Hello.

I am in process of replacing the master cylinder on my 1981 240D - see my following post:

leaking oil under dash/carpet? clutch
I am under same dilemma, the original factory rod is bit longer than the new ordered ROD (Part number: 000-295-08-33) with new master cylinder (Part number: 001-295-44-06). Should i install the shorter rod in the new cylinder or order the original size?
Thank you.
Mac

The thing to remember. The fill port in the clutch master is being obstructed even with the "right" shorter pushrod in place. It may make no difference unless there is a fluid loss below the clutch master somehow. Once bled. That is not too likely to occur either.

You just loose the resupply of fluid if ever needed then. I have never done a 240d clutch. If there is an adjustment where the rod connects to the pedal arm. There may be another at the top of the pedal arm.

I would not get excited about this. Something is just outside the designed component parameters. Or the total range of designed adjustments is not being employed. More likely still they are just inadequate in range.

As you are unfortunately all too well aware the port is blocked with the rod in position. This may be more common than suspected as far too many have had far too serious a struggle with bleeding that system.

All I am totally certain of if the dry system holds a vacuum from the bleeder on the slave cylinder. Plus no adjustment gets it stopped. You will have to disconnect the pedal rod to fill and bleed this system easily. As someone mentioned five minutes should be enough.

Otherwise it will be a massive struggle. It even sounds like the vast majority are at least partially obstructed. Again there has just been too much grief over such a simple system to be otherwise. Bleeding from the top with pressure is not going to provide a rapid enough fluid flow to stop the air being driven out either with the rod connected on many. The air has enough time to float upward. In relation to the fill speed entering.

A quick test may be to put some tape on the bleeder screw and attempt to pull a vacuum first from the slave cylinder if the system is dry. If you have installed new parts. Or even if you have only installed a new slave cylinder. You should not be able to pull and sustain one.

Reverse filling and bleeding of that system makes complete logical sense. As air will always be pushed ahead of the entering fluid.

In most cases is there a reason the original rod cannot be reused? As I stated you may still have issues with even that.. I ask because I have never had to do anything with the clutch hydraulics on these cars. I would bleed the system without the rod bolted up.. As long as you do not have to apply a lot of force against the rod to hook it back up it should be fine. The piston will easily slide ahead until the fill port is partially or totally covered. You will be pushing against the pressure of the clutch fingers after that and really know it. You also do not want to do that. So either the vacuum test first. Or if the refilling is difficult. Anyway to remove some of the rod pressure against the piston if possibly workable should be attempted.

. Apparently the poster had no major issue in this regard so it may be no issue at all. He could mention if there was an issue getting the clutch master cylinder rod bolted back up. If your new rod is only a very small amount shorter. There may be adequate compensation with the eccentric on the pedal assembly. Or more in sync with the available adjustment range provided.

If only slightly shorter it might be a design change to overcome the original issue with this system. By trial and error try using it. The rod has to have no actual play in place when installed. At the same time you do not want it exerting pressure against the piston in the clutch master cylinder with enough force to move that piston. With no pressure applied to the pedal. with a full and bled clutch system.If you can get that with the eccentric provided you are in business. What I really suspect is in a lot of cases the piston is just moved ahead enough to either semi obstruct of totally obstruct the port in the master clutch cylinder.

So there is really no issue with the clutch. Plus no difficulty in bolting it on after the system is filled and bled. They had to be doing something other than playing around of the assembly line trying to get this clutch hydraulic system filled and bled. If you had to push really hard to get the rod bolted to the pedal arm up after filling and bleeding. Then you have a concern with the rod length. Because you have lost the mechanical advantage the pedal arm provides. You are probably not strong enough to move that piston past the fill port anyways. So you could not bolt it up.