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--GM STUFF--

Throwout Bearing Installation
One of the most common mistakes made on GM vehicles - mostly pickups - is the improper installation of the throwout bearing onto the clutch fork. The spring (in black) on the clutch fork (in red) should be placed in the gap between the rear flange on the bearing and the front flange. You should not be able to see the spring on the back of the bearing. Symptoms of an improperly installed bearing are poor release, a mushy feeling pedal, short clutch life, and not being able to adjust for correct free play on mechanical linkage systems. This bearing and fork spring combination has been used from the late 1960's up to the present.




Pilot Bearing Removal
A worn pilot bushing can cause chatter, poor release, and can loosen the hub clutch disk. If the center hub of your old disk is loose, be sure to change your pilot bearing. Installing a new pilot bushing or bearing sounds simple. Removing the old one can be difficult. One of the old tricks is to fill the bearing with grease and then drive an alignment tool into the bearing, letting the grease push it out. This usually messy, but it normally works - unless you have a bushing that is worn. If the hole in the bushing is much larger than the alignment tool, you get a face full of grease when you try to knock it out. Another trick is to find a bolt that you can thread into the bushing - you may have to tap some threads into it. Screw the bolt into the bushing. When it hits the bottom keep screwing it in and the bushing will be pulled out by the bolt. Some applications use a needle bearing. These can be difficult to remove. Try the bolt trick on these too. If you prefer a bearing instead of a bushing, some earlier Ford's and Chevy's can accept the needle bearings that are used on the later engines.




Convert from a 11" clutch to 12"
Almost all 11" GM clutches can be replaced with a 12" clutch & pressure plate. I don't know of any that can't be changed, but I'm sure that someone will find one; so, I'll say almost all can be changed. To do this you MUST surface the flywheel.
There are two basic styles of pressure plates - lever type & diaphragm type. The lever type has a lever height of 2 inches, while the diaphragm type can have several different heights, depending on the application. The earlier styles had a flat diaphragm and used the tall throwout bearing. The later models used a raised diaphragm and the short bearing. If you replace the 11" flat diaphragm pressure plate with a 12", you must use the short bearing. The 12" will have a lever height of 2" whether it is a lever type or diaphragm type. You can also have choice of strength with the 12" pressure plates. The 12" used in the 454 cid applications can installed in place of the 350 cid unit. Just tell your clutch shop that you want a CA1908 instead of a CA1909 and he will know you want a heavy duty version.




Flywheel Problems
Flywheels are one of the parts of a clutch job that are very often overlooked. The flywheel is exposed to just as much heat as the pressure plate. It can and does warp just as much as the pressure plate. It deserves just as much TLC as the pressure plate and clutch. Check it for hot spots (discolored areas), warpage, and scoring. While you are doing this, look at the ring gear. If the teeth look worn, now is the time to replace the gear. It is a usually an inexpensive item. Change it if it looks worn.
Some flywheels (mostly imports) cannot be surfaced very much at all. They have such a short throwout bearing travel that grinding the flywheel might move the pressure plate toward the engine far enough that the clutch may not release properly. Chevy's have a problem when the flywheel has been surfaced too much. The flywheel bolts hit the springs in the clutch disk. This is easy to check with the flywheel off. Put a bolt and lockwasher in the hole, lay the disk in place and look through back of the flywheel to see how much clearance you have. Some Ford's also have a common problem. Some aftermarket disks have some small rivets that will rub on the flywheel's inner diameter just inside the wear surface. This is easily fixed. If you don't have access to another brand disk, while your flywheel is being surfaced, have a small recess cut on the inner diameter. About 1/8" is usually enough. If the rivets rub the flywheel, you will get a poor release and possibly some slipping.




Borg & Beck Lever Style Pressure Plate
The lever type pressure plate is almost a thing of the past in Chevy's. It was used on almost all GM trucks from the 50's to the early 80's. The same basic design has been used on vehicles from the 30's to the present in everything from fork lifts to farm tractors. It is still a very common unit in the industry. Many suppliers now replace this unit with the diaphragm pressure plate. The lever style will tolerate much more heat and abuse than the diaphragm style; but, it is more expensive to build, so we now see more of the diaphragm units in the older trucks that were originally equipped with the lever style. The lever style can usually be rebuilt several times, while the diaphragm type is normally a boat anchor by the time it needs to be replaced.
If you are working on a lever type unit, there is one thing to to keep in mind. When the unit is bolted to the flywheel, the levers will move toward the engine about 1/2". This is normal. As the clutch wears, the levers will move toward the rear. This will reduce the free play at the bearing and is the reason you have to adjust the clutch periodically. DO NOT reach in and lift the levers or allow the transmission shaft to drag on them. If this happens, a small strut under the rear of lever can fall out of position. It can be put back in place fairly easily with a small mirror and a piece of wire. If this happens, it is usually the lever at the 6 o'clock position that has the problem. The struts on the levers at the top cannot fall out of position.




