454 cdi transmission problem

[dopey454]

Hi Guys long story. Originally had a problem starting the CDI . MBstar report identified either faulty wiring to the clutch actuator or new clutch actuator needed. Main dealer offered new actuator at £583 +labour fitting and clutch reteach on MBstar. I declined. Local garage moved clutch actuator 3 vernier markings - problem solved for 3months. Then No start returned.
Bought new clutch actuator off Ebay cost £207 delivered (Main Dealer take us for mugs).
Fitted clutch actuator 2 vernier markings car starts ok. Test drive ok but when I got back and was stopping the car continued in drive even though brake pedal was depressed so the clutch did not release ? I switched off car. On restarting the car had 0 in speedo where A or 1 should appear.
Pushed car into my garage , put it on axle stands. Cleared p0702 transmission electrical fault then disconnected battery 30 mins then reconnected and started car. A or 1 now in speedo . Wheels turning in thin air ok. Alternated between N and A for car to learn new clutch bite position. Pressed brake and again drive continued then ceased altogether. I am Baffled. Any ideas anyone ?

[Ocracoke]

Hey there, welcome to the forum!

After having the clutch actuator installed, did you have the gearbox and actuator retaught on a STAR machine? Although it can roughly be installed just through the markers on the actuator, it needs to have proper calibration via the diagnostics machine. From the description, it sounds as if the car thinks the actuator is further out than it actually is so the clutch continues to deliver power to the wheels. I am fairly sure that there isn't a learning mode in the ECU that allows calibration like this without being hooked up to a STAR.

[dopey454]

Hi Ocracoke thanks for your reply. No I did not get a gearbox and clutch reteach - I was hoping to get it in a drive state so I could drive it to a MBstar or Winstar garage to get it done.
I am interested in your line of thought though. The actuator is definitely further away from the clutch fork compared with the old position.ie less markings pushed up.
Relearning
this is a post by tolsen admittedly a fortwo but I guess the principles are the same ?/
tolsen
19-02-2014, 10:26 AM

Early start this morning:
Tested what effect clutch actuator preload or absence thereof has on gear changes.
Findings:
Clutch bite point was unaffected. Looks like the car will find and learn clutch bite point regardless how poor the mechanical adjustment of clutch actuator.
Gear changes speed up with increasing clutch actuator preload. Obviously because actuator needs travel less to disengage clutch.
Regardless how hard I preloaded, I could not make clutch burn and slip due to excessive preload. I applied manual force to actuator without use of tools or levers to create any mechanical advantage when preloading.

Conclusion:
Preload is important but actual preload is not critical as long as there is some preload. I think no preload at all is not advisable, especially on a diesel. Vibration may rattle the guts out of both fork and actuator push rod leading to punch trough. There will also be unnecessary wear on trust bearing and fingers of clutch diaphragm due to stops and starts . With preload, the trust bearing will be spinning at all times with engine hence better for the bearing.

[Thrumbleux]

Don't know if this applies to 454 but when I fitted a new actuator to my 450 the advice given to me was to push the actuator in toward the engine until the rod could just be spun between fingertips ie, no discernible free play but not so tight as it couldn't be twiddled by fingers.
Worked for me though clutch could definitely use a reteach to finish the job.
Many many views out there about how the pre-loading should be done but I can only talk of what works for me.

[tolsen]

The 454 clutch actuator is similar to the one for the 451. Mechanism inside actuator compensates for clutch wear.
Explanation on their internal workings here in post 104 and 106 complete with photos.

http://www.smartz.co.uk/showthread.php?22606-451-diesel-gearbox-update/page11&highlight=Clutch+actuator

[tolsen]

Perhaps best read post 98 first to view photos of actuator mechanism internals.

[dopey454]

Thanks Tolsen I managed to work out a little of the workings of the inside of the actuator myself after looking inside and that info you pointed me to certainly filled in the many gaps. Now I understand why main dealers do not adjust the actuator position.