From: Rad Davis Date: Wed, 19 Oct 94 10:10:00 UTC To: corvair@shadow.mitre.org Subject: re: greenbrier clutch adjustme >Sub: GreenBrier Clutch Adjustment >To: corvair@shadow.mitre.org >From: hiero@netcom.com (David Miles) >Subject: GreenBrier Clutch Adjustment > >Question: > >How does one go about adjusting the clutch and shifting linkage on >a Greenbrier? The clutch is beginning to slip a bit and occasionally It'll >get knocked out of gear by a bump in the road while it's not pulling a >load. As usual I'm still without anything but the Chiltons manuals at this >time. Might be able to figure it out for myself but you folks probably know >better. >Thanks in advance for any and all help. > > Dave Miles > 1963 Greenbrier (Lucky) Ah. Possibly the trickiest adjustment on the FC's. GM never really found the best answer. The clutch pedal travel and the torque multiplication of the lever system mean that the pedal travel always seems to exactly equal the required travel of the clutch between "just barely not touching" and "clutch fully released". If all the components of the clutch system are functioning perfectly it will just barely work right. But it *WILL* work right. Your case is complicated by the fact that there was a running production change on FC's in 1963. Shifter linkage and clutch linkage were affected, and so here I address both types. The easiest way to tell one from the other is the shift lever: Early '63s have the lever going into the bulkhead under the seat above the heater outlet, like '61-62. Late '63s have the lever mounted on the floor like a car, as do '64-65. The adjustment technique on either an early or late '63 van is the same, despite the changes in linkage. There's a threaded fork which is screwed onto the pull rod which goes into the bellhousing. To adjust, disconnect the return spring (on early linkage, it should be connected to the lever and the bellhousing tab, on lates, it is on the extra tab at the adjusting clevis), remove the clevis pin which connects the clutch cable to the pull rod. Loosen the locknut behind the adjusting fork on the pull rod. Loosen the fork until the clevis pin will fit into all the holes easily. On earlies, flip the lever out of the way. If it's rusty, apply a little grease to the fork on the end of the cable and to the threads on the pull rod, and make sure that everything turns freely. Hook up the linkage with the clevis pin. On lates, attach the return spring mount in the usual way. Tighten up the linkage by turning the whole thing clockwise until all the slack goes away--detect the slack by wiggling the rod/cable side to side. If you've been doing this for a while, you'll get very close with just this. In any case, the best way to check the adjustment is to test it. Start the engine in neutral (yes, with it only partly together). Listen carefully. You can hear 1) the engine idling, and 2) the primary shaft turning in the transmission. If you press the clutch, the sound of the input shaft should go away. IF you can't hear the difference, test by putting it in reverse(wait a few seconds for the disk to stop turning). IF you get a grunch, crawl under and tighten 1/2 turn. IF you didn't get a grunch, loosen the linkage 1/2 turn. Repeat the pedal test. Do this test/adjust cycle until you have it so that the shaft just stops turning completely with the pedal on the floor. Tighten another 1/2 turn, and set the locknut. On lates, you only have to disassemble the clevis pin if the return spring mount is pointing the wrong way for the spring to attach. If so, remove the pin, put on the mount the right way, and hook everything together for good. With earlies, you have to unhook stuff regardless to attach the lever that the return spring hooks to. A phillips screwdriver helps align the holes so you can get the blasted pin back in. In all cases, don't forget to put on the retaining clip and return spring. Test driving will show if you need another 1/2 turn to get the clutch to work right all the time--you'll get balky shifting if it's too loose. Frame flex and the rear suspension moving around can affect the adjustment, so don't be surprised if you have trouble getting it to shift right even if the adjustment in the driveway was OK. Just tighten it up another 1/2 turn or so until it doesn't grunch into reverse. The good news is that you don't have to do this adjustment very often unless you have just put in a new clutch disk. The popping out of gear thing is a different problem. It has been around for a while. Here I quote from SAE tech. paper 313B, "THE CORVAIR 95 Chevrolet's Space Age Panel Truck" which was presented at the January, 1961 SAE congress: Another problem was that of frequent high gear disengagement when running on rough roads (fig. 38[picture of rampside on dirt road kicking up trail of dust]). We felt at first that the long longitudinal control rod vibrated vertically, causing a length change. This change pulled the shift lever fore and aft and eventually forced the transmission out of gear. The rod was stiffened generously but to no avail. Its weight was decreased and increased, but still no cure. Various methods of tuning the linkage with heavy rubber insulated knobs were tried without success. It was discovered that the primary vibration of the shift linkage was at rear wheel hop frequency or at about 12 cycles per second. The truck was then put on the Bump Rig and run at wheel hop frequency; high gear disengagement occurred consistently. Observation indicated that at this frequency, the powerplant was vibrating fore and aft on its mounts with sufficient amplitude to cause gear disengagement. Retuning of the power plant mounting system frequency halted the motion and eliminated the disengagement of the transmission. Power plant isolation remained adequate. Well, they did fix the problem. But it comes back to haunt us FC guys once in a while. Basically, the manual trans. FC powertrain likes to resonate at about 12 Hz. The system is designed to damp this tendency enough that it doesn't cause the transmission to pop out of gear. A variety of things tend to wear with decades of age (and FC's are seldom gently used); several of these tend to aggravate the natural tendancy that GM noticed in prototype of the FC. I had this problem myself. What caused it? What can cause it? 1. a well-worn 61-63 4-speed. The transmission was on its third vehicle, and was definitely due for a rebuild. It was a '61 4-speed, because it had a drain plug. The early corvair 4-speeds have less strong detent springs than the later (64-65) ones do. We're ignoring Saginaws here, which aren't really "Corvair" transmissions and don't fit FC's anyway. Add about 150,000 miles of wear, and you get a transmission that isn't too firmly in gear under normal circumstances anyway. 2. Sagging front powertrain mounts. You know, those rubber and steel things that bolt into the transmission mounting crossmember and the suspensions crossmember. If the rubber on these is perished, you are going to get more vibration of all types. 3. Slop in the rear powertrain mount. See 2. This is just squished rubber donuts- -an easy fix. 4. A loose fitting transmission shift rod clevis pin. IF it isn't a pretty close fit into the shift rod fork and the hole in the transmission shift rod, you're going to get sloppy shifting and a greater tendency for things to pop in and out of gear unexpectedly. I turned an exact fit pin out of a GR 8 bolt in a hand drill. 5. A sloppy shift rod bushing. You have to determine if you have an early '63 (shift rod under gas tank) or a late '63 (shift rod through gas tank). The early system has different bushings than the later one. The later one has a single bushing in the little box under the stickshift. 6. Worn out rear suspension crossmember bushings. These eight bushings support the whole back of the FC and locate its rear suspension. Since the powertrain is attached to the suspension crossmember, these bushings also affect the powertrain's movement. The bushings and mounts are all available from mail-order vendors. The detent spring on an early 4-speed can be shimmed or replaced, if the synchros are in good health. If you get grunches when shifting and you know the clutch is working right, consider changing transmissions or rebuilding the one you have. If you find that the van is difficult to get rolling, you may have a car transmission instead of an FC trans. The FC gearing really is much better for the 1000 lb heavier vans. One good way to tell an FC 4-speed from a car one is that most cars with 4-speed came with back-up lights, and have the switch on the transmission for this. FC transmissions won't even have the hole drilled in the mounting boss. Yes, FC's definitely have different linkage type problems than the Corvair cars do. For myself, I'd really like to put a hydraulic clutch release mechanism on the thing... Hope this helps. Rad