Technical Car Experts Answers everything you need: CJ-3A, CJV-35/U, and M38 Fuel pump information and rebuilding?

Description of operation

These mechanical fuel pumps are the diaphragm type, driven from an eccentric on the engine camshaft. As the eccentric moves the rocker arm the diaphragm is pulled against the pressure of the diaphragm spring. A vacuum is formed in the fuel chamber and fuel is drawn in through the inlet check valve(s) from the fuel tank. As the eccentric rotates the pressure on the rocker arm is released and the diaphragm spring pushes the diaphragm forcing fuel out to the carburetor through the outlet check valve(s). When the carburetor does not require fuel, the pressure in the fuel chamber holds the diaphragm and diaphragm spring in compression and fuel does not flow. The fuel pump output pressure is proportional to the force of the diaphragm spring.

The vacuum booster section of the fuel pump operates in the same fashion as the fuel pump. Its purpose is to provide vacuum for windshield wiper operation under higher throttle conditions where engine manifold vacuum is too low for satisfactory wiper operation. When engine manifold vacuum is greater than that created by the pump, the stronger manifold vacuum pulls the diaphragm into the air chamber against spring pressure and the pump does not pump.

Helpful information

The CJ-3A, CJV-35/U and M38 utilize spacers between the fuel pump and the engine block. Over the years these spacers are often removed for various reasons. The CJ-2A style fuel pump is often retrofitted to these vehicles due to its lower cost. This is a fuel pump only, without the vacuum booster section. It does not require a spacer for proper operation. Lack of a spacer on the original CJ-3A, CJV-35/U and M38 fuel pumps can cause excessive fuel pressure. Fuel pressure can be lowered slightly by adding extra gaskets between the fuel pump and engine block.

Old stock pumps and rebuild kits. Diaphragms stretch and deteriorate with age. Old diaphragms are not made to withstand today's fuel compositions. It is best to use modern replacement diaphragms.

Venting of the fuel pump. CJ-3A fuel pumps have a vent in the body of the fuel pump, as most fuel pumps do. Since the CJV-35/U was designed to operate underwater, the vent is eliminated as well as the upper oil seal. M38s before serial number 53262 originally had a plug in the body center threaded hole. This is where a vent would normally be located. Apparently there were problems with this arrangement since many vehicles were retrofitted with various vents here. M38s after serial number 53262 had a different underwater ventilation system and the fuel pump was vented at the center of the body.

Testing

Caution Gasoline and gasoline vapors are highly flammable. A fire could occur if an ignition source is present. Have a dry chemical (Class B) fire extinguisher nearby.

Fuel pump pressure test. Connect a fuel pressure gauge to the fuel pump output line. Run the engine at a fast idle and note the pressure. CJ3A and CJV-35/U fuel pressure should be 2-1/2 to 3-3/4psi and M38 fuel pressure should be 4 to 5-1/4 psi.

Fuel pump capacity test. Connect a hose to the fuel pump output and place in a container. Start the engine and run at idle speed. It should take 20-30 seconds to pump 1 pint of gasoline into the container.

Vacuum pump test. Disconnect the vacuum line going to the intake manifold and plug the manifold side of the line or fitting. With the engine idling, if the windshield wipers operate even at a slow speed, the vacuum pump is satisfactory. With the manifold line still disconnected, attach a vacuum gauge to the line that goes to the wipers. Vacuum should be about 10 in. of vacuum at a fast idle.

Problem and possible cause

Low fuel pressure - Mechanical wear, Stuck or leaking valves, Leaking diaphragm, Fuel supply problem,. Dirty filter screen, Suction side air leak

Low fuel volume - See low fuel pressure

High fuel pressure - Tight diaphragm, Diaphragm spring too strong,. Frozen link, Missing spacer, The 1956 Utility service manual states "High fuel pressure may be corrected by adding gaskets between the pump body and engine block."

Fuel leak at center of fuel pump - Ruptured fuel diaphragm

Fuel in engine oil - Ruptured fuel diaphragm

Low vacuum - Ruptured vacuum diaphragm, Air leak, Mechanical wear.

Slow wipers - Ruptured vacuum diaphragm, air leak, Mechanical wear.

