I’ve a 1981 Chevy C30 dually truck with a 454 massive block and a 3.73:1 rear gear. I’d wish to take away the TH400 and exchange it with a 4L80E. Is that this attainable?
R.M.
This can be a nice utility for an overdrive transmission for a number of causes.
First, the overdrive will work very nicely when mixed together with your rear gear ratio. The 4L80E is actually a TH400 with a 0.75 overdrive ratio in fourth gear. This successfully cuts cruise rpm by 25 p.c. Plus, the 4L80E is a really sturdy transmission so it’s designed to deal with the torque of your massive block.
Let’s take a look at the some specifics as to the distinction in cruise rpm with the overdrive versus your present state of affairs.
With the three.73:1 rear gears, we are going to assume you’re working fairly near the inventory rear tire diameter of 30 inches. We plugged 70 mph into our rpm equation to get a cruise rpm at 70 mph with a TH400 trans.
The equation seems like this:
RPM = MPH x Gear Ratio x 336 / Tire Diameter
This offers us a cruise rpm of two,925 at 70 mph, however doesn’t have in mind slippage from a standard, non-lockup converter. We’ll add one other 200 rpm to this which provides us a cruise rpm at 70 mph of three,125 rpm.
A 4L80E reduces engine pace by 25 p.c which takes 3,125 right down to 2,242 rpm. However the 4L80E additionally makes use of a lockup torque converter (that is an possibility for the 4L80E but it surely’s a good suggestion particularly in your case) so we are able to now cut back that quantity by one other 200 rpm right down to roughly 2,040 rpm. So you may see that it will cut back your engine pace dramatically, which ought to enhance gas mileage by at the very least 10 p.c.
That ought to deliver a smile to your face.
Some Different Concerns
There are some caveats to this swap. Whereas we don’t have any expertise with these massive 2500 sequence vehicles, the transmission ought to match underneath the inventory ground with no hassle. The cross member will most likely need to be relocated however that too mustn’t current any issues. The 4L80E is round 4 inches longer than a typical TH400 relying on the size of the inventory extension housing which implies you will want a shortened driveshaft.
The most important total conversion issue will likely be that the 4L80E will want an aftermarket stand alone transmission controller to function correctly. There are a number of firms providing a stand-alone controller together with FAST, Holley, HGM Electronics, MSD, Painless, DIY Autotune and several other extra. We’ve obtained their half numbers within the elements record under.
All of those controllers work nicely, however we’ve had actually good success with the controller from HGM Electronics. One side of their new Sport model is that you would be able to now arrange and run the controller with a easy Bluetooth wi-fi connection to your sensible cellphone. This enchancment to this controller has not solely diminished its total value barely however is de facto useful, assuming you utilize both an iPhone or a Android cellphone.
Don’t Overlook the TPS, Torque Converter, or Transmission Cooler
Assuming that your engine is carbureted, one other level is that you’ll want to put in a throttle place sensor (TPS) sensor in your carburetor. Once more, HGM provides a really good and compact stainless-steel TPS mount with particular brackets for a Holley, Edelbrock, or Q-Jet carburetors. The TPS sensor is required for any of the aftermarket controllers however I’d select HGM’s TPS total the opposite bracket—it’s actually easy and stable.
One other vital selection will likely be a torque converter. We’re going to imagine that you may be doing a little heavy obligation towing together with your dually, so a converter is a crucial selection since a bit of little bit of stall pace will assist get the truck and trailer transferring—however then a lockup converter can be a good suggestion for when you find yourself driving with out the trailer. We usually don’t tow heavy hundreds in overdrive because it places a larger load on the trans and the engine. If the lockup clutch is regularly unlocking due to load, then it is likely to be a greater concept to tow in third gear somewhat than in overdrive fourth.
A bigger or further transmission cooler can be a good suggestion in case you intend to do a of heavy towing. Ideally, monitoring the transmission temperature is a good concept. I’m fairly certain the 4L80E has an inner temperature sensor that may be monitored by way of the sensible cellphone connection at the very least with the HGM controller. It’s greatest to maintain ATF temperatures under 225 levels F to make sure lengthy transmission life. That’s true for any automated transmission together with utilizing an artificial fluid that may deal with larger temps with out dropping lubricity. Good luck together with your swap!
