Category: GM

Miss conceptions about the 4L60E 4L80E

1-What controls the shifts in a 4L60E 4L80E and can I replace the PCM with a vacuum modulator.

The answer is the PCM is in complete control of every aspect of when and how the 4L60E shifts, Line Pressure and Lockup. If the command is given barring any mechanical failure clutches, Band ETC the transmission must make the shift or slip and burn itself up trying. Alternately It cannot shift before its commanded.
Lockup again is strictly a function of the PCM turning on the lockup solenoid and pulsing the PWM solenoid.
I hear a lot of people say my converter locks up sometimes and other not what wrong with it. Well If your converter locks up properly anytime. Then its more than likely a tuning issue and not a TRANSMISSION/CONVERTER issue.
On the matter of the vacuum modulator, It cannot replace the PCM it only takes over the PCM ability to control line pressure’s. I have a lot of people ask if I do the “vac mod” will it fix my shift timing issue? The answer is no.

2-Shifts become softer or slipping after a converter install.

No in fact the shifts remain the same as before the converter install. They feel softer because of the converters shift extension/looseness. The transmission it self is doing exactly the same as it did before the converter. Now It can be advantageous to firm the shifts up since more torque is being transferred though the trans at WOT.

3-Increasing line pressure in tuning is a good way to firm up shifts.

Well it will firm the shifts but at a price of more strain on the hard parts and greater load on the pump. A common failure for instance to raising the line excessively can be the failure of the input drum at the 3-4 clutch snap ring or even pump failure due to the extra stress. There is even the possibility of having so much line that there are enough cross leaks to partially apply clutches or bands when they should not be on. In my opinion the proper way to improve shift quality is to install and shift kit. I have no preference to type since all I have seen with only minor variations accomplish the goal not so much by raising line but by increasing the rate or volume of fluid being supplied to the clutch in a given time.

4-Synthetic fluid will make your transmission slip.

I will likely get some flack on this one but this has not been my experience at least not with fluids that meet or exceed the requirements for that particular application. What this means is the product regardless of type or brand must meet the minimum requirements it specifies. For instance if it says meets or exceeds dexron/mercron requirements then it must perform equal to or better than the specifications of that fluid. Now don’t think I mean that everyone should go buy synthetic because personally I think its overpriced for what you get. The only real advantage I have seen is the ability to with stand heat better than petroleum based products. However if you have adequate cooling this should not be and issue anyway, IMO use the fluid you like or what your converter or trans manufacturer requires. We have no requirement here.

5- TRANS Fluid can get to cold and gel at subzero temps.

No it can’t at least not at any temperature where people can live. Think of it this way if it could then in Canada or Alaska the fluid would be gel in the pan in the morning on start up and would wipe the pump out immediately. I have poured fluid from a bottle at -5 degrees and while it’s just a little thicker it’s certainly not gel. Transmission fluid is made to have a very stable viscosity at all temperatures. I am sure like all liquids there is a temp where this could occur but none I have seen.

6-Allowing a transmission to set either in or out of the car for extended periods (months/years) can result in failure.

Yes actually it can. As the transmission sets for long periods of time fluid will slowly run down and away from the clutches and hard parts. The seals can even dry rot similar to the way tires do and more in damp climates moisture can enter and cause rust on hard parts and even under the lining of the friction materials and cause them to separate. I have heard the ‘It worked great when I took it out 2 years ago story’ and its likely a true statement only to hear later that someone put it back in and it died in days or weeks or slipped or other wise acted up from sticky valves. My suggestion for storing a transmission for any length of time is to plug all the holes and fill till the fluid begins coming out of the overflow tube. Then cap this to as that will insure all parts are submerged in fluid. You will just need to drain before restarting after storage. This may help avoid some post I see with transmission complaints after taking a car out of storage that has been setting all winter.

About the Author

For more information on 4L60Eand 4L80E and Performance Transmission please visit http://www.performabuilt.com/

Feb 03, 2010 | 0 comments | View Post

Transmission fluid levels are important

Fluid level is spoken about often here are the facts. With and auto trans and in particular the 4L60E there is no such thing as low. If you let the trans get even 1/2 quart low you will and or have damaged your transmission. They are absolutely not forgiving. We recently did some intentional test with a unit we use to check different ideas. Here is what we found, At 1/2 quart low approximately 1/2 inch bellow pan rail we ran the transmission. We monitored pressure. The pressure in this condition was completely unstable. Jumping from very low to beyond the max of our 300 PSI gauge’s. When you changed gears particularly on the 2-3 3-4 and the reverse gears this condition became worse. I could easily see how after doing these test you could do a lot of damage to your transmission even this small amount low. In the case of the low pressure the result would be obvious burned frictions however at the same time the pressure spikes could just as easily break parts, push out snap rings etc causing serious damage and or sudden failures.

Now in a past test several years ago I did a similar test going in the other direction too much fluid. Here is what happened there, this was however unlike the first test with a 4l60e it was a 700r4 though would imagine the results would be similar. Adding one quart over after hitting the full line did not seem to have any notable effect. However adding two quarts over the trans began again to have pressures resembling the low fluid scenario the pressure dropped and spiked erratically and of course the fluid began quickly to resemble the appearance of the low fluid trans lots of air bubbles and since a trans is not so different from a brake system the result was similar. You cannot have stable hydraulic pressure with air in the fluid.

The air created in the low fluid scenario is a result of the filter becoming uncovered and the pump pulling air into the system. With the resulting crazy pressure readings and the extremely high fluid this occurred because the internal rotational assemblies in the transmission were acting a lot like a blender and churning air into the fluid more rapidly than it could bubble out.

The Point on this is fluid level is imperatively important with and auto. There is no such thing as a little low. A little low means you just took years off the life of your transmission or even killed it right now.
All transmission should always be kept at the top of the crosshatch level warm running in park or neutral. Ideally I wish there was a way to assure the transmission fluid was equal to the pan rail level in gear running . But I do understand why they don’t have you checking it that way

Another thing that should be addressed is aftermarket and stock deep pans. Some aftermarket pans while deep do not require a deep filter. Others require and extension. Still others use the deep filter like goes in the truck 4L60E. Always carefully read the pan manufacturers instructions. While regardless of the pan type the dip stick will still read the level correctly. If you for instance use a deep pan with the wrong filter bear in mind GM actually used the bottom of the pan to hold the filter up in place. True the little seal feels tight holding it in the pump but it can work its way out and drop into the pan when used this way. This will result in the transmission acting like its low on fluid even when its not. At the same time if you place a filter that’s too tall for your pan combination it will crack in the neck area and again cause the symptom of low fluid. I thought I would mention this because we have run into this with some of our own customers changing pans and not being aware of the filter differences and requirements. So always make sure you are using the correct type filter for the pan you are installing. Also note when installing a transmission. If you do not provide even support across the pan again you can bend the pan and damage the filter causing the same set of symptoms.

About the Author

David Watson provides interesting articles about Performance Transmission . For more information regarding 700R4and and 4L60E please visit http://www.performabuilt.com

Feb 03, 2010 | 0 comments | View Post