Rough idle - Ruptured vacuum diaphragm, air leak

Oil consumption - Ruptured vacuum diaphragm

Removal and installation

Caution Gasoline and gasoline vapors are highly flammable. A fire could occur if an ignition source is present. Have a dry chemical (Class B) fire extinguisher nearby.

Remove fuel cap to relieve pressure. Disconnect the fuel and vacuum lines from the pump. Plug the fuel supply line so gasoline will not gravity drain from the tank. Remove the 2 bolts that attach the fuel pump to the engine block. The M38 uses special bolts with and extended hex section to allow easier removal and installation of the fuel pump.

Clean the old gaskets from the pump, spacer and the block.

For easier installation of the fuel pump, rotate the engine crankshaft until the fuel pump camshaft eccentric lobe is on the low point. Look into the fuel pump opening to determine the low point. Alternately the engine can be set at top dead center of cylinder number 1 compression stroke so the lobe is at the low point. Pre-lubricate the fuel pump arm where it will contact the camshaft. Place the bolts in the fuel pump holes. Install 1 new gasket over the bolts. Install the spacer over the bolts. Install the second gasket over the bolts. Insert the fuel pump arm into the block being sure the arm goes on top of the camshaft eccentric lobe. Start the bolts in the block threaded holes and evenly tighten them. Connect the fuel and vacuum lines.

Part numbers

The fuel pump part number is usually stamped on the edge of the mounting flange. Some high production pumps have the part number cast into the body beneath the diaphragm flange.

CJ-3A
Pump WO-647911
Spacer WO-647669, approx. 1/8" thick

CJV-35/U
Pump WO-648379, AC-1539556
Spacer WO-647669, approx. 1/8" thick

M38
Pump AC-1539585, WO-800350, ORD-7375380 through engine #74419; AC-1539917, WO-807641, ORD-8330132 after engine #74419
Spacer WO-800361, ORD-8329708, approx. 1/2" thick

WO Willys part number
AC Manufacturers part number
ORD Military part number

The following information is copied from

TM 9-1828A
Fuel Pumps
December 1952

Special Vacuum Diaphragm Tool

Figure 32 and figure 33, Special Tool

CJ-3A, CJV-35/U pump rebuilding

Section XXVII. SERIES CF FUEL AND VACUUM PUMPS

Figure 57. Fuel and vacuum pump, series CF.

87. Disassembly (fig. 58)

a. Separate Fuel Cover From Body.
(1) Mark edges of fuel cover and body diaphragm flanges of series CF fuel and vacuum pump (fig. 57) with a file. Mark heat shield stud if used. The parts then may be assembled in the same relative position. Note that the fuel diaphragm flange is symmetrical and the vacuum diaphragm flange has bulges where the screw holes occur.
(2) Remove cover screws and lock washers. Also remove heat shield stud, if used. Separate cover from body by jarring cover loose with a light plastic hammer.

b. Separate Vacuum Cover From Body.
(1) Mark edges of vacuum cover and body diaphragm flanges. Mark at heat shield stud, if used. The parts may then be assembled in the same relative position.
(2) Remove only two cover screws front opposite sides of the cover and substitute for them two No. 10-32 x 1-1/2" fillister head screws. Turn the two long screws all the way down then remove the balance of the regular cover screws. Alternately back off the two long screws, a few turns at a time, until the force of the heavy vacuum diaphragm spring is no longer effective. Tap the cover with a light plastic hammer if the flanges stick together. Remove the two long screws, the cover assembly, diaphragm spring, and spring retainer.

c. Disassemble Body.
(1) File riveted end of rocker arm pin flush with steel washer. Drive out the rocker arm pin with a drift punch and hammer. Wiggle rocker arm until links unhook from both diaphragms. Remove rocker arm spring, rocker arm, and link assembly.
(2) Remove bushing from rocker arm which disengages two vacuum links, one fuel link, link spacer, and link washers.
(3) Lift vacuum diaphragm out of pump body. Lift fuel diaphragm out of pump body and remove spring retainer and spring.

d. Disassemble Vacuum Cover.
(1) Remove two screws holding valve and cage retainer. Lift out valve and cage retainer, two valve and cage assemblies, and gasket.
(2) Remove bowl screw with gasket. Remove bowl, bowl gasket and screen.

e. Disassemble Vacuum Cover.
(1) Remove valve and cage retainer screw. Lift out retainer, two valve and cage assemblies, and two gaskets.
(2) Remove cover plate screw with gasket. Lift off the cover, cover gasket, screen retainer, and screen.

