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View Full Version : TR2/3/3A Clutch Swallows Air -- TR3



Moseso
08-07-2012, 01:49 PM
Today, I present my baffling and annoying problem.

Air gets into my clutch hydraulics even though FLUID DOES NOT LEAK OUT.

The specifics:
1) Bubbles are in the slave cylinder, which is to say, low in the system, not up in the master. Three pumps on the pedal while bleeding and they are gone.
2) Sometimes this happens after 3 months. Sometimes only 2 weeks between bleeds.
3) The fluid level in my reservoir goes UP -- displaced by the air that somehow gets in. There is NO indication of fluid loss. Only air ingress.
4) It seems to happen overnight -- as in -- the car was driving just peachy when garaged for the night. I get in to start it in the morning and my clutch is WAY down from the last time I pushed it.
5) Sometimes it happens just a little bit. I notice the clutch pedal is a <span style="font-style: italic">little</span> lower -- and I can pump it up -- but it's not so bad I have to bleed it right now. It may stay that way for weeks and then, bango, see item 4.

I can think of no mechanism whereby this should occur. Therefore I am at a loss as to what to fix. Last year, I rebuilt the master, hoping to cure this. I am about to R &amp; R the slave, but I don't know why. I'm just swatting at things that <span style="font-style: italic">could</span> be the culprit, without any real treatment plan.

Comments? Suggestions? Excorcism will not be considered without a sound theological discourse.

TR3driver
08-07-2012, 05:02 PM
How's the return spring on the slave? Have you tried pushing the pushrod back into the cylinder by hand?

The slave spring should always immediately return the slave piston against the internal stop, but if the spring is weak (or someone has tried to substitute an old screen door spring or whatever), it may not always return the piston. If the spring inside the MC returns the master piston faster than the slave piston, it might pull somewhat negative pressure on the hydraulics, which might pull air past a worn slave seal.

Not likely, but the only thing I can think of offhand.

TomMull
08-07-2012, 06:31 PM
I am about to R &amp; R the slave, but I don't know why.

That's what I'd do, for what it's worth.

Tom

sp53
08-07-2012, 08:55 PM
You Might not be experiencing air, but rather the plunger just going right down without generating any pressure and not leaking yet. I would try a new and different master cylinder.

Moseso
08-07-2012, 09:00 PM
I'm with you, Randall. Negative pressure inside the slave could easily draw a little air past the rubber seal. Sadly, I have a perfectly fine spring, drawing the clutch lever back into the slave -- not to mention that the clutch cover springs would <span style="font-style: italic">certainly</span> prevent negative pressure inside the slave. My rod-to-slave freeplay is negligible -- almost bottomed.

This one's got me buffaloed. I've been rebuilding hydraulic car parts since 1969. In all that time, I've never seen these symptoms. Where's my sound theological argument -- so I can decide to perform an exorcism? Short of that, where's my negative pressure in the system?

Moseso
08-07-2012, 09:02 PM
You Might not be experiencing air, but rather the plunger just going right down without generating any pressure and not leaking yet. I would try a new and different master cylinder. I am definitely experiencing air. Bubbles definitely bleed out when I decide that the car won't run without another clutch bleed. Then it works right (for a while) again.

tdskip
08-07-2012, 11:26 PM
I'm a game as the next guy for a good exorcism, but wouldn't a seal on the way out display very similar symptoms?

TexasKnucklehead
08-08-2012, 12:16 AM
I see some Master Cylinders with bolts at the end to limit the return of the MC piston and/or pedal travel. Is it possible yours are too far out, allowing the piston to travel so far back that it allows air in, without letting fluid out? Seems unlikely.

Sarastro
08-08-2012, 10:36 AM
I like Randall's assessment of the situation, even if the spring is OK.

The seal in the slave cylinder is designed to seal against high pressure in the cylinder. If the pressure inside is below that of the atmosphere, it's easy for air to leak past the seal into the cylinder. I've had this happen with my Bugeye Sprite.

Even if everything appears to be OK, it's possible that somehow, sometime, you might have a situation where the return of the piston in the slave is sluggish, and you get a little air into it past the seal. This situation may not present itself easily or often, but you stated that it happens only occasionally, so I think it all makes sense.

