TRANSMISSION THERAPY My Dad s by Larry Frash Trans Brake This issue of Transmission Therapy is dedicated to my father, Larry H. Frash, who passed away February 4, 2004. He taught me all about transmissions growing up. Please read about this amazing man and great father, on page 34. Figure 1 Dad s Trans-Brake Manual Low/Trans-Brake On Figure 2 The main goal of drag racing is to drive through a quarter mile from a dead stop as quickly as possible. So when you re using an automatic transmission, it s best to power brake until the light turns green. This gets the engine up to its power range and puts the torque converter into full torque multiplication before the car even moves. One way to power brake is to apply the brake with your left foot and full throttle with your right foot. The problem is that most rear brakes won t hold during power braking, even with a mild racing engine. The wheels will start to spin, and the car will often roll through the starting line, disqualifying you from the race. The other drawback with using the brakes is that it puts the rear suspension in a bind. In drag racing, it s best to keep the rear suspension relaxed until you start the race. When the differential twists under power, it s supposed to pick up the weight of the vehicle and drive the tires into the ground. An alternate and better way to power brake is to put the transmission into a bind, 4 GEARS August 2004
Our seals can go thousands of miles without a leak. What aggravates you more than seeing a rebuilt transmission leave your shop only to return with a leaking seal? Precision International can help you avoid this type of messy scene. That s because we rely upon the same trusted manufacturers who supply the OEMs; thoroughly inspecting every incoming parts shipment for size, fit, material and appearance. Beyond that, we constantly monitor the OEMs for product changes or updates. Then there s our technical advisory group; transmission repair experts who test our kits out on the latest transmission designs, before they go to market. As a result we ve been able to solve inherent transmission design problems even before the OEMs discover them! For hundreds of thousands of leak-free seals, call the Problem Solvers. Precision International offers a complete range of automatic transmission kits for virtually every make of car, truck and marine vehicle, foreign or domestic. And, no matter where those vehicles go, their transmissions are assured of being virtually leak free, thanks to our world-class quality. If you never want to see another seal that leaks, then call or write Precision International today. THE LATEST SOLUTION FROM THE PROBLEM SOLVERS TM Every Precision kit comes with great reading material. Making your job easier means making our kits easy to use. So we take the time to pack our parts into sub-kits, making sure the parts that go together, come together. These kits also contain easy-to-understand bilingual instructions, how-to guides, product updates and other helpful hints. If you have additional questions, there s our toll free Tech Line, manned by rebuilding experts who can help you solve virtually any problem. The Problem Solvers. 210 Knickerbocker Ave., Bohemia, NY 11716 (631) 567-2000 Fax (631) 567-2640 Toll Free: 800-872-6649 Florida Office: 455 Lakeview Drive, Coral Springs, FL 33071 (954) 509-9950 Fax (954) 509-9945 E-mail: sales@transmissionkits.com www.transmissionkits.com
My Dad s Trans Brake Exhaust Hole 7 Manual Low/Trans-Brake Off Figure 3 to buy an aftermarket trans brake. My dad was simply the type who wouldn t buy something that he could design and build himself. The intent of this article is to show you a really cool device that you may be able to build for yourself. Just keep in mind that there are a lot of modifications necessary, and some tricky machine work involved. Much of your success will depend on your creativity and patience. Figure 1 shows the completed trans brake. It basically consists of a THM350C lockup valve body with a thick aluminum plate bolted to it to seal oil pressure. This assembly is connected to the transmission by several tubes and one bolt. The THM350C lockup solenoid is wired through the kickdown solenoid case connector. This trans brake requires eliminating the governor circuit, so you ll have to convert the valve body into a manually-shifted unit. We ll cover these modifications a bit later. Figures 2, 3 and 4 are oil circuit diagrams to help you understand how the system works. The items labeled in red will be demonstrated with illustrations. Manual Second Figure 4 and then release the bind when the light turns green. This is done by using a trans brake. The driver turns the trans brake solenoid on in manual low. The trans brake applies either the direct clutch or the 2 nd clutch, binding the transmission. When you turn the solenoid off, the trans brake quickly releases the clutch and launches the car like a missile. In this edition of Transmission Therapy, we re going to take a look at the Larry H. Frash (aka, Dad) homemade THM400 trans brake: how it works, and all of the holes, plugs, tubes, etc. Keep in mind that it s much easier Manual Low/Trans Brake On (figure 2) Manual low pressure is supplied to the trans brake (350C lockup valve body) from the low/reverse servo cover through tube 1. From there, it supplies the normally-open solenoid and the trans brake valve (350C lockup valve). Because the solenoid is on (closed), the trans brake valve is forced toward the end plug. In this position, trans brake apply oil flows past the 6 GEARS August 2004
