Inside The 4l60E/4l85E Q&A's

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mike56BA:
As a Transmission rebuilder and member of CAFCNA, I thought I would share some of the inner workings of the 4l60e and 4l85e transmissions, and some of the common problems Iíve seen with them over the years.
     The 4l60e,was introduced in 1993, is an electronic version of the 700r4, which was introduced in 1982. The 4l65E is heavy-duty unit for use behind the 6.0L engines, and was introduced in 2001. Some of the parts were improved to increase its torque capacity. Input and reaction carriers were changed from 4 to 5 pinion gears. An extra clutch was added to the 3-4-clutch pack, hardened input shaft, heavy-duty low roller clutch with wider rollers, and a heavy-duty sun shell and sun gear. All of these parts can be used in the 4l60E. I think they should just use the 4l65E in all applications instead of having two versions of the same transmission.  ::)
     The 4l80E has been around since 91 and is basically a turbo 400 with overdrive and electronic controls. A lot of the parts have virtually remained unchanged since 64 when the 400 was introduced. The 4l85E came about in 2002 and has a higher torque capacity. Parts that were improved were the input and reaction carriers, from 4 to 5 pinions gears and an improved overdrive planet and drum. The 4l80E in my opinion is a very strong tranny. Itís had its share problems over the years but currently is the best itís ever been. One common complaint I see a lot is ďno reverseĒ.  In the 91-96 units I see a lot of direct/rev pistons broken in two. These are made of aluminum. In 97 they went to a metal piston with the rubber seals bonded to the piston. I have yet to see one of these fail yet and use this type when I rebuild them. The reason they break is due to high line pressure in reverse. The reverse boost valve wears out and causes uncontrollable line pressure. Iíve heard of cases where line pressure has exceeded 600 psi, and when this happens you can get some serious parts breakage. Iíve heard of cases splitting in two and have seen myself a direct drum, which is made from cast iron, split apart. Every time I see a unit with a reverse problem it always has a worn out boost valve. The latest 4l80E Iíve worked on was a 2000 with no reverse. I was a little surprised to see this complaint on this late of tranny because I knew it had a bonded rubber piston, which donít break. Took unit apart and everything looked perfect except the reverse band was burnt, which really hasnít been a problem with these. Anyway the cause of the problem again was the boost valve. So if there is one thing that I would like to see improved with the 4l80E is that of improving the reverse boost valve. Are there any drawbacks with the 4l80E? Not really, except maybe with the weight of the unit. The torque converters on these things weight nearly 70lbs! I think there is quite a bit a horsepower that is lost driving this unit.
     As for the 4l60E not to many changes have been made to the hard parts (planets, drums, gears, etc.) since 82. A larger input sprag and low roller clutch is about all thatís been changed and that was back in 86-87. Once again ďno reverseĒ is fairly common complaint with these, but for a different reason. I see a ton of broken sun shells. There is a splined area of the shell (splines on to reaction sun gear) that breaks clean off. This area is just not strong enough. So GM has come out with a redesigned shell in the past couple of years to help with this problem, itís a bit thicker and has more of a radius where the splines meet the base of the shell. Well guess what? Now instead of breaking, the splines are now striping out! Iíve seen this many times on 2000 units, and have heard this from other builders too. I am a little reluctant to get new shell from the dealer because of this current problem. Iíve heard from other builders that new shells they bought and put in have been striping out in as little as 20,000 miles! Not good. >:(  So currently I think the sun shell is the weakest part of the 4l60E. I try to use an aftermarket shell that has hardened splines whenever possible. I havenít seen what the 4l65 shell look like yet.
     There are a few other common problems I see, there is a check ball that likes to wear out the separator plate, and blow thought it eventually. Doesnít seem to happen to all units. Might depend on how hard it is driven. In the mid 90ís, I saw quite a few bearings in the planetaries fail, usually would cause a lot of damage, but I think that was due to a bad batch bearings.
     In the quest for better gas mileage GM has changed the lock up strategy of the torque converter over the years. The original 700 and 93-94 4l60e used an on/off type lockup. Meaning it was off or fully locked on.
In 95 they went to a PWM (pulse width modulated) lockup, which controls the aggressiveness of the apply and release of the torque converter clutch and allows a bit of slippage for a smoother feel.
     In 98 GM went to a different strategy called ďEc3Ēor electronically controlled capacity clutch.
This strategy has made a big difference in fuel economy by starting the apply of the Tcc at much lower speeds and continually slips until it reaches highway speeds. It begins to apply in 2nd gear and slips up to 250 rpms depending on speed and engine output. In order for this strategy to work a new converter clutch lining had to be developed to withstand the slippage and heat generated. What GM came up with is a woven carbon fiber material that is very porous that allows fluid to flow though it for better heat transfer. This stuff is practically indestructible. One of the problems shops face is getting a replacement converter when doing a rebuild. GM holds a patent on this material. The aftermarket converter companies have been trying to find a suitable replacement material that will hold up. Several companies are very close to releasing their own material. Until then we have only two choices, get a rebuilt converter with a good ďusedĒ woven clutch or buy the converter from the local GM dealer. I personally prefer to go new. I just donít trust a used lining although this stuff is extremely durable.
     The 4l80E uses the PWM type strategy and uses a graphite/ Kevlar composition lining for the Tcc.
The 4l60E PWM units use this material also.
            Both the units have been using a High Energy Graphitic lining on the clutch plates and bands for several years now. This material is very durable and can withstand high temperatures. Itís not uncommon to take apart a high mileage unit and find that the clutches look in perfect condition.

