• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Question- and I don't have a clue

Share this page

jlaird

jlaird

Great Pumpkin
Country flag
Offline
The clutch side of the MC and line and slave cylinder is a straight push pull form the MC to the Slave. Correct?

Easy to push fluid down the line to the slave, lots of pressure.

Now what pulls it back, only that smallish spring in the MC?

So, and please, correct my thinking if necessary. If that spring was weak which is unlikely or there was junk in the line it would not pull back to the MC as fast as it should. Correct?

The more RPM on the engine the harder the clutch engages, therefor the more force is needed to move the slave.

You all know the prob I have shifting quickly over 3500 RPM, the pedel goes down to the floor like there is air in the line, not. Also the other day when messing as I came to a stop sign the pedel went all the way to the floor on the first push, one pump and it was ok. Oh yea, when shifting at High RPM if I pump the pedel it is preaty much ok.

Now for the real question, have I still got crap in the line that needs cleaned out. Like small chunks of something that move back and forth? and slow the action. I can not see any slowing when the engine is off and I am under the car watching as the pedel is pumped as fast as it can be.

How about this, remove fluid from MC with a baster or something, remove line from slave and MC, fit a plastic hose firmly over each end (even clamp them) and put the compressed air to it both directions into a bucket with a bit of a strainer and see what comes out? I can go to 120 pounds of air without prob.
 
Jack, is there any evidence of fluid at the front cover-plate on the MC? You actually may not see any there but the bore on the pushrod side could be getting wet (it should stay dry!)! It still sounds to me like there is fluid getting past the cups in the MC which would make it feel like there is air in the line! The little spring at the MC should be adequate to do the job, along with the hydraulic pressure on the fluid in the system, but if a cup is bad in the MC, then the hydraulic pressure would be diminished! Does that make sense? I had a problem like this on the brake side once and it was all due to a TINY slice/cut in one of the cups allowing fluid to get by, only when pressure was applied to the pedal!
 
Yep, that does make sense but I see no fluid there. Will remove the front cover and check it out for sure though.
 
Jack,

The people who rebuilt your MC don't have exactly a stellar reputation. I've heard their name taken in vain by more than one poster to several different lists I subscribe to. I bit the bullet when redoing Bugsy's Master ans Slave and went all new. In my case the old Master ans Slave were disconnected and laying in the trunk. It cost me some $300+ 6 years ago but MC and Slave have been "knock on wood" 100% trouble free. Now I've got the tandem in my '68 but not an issue.
 
The reason I went with White Post is that I had used them before. Back about 1974 and never had a problem.

The MC does have a lifetime warenty on it, if I can figure what is wrong I will send it back for a redo.
 
Jack
Have you tried adjusting the master push rod?
Sounds like your fluid is not returning fast enough.
If the adjustment is "at the border" all will seem OK until you try to shift fast.
Try loosening the rod by about 1/2 a turn.
Also, if your clutch pedal is way at the top, the rod is too long thus not returning past the bleed back hole in the master thus making for no fluid when you go for the clutch the next time.
You could try cruising at high rpms in 3rd for a while before shifting to 4th, the extra time should allow the fluid to return, if this works, it's the rod length for sure.
 
Oh my gosh Frank, I forgot about that bleed back hole. I have that sucker adjusted way high, in fact as high as it will go I bet.

I will try your suggestion in the last couple of lines as soon as the weather allows, like fri or sat. That is if I can wait that long.
 
Exactly what I was trying to ouline, Jack, the weep-hole would act like a fault in the cup! EASY fix (I'll keep my fingers crossed!)!!!! /bcforum/images/%%GRAEMLIN_URL%%/thumbsup.gif
 
Jack, how old is your clutch line? I have seen comments in other related threads that indicated that an old clutch line can collapse internally causing a restricted flow of fluid. If all else fails, you might look there.
 
65 sprite, that would only apply to the flexible section of the line! I believe Jack has a hard line all the way to the slave (standard for the BE!)!

Jack, judging by the weather down here, you will be lucky to get to it by Fri. Sat or Sun. should warm up enough (at least I hope...work is starting to backlog!!) /bcforum/images/%%GRAEMLIN_URL%%/eek.gif
 
The strong springs in the pressure plate are what pushes the slave rod back into the bore and the fluid back upstream.


Glen Byrns
 
Hard line all the way.

I still am convenced I got junk in there that does not allow the MC to reload timely.
 
Hi, sureley if there was something in the slave or line stopping the fluid going back to the MC then the clutch would remain depressed and slip?Is the run of the pipe to the slave anywhere too close to exhaust making fluid too hot?
 
Had another thought about the idea of the seals in the MC being bad,:-if you keep your foot on the clutch pedal for a long time does the car start to creep?If the seals were letting by in the MC I would expect this to happen.If not I would think the seals are ok.
 
jlaird said:
You all know the prob I have shifting quickly over 3500 RPM, the pedel goes down to the floor like there is air in the line, not. Also the other day when messing as I came to a stop sign the pedel went all the way to the floor on the first push, one pump and it was ok. Oh yea, when shifting at High RPM if I pump the pedel it is preaty much ok.
Click to expand...

I had exactly this problem with my bugeye, and all it did was to convince me that I don't understand master cylinders very well. I wish I had a solution; I'm eager to see what you find out.

First, what is the "bleed back hole" in the MC? Is this just the hole from the MC reservoir into the cylinder? Or is there something else I'm not aware of?

I've noticed that I can push the piston of the slave cylinder back into the cylinder, forcing fluid back into the MC reservoir. I'm surprised that this is possible. It seems that fluid is getting past the outer seal of the piston (the one on the left in the figure below), in the reverse direction. Then, when you step on the clutch, the rightmost seal passes the hole, and there is no path for fluid to get back into the reservoir, so it holds pressure and the clutch operates correctly. This makes me wonder what the leftmost seal is supposed to do. Maybe it seals only at high pressure; I dunno.

I eventually concluded that this was happening: at high speed, centrifugal force was causing the pressure-plate release fingers to push outward, forcing the release bearing backwards (away from the pressure plate), and forcing the piston back into the slave cylinder. This pushed fluid back into the reservoir, so, next time I pushed on the clutch, it went almost to the floor. Then, a couple more strokes filled up the system with fluid again, and it operated normally. I found that small pressure on the clutch pedal, so the rightmost seal was past the reservoir hole, prevented this.

So, what to do? You could limit the travel of the release fork, but then there would be pressure on the graphite bearing, which would wear it. Or, you could try a different pressure plate--but that's an expensive experiment. Since I have the whole thing apart right now, I'm trying the latter--I should get it back together in a week or so, and I'll let you know how it works. I'm also planning some experiments to test my my hypothesis about the pressure-plate fingers.
 
Got to be, I got dirt. Soon as weather warms up again I will go after it.
 
Back
Top