COMPLAINT: CAUSE: Tapered threads of OE fittings crack case when overtightened. CORRECTION: The Sonnax adapter allows the case to be salvaged without removal. The adapter seals on the leading edge and is not a tapered thread. Part Nos. 22000-01K 5 Cooler Line Adapters & 1 Tap 22000-01 1 Cooler Line Adapter OIL LEAKS DUE TO CRACKED CASE OEM Fitting COOLER LINE ADAPTER KIT Location of case fitting case crack and fluid leakage Cooler Line Adapter Chrysler RWD (With 1 4" Pipe Fittings Only) Also available from Sonnax : FORD 89-UP AXOD & E AX4S P/N: 96728-01 Low/Intermediate Servo Cushion Spring Retainer Adapter seals on leading edge, preventing fluid from reaching crack COMPLAINT: Also: Wrong gear starts CAUSE: OEM steel governor seals wear the aluminum bore. CASE WEAR AT THE GOVERNOR HUB SEAL AREA GOVERNOR BORE SLEEVE 180C (3L30) 1969 & Up RENAULT DPO P/N s: 120001 Pump Bushing 120001A Finish-in-Place Pump Bushing CORRECTION: This governor bore sleeve restores hydraulic integrity to the case. Part No. 54251-02 MACHINING REQUIRED Governor Bore Sleeve See your nearest Transmission Specialties distributor & ask for Sonnax quality engineered products. VISIT OUR WEBSITE FOR SONNAX REAMERS & OTHER TOOLS. Automatic Drive P.O. Box 440 Bellows Falls, VT 05101-0440 USA 802/463-9722 800/843-2600 fax: 802/463-4059 info@sonnax.com www.sonnax.com 2004 GEARS Sonnax July 2004 7
My Dad s Trans Brake 350 Low Sprag Roller To fitting adapter from tube#4 to valve body File solenoid feed slot Fitting adapter to tube#3 from valve body Fitting adapter to tube#2 from trans-brake Position of roller in manual low with trans-brake on Position of roller in manual second 1/8" Pipe T Note: Tap the roller against both fitting adapters to form a uniformed seal Drill exhaust hole #7 0.250" 0.300" Drill extra exhaust hole Drill extra exhaust hole Install a spring that weighs 6 1/2 lbs. at 0.300" Grind an exhaust slot across the side of the end plug Cut-Away view of the T-valve and Roller Figure 5 Trans-Brake (350C lockup valve body) Modifications Figure 6 Install fitting 1B valve, through tube 2, into the T-valve. The oil seats the roller (located in the T- valve), and is routed into tube 4 to apply the 2 nd clutch. Because the low/reverse servo and the 2 nd clutch are applied at the same time, the transmission is now in a bind. In this condition, the function of the T-valve roller is to prevent trans brake apply oil from leaking into tube 3 and exhausting past the 1-2 shift valve. Manual Low/Trans Brake Off (figure 3) When the solenoid is turned off, it exhausts pressure, allowing the spring Aluminum plate with bolt holes drilled Install fitting 2A Aluminum Plate Top Side Figure 7 to push the trans brake valve away from the end plug. In this position, trans brake apply pressure exhausts through the trans brake exhaust port (hole 7). This releases the 2 nd clutch, and the bindup is gone. Hang on, because the race car seat is going to smack you in the back of the head very hard! Manual Second (figure 4) When you move the shifter into manual second, manual low pressure exhausts. This allows drive pressure to stroke the 1-2 shift valve into the second gear position. This routes drive oil past the 1-2 shift valve, through tube 3, into the T-valve. The oil seats the roller (located in the T-valve), and is routed into tube 4 to apply the second clutch. In this condition, the T-valve roller prevents drive oil from the 1-2 shift valve from leaking into tube 2 and exhausting past the trans brake exhaust hole. Now we ll look at the modifications needed to make this trans brake work. As you compare each modification to the oil circuit diagrams, you ll start to understand how the system works and why these modifications are needed. Keep in mind that the items in the oil circuit diagrams (labeled in red) will match the corresponding modifications. Just a reminder, if you try building your own trans brake, you ll need some creativity and machining skills. We won t be covering all of the exact specifications because valve body castings, brass fittings, tubing, etc. aren t exact. And it would probably take some of the fun out of it! T-Valve (figure 5) This valve consists of a 1/8" pipe T with a THM350 low sprag roller inside. These fittings vary in dimension, depending on the manufacturer. The important thing is that the 8 GEARS August 2004
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My Dad s Trans Brake roller shouldn t be loose in the bore, but it must slide smoothly. You may need to enlarge the bore or find a roller with a different diameter to accomplish the proper fit. The cutaway view in figure 5 shows how much the roller needs to travel between the pipe fitting adapters, which act as the seats. You ll have to Use the gasket impression to get a basic idea of tube location Fitting 2A Grind a flat spot across land #3 of the 1-2 shift valve Plug #1 tap on the roller several times with a punch and hammer until you create a uniformed seat on each of the pipe fitting adapters. Trans Brake Modifications (figure 6) Drill exhaust hole 7 between 0.250" and 0.300" in diameter. This Fitting 1B Aluminum Plate Gasket Side Figure 8 Drill tube hole 4A Plug #7 (1/8" pipe plug) Plug #4 (1/8" pipe plug) Drill tube hole 3A Note: The tube should be notched to allow oil to flow Lower Valve Body Modifications Figure 9 will be the trans brake exhaust when the trans