To improve shift quality in Ford’s venerable C4, you can look to B&M Racing & Performance, which has been producing some of the best transmission performance parts in the world for more than 50 years. The B&M story dates back to 1953, when Bob Spar and Mort Schuman put their heads together and founded not only a great company, but also an institution for the automotive masses that’s still going strong. Their first effort was known as the B&M Hydro Stick 4-speed automatic.
B&M’s vast experience with automatic transmissions includes the Ford C4 Transpak kit (PN 50227), which is for 1964–1966 C4 Dual- Range Green Dot transmissions, a rare treat for these early first-generation C4s with their unique valve bodies. The kit comes in three basic configurations: Heavy Duty, for towing; Street, for cruising and drag racing; and Competition, for all-out drag racing. While almost everyone else in the transmission business has given up on the Dual- Range C4, B&M has stayed with it, making firm shifts and longevity possible for these first generation C4 units.
This Tech Tip is From the Full Book, HOW TO REBUILD & MODIFY FORD C4 & C6 AUTOMATIC TRANSMISSIONS. For a comprehensive guide on this entire subject you can visit this link:
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Although I refer to this B&M Transpak kit, my main focus is the more-common 1970–1982 C4 transmission and the Shift Improver Kit (PN 50262) available for these slush boxes. This B&M kit is engineered to work with all 1970–1982 C4 transmissions. To make the most of a Shift Improver Kit, you have to start with a healthy transmission—with fresh clutches, bands, and seals.
B&M suggests allowing your C4’s transmission pan to cool down before removal because these units operate at temperatures close to 250 degrees F. A cool-down period also allows contaminants to settle in the sump before removal and drainage. Although it’s a good idea to change all transmission fluid, it’s not always good to drain the torque converter because you run some risk of pump cavitation and a dry startup, which you do not want.
Another thing to prevent is fresh fluid “shocking” the seals. This means you want some of the old fluid (as long as it isn’t burned or heavily contaminated with clutch/band material) mixed in with the new. Though this has been suggested to me by transmission professionals, it may not be gospel. But you do want to keep a certain amount of fluid in the converter to keep the pump primed if for no other reason.
Step-1: Remove Bolts & Drain Fluid
After your C4 has cooled down, carefully remove pan bolts and allow fluid to drain. Observe fluid color and consistency. If it is burned (brown in color), you need more than a shift improvement kit. Fluid should be pink and smell fresh. Burned fluid is a sign of deeper troubles and the need for a teardown.
Step-2: Examine Filter (Critical Inspection)
Remove filter and examine screen for contaminates (friction material). Take note of bolt locations and lengths. Fluid here looks pink and clean indicating a healthy C4 transmission. Valve body removal involves several bolts using a 3/8-inch socket.
Step-3: Remove/Replace Throttle Valve
With each transmission service, replace the throttle valve, also known as the vacuum modulator. It’s a good idea to remove the throttle valve and rod prior to valve body removal. Keep close track of the actuating rod because it’s easy to misplace.
Step-4: Prepare Shift Kit
This is B&M’s Shift Improver Kit (PN 50262) for 1970– 1982 C4 transmissions. You may go with this simple kit or the more complete Transpak (not shown), which includes filter, throttle valve, springs, and valve parts. Either way, follow B&M’s instructions carefully.
Step-5: Use New Filter & Gasket
When you install any B&M kit, you should also install a new filter and gasket for best results.
Step-6: Remove Valve Body Bolts (Documentation Required)
There are two halves to the C4 valve body. Remove all bolts using a 5/16-inch socket, taking note of where each bolt goes. Remove the manual shift detent last.
Step-7: Remove Drain-Back Valve (Important!)
The torque converter drain-back valve comes free when the filter is removed. One mistake I hear about more than any other is this check valve being lost during C4 service. Whenever you’re replacing the filter, don’t forget this very important part, which is easily lost in a drain pan.
Step-8: Remove More Bolts
Use a 5/16- inch socket to remove the rest of the bolts on the top half.
Step-9: Rotate Valve Body
Before continuing, flip valve body over. This prevents check balls from being lost.
Step-10: Remove Separator Plate
Remove the separator plate from the bottom half.
Step-11: Note Location of Check Balls (Documentation Required)
On the left is the bottom half of the valve body with filter. On the right is the upper half with valves. Both halves have check balls, which should be properly located and noted during disassembly. B&M’s instructions are very specific about which balls go back and which ones do not.