     One of the areas that I would like to explore further and have some questions about is that of the adaptive learning strategy with both of these transmissions. The adaptive strategy has been in use since 93, but in a basic form compared to what it is today. What is does is it makes adjustments in line pressure to obtain consistent shifts and helps to increases the life of the transmission. As clutch material wears, clutch pack clearances increase, the timing of apply can change resulting in shift overlap. Shift overlap is the time it takes to complete a shift. There are several types of Adaptive learning in use and depends on application what strategies are used. The most common types are, Shift adapts, steady state adapts, and garage shift adapts. Shift adapts are what measure the overlap time between shifts. First the computer must recognize an up shift as adaptable. There are some conditions that can cause an incorrect line pressure adjustment such as the a/c compressor cycling during a shift or a radical change in throttle position, and these types of shifts wonít adapt. When a shift is started a number of things are checked such as throttle position, transmission temp, vehicle speed, and engine rpm, in order if the actual shift time is valid to compare to the calibrated desired shift time. If these items are met during the entire shift the shift is considered adaptable. Once the shift is adaptable the computer compares the actual shift time and the desired shift time and calculates the time between them. This time between the two now becomes shift error. Actual shift time is the time from when the computer commands the shift to the time the engine rpm begins to drop from the commanded shift.
If the actual shift time is longer than desired shift time (slow engagement, soft feel) the computer will adjust the current to the pressure control solenoid to increase the line pressure for the same up shift next time under identical conditions. If the actual time is shorter than desired shift time (quick hard shift) the computer will decrease the line pressure for the same shift under identical conditions.
     Steady state adapts is a strategy that allows the computer to make adjustments to line pressure if clutch or band slippage is present. The computer monitors vehicle speed and engine rpm to determine if slippage is present, if there is the current to the pressure control solenoid will be driven down until the slippage stops or sets a code for max adapt. The computer will constantly adjust the current and determine if the slip is still present. If slippage is gone, computer will raise the amperage to the PCS.
     Garage shift adapts are for controlling feel when shifting into forward or reverse from park. Shift times are taken from the time it takes for the engine rpm drops from the time the range switch indicates movement from the park position. When the brake is applied line pressure is increased and the time taken will determine for how long it should remain boosted for the proper engagement.
     One of the Questions I have is, how will installing a shift-enhancing product affect the shift adaptive strategy of todayís transmissions. If a shift is shortened isnít the computer going to try and compensate by reducing line pressure? Reducing line pressure during a shift in a performance type application is not a good idea in my opinion. (Just a side note: Iím going to refrain from using the term ďshift kit ôĒ because it shouldnít be used as a generic term. It is a regeristed trademark of Transgo along with ďreprogramming kitôĒ and they donít like it if it is used to describe someone elseís product.) Is there a way around this Problem? Transgo does make a product that replaces the pressure control solenoid with a vacuum modulator like we use to see on the 350ís and 400ís, to control line pressure. By using vacuum to measure engine load, the computer wonít be able to make adjustments to the PCS, hence more stable line pressure during shifts. I donít know if it can be disabled thought the computer by reprogramming it or not. Maybe there are some hardcore computer guruís out there that know a way around it.
     I think that some of the shift complaints that some people have posted on different boards might just be that the transmission hasnít fully adapted yet. When I first bought my Avalanche, it was the first vehicle Iíve owned with the 4l60e, although I build these transmissions all the time I did question some of the shifts for the first few months. I had an occasional harsh 1-2 shift and a clunking 2-3 shift, both have disappeared and now shifts smooth as can be. I think it takes time for the adaptive learning to fully work because not all shifts are adaptable. But if you have a 1-2 shift that is hard all the time, that could be a different story. The first thing is to have it scanned for codes. Some trouble codes will default the transmission to high line pressure, which will give harsh shifts.
     One code that has been a big problem with the 4l60e is code 1870 trans component slipping. In 1995 the lockup torque converter went to a PWM type control (pulse width modulated) from the on/off type used on the 700ís and 93/94 4l60e. Two of the valves used, called the tcc regulator and isolator valves wear out the valve body bore because they are constantly moving. This causes excessive converter slippage and sets the code. GM has been working on this problem for several years. I know that when a customer with this problem took their vehicle to the dealer, they would put in a remanufactured service replacement valve body in. These valve bodies had the bore reamed out and a larger valve put in. The only problem is that these larger valves still wear the bore out. In 2000 GM made a change to the separator plate and gaskets to help with this problem. I attended a transmission seminar last year on the 4l60E transmission and was told that GM has issued their final fix for the problem for the 2002 model year vehicles. I guess only time will tell if it is fixed or not. What I do on all 95 and up units is replace the valve assembly with an aftermarket one that has been designed to eliminate 1870. Itís made by a company that produces high quality transmission products that fix the common problems with various transmissions. It works very well and wonít cause any further wear to the valve body.