88. Cleaning and Inspection (CJV-35/U fuel pumps did not use an oil seal in the body on the fuel side)

a. Clean All Parts
(1) Clean all metal parts in dry-cleaning solvent or volatile mineral spirits. Blow out all passages with compressed air. If difficulty is experienced in cleaning parts, use carbon remover solvent.
(2) Check fuel Pump number on edge of mounting flange and select propel repair kit using table II. All parts in the standard repair kit must be installed when a fuel pump has been disassembled for rebuild.

b. Inspection.. Make the following inspection of fuel pump parts which are not included in the repair kit:
(1) Top cover. Discard cover if cracked or broken, or if the diaphragm flange is warped more than 0.010 inch. If warped less than 0.010 inch, flatten with disk grinder. Discard cover if bowl gasket seat is warped more than 0.010 inch. Discard valve seat insert-type covers when any part of raised valve seat is worn flush with shoulder of valve. Stripped or crossed threads can sometimes be corrected with a thread chaser, or drilled out and retapped to a larger size.
(2) Body. Discard body if diaphragm flange is warped more than 0.010 inch. If warped less than 0.010 inch, refinish with disk grinder. Discard cover if threaded holes in diaphragm flange are stripped or crossed. Stripped or cross threads can sometimes be corrected with a thread chaser, or drilled out and retapped to a larger size. Discard body if rocker arm stop is broken.
(3) Rocker arm. Discard only if obviously worn or broken.

Figure 58 Fuel and vacuum pump-disassembled view (typical series CF construction)

89. Assembly

a. Assemble Body (fig. 58).
(1) Assemble link spacer over fuel link. Place one vacuum link out each side of the fuel link. The hook ends of the vacuum links must come together so they surround the fuel link. All link hooks should point in the same direction. Place assembly of links and spacer between lobes of rocker arm with one spacer washer to the outer side of each vacuum link. Slide rocker arm bushing through holes in rocker arm, spacer washers, and links.
(2) Stand the pump body on the bench, fuel flange down. Set rocker arm spring in position with one end over cone cast into the body. Slide rocker arm and link assembly into body. Outer end of rocker arm spring slips over projection on link spacer; the open end of all link hooks must point toward vacuum flange. Align rocker arm bushing hole with hole in body and retain assembly by driving rocker arm pin through body and bushing. Place washer over small end of pin and retain by spreading end of pin.
(3) Soak fuel diaphragm in clean kerosene. Fuel oil may be used, but do not use shellac or sealing compound. Place spacer in pull rod well of body casting. Set the diaphragm spring on the spacer and the spring retainer on top of the spring, dish side down. Hook diaphragm pull rod to center fuel link.

b. Assemble Fuel Cover.
(1) Place valve and cage gasket or two separate gaskets in recesses provided. Place valve and cages on top of gaskets. Inlet valve must have 3-legged spider facing out of cover; the outlet valve must have 3-legged spider facing into cover. Secure valve and cage assemblies with retainer and screw.
(2) Install strainer screen, cover gasket, cover, cover screw gasket, and cover screw in the order named.

c. Assemble Fuel Cover to Body.
(1) Install cover on body, making sure that file marks on cover and body line up. Push on rocker arm until diaphragm is flat across body flange. Install cover screws and lock washers loosely until screws just engage lock washers. Push rocker arm in full stroke and tighten cover screws securely. Release rocker arm.
(2) Diaphragm must be held in flexed position while tightening cover screws or pump will deliver too much pressure.

d. Assemble Vacuum Cover.
(1) Place two gaskets and two valve and cage assemblies in cover. Inlet valve must have 3-legged spider facing out of cover;
outlet valve must have 3-legged spider facing into cover. Secure valve and cages with retainer and screw.
(2) Turn cover over, and set screen in recess over valve hole. Set screen retainer on screen. Place cover gasket, cover, cover screw gasket, and cover screw in position in the order named. Tighten cover screw.