I'd rebuild the slave cylinder. When you do that, check carefully for pitting, and hone it out well anyway. Even though I've worked with seals a lot (high vacuum, not in the zoo), I'm continually amazed at how a seemingly perfect surface and new seal still can leak. If it's not perfect, you're all that much worse off.

CJD
08-08-2012, 11:02 AM
Check the vent on the reservoir. Fluid gets hot and expands. Fluid cools and contracts, making a vacuum and pulling air in. If it can't come in through the vent...it'll find another way.

John

Moseso
08-08-2012, 12:24 PM
John --
I like this idea. It goes well with the "happens overnight" symptom.
A simple fix, too, if it's the issue.
If it is the issue, thank god it isn't happening to the brakes too!

Will report on findings...

TR3driver
08-08-2012, 02:29 PM
Check the vent on the reservoir. Fluid gets hot and expands. Fluid cools and contracts, making a vacuum and pulling air in. If it can't come in through the vent...it'll find another way.

Good thought!

If the vent is OK, you might double-check that the pedal is returning fully every time. If the MC piston were remaining just slightly depressed sometimes (enough for the 'foot' valve to stay closed), you could possibly get the same effect.

tomshobby
08-08-2012, 08:58 PM
Just had the same problem. I had just driven 1500 miles to Provost, AB' The next day the clutch went to the floor with out disengaging. My cousin put it up on his hoist and we found much air in the cylinder. Only having domestic car and truck parts we rebuilt the slave and bled it. It worked great so we though it was fixed. That evening we went to the Bunnock championship matches at Macklin, SK. When we were leaving the clutch had the same symptoms.

So we decided to make the drive from Provost to Calgary with no clutch to connect with Dave More who is also a TR6 driver. And along with his neighbor Shawn, have a considerable catch of TR parts. A different master cylinder did the trick. Tonight we are in Jasper, AB after a beautiful 7 hour drive in the Rockies.

My slave and master were both less than a year old. GIGO.

Moseso
08-09-2012, 12:23 PM
I pulled the cap on the reservoir and took a look. I had been unable to find a proper sized gasket for the top, when I was putting things together, but I found a generic brake reservoir cap rubber gasket at the FLAPS. I trimmed it to fit the TR cap, and poked a hole in the center of it. It is not a ring, it's a disc. Looking at this arrangement, I decided it is conceivable that it <span style="font-style: italic">could</span> have sealed the cap vent, on occasion. So I cut the center out of it, totally clearing the vent in the metal cap.

<span style="font-style: italic">MAYBE</span> this will prevent recurrence of my weird-ass clutch mystery. Time will tell. I'll burp it again, just to be sure I'm getting a good fresh start, and see what happens. If you never hear me complain about this again, that will mean "good news."

CJD
08-09-2012, 01:05 PM
Well, that will fix the air sucking, but now you will get brake fluid out of the vent hole. The way this arrangement works is that the rubber gasket acts as a bellows. It moves to allow pressure in and out, but it is supposed to totally seal the fluid in...no holes at all. The vent that needs checking is the one in the metal cap. It allows air to the top of the bellows gasket to equalize the pressure in the system as the fluid expands and contracts.

John

TR3driver
08-09-2012, 02:47 PM
John, I think Moses' point was that his generic seal is flat, and blocked the original vent through the metal cap. The original TR3 reservoir (and even later TRs as I recall) did not use the bellows arrangement that you are talking about.

If you or anyone knows of a bellows seal that will fit inside the TR3 reservoir cap, I would like to know about it. Strikes me as a very worthwhile modification, not visible to a judge (not that I care about judges).

Geo Hahn
08-09-2012, 03:25 PM
...If you or anyone knows of a bellows seal that will fit inside the TR3 reservoir cap, I would like to know about it. Strikes me as a very worthwhile modification, not visible to a judge (not that I care about judges).

One of the local Healey guys (same reservoir as the TR3A I think) came up with a GM seal from the Help! section of the FLAPS.

Possibly this one: https://www.dormanproducts.com/p-21904-42104.aspx

https://www.dormanproducts.com/images/product/icon/42104-007.JPG

Can't guarantee a fit as I held one in my hand but didn't get to actually try it on the TR.

TR3driver
08-09-2012, 03:39 PM
Cool, Thanks! I'll see if I can pick one up.