     As for specific problems related to the Avalanche, Itís to early for me to tell. I work for an independent shop and probably wonít see an Avalanche for at least another year, as most people take it to the dealer under warranty. The latest trucks Iíve worked on are 2000ís with high mileage or bought used. Iíve have experienced a few things with my own that others have posted on the different truck forums. Twice I have taken off from a stop and it feels like it starts in second then rapidly shifts 2-1-2-1-2-1. I believe there is a TSB about this. Something about metal shavings in the valve body hanging the shift valve. Since itís only happened twice and not in the past 6 months, Iím not too concerned about it. I have a feeling if I took it to the dealer, I would get an answer I already know they would say, ďroad tested vehicle, canít duplicate problemĒ. >:(  Overall Iíve been very happy with the way the 4l60E has worked in my Avalanche. Do I have any plans to do any mods to it? Probably not until the warranty runs out in a few years. As my daily driver, I prefer the smooth shifts. Although I do like firm shifts in performance applications.  ;D

     Hope this helps with some of the questions about these transmissions. If you have any, feel free to ask, Iíll try to help.  :B:

           Mike

tjcdmc:
That was one of the best articles I've ever read on transmissions. I don't know where your located but if I ever have transmission problems on my AV I'm sending it your way.
I do have one infrequently occuring problem(about once a month or so) that you might be able to shed some light on.
When excelerating from a stop a little faster than normal the transmission stays in second gear until you let off the gas.  I don't know how long it will stay in second if you maintain speed (30-35 mph).
I was thinking it might be the passing gear linkage mis adjusted, but I don't know if these things even have passing gear linkage any more.
Any thoughts?  

bmontini:
mike56BA

dang!!!  You sure have seen alot of stuff on these trannys...

I posted another thread (Tranny Problems

Any thoughts on this problem??

jackalanche:
Mike, I am with bmontini - after reading your fantatstic post, all I can say is DANG, that guy knows a thing or two about the topic. Great info.

wrchism:
Wow . . . excellent article and insight!  I'm impressed with the Av's tranny . . . generally seems to do what it should when it should.  I'll admit though that the complexity is a bit scary - sure takes more to service today's units than it did in days past.

I guess this is part of why I've always been a fan of manual trannies . . . they're simpler . . . but alas not offered on the Av.

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