Author Topic: Clutch plate driven "sprocket"  (Read 209 times)

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Offline Laurie

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Clutch plate driven "sprocket"
« on: 01 Sep 2022 at 14:35 »
My Mark V gearbox clearly has no seal whatsoever behind the "sprocket" driven by the clutch plate. Looking at the exploded parts diagram there seems to be no impediment to removing the retaining nut and lock washer and drawing it off. Or is there given that a 12 ton hydraulic puller wont shift it without risking the threads on the shaft?
On that subject the tapered shaft has an aluminium? insert in the end. I've assumed that's normal to stop oil coming through from the mainshaft but it strikes me as a risky practice given that it reduces the threaded part of the shaft to a tube with 1/8" thick walls. it's that possible weak spot that's prevented me from going full throttle on the puller!
It could be that I have to resort to splitting the sprocket? If that's the case does anyone have a spare?
Laurie Packer

Offline eddie

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Re: Clutch plate driven "sprocket"
« Reply #1 on: 01 Sep 2022 at 15:35 »
Laurie,
           There is no seal behind the coupling on the front of the Mark gearbox. There is just an annular groove to collect the oil that comes through the bearing. At the bottom of the groove there is a drilling that feeds that oil to the front layshaft bearing. It is important that you only use an open bearing on the front of the layshaft, otherwise the oil will have nowhere to go, and will eventually spill from behind the coupling.
   The coupling is on a large taper and is often difficult to shift. If you have the front plate off the gearbox, put a reasonable pressure on the puller, and then try giving the coupling repeated squeezes in the vice  eventually, it will give up and break free.
   
   Hope this helps,
                           Regards,
                                         Eddie.

Offline Laurie

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Re: Clutch plate driven "sprocket"
« Reply #2 on: 02 Sep 2022 at 10:26 »
Many thanks Eddie.
When splitting the engine from the gearbox I didn't drain the gbox oil. Replacing it we tilted the gbox to overcome a difficulty in meshing the plate. A large amount of oil was dumped into the clutch! I thought I remembered mention of a felt washer in a guidance sheet written by either BMS or JS but I hadn't taken on board the annular groove effect. Now you've confirmed taper and difficulty I will try again with a a hot airgun brought into play. The aluminium plug in the end of the tapered shaft remains a concern though. Is it to block a through drilling for the layshaft? I used a brass bar cutoff 1" x 1" between the puller and  the threaded shaft and the plug has moved in about 1/10". The gearbox has gone tight. I'm hoping I can draw it back if it's deep enough to take a thread or remove and replace. What are your thoughts?
Regards
Laurie

Offline eddie

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Re: Clutch plate driven "sprocket"
« Reply #3 on: 02 Sep 2022 at 11:24 »
Laurie,
           There is a felt seal further into the 'box, but you have to partly dismantle the 'box to get at it. If your oil leak was caused by tilting the 'box forward, that would happen even with a new seal - the raised oil level as you tilted the 'box has caused the oil to travel back up the drilling and escape around the coupling. If, previously, you had no problem with gear oil leaking from the bellhousing drain hole, I would leave well enough alone.

  Regards,
               Eddie.