balancing throttle to minimize slip in 4th. Still might have burnt the clutches all to hell but then again they might not have had enough pressure on them to burn. I guess we will see when it eventually comes out. Anyway, checked the fluid again once I finished the drive and still not burnt, but doesn't mean the clutches aren't. Really wish GM had just put a pressure sensor in the trans - they really aren't that expensive and would be good health diagnostic to have it there all the time.
Low pressure in 3rd and 4th confirmed. 2nd gear gets to about 140 where it shifts, 3rd and 4th never get above about 80 psi. What is the most probably cause for a pressure issue to occur suddenly while on the highway?
A. what is the scanner commanding. PCS amperage needs to be looked at. If the PCS amperage is near 1 amp...80psi is normal
If it's more like 0.2 amp...not normal
B. all kinds of leaks in the 3/4 circuit are possible
A. what is the scanner commanding. PCS amperage needs to be looked at. If the PCS amperage is near 1 amp...80psi is normal
If it's more like 0.2 amp...not normal
B. all kinds of leaks in the 3/4 circuit are possible
Valve body
3rd accumulator checkball capsule in the case
seals in the drum
shaft to input drum press fit
What all was done when the unit was rebuilt?
Thanks for the response. I went out and got another batch of data, although not sure what it means, would you please be so kind to interpret? So are you suggesting the PCS is not commanding enough pressure? What would cause that?
At that point in your graph are you in the throttle accelerating?
BAsed on the road speed and engine RPM I'd assume yes but can't see a TPS datapoint
PCS amp being .92 there and requesting 4psi seems quite a ways off to me
Has there been tuning done?
You said trans was done 20k ago...if it made it that long, and the tune hasn't been messed with, I may have sent you down a rabbit hole. Apologies.
I saw mention of HP Tuners and thought it had been messed with.
if it lived for 20k miles and now is taking a dump...it's either low on fluid, or it has a mechanical issue you'll likely need to pull the transmission out to repair
Thanks for the response. Trans tune is bone stock. I was only on the throttle enough to get it to shift, but you can see on the left side the values at the indicated vertical line, so 37, 43, 29, and 42 %. I did see .92 PCS amp and now that you mention it that does seem low. I looked in the tune and I see no way to adjust that, is there a table that adjust desired PCS? I would have though it would have been closer to .2 or .1 as you stated, asking for plenty of pressure. It drops to .62 amps just before 2nd gear shift, but then in 3rd gear at some point it is commanding .66 amps. I know the 3-4 clutch is usually the issue in these but it did feel like a loss of pressure issue when it happened initially. What makes no sense to me is why the o-ring on the piston or the shaft would give up once it was already in 4th on the highway. Steady highway driving at around 75 mph and all of sudden revving in 4th. Even after that with all the slip it wasn't really getting hot or acting like the clutches were gone, just like not enough pressure was being applied to the piston. Oh well, I guess rebuild here I come. I will probably just buy a reman and not bother diagnosing failure although I am dying to know just from a curiousity standpoint. I hate that these local shops around the country only offer a 1 year warranty on what is obviously a stock truck used for DD duty.
Yeah I know, but Goodwrench is 3 yr 100k on reman, and if you are doing the work right why not warranty longer? Because obviously you don't do the work good enough to warranty longer because you would have too many callbacks.
Yeah I know, but Goodwrench is 3 yr 100k on reman, and if you are doing the work right why not warranty longer? Because obviously you don't do the work good enough to warranty longer because you would have too many callbacks.
Awfully strong words for the guy not building or warrantying a transmission and is online asking guys like us who "obviously don't do the work good enough" for help
05-11-2024, 09:48 PM
4L70E low mile rebuild 3-4 slipping issues 