Check the Bearing Retainer
The throwout bearing retainer, which is bolted to the front of the transmission, is an item that is usually ignored and very often worn out. It should be smooth and be free of any low spots. Ford's and Chevy's are both prone to having problems here. Many Ford's were originally equipped with an aluminum retainer, and is frequently found to be galled. Aftermarket suppliers usually have cast iron retainers. Get one of these if you can. Chevy's are all cast iron. Some Ford front wheel drive cars have the aluminum retainer made into the transmission. If you find one of these worn, you don't have to replace the transmission case. There is a repair sleeve with a special bearing available. The ID is larger than in the OE bearing. Be aware of this. You might find one that has been repaired, and the original size bearing will not fit the retainer. The bearing should slide back and forth easily without any binding. Do not put a coating of grease on it. You can put a small amount on it and then wipe it off, leaving only a light film of grease. A worn retainer can cause a high pedal effort, clutch chatter, and poor release. While you're looking in this area, check to see if there is any transmission grease around the inside of the retainer. If you see any grease here, remove the retainer and replace the seal inside the retainer. Reinstall with a new gasket. Do not use a gasket compound in place of the gasket, because it also acts as a spacer. Put some thread sealer on the retainer bolts to prevent transmission grease form migrating through the threads and contaminating the disk.




Clutch Fork and Ball
There are several things to check on the fork. Make sure the spring on the back is not broken. Some early GM forks did not have springs. The springs showed up in the mid 1970's. The spring not only holds the fork to the ball, but holds the bearing back toward the fork so it does not rattle around. The ball should snap solidly in place in it's socket. The spring should hold it in place and should not try to slip off the shoulder of the ball. The socket should be smooth and not worn. Put a small dab of grease in the socket. If the socket is worn, you will usually hear a popping sound when the pedal is pushed. S10 pickups have a common problem of a squeaking sound. This usually occurs when the clutch is not depressed, but can sometimes be heard with the pedal pushed in. This is caused by a dry pivot ball. It is not serious and will not cause any damage, but can be very annoying. There is a bulletin that shows how to make the ball greasable from the outside. It's worthwhile doing this if you already have the bellhousing off. Ford's use several different systems that hold the fork on. One common problem with Ford's is the type that uses a small "L" shaped bracket as the pivot. This bracket is bad about working loose in the bellhousing. A replacement repair kit is available from Ford.




Turbo Diesel Dual Mass Flywheel
When GM introduced the 6.5 l. turbo diesel engine, a new type flywheel was used. It was called dual mass. The flywheel consists of a separate plate for the friction surface and another unit bolted to the crankshaft. The two units spin in unison, with the torque transmitted through thin friction surfaces internal to the flywheel. Belleville spring washers keep a preload on the friction surfaces. Some large springs on the outer diameter of the flywheel absorb the shock load of the engine that would normally be transmitted to the transmission. The purpose of the flywheel is to save the transmission. With all this stuff inside the flywheel, it's easy to see that there is a much greater chance of problems occurring in this area - and it does! When the clutch and pressure plate has to be changed in one of these trucks, the flywheel usually must be replaced. The main plate surface is steel and is normally severely warped. These plates can very seldom be resurfaced. A replacement conventional flywheel and clutch set with a special dampner yoke has been introduced for this unit, but it has been even less successful than the original. Under heavy duty use, the disks have a tendency to mechanically fail. Even though the dual mass unit is much more expensive, it will normally be more cost effective in the long run. GM. has dropped the dual mass unit, but it is still available through clutch shops.




--FORD STUFF--

Firewall Flex
When Ford introduced the hydraulic clutch master cylinder in 1984 in their pickups, a rash of clutch release problems starting showing up. The area where the master cylinder is bolted to the firewall is prone to flexing when the clutch is depressed. This can get so severe that it will crack the firewall. If the firewall moves when the clutch is depressed, the volume of fluid to the slave cylinder is decreased which reduces the travel of the throw-out bearing, which will not allow the clutch to release completely. The only repair for this condition is to reinforce the firewall area. A brace for this is available from Ford dealerships. This is a sheet metal part which must be screwed in place. Another style brace is available from many clutch shops. It is made of steel plate and does not require any drilling. It simply mounts behind the master cylinder.