e . Assemble Vacuum Cover to Body.
(1) Soak diaphragm in clean kerosene. Fuel oil may be used, but do not use shellac or sealing compound.
(2) Lift the pump body above eye level, facing the vacuum diaphragm flange. The two vacuum links will swing down so that the diaphragm pull rod can be hooked to both links.
(3) While holding the vacuum diaphragm in position, the body should be clamped in a vice, vacuum side up. Clamp on either side of the mounting flange. The vacuum diaphragm must be held level with the body flange during the following operations. The diaphragm is held level by inserting a 3/32-inch piece of metal between rocker arm stop and body. This tool can be made from a piece of steel, 3/16 x 3/32 x 6. Bend one end to form a right angle hook three-eighths of an inch from bend to end (fig. 32).
(4) Place spring retainer on riveted end of diaphragm pull rod and the spring on the retainer. Place vacuum cover over spring and align the file marks.
(5) Insert two No. 10-32 x 1-1/2 screws in opposite holes in cover flange. Turn these long screws down alternating a few turns on each. Insert regular screws with lock washers and tighten until screws just engage lock washers. Replace two lng screws with regular screws and lock washers.
(6) Remove 3/32-inch tool from rocker arm position. This allows the heavy vacuum spring to push diaphragm into flexed position. Tighten all cover screws securely.

f. Test. Fuel and vacuum pumps cannot be bench tested.

M38 pump rebuilding

Section XXVIIL SERIES CU AND CY FUEL AND VACUUM PUMPS

Figure 59. Fuel and vacuum pump-series CU and CV

90. Disassembly
(fig. 60)

a. Separate Fuel Cover From Body.
(1) Mark edges of cover and body of series CU and CY fuel and vacuum pump (fig. 59) with a file. The parts may then be assembled in the same relative positions.
(2) Remove only the outer circle of screws (long) and lock washers. Separate body from cover at diaphragm flange near body. If cover sticks, it can be jarred loose with a light plastic hammer.

b. Separate Vacuum Cover From Body.
(1) Mark edges of vacuum cover and body diaphragm flanges. Mark at heat shield stud, if used. The parts may then be assembled in the same relative position.
(2) Remove only two cover screws from opposite sides of the cover, and substitute for them two No. 10—32NF x 1½ filster-head screws. Turn the two long screws all the way down; then remove the balance of the regular cover screws. Alternately back off the two long screws, a few turns at a time, until the force of the heavy vacuum diaphragm spring is no longer effective. Tap the cover with a light plastic hammer, if the flanges stick together. Remove the two long screws, the cover assembly, diaphragm spring, and spring retainer.

c. Disassemble the Body.
(1) File riveted end of rocker arm pin flush with steel washer, or cut off end with 3/8-inch drill. Drive out rocker arm pin with a drift punch hammer. Wiggle rocker arm until links unhook from both diaphragms. Remove rocker arm spring, rocker arm, and link assembly.
(2) Remove bushing from rocker arm to disassemble rocker arm, two vacuum links, one fuel link, link spacer, and link washers (there may be one or two link washers).
(3) Lift vacuum diaphragm out of body. Remove fuel diaphragm by pulling straight out.
(4) The diaphragm pull rod seals must be removed if they exhibit wear or the sealing surfaces are torn. To disassemble seals, it is necessary to remove metal displaced by staking operation. Use a small chisel, round file or small grinding wheel. Pull seals out of body with hook-shaped tool, being careful not to damage seal seats.
(5) Push the staked-in valve off its seat with a thin rod or pencil. If the valve sticks to its seat under very light pressure, if it moves downward and does not rebound, or if the cage is damaged, the complete valve must be replaced. Remove staking with half round file and pull valve out with hook-shaped tool.

d. Disassemble Fuel Cover. Remove two cover center screws and lock washers. Lift off the pulsator cover plate and three layers of pulsator diaphragm. Remove four screws from each of two valve and cage retainers. Remove two retainers, six valve and cage assemblies, and six gaskets.

Figure 60. Fuel and vacuum pump, disassembled view (typical series CU and CY construction).

