Needles and Linings Most of my auto mechanics students are on an extremely tight budget, and it’s not uncommon for one of them to have a ticket written on their own vehicle. This month’s MA Garage story was born when Steve (one of my students) decided to replace the slave cylinder in his 1997 Explorer. This Explorer’s problem was that the clutch pedal required some heavy thigh power, and occasionally the transmission would clash while shifting into gear, particularly reverse. I encouraged Steve to go deeper than the slave cylinder/throwout bearing assembly once he and his partner got the transmission out; the difficulty in shifting and the gear clash he was experiencing in reverse evidenced the fact that something was applying rotational force to the transmission input shaft when the clutch was depressed in spite of the fact that the clutch had full travel and no free play. It started out to be a pretty straightforward job. Push, pull click, click, and drive it home. With the transmission out and the pressure plate removed we found a clutch disc whose useful life had slipped away; the lining was worn almost to the rivets. The root of the undesirable input shaft rotation seemed to be tied to a disintegrating pilot bearing. Aftermarket clutches come only in sets nowadays, at least in this part of the country, and the price of a matched set hovers near $200, a little rich for Steve’s wallet. Fortunately, we were able to purchase a clutch disc separately from the Ford dealer. With the new slave cylinder cashing in at $55, the pilot bearing at $16, and the clutch disc at $60, Steve had a bit more than $125 invested, but not nearly as much as he would have with a parts house set. I was fortunate enough to find an old Ford input shaft from a trainer transmission, and Steve used it as an alignment tool. In an hour or so, the transmission was back in place with a minimal amount of trouble. Bleeding the new slave cylinder is a pretty involved process in the Ford shop manual, but it turned out to be a snap this time around. The air burped out, the clutch pedal was nice and tight, and it didn’t require nearly as much of a meaty leg to operate the pedal. But with the engine started, it became obvious that something was still rotating the input shaft, and the problem was slightly worse than before. As a matter of fact, the engine had to be shut off to get the transmission in reverse. Steve decided to drive the Explorer for a few days until we could get it back on the rack and re-yank the transmission for another look. Another Look The second trip Steve and Big Country (his partner’s nickname) made into the bell housing revealed nothing out of the ordinary on our initial inspection; the pilot bearing was still intact and rotating freely, but I was interested in having a closer look at the new slave cylinder. Steve removed it, and we stood it up next to the old unit for comparison and found that the old cylinder was about 3/8 inch taller. Our line of reasoning was that the newer, shorter slave cylinder just didn’t have the travel that the original cylinder did, thus it wasn’t completely disengaging the clutch. It made for good theory. To further undergird our hypothesis, we did some research and found that the original slave cylinder was an earlier model; indeed, the stamping number on the transmission was for a ’95 model; it was ostensibly two years older than the Explorer we were working on (unless the F5TZ number was used in the ’97 models), and Steve said he remembered the previous owner admitting that he had replaced the transmission. Steve and Big Country installed the new slave cylinder, slid the transmission back in place, and found that the hydraulic line wouldn’t mate properly with the second new slave cylinder’s fitting. This clutch hydraulic line snaps into the fitting using the same principle Ford fuel lines have employed since 1991, but the fitting is substantially larger than a fuel line hookup. For removal, a plastic sleeve built onto the male fitting releases the fingers that hold the line into the female part of the fitting, and shop manual procedures call for a special forked tool to operate the plastic sleeve. The line looked as if it should have snapped into the second new slave cylinder, but it would pop right back out each time we tried to snap it in. How the previous installer had snapped the line into the original slave cylinder is beyond understanding, and fluid restriction due to the improper line hookup may have been the reason for the original hard pedal concern, especially since we didn’t replace the pressure plate. From another transmission I was using for a trainer, I retrieved another slave cylinder like the shorter one we had rejected, and we could see right away that the fittings were indeed different. Steve pulled the transmission back, removed the slave cylinder, and swapped the fittings to mate the line with the new cylinder. Bleeding the Unbleedable The first new slave cylinder had eagerly embraced fluid and spit out air like it actually wanted to be bled. This second cylinder seemed to like air a lot better than fluid. We couldn’t get it bled. The pedal stayed mushy and uncooperative. The Explorer stayed on the lift that weekend and Big Country gave Steve a ride home. Monday morning, with the transmission removed once more, we found that Bi Country’s fitting swapping operation had been hastily done and that the fluid had been leaking at the point where the fitting feeds the slave cylinder. With the o-ring seal properly in place and the transmission reinstalled, the slave cylinder bled out quite nicely, but the clutch still wouldn’t release. Confused by circumstances into believing we had some sort of oddball mismatch between the ’95 model transmission and the ’97 Explorer, we reasoned that the clutch had worked properly with the longer slave cylinder in the first place, but that the clutch disc had been thinner. We also reasoned that the shorter slave cylinder had worked better with the new clutch disc than the longer one did. With that in mind, we decided to reinstall the shorter slave cylinder, but with a homemade steel shim installed between it and the bearing cover that would give it the necessary support, yet enable it to have more travel. With the transmission back in place and the cylinder bled out, we had the best pedal we had ever felt when that silly modification was made, but the clutch still wouldn’t release, and the concern actually seemed to be getting worse. This was getting ridiculous; replacing a clutch isn’t rocket science: We were obviously missing something very basic. One of the other students claimed he had fixed a problem like the one we were having by replacing the pressure plate. I wasn’t convinced. We took the clutch back out, removed the flywheel, installed the clutch disc and pressure plate on it, and mounted the whole assembly in the shop press with the dummy input shaft splined into the clutch and inserted in the pilot bearing. Utilizing an old locked up slave cylinder and a big socket, we depressed the diaphragm spring until we could rotate the clutch disc. We marked the amount of travel required to release the clutch. The fingers had to move a full ½ inch to release the clutch. I picked up a Ford authorized remanufactured pressure plate from the dealer, and we performed the same press test, comparing the travel required to release the clutch. The new pressure plate actually required more slightly travel than the old one. So much for the pressure plate theory! Finally! Taking another really close look at everything in the bell housing once more, I decided to slide the clutch disc on the transmission input shaft and spin it. At first it seemed to be straight and true, but then the more I observed it from different angles, the more I realized the disc was slightly warped. Fetching a dial indicator, I set it up to measure lateral runout and found a whopping 0.065 inch of runout that would scrub against the pressure plate and flywheel, effectively rotating the input shaft and sabotaging the release operation of an otherwise healthy clutch assembly. Since a transmission jack was used and we never forced it through the clutch disc splines with long bolts or let the weight of it hang, we had to conclude that the remanufacturer had relined a warped disc without checking it for lateral runout. Conclusions Steve and Big Country did a lot of work on that Explorer, but there were a couple of “up” sides to the deal. 1. Nobody who watched this drama unfold and understood what was going on will EVER install a clutch and pressure plate without closely examining the disc for lateral runout. 2. Steve and Big Country can now remove and reinstall an Explorer manual transmission in less than an hour; not bad for first semester auto mechanics students. 3. The fact that it was Steve’s personal vehicle made him a lot more motivated than he ever would have been if it had been a trainer unit. All in all, it was an excellent experience none of us will forget any time soon.
Posted on: Wed, 06 Nov 2013 09:18:34 +0000