Building A Transmission For Racing That Will Last
by Burt Brown ©2003
The Automatic Transmission has found its way into auto racing the same as other OEM stock production parts such as; engines, rear ends, brakes and etc., but not without some serious help, updates and modifications. Using stock components without modifying them for the abuses of racing is just asking for the risk of failure. Taking a bone yard, stock, bargain or unmodified transmission and racing with it on the back of 500 horse power or more engine is like betting on a dead horse. This is where the automatic gets a bum rap.
It is also faulted when proper care and clearances are not observed during installation of the transmission and drive coupler or torque converter. This is when serious pump damage can occur. The drive coupler and converter clearances must be between 1/8 to 3/16. The transmissions and engine should never be forced together! If you sense something isnt right, stop & get help or call or e-mail me.
I would like to focus on what to install into a racecars transmission for the abuses of racing, to help make the difference between failure and winning races. We are going to cover the GM Powerglide 2-speed transmission, due to its growing popularity into auto racing.
The first step is to take the transmission apart. The transmission should be disassembled and reassemble in the vertical position. Take the dirty Powerglide core, scrape and degrease it as well as possible to expose the case. Note: during disassembly lay parts out carefully, noticing how things came apart. Place them in order & take notes or pictures to help during the reassembly process. Start by first removing the front pump and dividing the two pump halves. Prick punch both gears lightly to indicating this side up. Take careful notice the condition of and pump gears. If damage is seen or suspected, replace the gears or the complete pump. Next you need to evaluate the condition of the parts. Clean and install a new bushing seal in the pump while its apart. Replace the pump gears also if needed.
Then you need to square up the pump halves. Use one large or several small hose clamps on the outside diameter of the two pump halves to align and square them. Tighten hose clamp and replace the 5 bolts by hand tightening. Then torque the 5 pump bolts to 18-20 foot pounds. After torquing the bolts you must remove the hose clamp. Remove the low gear servo cover, piston, spring, high gear drum, band, band struts, and caged needle bearing. The needle bearing only needs removed if its a 1.76, if its a 1.82 the needle bearing will stay in the planetary.
To finish disassembly set the transmission on its pan to remove the tail shaft housing, speedometer gear, and governor assembly. Then pull the rest of the planetary assembly out through the front along with the reverse clutches, retainer, springs, and apply piston. Remove the pan and valve body. You may want to have the case and tail housing glass beaded to get down to the factory finish to better inspect for cracks, chips or defects This way you can either have them repaired or use a better case or core. Take the high gear clutch pack apart, removing the snap ring, planetary gear/pressure plate assembly, clutches, clutch hub, retainer, springs and apply piston. The reverse and high gear apply piston can be turned down on a lathe to install the desired amount of extra clutches for stronger holding power, resulting in less slip and longer transmission life. Replace the weak cast high gear hub with your choice of aftermarket, heavy duty steel hub. Not only is this hub stronger, it is taller for adding extra clutches. Also, replace the weak input shaft with a high quality aftermarket input shaft of your choice, noting whether or not you have a 1.76 or a 1.82 planetary. The 1.76 input is 12-7/8 long and the 1.82 input is 12-5/8 long. The 1.76 is the stronger transmission of the two and can handle gobs of abuse and higher horsepower.
I make my own race manual valve bodies with no instructions, but for the do-it-yourselfer I recommend using the Transgo PG-2 Powerglide shift kit. This kit will make your valve body manual shift and race-ready. The Powerglide works so well in racing because of its smaller, lighter, rotating mass!
The Powerglide weighs 95 pounds and has small diameter parts close to the spinning center line that will spin up faster. The Powerglide also has straight in and out straight through gear changes that reduce friction and spin up faster for those quick, burst of speed, jack rabbit starts off the corners and down the straightaway. Because of the lack of rotating mass on the back of the engine, your car will slow down faster into the corners, so using the brakes becomes less of a factor. This is because there is less spinning inertia without that 40 pound converter or 15 pound clutch for the engine to turn. It has been suggested that the converter being discarded gives you about 50 more usable horsepower. Another concern, case breakage, a cast aluminum transmissions weighing 95 pounds dangling off the back of an engine, swinging, bouncing, and car crashes without support, can also be prevented.
If you take a look at your everyday transportation vehicle, youll notice that the transmission has a cross member support. In most cases a cross member is not practical in circle track cars due to chassis and engine flex. Thats why we use a trans-brace that comes off the two top engine bolts and helps stabilize the transmission from flexing. Its race proven. Also when using a mid-plate or mid-plate style engine mounts, use the longer, engine to transmission, 2 alignment dole pins for better support and center alignment.
We have a Dirt Late Model that runs a Powerglide with a 421 cubic inch engine that has been using the same Powerglide with a trans-brace for 3 race seasons without one transmission failure or broken case. Now that is tons of abuse! Powerglide automatics have a feature that is shared by no other
shifting from low to high without lifting off the throttle on the restarts with no clutching! If you are going to utilize the benefits of the up shifts, make sure a good quality shifter is used with safety stops! Up shifting from low to high on a restarts is cool, but up shifts from low to reverse or park are not!
There are several ways of modifying Powerglide for direct drive. One option is the modified, at bottom of pump design, located at 7 oclock and 5 oclock, where two fluid veins are drilled and tapped to receive two 3/8 pipe X &Mac184; flare fittings, used with a true &Mac184; ball valve and two good quality 5/8 hydraulic hoses. Then theres the internal/pedal valve body kit that works off a spring loaded lever on the side of the transmission with an internal by-pass and another that works off a electrical switch that goes to a electronic solenoid mount where the modulator use to be. Theres also the push start/ push pedal to move in low using a hydraulic master cylinder and a push start kit which works like a brake caliper applying low gear band from the outside of the transmissions at the low gear apply servo. With this set up you will have to drill a hole in the reverse piston to about 5/32 or a tad larger to use reverse in the direct drive mode.
When you have all components reworked and cleaned to your satisfaction. Its time for reassembly. Stand the case up in the vertical. Using petroleum jelly to help in installing the seals and holding small parts, reassemble the transmission using all new clutches, seals, gaskets, bushings and filter. If you prefer not to use a trans cooler, an aftermarket stock capacity finned aluminum pan can be used to aid cooling the transmission without a trans cooler.
Now that your Powerglide has been built right using quality parts, its time to win races with a quality built automatic!