Step-12: Remove End Plates
Remove the end plate for the transition valve, 2-3 back-out valve, and cut-back valve.
Step-13: Remove Valves
Carefully manipulate and remove back-out, transition, and cut-back valves.
Step-14: Replace Springs (Professional Mechanic Tip)
When you remove the back-out, cut-back, and transition valves you may find that the springs have already been discarded during a previous performance buildup and two 7/32-inch check balls were installed. B&M suggests discarding the back-out and transition-valve springs as part of the PN-50262 modifications. One 7/32-inch ball and the brass disc in the kit do the same job as these balls.
Step-1: Reinstall Valves
Reinstall the back-out, cut-back, and transition valves. Valves must be flush.
Step-2: Reinstall End Plate (Professional Mechanic Tip)
Reinstall and torque the end plate; Ford suggests 20 to 30 in-lbs. B&M prefers10 to 15 in-lbs, at the most.
Step-3: Install Check Ball (If Applicable)
A 7/32-inch check ball is installed here on all except Pinto, per B&M’s PN-50262 instructions. Discard the original rubber disc (arrow).
Step-4: Examine Separator Plates (Critical Inspection)
Examine both separator plates to determine a proper course of action. B&M suggests laying plates on top of each other to determine compatibility. In other words, make sure the B&M plate matches your C4’s valve body.
Step-5: Drill Separator Plate
Use your C4’s separator plate as a guide for drilling and follow this illustration, which applies to all C4 applications except Pinto in 1970–1982.
Step-6: Drill Pinto Plate (If Applicable)
If you have a Pinto C4 separator plate, drill per this illustration.
Step-7: Drill Pinto Plate (If Applicable)
If you have a street/strip application, drill two 3/16-inch holes per B&M’s instructions. After these holes are drilled, take a larger bit and deburr the edges.
Step-8: Install Check Ball
Install a 7/32-inch check ball here.
Step-9: Install Separator Plate (Professional Tip)
Install separator plate as shown. B&M suggests not using a gasket here.
Step-10: Reunite Halves
Reunite the halves, making sure all check balls are in place. Use transmission assembly lube to secure check balls before assembly.
Step-11: Torque Bolts (Torque Fasteners)
In a crisscross fashion, torque valve-body half bolts to 20 to 30 in-lbs each, per Ford. This might be too much torque, with the risk of pulling threads out.
Step-12: Reinstall Drain-Back Valve
Reinstall the torque converter drainback valve with valve cup toward the inside.
Step-13: Reinstall Manual Valve Detent
Reinstall the manual valve detent.
Step-14: Inspect Assembled Valve Body
Assembled 1970–1982 valve body should look like this. Remember, there are two basic types of manual shift valves: one with an external detent (shown) and one with an internal detent (not shown). Internal detent is 1964 through the early 1970s. External detent came along in the 1970s. Make sure you don’t get these two types mixed up.
Step-15: Note Shift Valve and Kickdown
A closeup of the manual shift valve (top) and the kickdown (bottom).
Step-16: Note Detent
An earlier C4 valve body with internal manual valve detent, which is quickly identifiable by the manual valve detents in the valve itself. External detent is smooth.
Step-17: Inspect Transpak Kit
This is B&M’s Transpak kit (PN 50227) for 1964–1966 C4 Dual-Range transmissions.
Step-18: Drill Separator Plate
If you have the PN-50227 kit, use the pattern on the left to drill the separator plate for 1964 Dual-Range only. For 1965–1966 C4 Dual-Range, follow the pattern on the right.
Step-19: Avoid Leakage (Professional Mechanic Tip)
Because C4 pans are notorious for leakage, go with a new reproduction pan or dolly yours straight. Leon’s Transmissions suggests a thin film of Permatex Form-A-Gasket (nonhardening) on the pan side of your gasket. Not all transmission professionals agree with this approach, but it works.
Step-20: Adjust Throttle Valve
After you’ve properly reinstalled the valve body with manual and kickdown valves correctly positioned, install the new B&M throttle valve. Adjustment calls for turning clockwise to increase pressure and counterclockwise to decrease pressure. One full turn clockwise increases control pressure by 2 to 3 pounds, and counterclockwise reduces pressure by 2 to 3 pounds.
Written by George Reid and Republished with Permission of CarTech Inc
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