*Note: If you're looking for the Autocrawler update, scroll down to the sidebar "Web only: How It Works in the Real World."
This is not an attempt to convince diehard manual transmission lovers that their granny-low four-speed is junk. This story is about an experiment. This story is about taking an automatic transmission to the next level and making it the best rockcrawling transmission it can be. To do it, we had to identify the faults of automatic transmissions and then find ways to correct them. Figuring out the benefits of an automatic transmission is simple. They're easier to drive and don't require such low gears, and you never need a third foot. Finding the faults isn't so easy.
Building the Autocrawler involved months of research, one blown-up transmission, two valvebodies, six valvebody gaskets, and dozens of quarts of Mobil 1 ATF because "this time it's got to work." It does finally work, but when we went to press everything still wasn't quite smoothed out. We can't thank our partners enough (especially TCI in Ashland, Mississippi). Without them, this never would have happened.
An automatic transmission should operate between 160 and 195 degrees. Until now, it has been tough to know what size cooler to run, where to mount it, and whether to run it in series with the stock cooler in the radiator. Flex-a-lite's answer is this 30,000-pound GVW transmission cooler (PN 45951) that includes its own thermostatically controlled electric fan. We mounted it in front of our radiator but could have put it anywhere thanks to the fan. We also chose to bypass the stock cooler to reduce the strain on the engine's cooling system.
Every automatic transmission should have a temperature gauge to keep the driver from doing damage. We need to know if the fluid is getting hot so we can idle the engine in Neutral to cool it down. We mounted a 25/8 Auto Meter Pro-Comp gauge in a black mounting cup right on top of the dash where the driver can't miss it. We found that this gauge also helps in tuning the thermostat on the Flex-a-lite cooler. Because this project involved some development work with TCI, we also added Auto Meter's matching mechanical pressure gauge to keep tabs on the TH700R4's main line pressure. We used a 72-inch-long braided Kevlar hose from Auto Meter to lessen the chance of getting sprayed with 300 psi of ATF, but recommend that you mount any type of mechanical gauge on the hood or cowl to be safe.
Factory column-mounted transmission shifters are fine if all you want to do is shift from Park to Drive. We plan on doing a lot of shifting with our transmission, so we wanted the proven performance and reliability of the Art Carr gated shifter. This is the same shifter you find in nearly every desert race truck and serious rockcrawling vehicle. Its aluminum gates let you toggle between two gears by slapping the shifter forward or back, and unlike other automatic transmission shifters on the market you always have a visual representation of what gear you're in once you've applied the shift-pattern decals. For now we have the shifter mounted to the floor, but we plan to reposition it within easy reach just above the driver's thigh.
We didn't want any transmission plumbing failures on the trail, so we called Orme Brothers in Northridge, California, to get advice on what type of fittings and hose to use. Orme Brothers recommended Goodridge 200 series braided stainless steel hose and AN fittings. They had everything we needed to adapt the factory brass fittings on our TH700R4 to the -10 fittings we specified on the Flex-a-lite cooler. Assembling our own lines took some time, but we were able to route them out of harm's way without having to go through the hassle of bending solid tube.
The Art Carr shifter uses a flexible cable to work through the transmission detents and is unaffected by worn body mounts or chassis flex. When we installed the gated shifter our cable mount bracket only lined up with one of the transmission pan bolts (arrow), but we've since modified the bracket to work just fine. To keep the shift cable from binding, we routed it through a large rubber grommet in the floor and used large-radius bends to get the smoothest shift feel. While we were under the truck we also added a larger-capacity TCI aluminum transmission pan to improve cooling and stiffen the transmission housing. If you're worried about how well this pan will hold up to rocks, you need to add a skidplate.
Because some transmissions slip like they're in Neutral when you climb steep obstacles, people have gotten into the habit of overfilling the pan. Sometimes this makes things worse because the extra fluid gets whipped into foam. We think we've found the real solution to the problem with this Accusump from Canton Racing Products. The Accusump can provide 3 quarts of pressurized ATF automatically or at the flick of a switch to keep the clutches inside the tranny applied. Just make sure you use a genuine Accusump, because other accumulators on the market are not rated to handle the pressure of an automatic transmission. Our initial test also suggests that with the optional electric valve, we could use the Accusump to "push-start" the engine without using the starter.
In order to plumb our Accusump, temperature gauge, and pressure gauge into the transmission, we needed to access the main line pressure of the transmission. No problem. All TH700R4s have a 1/8-inch NPT main line pressure port above the shift shaft. Using two brass and two AN adapters, Orme Brothers made this small manifold to handle all three upgrades. The Accusump feeds into the -6 AN line (A), the pressure gauge reads from the -4 AN line (B), and the temperature gauge reads from the Auto Meter sending unit (C). We used Teflon tape on all the NPT fittings, and the whole thing only sticks out about 4 inches from the case.
Most people are familiar with National Pipe Thread (NPT) fittings. Here you can see what a -4 Air Corps/Navy (AN) fitting looks like on the back of the Auto Meter pressure gauge. The higher the number (-4, -6, -8), the larger the outside diameter of the fitting and hose, in sixteenths of an inch. AN fittings are common in motorsports, aviation, and even aerospace because they seal better than NPT fittings and tolerate disassembly and reassembly better. To avoid leaks you should always use Teflon tape on the male threads of NPT fittings, but never on AN fittings!
Working closely with TCI, we asked the valvebody engineer to reprogram a TH700R4 valvebody to give us a full manual, reverse shift pattern (Park, Reverse, Neutral, First, Second, Third, Fourth instead of Park, Reverse, Neutral, Fourth, Third, Second, First) with compression braking. This new valvebody lets you shift from First to Reverse without going through three other gears. The full-manual part of this valvebody means the transmission will stay in any gear you tell it--even at startup--and that shifts will be as firm as possible! As far as we know, nobody else offers a valvebody for the TH700R4 with this shift pattern and still applies what is known as the overrun clutches in the transmission to keep compression braking. In fact it's so new that TCI asked us not to show you any modifications just yet.
The mounts that hold the transmission/transfer case in place are a critical component of the vehicle. We upgraded our worn rubber pieces to these oil-resistant urethane parts from Daystar Products. Yes, they are stiffer than rubber, but they provide the control needed to transmit engine torque to the ground instead of wasting it by rocking in the mounts. We also replaced the engine mounts with Daystar urethane because they are part of the transmission/transfer case mounting system too. You are asking for poor performance (or even a cracked transmission housing) if you don't replace all three (or four) mounts at once.
The last modification that we were working on as we went to press involved using TCI's torque converter lockup kit to apply the converter clutch via a switch when in First gear. This would give the ultimate in hill-decent control from an automatic transmission because the engine would essentially be locked to the output shaft of the transmission.
The transmission we ended up with is a serious competition piece that, ironically, we've rendered unable to automatically shift. It is still a very streetable transmission, but you must upshift and downshift every gear like you would a manual--only without the clutch. And when you do shift, be ready, because this thing has the firmest shift you can get from an automatic transmission. We'll put it to you this way: We have 1410 U-joints in the rear driveshaft, and that's the only reason we're not afraid to make full-throttle upshifts on the street with 35-inch tires!
Fountain Valley, CA 92708