3lt D4D Clutch Issue

[Mars67]

I thought I would share an interesting experience for future reference if someone comes across a similar situation. My sister-in-law has a 3lt D4D 4X2. It has done 200 000 ks now. My brother realised that the gear shifts were getting progressively more notchy (as if the clutch is not releasing). He decided that it was the clutch master cylinder and replaced it with a new unit. After battling for two days to try and bleed the system and also replacing the slave cylinder in the process he called me. What was happening was that it would bleed out fine but after depressing the clutch lever a few times it would become spungy again and if you then bled it a lot of air would come out again. I crawled in under the bakkie and tried to bleed it again and then noticed that the clutch fork seemed to be too far back. If you bled the system and depressed the clutch you could also hear the sound of the clutch pressure plate springs depressing. Its hard to describe but it sounded like springs being compressed beyond their limit. The clutch was also very stiff. I ended up towing him to my place as I have a service pit and we then removed the gearbox and replaced the clutch with a Sachs clutch. I inspected the old thrust bearing and the "fingers" on the pressure plate but other than some noticeable wear on the fingers there appeared to be nothing wrong with the old clutch. The clutch plate obviously showed some wear but was actually looking fine with what seemed to be many more miles left on it. The difference with the new clutch is remarkable. It is much softer with a much better feel to the pedal. Needless to say the system bled out very easily and is working great now. The old clutch required too much force to depress for some reason but I can still not figure out why that would lead to air being introduced into the system. It would seem more logical to me that it would push brake fluid out and cause seepage on either the master cylinder or the slave. This was not the case.

Another interesting thing that I found was I took the master cylinder apart. IT does not work with a conventional piston but has a rod that passes through two static U-cup rod seals. One in front (the pressure side) and one at the back preventing seepage out the back of the cylinder. The rod does not come into contact with the cylinder and it can therefore not wear it out. The only wear on the unit was the front seal was quite badly corroded on its sealing surfaces. The rear seal had no signs of wear at all. I then took apart my old slave cylinder and found the exact same thing. I then took the good rear seal from the one cylinder and replaced the worn front seal with it on the other and re-assembled the unit. As an experiment we put this "refurbished" one back into the bakkie and bled the system. It worked perfectly and is still in the bakkie!
Now to try and find that front seal as a replacement somewhere. This means that if your master cylinder packs up it requires the replacement of a single seal which would cost less than R20 or R30 in stead of the R1300 odd from the dealers.

[MCHILUX]

The pressure plate was faulty causing the hard feeling and notchy gearshifts common problem.On the the diesels and v6 there is an accumalator valve that needs to be replaced when replacing the mastercylinder , this valve can make bleeding a nightmare if not replaced