Classic Restorations tech...
Classic Restorations tech Scott Hand lowers the Turbo 400 trans from the SD-455 T/A as the 4L85-E SuperMatic awaits installation.
As you learned reading Part I of this story in the last issue, our plan is to install GM Performance Parts' (GMPP) new 4L85-E SuperMatic four-speed Overdrive (OD) transmission (PN 19154550) and its included lockup converter (approximately 1,800-to-2,000-rpm stall speed) in HPP contributor Melvin Benzaquen's street/strip '74 SD-455 Trans Am. Many of the advantages of this new transmission over the original Turbo 400 and the previous GM O.D. boxes like the 200-4R, 700-R4, 4L60-E, 4L65-E, 4L70-E, and 4L80-E were discussed in Part I, so here is a very brief review.
The 4L80-E shares its forward gear ratios of 2.48:1, 1.48:1 and 1:1 with the vintage Turbo 400, but the newer trans added an Overdrive gear of 0.75:1 and electronic control, among other upgrades. It's rated to handle 440 lb-ft of torque. GM's 4L85-E is a heavier-duty version of the 4L80-E and incorporates a five-pinion planetary design, torque-converter upgrades, a 34-element intermediate sprag, an induction hardened input shaft, and a hardened forward hub, all to increase durability and its torque rating to 460 lb-ft. GMPP's new 4L85-E SuperMatic was conceived to hold up behind the ZZ572/720 crate engine package. This trans features more clutch plates with upgraded materials in the intermediate, direct, and forward clutches, an improved overrun roller, and selective-fit intermediate sprag outer race. Mods to the direct-clutch housing prevent centrifugal apply at high rpm, fluid pressure was increased, and revisions were made to the valvebody to further firm up the shifts. The torque rating for this trans is 685 lb-ft.
With that step up in torque rating, the SuperMatic can be purchased and bolted in behind most potent Pontiacs without the worry of grenading it. Also, the Overdrive gear and lockup converter will allow Melvin to replace the 3.08:1 rear gears for a more aggressive setup to improve dragstrip performance, without losing highway cruiseability due to high rpm. And finally, a major advantage of having electronic control over the transmission's functions is tuneability via GMPP's transmission controller (PN 1249736). Part- and full-throttle shift points can be programmed, as can parameters for downshifting, line pressure, converter lockup, engine braking, slapstick-type shifter operation, pressure curves for each gear, and more.
If these attributes sound like what you are looking for in an automatic Overdrive transmission, then read on to see how it was installed at Classic Restorations. For this installment, we will deal with the hardware. In the next issue, we will delve into the electronics, and cooling aspects. First, let's address questions and concerns you may have pertaining to this swap.
Midway up the driver's side...
Midway up the driver's side of the SuperMatic are black connectors for the transmission input and output speed sensors. The large, round bluish-colored 12-pin connector down lower accepts the plug for the transmission controller, which will be discussed in the next issue. Also, the shift lever and shifter-control cable bracket for the Shiftworks Shifter Conversion Kit, to make the stock three-speed shifter more compatible with the four-speed Overdrive, have already been installed.
On the factory Turbo 400's...
On the factory Turbo 400's driver's side, we see the electrical connector for the 12-volt kickdown switch and the mechnical speedo gear sleeve with cable access.
Note the Chevy-only bellhousing...
Note the Chevy-only bellhousing bolt pattern on the SuperMatic (left) as compared to the B-O-P pattern of the factory Turbo 400. As you may imagine, the converters are a bit different as well, but will still bolt-in without a problem. The SuperMatic converter is set up for lockup whereas the Turbo 400 is not. The SuperMatic has six attachment points for the flexplate and the Turbo 400 only three, so three bolts will be used for our application.
Frequently Asked Questions
Regarding Bolting In A
Late-Model Od Transmission
Q: Will the SuperMatic bolt right in with the existing Pontiac block bolt pattern?
A: No, an adapter plate will be required. We used one from Trans Dapt.
Q: Will the floor have to be cut or hammered to fit the SuperMatic?
A: Not in our case, as the '74 T/A had ample floor clearance.
Q: Will I need to modify the crossmember to install the transmission?
A: Yes, the crossmember mounting point on the SuperMatic is approximately 31/4 inches further back than the Turbo 400. (Included in the measurement is the 5/16-inch thick adapter plate used with the SuperMatic.) Be sure to take your own measurements for your swap.
Q: Will the trans mount have to be changed?
A: Yes, the bolt spacing on the trans is 41/4 inches for the Turbo 400 and 33/4 inches for the SuperMatic. The Turbo 400 mounts to the crossmember via two bolts and the SuperMatic with a single stud and nut.
Q: Will the driveshaft have to be shortened?
A: Yes, because the SuperMatic is longer than the Turbo 400. Our driveshaft needed to be shortened approximately 35/8 inches. Take your own measurements on your Pontiac before you have the shaft cut.
The passenger side of the...
The passenger side of the SuperMatic simply has the two ports for the cooling lines (shown here covered with plastic caps) that use modern, quick-disconnect fittings. The opening for the dipstick tube near the pan rail is just behind the bellhousing.
In comparison, the Turbo 400...
In comparison, the Turbo 400 cooling lines use typical NPT fittings and are positioned differently than those on the SuperMatic, so new cooling lines and fittings will be required for the swap, which we will cover in the next issue. Also shown is the four-bolt governor cover near the tailhousing and the vacuum modulator up front near the pan.
The flexplate was replaced...
The flexplate was replaced for this project but not because the stock one won't work with the SuperMatic-it will. Rather, the old flexplate has a few damaged teeth. Also note the transmission dowel in the upper portion of the photo. Since we will need an adapter to mate the Chevy-bolt-pattern trans to the B-O-P-pattern engine, both dowels will have to be replaced with longer ones.
Scott employed an old shop...
Scott employed an old shop trick, which is to weld a nut onto the end of the dowel; then screw a slide hammer into the other end of the nut and use the tool to pull the dowel like so. If you are doing this swap at home, to avoid welding, you can try a pair of vise grips first to twist and pull the dowel out. If that doesn't work, you can grind two flat sides into the dowel using a Dremmel tool until a wrench will fit on it, and then twist and pull it.