91. Cleaning and Inspection .
a. Clean All Parts
(1) Clean all metal parts in dry-cleaning solvent or volatile mineral spirits. Blow out all passages with compressed air. If difficulty is experienced in cleaning parts, use carbon remover solvent.
(2) Check fuel Pump number on edge of mounting flange and select propel repair kit using table II. All parts in the standard repair kit must be installed when a fuel pump has been disassembled for rebuild.

b. Inspection.. Make the following inspection of fuel pump parts which are not included in the repair kit:
(1) Top cover. Discard cover if cracked or broken, or if the diaphragm flange is warped more than 0.010 inch. If warped less than 0.010 inch, flatten with disk grinder. Discard cover if bowl gasket seat is warped more than 0.010 inch. Discard valve seat insert-type covers when any part of raised valve seat is worn flush with shoulder of valve. Stripped or crossed threads can sometimes be corrected with a thread chaser, or drilled out and retapped to a larger size.
(2) Body. Discard body if diaphragm flange is warped more than 0.010 inch. If warped less than 0.010 inch, refinish with disk grinder. Discard cover if threaded holes in diaphragm flange are stripped or crossed. Stripped or cross threads can sometimes be corrected with a thread chaser, or drilled out and retapped to a larger size. Discard body if rocker arm stop is broken.
(3) Rocker arm. Discard only if obviously worn or broken.

92. Assembly

a. Assemble Body (fig. 60).
(1) Place fuel section seal in recess of body with large dished portion of seal down. Press retainer down firmly with flat end of 7/8-inch diameter round bar. Retain by staking die cast lip in four places.
(2) Place gasket in recess for vacuum section pull rod seal and follow with seal, narrow diameter first. Press down firmly with flat end of 7/8-inch diameter round bar. Retain by staking die cast lip in four places.
(3) Place neoprene gasket in vacuum section valve recess next to oil seal and follow with valve and cage, spring and cage down. Firmly press valve and cage against neoprene gasket and retain by staking die cast in three places around valve.
(4) Assemble link spacer over fuel link. Place one vacuum link on each side of fuel link. The hook ends of vacuum links should come together so they surround the fuel link. All link hooks should point in the same direction. Place assembly of links and spacer between lobes of rocker arm with one spacer washer on the outer side of each vacuum link. Slide rocker arm bushing through holes in rocker arm, spacer washers, and links.
(5) Place pump body on bench, fuel flange down. Set rocker arm spring in position with one end over cone cast into body.
Slide rocker arm and link assembly into body. Outer end of rocker arm spring fits over projection on link spacer. The open end of all link hooks must point toward vacuum diaphragm flange. Temporarily retain rocker arm and link assembly with a 4- or 5-inch length of 1/8-inch rod.
(6) Soak diaphragm in clean kerosene. Fuel oil may be used, but do not use shellac or sealing compound. Turn pump body over so fuel diaphragm flange is up. Set the diaphragm spring on the staked-in seal and the retainer on top of the spring. Push diaphragm pull rod through retainer. spring, and oil seal. Flat of pull rod must be at right angles to fuel, link. Hook diaphragm pull rod to short, center, fuel link.
(7) Drive temporary pin out with permanent pin. Place washer over small end of pin and spread pin end to retain washer.

b. Assemble Fuel Cover. Place six valve and cage gaskets in cover with six valve and cage assemblies on top of gaskets. Inlet valve and cages must have 3-legged spider facing into cover; outlet valve must have 3-legged spider facing out of cover. Retain each set of three valve and cage assemblies with one retainer and four screws. Place three layers of pulsator diaphragm on cover, and follow with pulsator cover plate. Aline two center screw holes, and insert two screws with lock washers through cover plate, pulsator diaphragm, and into pump cover. Tighten screws securely.

c. Assemble Fuel Cover to Body.
(1) Install cover on body, making sure that file marks on cover and body line up. Push on rocker arm until diaphragm is flat across body flange. Install cover screws and lock washers loosely until screws just engage lock washers. Push rocker arm in full stroke and tighten cover screws securely. Release rocker arm.
(2) Diaphragm must be held in flexed position while tightening cover screws, or pump will deliver too much pressure.

