Back Back 2CV Restoration - Technical tips - Keep your transmission safe

Backing up without destroying the transmission

Never back up uphill or start very fast backing up! 2CV's with disc brakes have a severe problem: While backing up with a high tourque, the collar for the center shifting fork twists off the gear assembly (see sketch).

The reason is that this collar was not tightened enough during production. Afterwards it is almost impossible to tighten it more. This requires disassembling the transmission. When you back up very hard you put a high load on the transmission, which leads to friction between the shifting fork and the collar.

Upper shaft

The gear assembly warps and the collar twists off the thread. The collar is peened in a few spots, but this cannot stand the force. Once the collar is twisted off completely the gear assembly will pull apart. Mostly this leaves the transmission in permanent 3rd gear.

The synchro-ring twist and the gears cannot engage anymore. Maybe you can manage to engage another gear - a transmission with two gears engaged simultaneously - it will lock up. To press the clutch won't help because it is not the motor what blocks!

A repair is challenging. In most cases the transmission will need to be replaced. This is the reason why it is so hard to find a good used transmission with disc brakes.

So be gentle in reverse, try to avoid a high tourque. Typical situations where the transmission is threatened are steep downhill driveways to your garage or house. If there isn't enough space at the bottom to turn around on a level surface, go down in reverse. This way you have the high tourque coming back up in 1st gear, where it doesn't harm the transmission. Also it makes it easier to leave the driveway pulling out foreward.

Also don't fall for the urban legend that "if you can't make it up a hill in 1st gear, turn around and go in reverse". This was true in the old 2CVs with 12 or 16 HP engines. In the later model 2CVs with a 602cc motor, the gear ratio for 1st and reverse gear is identical!

Another typical situation where we saw many transmissions damaged was with plenty of snow in winter. The 2CV got stuck in snow. The usual response would be to go in reverse to get back out of the mess. Usually one wheel has less traction, so this wheel will just be spinning. The other wheel is standing still. The spinning tire rubs on the snow and ice surface. The friction creates heat and melts the ice away. Once the tire hits the bare pavement under the snow, it suddenly has good traction. This gives the transmission a very high tourque impuls, quite often enough to pull the collar off the shaft.

The best way to keep this problem from happening is to be aware of the situations that will cause it, and simply avoid these situations.

Treat your transmission well

For many years now, the production of transmission has been discontinued. Spare parts are limited to a few bearings, which makes it hard to rebuild a transmission. The only way is to salvage core returns, which mostly show the same problem as your dead transmission. So finding good parts from returned transmissions is getting harder with the higher mileage these boxes have seen. Already, the ratio is about 50%, meaning, that it takes approximately two transmissions to salvage, to gain one good unit. So treat your transmission well and don't throw it away when it is defective. Parts of it might help keeping another 2CV going in the future!

Things you could do to extend the lifetime of your transmission

Change the oil regularly after about 15000 km
The transmission needs 80W90 Hypoid oil. Don't use synthetic oil. This has caused problems in the past. Just stick with regular oil of the right weight and very important, the oil must be for "hypoid" transmissions and differentials. In many vehicles, the transmission and the differential are separate units. The pressure between the gears in a regular transmission without a differential built in is normal. So regular gear oil will do the job here. In the differential however, the pressure between the gears is extremely high. In regular gear-oil, the molecules would just break apart under his pressure. This is why the oil for the differential is of a higher grade.
In the 2CV transmission, the differential is integrated. Both sides in the box, gears and differential share the same oil. So make sure that you use the right oil.
Change the transmission oil with every second oil change for the engine. Drive the car to get the oil up to temperature and drain engine oil and transmission fluid together. To drain the transmission fluid, just remove the drain plug on the underside. Allow it plenty of time to drain. Check the drain plug magnet for metal particles. Don't be shocked, there will always be some metal powder sticking to the magnet in the plug. The "cap" on the drain plug may get up to half an inch high. If it is more, or solid parts, like chipped off parts of gear teeth, it is highly recommended to have the transmission inspected and rebuilt.
To refill the oil, put the cleaned drain plug back in and pull it tight. Then open the plug on the passenger side of the transmission. Now fill a quart of transmission fluid trough the hole. There is no dipstick to measure the oil level. Once the oil starts running out the side hole, the filling process is finished. Put the plug back in and tighten it.

Don't shift too rapidly
For shifting, both gears have to turn at the same speed before the gears can be engaged. This is the job of the synchro-rings. When you shift gears, you will feel a little resistance in the shifting lever, just before the gears engage. This is the synchro-ring, retarding or accelerating the other shaft to the same speed. Once the speed is equal, the gears engage. This synchronization process causes wear on the synchro-rings.
You can control the wear by the way you shift gears. A very sportive, fast gear jamming way of engaging gears, leads to a high wear on the synchro-rings. Once the synchro-rings are worn, this is it. They cannot be replaced, and chances are that parts from other salvaged transmissions show the same wear. So subsequently, the transmission is doomed.
To prevent this, watch the way you shift gears. Don't force the gears in rapidly; applying gentle pressure, give the synchro-ring some time to synchronize the speeds. This way you can significantly minimize the wear on the synchro-rings.

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