You’ve probably read in some manual for VW’s about how to adjust the clutch. It goes something like “Turn the nut on the end of the cable to achieve 10 or 20 millimeters of free movement (play) at the clutch pedal.” WRONG!!
The result you’re really trying to achieve is to obtain the smallest possible distance between the release bearing and the clutch pressure plate. When the engine is running, the pressure plate is turning. In a properly adjusted clutch, unless your foot is actually pushing down on the pedal, the release bearing is not supposed to be touching the rotating pressure plate and thus not turning. If the release bearing is touching the plate when your foot is not pushing down on the pedal, the release bearing is always turning whether the pedal is pushed down or not and the bearing wears out rather quickly. The release bearing is a permanently greased ball bearing and constant turning wears it out real fast.
This condition also has an effect on the engine in that if there is too much pressure from the bearing on the pressure plate all the time if the release bearing is pushing really hard on the plate due to improper adjustment (negative slack on the cable), it can actually wear the case where number one main bearing is and damage the case thrust surface and make for a lot of end play over time and possibly ruin the case. Also, pressure on the plate due to no gap between the bearing and the pressure plate can make the clutch slip. It’s like your foot’s pushing down on the pedal all the time. Too much play, and it’s hard to shift and gears may grind. In fact, a cable with a lotta NEGATIVE PLAY (real taught) will destroy THE TRANSMISSION, THE CLUTCH, THE ENGINE, THE CABLE, THE CLUTCH PEDAL, THE RELEASE BEARING, AND THE TUBE THE CLUTCH CABLE RIDES IN. YEAH, THAT’S RIGHT – EVERYTHING!! It takes a long time, but I’ve seen it happen, no BS.
So the result your trying to achieve when adjusting the clutch is really a minute amount of slack in the cable.
To test for this, all you need to do is reach up to the lever on the trans and pull it forward just like the clutch cable does when you push down on the pedal. If you can feel just a little tiny bit of movement, that’s perfect. This means there’s a tiny gap between the release bearing and the pressure plate. Realize – just a teensy bit of movement at the lever. That’s it. The play at the pedal – it’s what you end up with after doing the former.
If you adjust as I’ve described and your car has a hard time shifting (grinding) or you really have to mash the pedal all the way to the floor to shift without grinding, your cable is probably breaking (one or more broken strands) or it’s stretching when you push the pedal down. Stretching is very rare, but it happens. If you have this condition and the cable has no broken strands, put a new one in and see what happens. If this does not solve a grinding gear problem with the cable properly adjusted, it’s probably a tired pressure plate but …
mostly on any VW except buses, the tube the cable rides in in tunnel is welded inside the frame in 3 places – at the pedals, just in front (maybe behind – it’s been awhile) the handbrake lever and right where the tube exits the frame – under the back seat in a bug near the shift coupling. If a weld breaks, the tube moves sideways in the tunnel when you push down on the pedal and thus some pedal movement is translated to moving the tube rather than sliding the cable within the tube and thus the lever on the trans doesn’t move as much as it should so the pressure plate doesn’t compress as far as it should an you get poor shifting.
On real early models, like a 1960 convertible for instance, the tube is only welded at the pedal end and at the rear where it exits the tunnel. These tubes were designed to operate a 180 mm pressure plate with the rather weak springs (old buses had 180 mm plates but double the springs type 1’s had even though the plates look identical) on a the original pressure plate found on a 36 horsepower engine rather that a later 200 millimeter disc. So you may have to add a weld to make the tube more rigid to operate the bigger,stronger clutch on a 1600 engine properly. Realize the pressure plate is really just a spring. You’ll have to cut one hole in the tunnel or even more when dealing with the clutch tube. Cut three sides so you can fold it shut again when done. When welding here, have a water hose ready. There’ is often gas or grease in the tunnel that’s accumulated over the decades and a fire is a real possibility. Fire extinguishers work but they make a real mess and the agent contained within is very corrosive – almost as bad as the fire, kinda. Use water!
For buses, all of the above applies except for the fire issue and it’s real easy to see a broken weld or movement in the tube with someone in the bus operating the pedal while you watch for unwanted movement from under the bus.
This entry was posted on Saturday, May 17th, 2014 at 5:08 am
You can follow any responses to this entry through the RSS 2.0 feed.