Rebuild a 4L80E Transmission with the TransGo HD2 Kit

Operation: Max Line Pressure

Eric McClellan Sep 19, 2013 0 Comment(s)
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Additional photos by One Guys Garage

It's crazy to think about, when you get down to it. Multi-turbo and high boosted supercharged cars were usually a strict drag racing only application just 10 years ago. But now, turbo and supercharged LSX beasts roam the streets almost as by rite of passage. With street cars these days routinely making quad-digit rear-wheel horsepower numbers, it's only natural that with big power comes the need for beefier parts.

The world is becoming a boosted colony, and the transmission needs to be able to handle the juice. If we could find a solution that also had an overdrive to help us run on the street is just pure bonus. That's where we got lucky and found the TransGo HD2 kit for the 4L80E, playfully called a “reprogramming kit.” This frankly is a bit misleading because you aren't required to reprogram the ECM or TCM, depending on the application.

The good news is that this kit will be able to safely handle big horsepower. They also said that this kit will end clutch burnout with the ability to hold 1st, 2nd and 3rd at virtually any RPM. TransGo said the kit will prevent case blow-out and drum breakage due to high line pressure. And it gets even better, if you factor in the cost of a solid donor core; you're just under a grand (total) invested. If that isn't good news, we're not quite sure what would make you happy, you big grump!

Built at Willow Run Transmission in Ypsilanti, Michigan, the 4L80E was introduced in 1991 as a replacement and advancement of the TH400. The 4L80E was installed in a lot of different GM trucks and vans, so they are plentiful and easily found at a junkyard. When you look into things, the 4L80E is a pretty great package. The easiest way to think about the 4L80E is it's the bigger, older and college educated brother to the TH400. They share a lot of the same parts, are equally stout building blocks for harnessing big power, but the 4L80E is just much smarter with its electronically controlled shift points.

To install the TransGo 4L80E HD2 kit, we went to Nate Shaw of One Guys Garage to show us how it's done. He's installed these kits on several other big horsepower builds with really solid success. This kit can be installed in a couple hours if you don't drop the transmission, and can be done on jack stands in the garage. But, Nate tells us, with great power comes a couple downsides, “One problem, if there is any, is the sheer weight of the unit and the cost of a quality torque converter. But for the power this thing will hold, it's a bargain in my book!”

So when you really think about it, an overdrive transmission that can handle big power and do it safely is a killer luxury of living in modern times. Nate tells us that if you want to step up your build to the next level this is an inexpensive way to keep the power under control. With 4L80E's being plentiful and relatively inexpensive, what the hell have you been waiting for? GO GO, WE SAY!

Just a word of warning before we jump right into things; this kit is primarily meant to modify the valve body. This means that the kit can be installed without dropping the transmission out of the car. Of course if you chose to do the internal modifications, it's just that much more venerable. So, with that in mind, while we rebuilt the transmission because our core condition was unknown, we won't be covering everything that goes into a major overhaul of the 4L80E.

4l80e Transmission Rebuild 2/14

1 Using our specialized transmission holder, we were able to get easy access to the innards of the unit. Here we’ve laid out all the parts in order so that we can remember how they go back together. We’ve acquired our TransGo reprogramming kit and a rebuild kit. This should be plenty of parts to keep us busy for quite some time.

4l80e Transmission Rebuild Check Case For 3/14

2 Looking down the business end of our gutted donor 4L80E, it’s always smart to check the case for cracks or broken teeth. There’s nothing worse than getting it all buttoned up and installed to find out you have to pull it straight back out again. Having it on a dedicated tranny stand will help with reassembly, although a five-gallon bucket often does the trick.

4l80e Transmission Rebuild Case 4/14

3 We technically didn’t have to tear down the transmission this far to install the TransGo reprogramming kit. However, if you’re willing to go this far to upgrade your 4L80E it might be worth the extra effort to do a complete rebuild. If you tend to pull parts from the junkyard and the history of your trans is unknown, it’s not a bad idea to go through it with a fine-toothed comb.

4l80e Transmission Rebuild Transgo Reprogramming 5/14

4 On the right, you’ll see what you get when you purchase the TransGo reprogramming kit. Our core was in need of an overhaul, so on the left is a kit we purchased for extra insurance that comes with brand-new clutch fibers, seals, and pistons. The thing you’ll notice about the TransGo kit is that it’s more about redirecting trans fluid than beefing up the clutches.

4l80e Transmission Rebuild Snap Ring 6/14

5 When rebuilding you’ll come across some parts that clearly need replacing. For example, here’s the intermediate stock snap-ring (right) that will be replaced with a much larger one (left). This larger snap-ring helps prevent broken case lugs, which was a weak point in the stock snap-ring.

4l80e Transmission Rebuild Snap Ring Location Case 7/14

6 Putting the transmission back is just a matter of reverse procedure of how it came apart, stopping periodically to replace stock parts with the TransGo kit versions. Pictured here is where our new larger intermediate snap-ring is located, just below the case lugs for our transmission.

4l80e Transmission Rebuild Transgo Kit Clutch 8/14

7 The TransGo kit comes with replacement clutch springs. These springs and the larger snap-ring are technically the only two internal parts that need replacing on the transmission. You can skip these two items if you do not wish to remove the transmission, and only modify the valve body and pump. Replacing the springs and snap-ring will give you added strength, but are not vital to upgrading the power capacity.

4l80e Transmission Rebuild Direct Clutch 9/14

8 If you do plan on replacing the direct clutch springs, you’ll need a compressor to get the job done. We made this homemade tool out of bar stock and left over threaded rod to keep the spring retainer compressed long enough for us to install the snap-ring. In a pinch you can use some specialized wood clamps or welding clamps if you have access to them.

4l80e Transmission Rebuild Drill Small Hole Pump 10/14

9 The TransGo kit instructions require a small hole to drill through the pump casting. This will be spelled out in the instructions precisely where to drill and what size bit to use. This will allow for a small amount of pressure to bleed off from the pump.

4l80e Transmission Rebuild Recalibration Boost 11/14

10 The main modification to the transmission is a recalibration of the boost valve. The kit includes a new valve and springs, as shown here on the right, and the stock version on the left. The kit comes with all hardware needed to complete this job, snap-ring, springs and all.

4l80e Transmission Rebuild Drill Hole Valve 12/14

11 Another hole must be drilled through the valve body passage for hydraulic circuit rerouting. This should be a no-brainer, but always make sure to clean the parts after drilling as it can make a mess of metal shavings, which is the bane of all transmissions.

4l80e Transmission Rebuild Pressure 13/14

12 The TransGo kit comes with a pressure plate and pressure relief valve that are meant to be installed on the valve body. The instructions didn’t specify exactly what this does, and because we missed getting our master’s degree in hydraulics in lieu of a raging kegger the night before, we must trust that TransGo knows what they are doing.

4l80e Transmission Rebuild 14/14

13 With the valve body, filter, and wiring harness reinstalled, all that is left is to bolt on the pan and a new gasket. Now that you’re done, you can install the tranny back into the car. This kit does not require a reprogramming of the ECM or TCM (depending on your application) to reap the benefits. However, tuning software can help further optimize the setup by tweaking the shift points as needed.

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