I have installed three separate B & M modifications and all are related to the transmission.
Transpak:
Installation of a Transpak involves removing the lower half of the valve body from the transmission and modifying certain components to change the shift action of the transmission. It is an exacting process requiring careful work and competent technical knowledge. Many a person has had to take the disassembled unit to a professional for reassembly after becoming hopelessly lost. The Transpak can be installed with two levels of shift action. The first is called Heavy Duty, which I implemented, and the second is Strip.
Following the instructions exactly will yield a functioning transmission that has firm quick shifts. What is not explained however, is that removing of one of the check balls as instructed will cause the transmission to slip when shifting from second to third gear. This is called second gear flare-up and can only be solved in two ways. Reinstallation of this check ball or installation of a Heavy Duty band apply servo. (See TCI Corvette Servo) Since installing the check ball would require removing the valve body again, I opted for the Servo. Unfortunately this made the 1-2 shift so hard that the car was very uncomfortable to drive. I again pulled the pan and was able to reset the 1-2 accumulator back to stock. This accumulator is a spring loaded piston that absorbs shift shock and its calibration affects shift smoothness. The 1-2 accumulator can be adjusted without removing the valve body whereas the 3-4 accumulator can only be accessed the hard way. Shift action to date is very firm. 1-2 shifts can easily illicit wheel spin and it has on occasion chirped into 3rd. Shift points are raised slightly and the transmission no longer bogs the motor at light throttle.
If the resulting shift harshness is not to your liking, you can adjust the Throttle valve cable at the throttle body. First adjust it as normal (ie engine off, pull the adjuster away from the throttle plates and then floor the gas pedal to let it ratchet back to the proper distance). To soften the shifts press the release button on the ratchet mechanism and allow the cable to move just slightly closer towards the throttle plates (which is the same direction it ratchets through when you press the pedal down.)
4-3 downshift valve:
My main reason for modifying the transmission was to install the 4-3 downshift valve. At part throttle the TH700R4 will downshift into third gear and refuse to shift back to fourth. This limits the top speed of the car to redline in third gear which is 120mph with a 3.08 rear end. The downshift valve delays the downshift until a much higher throttle angle. Coupled with the higher line pressure generated by the Transpak, almost wide open throttle can be applied before the transmission downshifts. (Low speed downshifting is unaffected.) It is then possible to drive in fourth gear at high speeds. Installation is simple and involves removing the pan and minor components in the transmission. Note that the car may feel slower at freeway speeds as it is more reluctant to down shift automatically to third. Note also that the RS has a 110mph electronic speed limiter, see JET Stage 2 chip, so installing this valve on a stock car will get you little. Recently B&M is offering a shift kit of sorts that supposedly allows full throttle upshift to 4th. Had they offered it then, I would have bought that. Look on their site under Street Transmission Products http://www.bmracing.com/catalog/fullline/page27.htm
Megashifter:
Ever despondent about no longer having a stick shift I have searched for improvements to the automatic. The Megashifter is what is called a ratchet shifter. It functions similar to the shifter on a motorcycle. A bypass lever is used to shift between Park, Reverse and Drive. Once in Drive, the shifter can be pushed and pulled from Neutral through First by ratcheting through the gears. This prevents overshooting gears. Installation is more laborious than it might seem. First and foremost to remember, is keep all the stock parts you removed.
The shifter itself is well made with good action. It comes with all the parts necessary for installation but the console requires cutting and drilling for fitment. If you don't own a variable speed Jig saw, it's time to buy one. They come in handy for many projects and can be bought for as little as $25. A Radio Shack relay is required to keep most of the electronic signals in tact so be prepared to do some wiring and soldering. Instructions are included with the shifter on the rewire. The stock loom wire colors may not match the instructions. However, you can verify the correct leads by their position in the stock connector.
After installation you will find that the trunk release switch only works with the ignition on and the car in Neutral or Park. This malady is not addressed in the documentation. In order to fix this problem you will need a non-zener diode such as Radio Shack 276-1101A. Take the cathode (striped) lead on the diode and tap into the lead which goes from the neutral safety switch to the coil terminal on the relay. B&M indicates this as connector 13. The easiest way to tap in is through the insulator on the clip at the neutral safety switch. Attach a length of wire to the anode lead of the diode and tap into the green wire on the trunk release switch in the center console. The Green lead should NOT be the hot lead, verify that the hot lead is the brown one on your car. In OEM form the trunk release only worked in Park and ignition on or off. With the B&M shifter the release only works with the ignition on and in Park or Neutral. With my wiring mod, the release ALWAYS works so be careful not to open the trunk while driving down the freeway. Like the door handles, they will always open.
