Early Citroen transaxles used with the 907 and 912 don't typically suffer this failure. The input shaft had an abrupt shoulder for the circlip to bear against, and it seldom gets past that.
In anticipation of the Turbo's increased torque, a number of strength "improvements" were made to the transaxle, including blending out any sharp edges and transitions that might cause stress concentration points. In that effort, the circlip's shoulder became a taper which is far less secure. Eventually, the taper can work past the circlip, and then the spring forces the input shaft forward against the end of the crankshaft. Their hearts were in the right place, but in hindsight, this was a bad "improvement".
There's no warning that the circlip is about to fail, but the wheels don't come off the wagon all at once. There are signs that something is wrong before all drive is lost, but you need to be sensitive to notice them, and then quick to take action. Delay becomes progressively expensive to repair.
Initially, the Nylatron washer will take the thust load when the circlip fails and the input shaft pushes forward against the crankshaft. The washer is a relatively low friction surface, but still, there will be an increase in drag between the crank and input shafts, and some amount of torque will continue to be fed into the gearbox even when the clutch is fully released. The synchros can deal with any continuous torque input very well, and that will lead to your first clue something is wrong. Sensitive owners with a little mechanical empathy will notice that it suddenly becomes more difficult to shift gears... especially getting into 1st while at a standstill. That's the first symptom most folk ignore.
The Nylatron washer can't take that friction load forever, and eventually gets chewed up to dust (the Nylatron washer is a victim, not a culprit). Then the shoulder at the front end of the input shaft bears against the spigot bearing's end face, and the end of the crank. It's metal-to-metal contact, so the friction goes up, more torque is fed into the gearbox when the clutch is fully released, and shifting becomes even more difficult than it was initially. Folk complain about Red Hose Syndrome, bleed the hydraulics, and adjust the clutch, but they keep driving the car.
When the clutch spline reaches the end of the crank, it makes a very effective milling cutter, and starts boring into the back of the crank. That's when serious damage to the crank begins. And now the friction torque load fed into the gearbox really goes up, and shifting becomes very problematic. Also, there's the distinct sound of milling cast iron/ steel when the clutch pedal is depressed, sometimes accompanied by a squeal. But that often gets lost in the general caucauphony in the engine bay, and doesn't get noticed in the insulated cabin. Folk keep driving the car, and complaining about the shifting.
As the input shaft bores forward into the crank, the male spline at it's back end is slowly disengaging with the female spine in the primary shaft, inside the transaxle. Less and less tooth engagement is available to transmit the engine's full torque when driving, the splines begin to distort (shafts are now shot, must be replaced to fix), and eventually the spllines shear. When that happens, all drive is suddenly lost. Select any gear, let out the clutch, and there is no drive at all... just a loud, piercing squeal, like amplified finger nails on a chalk board.
That's when folk start to pay attention, but it's way too late. The loss of drive was sudden... instant, even... but getting there took some time AFTER the circlip failed. So, going back to the first premise in this thread... define "sudden".
Pro-actively replacing the thin wire circlip with a substantial snap ring can prevent the problem from ever occurring. Harry Martens and JAE both offer snap ring upgrades. The mating abutment in the shaft is still a taper instead of the earlier step, but the "real" snap ring won't let the input shaft get by.
Both suppliers can also provide you with a replacement input shaft with a step abutment. It's not necessary to replace a perfectly good input shaft, but if your original is screwed up and must be replaced anyway, then the stepped version is an additional option.
The input shaft disappears into the back wall of the bell housing, and runs in a tube/ tunnel through the differential area... a separate compartment within the transaxle, separate from the "gearbox". The compartment is split fore and aft, with the back half (output shaft centerline back) being part of the gearbox housing, and the forward half being part of the bell housing. Gaining access to the circlip requires removing the output shaft housings which straddle the joint line, then removing the bell housing. So, yes, you are partially opening up the transaxle and revealing the CWP & differential, but not the "gearbox" portion itself. It's not an insignificant effort, but it's minor compared to a complete disassembly/ rebuild.
Once you get in there, actually replacing the circlip with the larger snap ring is only a few minutes work... plus some general clean-up. Then put it all back together. Since disassembly to this point frees the differential assembly, there's now an opportunity to replace the support bearings, and check & adjust the bearing pre-load and the CWP backlash. But that's optional (Shipwright's Disease) and not required for installing the snap ring upgrade.
If the splines between the input and primary shafts have gotten to the point of distorting, or stripping, then both shafts must be replaced. The input is easy, and can be done when you do the snap ring upgrade. However, the primary shaft is inside the gearbox, and replacing it requires full disassembly.
The pinions for 1st & 2nd gears are integral parts of the primary shaft. Since gears are made in matched pairs (or at least wear-in to become matched pairs), and should never be mixed and matched, properly replacing the primary shaft requires that you also replace the mating gears for 1st & 2nd. So the ripple effect to input/primary spline failure is both a lot more work, and more parts expense. While you're in there, inspect all bearings, and take the opportunity to replace the brass synchro rings.
The damaged crankshaft can be repaired in two ways. Both involved boring the pocket for the spigot bearing (release bearing) oversize, so that's a trip to the crankshaft machine shop. Then either install an insert to restore the original bore diameter, and replace the original needle bearing. Or install a real ball bearing, similar to what Lotus used on the later engines mated to the Renault UN1 transaxles. A simialr bearing, but with a 15mm bore for the Citroen, instead of 17mm for the Renault.
Then, if the circlip/ snap ring should ever fail again, and the input shaft pushes forward against the crankshaft, the ball bearing is capable of supporting the thrust load without further damage. If you're going to repair a damaged crank, I can't imagine ever restoring it to the original needle bearing configuration, and passing on the chance to upgrade to a ball bearing. I've posted a Word.doc with all the details to the Files section of the Turboesprit mailing list on YahooGroups. You can download a copy there.
I strongly suggest that any Turbo Esprit-Citroen owner who is rebuilding the engine, or has the crank out for any reason, take the time to upgrade the spigot bearing to a ball bearing. The ball bearing is cheap (actually less expensive than the OEM needle bearing), and the machining cost is insignificant compared to the benefit.
Similarly, any time the transaxle is out of the car for any reason, I strongly recommend upgrading the circlip to a snap ring. The part is dirt cheap, and if you can do the work yourself, the greatest cost is some of your time.
Any of the upgrades, an input shaft with a step for the circlip, a HD Snap Ring, or a ball bearing spigot can solve the problem alone. There's nothing wrong with using all three together... belt-n-suspenders, plus a crotch strap. The input shaft's purchase price is the biggest hurdle, but the ball bearing and snap ring are minor investments that pay a big dividend. I prefer to do the spigot bearing and snap rings, and not worry about the input shaft unless something happens to force it's replacement.
If you recently had work done to replace the clutch, flywheel or rear main seal, then NO !!, it is NOT reasonable to assume the snap ring upgrade was done without you asking for it. This is a grassroots upgrade, and not something normally done by mainstream specialists/ dealers.
Lotus Owners Oftha North (LOON)
Last edited by Esprit2; 11-12-2012 at 11:13 AM.