T56 to TH400 Conversion
Drivetrain Intro Street Twin T56 rebuild
Over the winter from '00 to '01, I replaced the ET Street DOT-legal tires with 10.5W ET Drags and also got a set of skinnies on 3.5" DragLites for the front. Much excitement surrounded the next visit to the strip because I thought the change might result in a serious wheels-up launch. But... on the first launch of the year the (brand new!) T56 mainshaft snapped in half (see Boom #6). That resulted in a focused effort to swap in a tranny that wouldn't break.
After asking around and reading some tea leaves, I chose a Carl Rossler TH400, a 3000-3500 stall, 10" Coan converter, and the Cheetah shifter by Turbo Action. The 400 has a full manual, reverse pattern valve body and a trans-brake. Carl did not think my application required his full-tilt, billet everything internals, so I saved a kilobuck there. However, not getting the SuperBell was a mistake - fitting any flex plate shield between the bellhousing and the tunnel will be a nightmare. The plan is to dial the car in without a shield, then pull the tranny and have it machined for the SuperBell.
The Coan converter is supposed to be a good compromise between street and strip duty. Theoretically, the stall is high enough for a good launch and to soften the shifts around town, but low enough to provide reasonable response pulling away from stop signs. The shifter seems very stout and high quality. It comes with a park/neutral safety switch (so the car won't start in gear!), but getting the backup lights to work will require some creativity.
Installing the 400 was a total non-issue. After the T56, bellhousing, clutch, and flywheel came out, it bolted right up and cleared everything with some room to spare. Even my homemade T56 tranny jack worked with modification. There are 2 small twiddles: the tranny mount hole in the T56 crossmember needs to be elongated as shown in the pic below left, and a spacer is needed to raise the back of the tranny up a bit. I'm setting the tailhousing as high as possible, while maintaining clearance between the y-pipe and the floorpan, in order to minimize the front u-joint angle.
Installing the shifter involved a bit more work. I really didn't want to deal with moving the airbag sensors between the seats, and the Cheetah shifter was clearly going to muscle in on airbag turf. The first shot (below left) shows the sheet metal bracket that the airbag stuff bolts to. Using a small cutoff wheel on a die grinder, I sliced away most of the bracket, leaving the 3 mounting holes in place. After the surgery, 2 of the 3 holes still had welds to locate them, but I had to add a small nut and bolt to the piece of bracket in the upper left corner of the left-most pic to hold it in place. The center shot shows the shifter sitting in its new home. On the right you can see that the airbag controller sits exactly where it used to. So far, so good...
Hold it right there, son, not so fast!!! What about your console, stealth-boy? Well, I wouldn't be publishing this page if that wasn't right, so check out the pics below. The 6-speed plate fit fine after the vinyl boot was removed, except that I'll have to mill off the raised shift pattern. The ash tray still opens, which is good because my manual fan control and line lock switches are mounted in there.
Well, I spoke (wrote) too soon. Turns out the 6-speed plate needed extensive surgery for the shifter to reach the 1st gear slot (the 400 is reverse pattern), and the ash tray lid had to go (right hand pic). I'm not very happy about this, and will check out some sort of custom plate once the car is up and dancing again.
The red button on the shifter stick is wired to the transbrake through a small, grommet'ed hole in the floorpan The tranny temp gauge sender wires also pass through this grommet
Here are a couple details of the shifter installation. First is the location of the park/neutral safety switch shown below left. It attaches to the front shifter bracket (the supplied shifter installation instructions are fine, BTW) and is wired to the former clutch interlock switch. I used beefy wire because this circuit sees some serious current. In the pic, the switch is seen peaking out from the from under the shifter. It has 2 red wires coming out of it that disappear into a short length of split loom. The right-hand shot shows the mounting strap I made from a 1" wide strip of aluminum. The shifter mounting is very solid.
OK, the 400 and shifter are mounted and connected, what about the all the wires that used to go to the T56: CAGS, reverse lockout (the PCM won't let you shift into reverse if the car is going more than 5 mph forward), VSS (vehicle speed sensor), and the backup lights? Like many T56 owners, I used a resistor to bypass CAGS is soon as I got the car home from the dealer. A similar resistor should make the PCM think it's activating the reverse lockout solenoid. I'll letch'all know what value worked.
Thanks to LT1-Edit listmember Wayne Jeffcoat, I have an A4 PCM file with all the tranny tests deleted, so not having a place to connect all the PCM wires is no longer a worry. I used LT1-Edit to copy all of my bazillionteen changes to the new file.
VSS seemed like a much bigger headache until I was introduced to Jags that Run. They recommended using the sensor and reluctor shown below, which I immediately ordered from Dal Slabaugh (800-362-9494 or lockitup@bright.net), my preferred source for GM parts. The sensor part number is 8655315 and the reluctor is 8655291. I'll post my backup light solution after I think of one.
Another potential headache that vaporized was the tranny dipstick. None of the "hot rod" style dipsticks were anywhere near long enough for a 4th-gen. And they all said "firewall mount". Right. But Madman Brian Jeffery came through with a stick that bolts to the bellhousing and fits perfectly. Whew!!
I still lacked a tranny cooler, but much time spent laying on my back under the car was not producing a reasonable location. So I decided to get a BeCool radiator with an integral tranny cooler. If it holds the temp in line, I'm done. If not, I'll look into an additional oil/water cooler that would fit behind the air dam. After slicing the driver side rubber radiator mount and bending the sheet metal lip per the BeCool instructions, the radiator dropped right in, but the top bracket that locks everything in place no longer lined up with its mounting holes. Getting that right required opening up the slots on the tabs that hook the radiator to the a/c condenser, which moved them closer together by about 1/2".
The next problem were the fans - the passenger side was experiencing negative clearance with the Meziere water pump, the driver side wanted to be where the Vortech idler pulley was. Using a 3" cutoff wheel in a die grinder, I did extensive plastic surgery on the passenger side fan and the radiator shroud. Essentially, there is no part of the shroud that is more than about 3/4" thick anymore. The passenger side fan clearance is shown in the pic below left.
With the radiator and fans installed, the next mod to accommodate the TH400 was a tranny temp gauge. The center pic below shows the sender screwed into a tranny pan bung welded in by TIG-meister Craig Hill. The right hand pic shows the Autometer gauge installed above the relocated cigarette lighter.
The temperature gauge revealed that things were way too hot with just the BeCool radiator, so I mounted a B&M 70266 tranny cooler horizontally in front of the passenger side front tire. This still wasn't enough, so I added a Spal VA11-AP8/C-29A fan to the cooler as shown below left. The fan helped, but the engine temp still passed the 1/4 scale mark even on just warm days, so I added the air dam shown below right. As of this writing it appears that the tranny temps are OK, but the engine temp still climbs more than it used to. I'll try not using the tranny cooler part of the BeCool radiator. If the engine temp still misbehaves, I'll have to assume that moving the fans closer to the radiator by slicing the shroud somehow messed up the airflow.
Spring 03 update: The tranny temps have been fine since bypassing the tranny cooler part of the BeCool radiator. I've never seen anything over 180, even when using the transbrake at the strip. I added a tranny blanket this spring, so the whole drivetrain is finally SFI-compliant enough for me to run 9's. Hooking up the blanket taught me what those ears on the Ultrabell are for ;-)