Pedal to Master Cylinder Link
A poor release on a Ford F series pickup with a hydraulic clutch can often be caused by a small link connected to the end of the clutch and brake pedal pivot shaft. This is the link that pushes in the master cylinder rod. The link is simply pressed onto the end of the knurled pedal shaft. Over time, this link will work loose on the knurls and will fail to push the rod into the master cylinder far enough to release the clutch. To check for this condition, remove the pushrod locking clip and slip the rod off the link. Raise the clutch pedal to the top of its travel and try to replace the rod over the link pin. If the pedal must be lowered in order to replace the rod, the link has slipped and must be replaced. Do not try to simply tighten the mounting nut. It will not work. The link must be replaced.




Alumium Throw-Out Bearing Retainer
The bearing retainer on many Fords is made of aluminum. These retainers are bad about galling, making the pedal hard to push. This will not only make your leg tired, but will also damage the pedal linkage. They can gaull to the point of actually breaking the pedal. The retainer must be smooth and free of nicks and scratches. If it is not too bad, it can be polished with emory cloth. If it will not clean up, replace it. Many clutch shops have replacement retainers made of cast iron. Use one of these if you can find one. They are not as bad about gaulling and will last much longer. Be sure to use a new gasket on the retainer and some oil resistant thread sealer on the bolts. Put a very light film of grease on the retainer and then wipe it off. The new throw-out bearing should have enough lube in its grease groove when you buy it. If not, put a small amount in the groove before you install it.




Plastic Adjuster
Some of the cable operated Fords have an automatic adjuster mounted on the clutch pedal. It has plastic teeth that can wear which will not allow the clutch to release completely. If you have one of these cars with a clutch that will not release, check to see if the pedal has excessive free play. If you can lift the pedal to the top of its travel and it will not stay, or will not move the cable whin depressed, then you might have a bad adjuster. There are metal replacements available.




Lever Style Pressure Plate
For several years, Ford used a pressure plate manufactured by Long in many of their vehicles from Mustangs to F series pickups. This pressure plate has 3 levers instead of a diaphram. The main problem with these units is that they have a tendency to chatter. A diaphram style pressure plate is available for these units. The covers are stiffer and the levers are eliminated. These replacement pressure plates are usually much smoother. If you can find one of these, use it rather than the lever type.




Diesel Upgrades
When Ford introduceed the 7.3 diesel with a ZF 5 speed transmission in 1987, a special flywheel was used on this engine. It is called a dual mass flywheel. The clutch used with this flywheel is 11" diameter. The same size clutch is used on the F250 and F350. It is not suprising that an 11" clutch in a 1 ton truck has a short life if it is used much at all. A 6 cylinder 1/2 ton pickup used an 11" clutch with almost the same clamp load. If you are changing out a dual mass flywheel on a truck that will see heavy use, you might consider one of the upgrades designed for your particular truck. The 11" 1988 thru 1994 F250, F350, and F450 7.3 non-turbo flywheel can be replaced by a special 11 7/8" flywheel designed for this retrofit.. This will allow you to use the 11 7/8" clutch and pressure plate designed for this flywheel. The 1993 and 1994 7.3 turbo diesels were equipped with the 11 7/8" clutch but used different flywheels.




Dual Mass Flywheel
The ZF 5 speed transmission in the F250 thru F450 Ford diesel trucks is very sensitive to the resonance that produced by the engine. In order to protect the transmission, the dual mass flywheel was developed. The flywheel has springs and friction surfaces in it instead of in the clutch disk. This relocates the dampner form the disk to the flywheel. The springs and rubber bumpers separate the main part of the flywheel, which is bolted to the crankshaft, from the secondary part of the flywheel where the clutch and pressure plate is mounted. Two friction surfaces inside the flywheel act as torque limiters to absorb any torque peakes that might damage the transmission. At the present time, Valeo is the only manufacturer of thes flywheels.




Flywheel Bolts
When replacing the Ford dual mass flywheels, always use new bolts. These are available from Ford. New bolts are important because they have a special thread sealant on them. If the old bolts are reused it is possible that engine oil can leak through the threads and contaminate the new clutch.