d. Assemble Vacuum Cover.
(1) Place two valve and cage gaskets in recesses provided and follow with two valve and cage assemblies. Secure valve and cages with retainer and screw.
(2) Turn cover over and set screen in recess over inlet valve hole. Set retainer on screen. Place cover gasket, cover, cover screw gasket, and cover screw in position in the order named. Tighten cover screw.

e. Assemble Vacuum Cover to Body.
(1) Soak diaphragm in clean kerosene. Fuel oil may be used, but do not use shellac or sealing compound. Push diaphragm pull rod through oil seal with flat of pull rod at right angles to double vacuum links.
(2) Clamp flange of pump in vise with vacuum section up. Place 12-inch section of pipe over rocker arm and rise vacuum links by moving rocker arm. Tilt diaphragm pull rod away from links, and as links are raised, bring pull rod back to vertical. Repeat until pull rod is securely hooked to both links.
(3) The vacuum flange must be held level with the body flange during the following operations. The diaphragm is held level by inserting a 3/32-inch piece of metal between rocker arm stop and body. This tool (figs. 32 and 33) can be made from a piece of steel, 3/16 x 3/32 x 6. Bend one end to form a right angle hook three-eighths of an inch from bend to end (fig. 32).
(4) Lift diaphragm cloth and position valve and cage in recess close to mounting flange. No gasket is required because the diaphragm seals this valve cage.
(5) Place spring retainer on riveted end of diaphragm pull rod and place the diaphragm spring on the retainer. Place vacuum cover over spring and align file marks.
(6) Insert two 10-32NF x 1½ screws in opposite holes in cover flange. Turn these long screws down, alternating a few turns on each screw. Insert regular screws and lock washers and tighten until screws just engage lock washers. Replace two long screws with regular screws and lock washers.
(7) Remove 3/32-inch tool from rocker arm position. This allows the heavy vacuum spring to push diaphragm to flexing stop in body. Tighten all cover screws securely.

f. Test. Fuel and vacuum pumps cannot be bench-tested.

Modification of M38 Fuel Pump

From TM 9-8012, Jan 1956

b. Modification of Fuel Pump (fig. 48). To minimize premature failures of fuel pumps caused by excessive pressures within the fuel pump and the trapped oil in the lower section of the upper body, modify the pump as described in (1) through (8) below.
(1) Remove machine screw and lockwashers which secure the flanges of the upper and lower section bodies.
Note. Scribe marks on outer edge of flanges for alignment during assembly.
(2) Remove upper fuel section body, diaphragm with pull rod, spring retainer, and diaphragm spring.
(3) Using a hook-shaped tool, remove oil seal retainer and oil seal. Exercise care during this operation to prevent damage to oil seal retainer.
Note. If oil seal retainer is staked in place, remove the staking with a small chisel, round file, or grinding wheel before pulling the retainer and oil seal from the pump.
Discard the oil seal but retain the oil seal retainer if fuel pump repair kit G740-73’75384 is used. Discard the oil seal and retainer if fuel pump repair kit G758-8329981 is used.
(4) Drill a l/8-inch hole in deck of body (fig. 48) to act as an oil return and pressure relief hole. Metal clips resulting from the drilling should be blown from the fuel pump with compressed air.
(5) Install new oil seal and original retainer when using fuel pump repair kit G740-7375384; if fuel pump repair kit G758-8329981 is used, install oil seal retainer G758-8329706.
(6) Install diaphragm spring and spring retainer.
(7) Install new diaphragm with pull rod after soaking it in clean kerosene. While holding the diaphragm flange in the upward position, insert the pull rod through the
spring retainer, spring, and oil seal retainer in the lower fuel section body. The flat of the pull rod must be at right angles to the fuel link. Hook the pull rod to the
short (outer) fuel link.
(8) Aline the upper fuel section body on the lower fuel section body in accordance with marks scribed in (1) above. Push on rocker arm until diaphragm is flat across body flange. Install original screws and lockwashers until screws just engage lockwashers. Push rocker arm in a full stroke and tighten screws securely. Note. Diaphragm must be in fixed (down) position while tightening cover screws, or pump will deliver too much pressure.