brake is released. Next, file a small solenoid feed slot across the wall to connect drive oil to solenoid feed. This is a critical slot and you ll need to keep certain things in mind: The smaller the slot, the quicker the trans brake will release. If the slot is too small, the trans brake won t apply. If the slot is too large, the trans brake won t release. The slot in figure 6 is about 0.020" wide by 0.020" deep and it worked very well. You ll need to install a heavier spring in the valve. This spring should weigh about 6 1/2 pounds at 0.300" height and have a free height of 0.900". The spring my dad used was from a THM350 direct clutch drum with one coil cut off to prevent coil bind. This spring has a 0.038" coil diameter. To prevent crossleaks from affecting operation, drill some extra exhaust holes into the unused circuits and grind an exhaust slot across the side of the end plug. Aluminum Plate (figures 7 and 8) Cut a 0.250" thick aluminum plate to the basic shape of the trans brake casting, and drill the bolt holes. Install two L-shaped, 1/8" pipefittings into the plate. Use the gasket impression in figure 8 to get a basic idea of the location. We ll call these fittings 1B and 2A. Attach the plate to the trans brake casting with nuts and bolts. Don t forget to bolt the solenoid on, just as you would on a 350C. Lower Valve Body Modifications (figure 9) Install plug 1 into the valve body casting and grind a flat spot into the 3 rd land of the 1-2 shift valve. Drivers beware: This modification will allow manual low engine braking at any speed! Next, install plugs 4 and 7 (1/8" pipe plugs) where the governor tubes used to go. Finally, drill tube holes 3A and 4A to a size that allows a tight fit for the tubing you ll be using. Drill tube hole 4A into the same passage that s plugged 10 GEARS August 2004
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My Dad s Trans Brake Drill hole #8 Install plug #3 Drill hole #5 by plug 4. Drill tube hole 3A carefully! into the circuit shown in the insert of figure 9. Plug #4 passage Install plug #2 Cutaway View of the Upper Valve Body Modifications Figure 10 Upper Valve Body Modifications (figure 10) Install plug 3 into the location shown in figure 10. This can be very tricky, and can crack the casting. Use a 5/16" drill to machine between the walls, a little deeper than the bottom of the worm track floor. Machine a round aluminum slug large enough so that it press-fits into the machined area. When the slug bottoms out, file it so that the top is level with the surface of the valve body. Stay away from the three bumps that the servo rests against Install checkball here Plug #5 Low / Reverse Servo Cover Figure 11 Plug #6 Fitting 1A Install checkball here Drill exhaust hole #6 Case Modifications Figure 12 Next, drill holes 5 and 8 using an 1/8" drill bit. Both of these holes should connect with the plug #4 passage. Finally, install plug 2 into the governor passage, somewhere between holes 5 and 8. You can jam a metal checkball in the passage and peen the casting so it can t move out of position, or thread the bore and install a setscrew. The main thing is that there s pressure on both sides of plug 2, so it must be tight and locked in place. Low/Reverse Servo Cover (figure 11) Install an L-shaped, 1/8" pipefitting into the low/reverse servo cover. The only critical part about this modification is to stay away from the three raised bumps that the servo rests against. We ll call this fitting 1A. Case Modifications (figure 12) For the low/reverse band to hold while the trans brake is on, you can t have any pressure on the release side of the servo. Install plugs 5 and 6, and drill hole 6 to exhaust any oil that leaks into the release side. Other Modifications To help exhaust the release side of the servo, remove both seal rings from the 1-2 accumulator piston (figure 13). Shim the front servo with washers so that it can t apply (figure 14), and leave the front band out of the transmission. 12 GEARS August 2004
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My Dad s Trans Brake Remove both rings from the 1-2 accumulator piston Use washers to shim the front servo, so that it cannot apply 1-2 Accumulator Piston Figure 13 Front Servo Figure 14 Plug this hole with a nail Install all twelve springs on the second clutch piston Cut the top of the kick down solenoid to make clearance for the Trans-Brake Kick Down Solenoid Modification Figure 15 Second Clutch Piston Figure 16 Tube #4 Hold-down clamp for tube #4 Tube #2 Solenoid wire to 12 volt switch Fitting 2A Fitting 1B Solenoid ground wire Tube #1 You can cut off and plug the top of the kickdown solenoid to make more room for the trans brake (figure 15). You should install all 12 springs on the 2 nd clutch piston (figure 16); this will provide quick release of the 2 nd clutch when the trans brake is turned off. Because this transmission requires good mainline pressure to work properly, don t run vacuum to the modulator. All that you need to do now is bolt the trans brake to the rear, 7/16"-headed valve body bolt, connect the tubes as shown in figure 17 with compression fittings, and run a 12-volt switch and a ground wire to the solenoid. Well, thanks for letting me share some of my dad s knowledge with you. If you try this project, let me know how it goes my dad would be proud. Tube #3 T-Valve Fitting 1A Please see page 34 to read about the man behind the Trans Brake story. Final Assembly Figure 17 14 GEARS August 2004