Diesel clutch master cylinder question

[biffa75]

Hi all,

We have recently bought a 75 diesel tourer. I've noticed that the clutch appears to slip at 2k rpm under full throttle. Having spent some time investigating I've found the clutch master cylinder is weeping from around the dust boot. No trace of fluid from where the box and engine meet so I'm hopeful the slave is okay.

I've also noticed that when driving, putting your foot behind the clutch pedal and attempting to pull the pedal upwards even though it doesn't move the pedal.. the clutch doesn't slip. So.. I've bought this master cylinder.

https://www.ebay.co.uk/itm/ORIGINAL-...-127635-2958-0

Upon attempting to fit it, I found removing the current master cylinder marked LUK is proving difficult to remove from the bulkhead but I'll sort that tomorrow, just pull the full pipework through the bulkhead.

Question is.. the Luk unit has a nut fitting at the begining of the nylon pipe where the original ap unit does not. So.. if I'm to swap the pipework over will I need a new pipe to fit the original ap unit fitted at factory?

Thanks
Rob

[biffa75]

My mistake.. just learnt the roll pin needs taking out

[biffa75]

All swapped over new ap master cylinder fitted. Just need to bleed the system. Any special ways required ? I do have an eezi bleed if needed. ThankS

[trikey]

Originally Posted by biffa75

All swapped over new ap master cylinder fitted. Just need to bleed the system. Any special ways required ? I do have an eezi bleed if needed. ThankS

Just bleed it the normal way, top up the master every couple of pumps of the pedal, this ensures no air will be drawn through.

[biffa75]

Thanks trikey

[macafee2]

would a leaking master cause clutch slip?

macafee2

[alanaslan]

Originally Posted by trikey

Nope, a leaking master would make gear changes difficult but once the gear is engaged, the master is taken out of the equasion.

A worn friction plate or a leaky slave can cause clutch slip.

Just as a matter of interest the difference in the thickness of a new friction plate and totally worn out one is 100 thousands of an inch.
Not much meat to play with but in the M47R I have seen nearly 200,000 miles on one plate. Useless facts from my senile old brain.


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[alanaslan]

Originally Posted by biffa75

Thanks for the advice macafee2.

A quick update*
The original Luk master cylinder (that was fitted to the car when the car was purchased only a few days ago) may have been causing the clutch slip, the slave wasn't leaking and the friction plate wasn't really worn.(could also have been the poor quality clutch kit that had been fitted?) Having removed it from the car and draining the fluid, we found the fluid was a gloopy black consistency and when drawing the push rod back and forth, you could feel when pulling the push rod back out, a sudden "slackness" became apparent. Waggling the end of the push rod revealed a sudden "thud" felt through your hands. We believe that a seal or something internal wasn't fully returning inside the cylinder which could also be the cause of the black goop in the bottom of the reservoir. Possibly the seals degrading and leaving traces against the bore walls causing the issue to be exacerbated perhaps? If this is the case, it could be giving the effect of someone sat with their foot partly on the clutch pedal, riding the clutch. Anyway... Was worth a try, the unit was leaking and it was getting difficult to engage 1st and reverse..

Changed the master cylinder for an AP unit and used the original pipework, bled the system a number of times to help flush out any gunk and black goop from the rest of the clutch hydraulics and... Unfortunately the clutch still slipped. The operation of the clutch pedal was a lot lot smoother and thankfully no more leaks.


I did fear that the damage may have already been done as we bought the car with the clutch already slipping (wasn't noticed in the test drive by my grandfather or by my wife who drove the car home, I couldn't go to view the car due to work).

Anyway.. today saw the gearbox being dropped out of the car, took little over an hour. With the clutch removed.. we quickly discovered a part number on the clutch friction plate. A quick eBay search revealed it to be an unbranded cheap clutch kit rated a heavy duty clutch kit??

We very quickly noticed.. the dmf was beyond re-using.. lots of stress cracks to the surface, lots of blue on the surface and a LOT of high spots.
High spots could also be seen on the clutch pressure plate too.

So with an Luk clutch kit ordered, dmf being collected tomorrow and a new guide tube and drive shaft oil seals.. hopefully this will put an end to this slippy clutchy business.

Thanks have to go to my brother who removed the gearbox while I was in bed having been on nights. He said it was one of the easiest gearbox removals he has done. (Me and my brother have done a few clutches over the years and some were a real PITA.

On a side note, while diving into the job, we know the egr has been blanked off, it has had the inline thermostat mod fitted.. I'm thinking at some point if the clutch all goes okay of visiting big Russ and seeing if he can tell me if it has had the 160map done.

Quick question tho guys..