The next problem is the linkage from the shifter. First off, installation of the shifter disables the Park lock feature which A: blocks the shifter in Park when the key is removed and B: blocks the key when the shifter is not in Park. I don't mind losing this feature. The serious problem is that the shifter action is easily bound up, is heavier and jams. This is due to several things.
One is the fact that the shifter itself has detents of its own whereas the stock shifter relied on the detents in the transmission. More on this later.
Second is the fact that the replacement cable is much longer than the stock unit and must be coiled under the car. Cable routing is poorly described in the instructions so I will describe the best permutation that I found. Run the cable from the selector lever at the transmission just above the transmission cross member and curve it around the trans mount and just over the cross member on the opposite side of the member. The other cable end is now pointing towards the front of the car. Now curve the cable along the floor pan over the top of the transmission and feed it through the hole in the floor pan to the console. It has now made another 180 degree U turn. The original console pan plug can be reused by slicing a hole in it but wait on this until you have thoroughly tested the shifter and are happy with it.
Third is that the linkage binds easily. At the transmission make sure the brackets line up the cabling straight when in Park. Bend the pan bracket as necessary. Make sure the replacement selector arm wobbles freely. Make sure that the swivel does not bind or hang up on the trans pan after being inserted. The pan lip may have to be bent. The selector lever can be bent ever so slightly as well. Apply grease to all sliding, rotating and flexing parts on the cable and transmission selector arm. If yours works freely thereafter, consider it a miracle.
If these hints do not make the shifter work properly there are two things you can try.
The first is to remove the detent spring on the Megashifter. The detent spring is the sprung arm that rides in the detents. Removing this arm is, in my mind, safer because it allows the transmission's detent system to control gear position. As you may have noticed, the stock shifter also does not have a detent system so what's good for GM is good for me. This mod will decrease the shift resistance but if you still have binding linkage then you will have to do the second mod below.
Remember I said keep the stock stuff, well we are going to reuse the stock shift cable. The reason for this is that the B&M piece is junk. Remove the B&M cable, bracket and selector arm from the transmission. Disconnect it from the shifter and then also remove the shifter from the car. Install the OEM cable as it originally was. On the Megashifter, bend the cable bracket flat so it is out of the way. On the OEM shifter you will use the handy jig saw and cut the off the shift cable bracket. NOTE: make sure to include that portion of the base plate, on the OEM unit when you are cutting off, which includes the slot so you can bolt your make shift bracket on top of the Megashifter's base plate using one of the bolts that holds the Megashifter in the console. Your new bracket should be L shaped and will need three things done to it (a vise is useful to have): enlarge the hole in the slot with a drill so that the bolt hole will line up the cable's eye to the pin on the shifter body; rebend the bracket so that the bottom of the cable attachment hole in the bracket is just above the bend; trim a few pieces here and there to make the bracket fit in its place.
After doing these two mods put the shifter in park adjust the linkage at the tranny then in low gear slide the make shift bracket in the slot or bend the top of it to get as close as you can to synchronizing the shifter with the detents in trans. First gear will never be perfect, but it will work. Check and recheck the adjustment. Make sure the cable does not hit the Megashifter's detent spring bracket. You can bend the detent bracket out of the way since nothing is attached to it.
So is it worth it? It looks sharp. After road-race track testing I would say absolutely yes. It makes shifting close to a stick. But note that these downshifts I describe are taking place under extreme deceleration where the car decelerates faster than the engine (ie engine braking takes place) and there is little load on the rear tires so the downshift does not cause the car to become very unsettled. Simply downshifting during light throttle will cause wheel lock. After performing the last two mods on the shifter, it shifts with the exact same smoothness and effort of the OEM unit except that it is better looking and has the aforementioned ratchet action. As you can see it took much thought to get right and as it comes from B&M, is not a drop in installation.
B&M Automotive Products, (818) 882-6422 www.bmracing.com