4L60E 3-4 clutchpack upgrades FYI

Hey everybody,

As most of you probably know, 3-4 clutchpack failure is a common occurrence in these cars. I've paid attention to this problem for literally years and I think it's finally properly understood and licked. In the early days most thought it was the clutchpack itself that was inferior. Thanks to a lot of detective work by the good folks at Sonnax (and probably others) the real culprits have been properly identified as valvebody wear and clutchpack distortion due to the design of the retainer plate.

Now with such great tools as Youtube and the availability of new Sonnax parts, the average DIY car owner can successfully replace the 3-4 clutchpack, upgrade the retainer plate and the valvebody with NO special tools.

A few years ago Sonnax introduced the "Smart Tech Input Housing" for the 4L60E which eliminates clutchpack distortion but it's overkill for anybody whose powertrain is nearly stock. I do know they were testing that in a boosted AWD Trailblazer SS that was consistently running 11s in the 1/4 mile, just to give you a sense of why YOU probably don't need that part, plus you'd need a lot of special tools and seal installers.

A cheaper and easier option is the Heavy Duty 3-4 Clutch Backing Plate Kit . The next 4L60E I'm in, I'd seriously consider installing this in, along with the specified clutchpack.

I'd also recommend installing every Sonnax valvebody upgrade valve available for the 3-4 clutchpack circuit to minimize leaks and keep pressure up in that circuit. Some may require reamers and other expensive tools; you may want to see if a local transmission shop has them and is willing to install those valves for you. Otherwise you can rEbay them when you're done.

Also, if you have snap ring pliers, I'd highly recommend installing the Smart Shell sunshell. It is by far the best designed aftermarket sunshell on the market.

Add that stuff and a 4L60E-HP-01 kit and you'll have yourself a very reliable 4L60E.

Another great article from Sonnax here..

There's no excuse for a rebuilder not to have the 3-4 clutchpack problems licked, whether it's a national chain (I've had great success with Jasper transmissions) or a local mom and pop (show them this article!).

What about the Z-Pack with a valve body upgrade?

I've used the Zpack before (I had it in my 9C1 for years) and it works, but it doesn't solve the real issue which is flexing and coning of the whole clutch assembly.  If you do a lot of full throttle 2-3 upshifts you may wear it out sooner. That said, I put all the goodies in my 9C1's transmission and it ran perfectly every time, including over 100 quarter mile passes and some road racing (albeit stock motor, stock torque converter and street tires).

See this video.  

Looks like the Zpack is around $60 on ebay right now. The Sonnax 74140 heavy duty backing plate is around $100 as I write this, and new GM 3-4 clutchpack isn't very expensive at all. Doing this would be fine for a nearly stock B-Body.  If it was me I'd buy the Sonnax plates and a new GM high energy 3-4 clutchpack setup (per the Sonnax instructions, as GM has several different 3-4 steel plate thicknesses available, FYI).

If your future HP/Torque level is over 450, I'd strongly suggest the heavy duty input drum. It alone is $500, but you'll never ever have to worry about a 3-4 clutchpack ever regardless of power level. One shop visit can cost that much. I will be putting one of these in an upcoming build.

Just wanted to add to this, The Sonnax 74140 HD backing plates are stout parts; while $100 isn't chump change, it sure beats a tow bill to a transmission shop. I also have the Smart Tech drum (77733-06K) on order for an upcoming build.

BE AWARE if you're tearing into a 4L60E, BEFORE you disassemble the input housing, stand it face down (shaft up) and air-check the three apply circuits. Remove the bearing and washer from around the shaft, pour some ATF in that area, then air-check the circuits. If there are any air bubbles, you need to have the shaft pressed out, dressed, and use Loctite 609 on reassembly.  I've got two input housings here and BOTH of them are leaking, one from the 3-4 circuit and one from the overrun circuit.  I've got too much other stuff to do so I'm sending them out to have them professionally fixed.  One is getting the Smart Tech drum so it needed to be pressed out anyway.

i'm just going to 4l80e it when the 60 turns into a 4lslippy...

Any builders/shops/sources you recommend for a one stop shop? I am currently shopping for a new transmission. Future proof for an LS swap.

4L80E - heavier, less efficient, and has its own problems. Plus you'll have time and money into getting it to fit.

Andebe - Depends on what your needs are.  If it's a car you're road-tripping everywhere and want a warranty, Jasper and GM Goodwrench are very good, assuming your power levels are not crazy (I can personally vouch for Jasper).  If you're making big power, get on LT1 Nation on FB or any of the F-body or Corvette sites and see what they're using for builders. One other alternative is to search the F-body sites and LT1 Nation for used built 4L60Es going dirt cheap. Just be sure to get a build sheet as otherwise you'd have to disassemble it to see what's in it.

One other idea - consider buying a engine/trans combo. The 6-speed autos are very nice for power and gas mileage and you wouldn't need to upgrade your driveshaft and stock 2.93 rear axle ratio. The newer PCMs also cut torque during shifts, greatly improving transmission durability.