The fly wheel bolts, are these re-usable or are new ones required?

Thanks
Rob

This is just another reason for hydraulic fluid lines to be fully flushed every five years and checked for water content every service or every year which ever comes first. You can pick up a reasonable electronic hydro check sensor for about £30.
If the fluid Is black and lumpy then the muck has to have come from somewhere. Seals passing or rubber hoses degrading.
The clutch in the M47R is not that bad a job. The question you have to ask yourself is whither to replace the DMF or not. Also do you fit another DMF or a solid flywheel. All the DMF does is make for a smoother gear change. Despite what some companies claim.
If a car needed a DMF to protect the drive train or crank. This retired engineer is a monkeys Uncle. The words utter bumpkin spring to mind. I remember being invited as a guest lecturer to a University in the midlands. The man up before me explained to the students why DMFs were required. I felt terrible when I proved with maths that his reasoning was out the window and the combustion forces on the crank exceeded by up to 8 fold the torque exerted by the flywheel. During coffee at the lunch time break the proff and I sat and discussed the pros and cons. Taking the manufacturer’s data and then disproving it with the mathematical model. He was astounded that so many manufacturers needlessly fitted expensive flywheels where a balanced lump of metal would do a better job and would reduce wear on crank oil seal wear.
We came to the conclusion it was so they could charge more to carry out a clutch change.
A bit like aero manufactures selling engines at anything to a million pounds less than cost. Knowing that over the next three years you will recoup that loss and then some with the sale of service parts.
Goodness knows what will happen when we go electric. If anybody knows of a company that can recycle lithium polymer batteries please let me know so I can buy shares in them. There is a mint to be made if it can be done. Then again dig a hole and drop them in who cares.


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[MSS]

Originally Posted by alanaslan

..............


The question you have to ask yourself is whither to replace the DMF or not. Also do you fit another DMF or a solid flywheel. All the DMF does is make for a smoother gear change. Despite what some companies claim.

If a car needed a DMF to protect the drive train or crank. This retired engineer is a monkeys Uncle. The words utter bumpkin spring to mind. I remember being invited as a guest lecturer to a University in the midlands. The man up before me explained to the students why DMFs were required. I felt terrible when I proved with maths that his reasoning was out the window and the combustion forces on the crank exceeded by up to 8 fold the torque exerted by the flywheel. During coffee at the lunch time break the proff and I sat and discussed the pros and cons. Taking the manufacturer’s data and then disproving it with the mathematical model. He was astounded that so many manufacturers needlessly fitted expensive flywheels where a balanced lump of metal would do a better job and would reduce wear on crank oil seal wear.

We came to the conclusion it was so they could charge more to carry out a clutch change.

A bit like aero manufactures selling engines at anything to a million pounds less than cost. Knowing that over the next three years you will recoup that loss and then some with the sale of service parts.

Goodness knows what will happen when we go electric. If anybody knows of a company that can recycle lithium polymer batteries please let me know so I can buy shares in them. There is a mint to be made if it can be done. Then again dig a hole and drop them in who cares.

Alan, What you say about DMF is interesting but I am sure you are more than aware that maths is only relevant if your mathematical model of the physical processes is representative.

As what you say will surprise most members of the forum, especially those such as marinabrian who have a lot of experience of the impact of DMF replacement with a solid flywheel, would you mind sharing details of your mathematical model and associated calculations please?

There is a basic flaw in your argument comparing ownership cost model of an aero engine with that of a car fitted with a DMF. DMF are not part of service schedules and are expected to last the car's lifetime, which they do in near 100% of cases. They do not therefore inflate the cost of a clutch change except in the very, very small percentage of failure situations. Such percentages will be irrelevant in terms of average cost inflation from a car manufacturer's perspective.

By comparison, aero engine servicing is a major element of the cost of ownership and a critical part of operating an aero engine. Without it, an aero engine becomes worthless and unusable.

Also, is it not the case that a DMF reduces the transient forces on the drivetrain at clutch engage time?

Thank you.

Perhaps you can respond in a new thread specifically for the purpose of discussing the needs for a DMF and impacts of solid flywheel replacement?

[HarryM1BYT]

Originally Posted by MSS

Perhaps you can respond in a new thread specifically for the purpose of discussing the needs for a DMF and impacts of solid flywheel replacement?

I'm with you on this point. My understanding of the DMF's purpose is that it helps smooth out and regulate the pulses of speed of the engine, as it fires. Rather than using a big, heavy flywheel to smooth it out, the flywheel can be much lighter making the engine more responsive, but avoiding the vibration of power delivery via the cushioning effect of a DMF.


I suspect it will make little difference so far as the smoothness of the gear change and take up.