Wednesday, September 7, 2022

How to (not) burn out the 3-4 Clutch pack in the most common engine transmission in the U.S.: The 4l60e centrifugal cavitation problem

 I got 270K out of the 4l60e in my dad's last car.

If the flexing as the 3-4 clutches was as bad as they say, how is it that GM can get 250,000 - 300,000 miles out of them.

So I actually did pretty well. So what did it in? The 3-4 clutch pack is "Notorious" for burning out. How?

 .these stock springs(slider springs theres two of them) will cavitate a pump at around 5500 rpm's...you'll watch it on the gage...it'll steadly rise till about 5500 rpm's than it will loose all pressure till you drop below the 5500r's....then it'll start pumping again...guess what your clutchs are doing??? they are falling off...(slipping) and grabbing (slipping)..then your burning...from the slipping....Then you think "wow" my clutch pack is junk. Then you start the cycle all over again....

 I want that apply oil removed as fast as possible, I don't want next gear bind up...Also I want stronger springs to prevent hi rev apply...this also burns your clutchs.nuf said about these springs...

 Cavitation!! 

In positive displacement pumps, cavitation causes a reduction in flow

Here's the Tech manual pdf for the 4l60e

 

OK Slide Spring - two of them! That must be it...

Fascinating!!

yeah maybe not....

200-4R, 4L60, 4L60-E, 4L65-E, 4L70-E Pump Slide Spring 77722-01K

https://www.sonnax.com/parts/2434-pump-slide-spring

In high performance applications, when engine speed exceeds 5800 rpm, the centrifugal force on the pump vanes acts to center the pump slide and reduce the pump volume. It's critical to maintain maximum pump volume in these vehicles in order to hold line pressure and avoid 3-4 clutch failure.

 The Sonnax spring is stiffer than the combined force of the dual OE springs and is able to hold the pump slide in a maximum volume position despite the high engine speed.

 

 add a .030" bleed hole to the outside edge of the aluminum drum under the 3-4 piston to prevent centrifuge bringing on the 3-4 clutch at high rpm in the top of 1st & 2nd gear. ...The 3rd gear feed hole needs to be addressed as well, drill to .125 and use the sonnax servo release checkvalve,

 I am planning on using the Transgo and Sonnax [3/4 clutch return] springs together as I no longer have the OEM 3-4 springs easily available.

  spring cages with new OEM ones and the new ones were all stiffer, which I expect after 20 years of use. But I do recall one of them being much stiffer and looking at a picture of the 3-4 cage spring

  using the Transgo Clutch Spring kit (included in the HD2) with this drum, although I suspect it applies to stock drums too. Transgo says this spring kit is designed for operation over 5500 rpm.

 The heavy springs purpose is to aid in a quicker release of the 3-4 clutches on a 3-2 or 4-2 downshift. ... (It seems logical that they would reduce friction in 1st/2nd gear by keeping the apply and backing plates separated.) ...The addition of the very light load of the load release springs is minor and helps release the 3-4 clutch on high rpm 3-2 downshift.

A clutch pack generally doesn't release as quickly/cleanly as a band.

 The idea is to design a transmission that will survive hundreds of WOT upshifts, and hundreds of part throttle downshifts at the OEM level.

 https://ls1tech.com/forums/automatic-transmission/1602822-ultimate-4l60e-3-4-clutch.html

  This patent-pending 4L60 / 4L60-E / 4L65-E, 3-4 Rapid Relief Valve replaces the ball capsule in the input drum with a spring-loaded ball valve to help eliminate clutch drag on the release, according to the company. It also greatly reduces centrifugal apply in high-performance applications. Cost $29.00

 I estimate that the 3/4 piston can exert about 850 lbs on pressure on the 3/4 clutch. Since even the five special "load release" springs on the Smart Drum compress with about 5 lbs each, you are only losing about 25 lbs of pressure, about 5%. It is unlikely to make a noticeable difference.

 It would be more important to put a pressure gauge on the trans and make sure you are getting 220-240 psi at full throttle.

. In 2002 the 7 clutch (instead of 6) BW Hi-E 3-4 setup was introduced, and this helped even more. I had pretty much solved the 3-4 clutch problem back in the 1995/1996 time frame, when they introduced the BW Hi-E's.

 Add the Trans-Go HD release springs to the overrun & 3-4 apply pistons in the input drum. This will keep the 3-4 clutches from trying to apply on the top end (above 5,000 rpm) of 1st or 2nd gear, and will release the 3-4 clutches much quicker on a 3-2 or 3-1 downshift.

 They make sense to me if the operator like to go to the redline regularly in 1st gear.... They are intended to keep the the clutches from dragging from high centrifugal force (high Rpm) when the clutch is not applied.
A cheapo rebuild will probably use only 6 cheap frictions in the 3/4 clutch; not even as good as the OEM ones.

 A year after using them for my 3/4 clutch, I opened the trans for more experimentation and while there checked the 3/4 clutch. While it had never slipped, the blue frictions had worn significantly and increased the clutch clearance. So maybe they are like "R" rubber tires - they stick very well, but don't last long. So unless you are the type who is going to rebuild their trans every year or few thousand miles, I would stay away from them and instead stick with the proven Borg Warner High-Energy or Raybestos GPZ frictions for the 3/4 clutch.

 A missing checkball will give you very abrupt clutch engagement.

The five spring assemblies help keep the 3/4 frictions separated in 1st and 2nd gear to reduce wear in those gears. They only reduce 3/4 piston pressure by about 10 lbs, an insignificant amount since about 800 lbs is applied when the line pressure is 200 psi.

 https://www.camaroz28.com/forums/drivetrain-44/fried-2nd-3-4-clutch-pack-1-week-406007/

  If you are doing 4-2 or 3-2 downshifts all the time , you better have a helper spring in that spot. If the focus is upshifting, I don't see it making much of a difference as long as there is a bleed hole in the drum and it is not blocked.

 https://www.yellowbullet.com/threads/3-4-release-springs.1384074/

 

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