DDK - Die Deutschen Klassiker

Have a problem with the seat back rest slipping back. If you lean back and put a little pressure on it you end up virtually horizontal. Supprisingly its on the passenger side which is seldom used.
Stripped the mechanism and all seems to be good. There is no noticable wear on the teeth although the fixed one is a bit rusty the spring return on the side release handle is working fine which keeps the teeth meshed.
Read on the net that some guy in the states had designed a nylon washer to overcome this problem but no idea how it helps as there appears to be no wear on the existing mechanism.
Anyone have some suggestions please

I've have the same problem on my 1965 seats. I think part of the problem is that when you lean back, the back rest doesn't go back evenly twisting the bar that connects the mechanism on each side. This twisting slightly disengages the teeth which then give way. Another issue that might affect mine is that I had everything chrome plated when I restored the seats 30 years a go, this might make them slip more. I am in the process of having the seats restored again and I have rebuilt the mechanism having filed the chrome off. I'll let you know when I have put them back together if it has fixed it. I have not heard of this nylon washer repair, If it works I might try it on my rebuild. Would be good to know if anyone has details.

Check your donut !

Take a look under the back of the seat. On one end of the rod that goes between the left and right chrome seat brackets (or black on 72/73 cars) is a sliding donut (it might have a rubber sleeve on it if it survived).

The backrest recline position is held by the teeth on the side of this sliding donut (the other end of the rod is not fixed, can turn). The donut slides on a set of splines. The lever sticking out of the chrome brackets at the donut end is what slides the donut back and forth to lock the recline position. The lever has a return spring.

Check that the donut slides back and forth - it might be that it is not fully seated. It might just need grease in the splines (you can do this without removing the seats from the car), or the return spring might be weak or broken (but you can help it by forcing the lever).

I dont know if twisting the seat back might influence this mechanism, but I would imagine that if the teeth were good and the donut was sliding back into position, no reasonable amount of twisting would unlock the teeth meshing, unless the return spring is broken or incredibly weak.

Hope that makes sense, and helps diagnose...

I think I may have found the problem.All the items mentioned are present and in good condition including the plastic covers. On stripping the mechanism I noticed that the sliding tapered gear that locks the position was not engaging in the fixed gear on the bracket. I thought this was due to wear or damage to the teeth. On separating there was no wear or damage to stop them engaging. I then had a light bulb moment. The splines are very fine with more teeth than the tapered gear. I shifted the gear around to the next spline and the gear went fully home. If this is the problem I can only surmise that when the seat was rebuilt before I bought it it was incorrectly assembled. As I only use the car on my own it’s never been an issue before but now I am selling the car I am looking for all the problems that need fixing.
I am painting the brackets before reassembling and will keep you posted in the next few days

Looks like my hunch was correct. By moving the splines a few teeth around i have the tapered gears meshing and holding the seat up.
Seats were completely rebuilt and recoivered before i bought the car so can only assume the guy made a mistake n reassembly

I have a similar problem on my Recaro Ideal S drivers seat, but not as severe. Whilst driving intermittently my seat back will fall back one spline. I have checked the teeth and they look okay. I tried refitting the bar that runs along the back, but still have the same problem.

Whwn you take the side plate assembly off the seat check that the sliding boss ( which is moved by the release mecahism fully meshes with the fixed gear on the side. . If not slide it off the shaft move it one spline at a time around the splined rod until it fully meshes. If you have no damage to the teeth then it will mesh fully. Mine was a few spilnes out so the only thing holding the seat up was the return spring and the friction of the unmeshed gears.

Good find Peter - I never considered that the teeth could get misaligned that way, but it makes complete sense