T-Series '80 MGB Clutch Master Cylinder-rebuild or replace

[Henson80MGB]

OK, this is a new question, but a continuation of my saga to get the clutch to work following the winter hibernation.

I have seemly successfully been able to replace the leaking slave cylinder, and with some persistence. I was able to remove the old rubber hose and install the new new from Moss. (the new one was between 1/4 - 1/2" shorter, but seemed to connect fine.

HOWEVER, in bleeding the clutch I'm still not getting any pressure in the lines.

After about 20 min of having the clutch pumped many times, holding and me opening up the bleeder valve getting the air out and closing the valve and repeating many, many rounds. (and making sure the fluid is full in the master cylinder) It seems the air is out, but I may be getting about 3 drops of fluid out for each round, and I see no movement on the push rod to the transmission.

I don't see any leakage at the steel hose connection at the master, the steel hose to rubber seems solid, and the rubber to slave has no leaks. The new slave I put in was moving, but was airtight when I tested before installing it.

A post indicated it did sounded to them like the Master cylinder and if I looked in the reservoir I should see the fluid going up when I pump. So, I looked and saw no sign of any fluid movement, but still started in on removing the Master Cylinder.

But,

1) started to remove the master cylinder and check out the seals. But how to gain access to remove the lower bolt on the master cylinder seems to be evading me.

2) So I thought I'd do some more "tests" with the master cylinder in place.
- I removed the steel line connector from the master cylinder.
- I held my thumb over the connection and had the clutch pedal pushed gently.
- fluid comes out with more pressure than I could hold!! But when I reconnect the steel line to the master cylinder and hold the other end (disconnected from the robber hose) with my finger over it, there does not seem to be nearly as much pressure on my finger.??
- Also when the pedal is pushed down and I keep my finger over the line connection on the master cylinder, the clutch pedal does not rise to the top, but rather is kept down by the vacuum being created by the finger over the line connection?

Again, it has been a long time since I worked and thought about this type of system, and chalked up the behavior to correct operation of the master cylinder, pushing and pulling the fluid.

So I thought maybe the steel line had developed a leak, but the steel line holds both pressure and vacuum.

So now, I'm rethinking and going beck to the Master Cylinder and realizing that the pedal being kept down by vacuum may not be correct. Shouldn't the master cylinder pull fluid from the reservoir and let the pedal back to the top to pump more fluid?

Is it possible for a master cylinder to "fail" in a way to not pull more fluid from the reservoir to refill the lines?

I connected everything back together and tried Bleeding again, but waiting 30 - 60 seconds between releasing the clutch pedal (following opening and closing the bleeder value); and starting to pump again. {attempt to let fluid seep in to the cylinder from the reservoir?)

This methods now results in getting pretty much a steady of fluid when I open the bleeder value, but not really with any pressure and the clutch pedal still has no resistance to speak of.

So, I'm really back to thinking something is wrong with the master cylinder.

So my two main questions are;

1) It seems the master cylinder can be rebuilt "in the car" from some searches, but is that really going to work well?

2) Is it better just to get a new master cylinder? Or if it's better to rebuild outside of the car?

If so, is there a trick to getting access to the lower master cylinder bolt to remove it?

Thanks, as always, Larry

 

[DrEntropy]

For the best solution, I'd say replace the M/C.

As for that bottom nut/bolt, the real trick is getting a long 1/4" extension and a swivel socket to access it. It <span style="font-style: italic">IS</span> a contest, though.

 

[sd80mac7204]

 

[JPSmit]

Not sire how the B compares to a Midget but I always try rebuild first. partly because the quality of old parts is typically better but mostly because a rebuild kit is cheap - cheap enough that if it doesn't work it doesn't matter while a new one gets pricey.

However if you get it apart and the cylinder is pitted, just buy a new one, don't ask me how i know.

 

[SilentUnicorn]

is not there access to that bolt from under the dash? after you remove the rubber plug?

I vote for new. That way (hopefully ) you only need to change it once....


m

 

[Shinsen774]

A set of these from Harbor Freight for $14.99 makes a world of difference on that bottom nut.

I found the rebuild didn't last long and I eneded up buying a new M/C anyway.

 

[Scott_Hower]

+1 on the rubber plug and a long 1/4 extension. That's how I did mine.

 

[DrEntropy]

That make an easy job of it, for certain.

 

[SilentUnicorn]

actually wrenches like These work real well in that situation.

once the nut is loose you can unlock these and do a push, pull thing.


m

 

[Henson80MGB]

So many TOOLS to choose from!!!!!!

And all to get the car my wife loves to drive (me too) back operational!

 

[Henson80MGB]

And with the use of the new s-wrenches, I was able to get the lower master cylinder bolt out. Then in removing the master cylinder, popped out the rubber cover to the underdash (which I didn't realize or understand the reference to in earlier posts )

Any way all put back together and I can shift gears!!!!
to all the great input.

Battery back in, started right up, and drives nicely again, seems to be ready for the summer (until the next crisis but that's half the fun right !! )