Moseso
08-10-2012, 10:49 AM
That looks a lot like what I have. What I had before was a fiber ring that sealed the cap to the edge of the reservoir -- but was open in the center. The TR cap appears to hope to contain the fluid by a "labyrinth" of sorts. If the res is filled just to the top of the center tube, I get no fluid escaping through the vent.

CJD
08-10-2012, 06:26 PM
Sorry, my seal from Moss was a bellows, so I assumed this is the way it was supposed to be. It looks like the pic above. An interesting point...every time I remove my cap the bellows is sucked down towards the reservoir.

John

Moseso
08-13-2012, 02:19 PM
Well... There IS another problem. My cap vent is demonstrably clear &amp; open -- yet, I lost my clutch again, Saturday night. Clutch was "low" but useable on the way to my gig. Two hours later, when I went to start for home, the clutch was useless. Grrrrrrrrr...

TR4nut
08-13-2012, 03:21 PM
Collapsed line potentially? Hard to think of ways to pull vacuum and get air in there

TomMull
08-13-2012, 06:53 PM
I know you said that you just did the master but a bad master would account for all your problems. Note Tomshobby post above.
Tom

Moseso
08-13-2012, 09:44 PM
I am confident of the master -- and its adjustment -- and, further, don't know how it could make bubbles in the slave cylinder without filling the feed tube first.

Collapsed line? That would make some sense, too, except my line is also &lt; four-years-old.

I suppose I should replace it (cheap enough) when I rebuild my slave. I'm really swinging in the dark at "why." I am certain of the symptoms but have no idea why. Fortunately, these are all cheap-&amp;-easy repair projects. But, dang it, I want to know WHY!

Also -- Fortunately, I am adept at driving with no clutch disengagement mechanism. There is talk of this in another current thread. I've driven my '65 Volksy bus for days with no clutch (broken cable). Also my '65 BMW cycle (ditto) (also, easier). Why don't they sell these oft-needed parts at the corner 7-Eleven? That's how I got home, last Saturday night. Speed-shifting, and watching way ahead for the signals.

TR3driver
08-13-2012, 10:05 PM
and, further, don't know how it could make bubbles in the slave cylinder without filling the feed tube first.
Easy, all it has to do is block the return port (sometimes) while the fluid cools overnight.

I'm not saying that is the problem, just explaining how the MC could cause the slave to suck air.

tomshobby
08-13-2012, 11:22 PM
I do plan on taking my MC apart when we finally get back home next weekend. Very curious to see what I find. If I get really ambitious I will also take the slave apart to show the parts I used to rebuild.

Geo Hahn
08-23-2012, 03:18 PM
...If you or anyone knows of a bellows seal that will fit inside the TR3 reservoir cap, I would like to know about it...

One of the local Healey guys (same reservoir as the TR3A I think) came up with a GM seal from the Help! section of the FLAPS...

Correcting my prior post, I picked up said seal at O'Reilly's but the Dorman p/n I had was not in their system. This is the one I found on the hook:

https://i1214.photobucket.com/albums/cc499/Ahwahnee18/TR3/BrakeReservoirGasket.jpg

It is just a skosch larger that the original seal but fits the Girling cap just fine:

https://i1214.photobucket.com/albums/cc499/Ahwahnee18/TR3/BrakeReservoirGasket2.jpg

Moseso
09-05-2012, 01:40 PM
STILL sucking air...

Did the slave cylinder, Saturday. Readjusted the pedal free-play on the master. The foot valve is demonstrably opening and closing. Becky pressed the clutch while I watched in the reservoir. There is a little spurt of fluid into the reservoir, just before the foot valve closes at the beginning of the stroke. Also, if the foot valve didn't open, I wouldn't be able to bleed the system -- no fluid could get into the master.

The problem has worsened. I can't get two days out of my clutch without it becoming totally inoperative.

The collapsed hose theory doesn't have much appeal to me, as I can see and feel the clutch returning smartly. There is no restriction in the clutch travel, either way. It's the only thing I haven't touched yet, so I'll probably replace it -- but I have lost all faith that I can repair this.

Reservoir cap vent: OPEN <span style="font-style: italic">check</span>
Master cyl: Rebuilt 2011, foot valve demonstrably doing it's job. Exterior dry as a BONE. <span style="font-style: italic">check</span>
Slave Cyl: Rebuilt last week. Interior shiny. Exterior dry as a BONE. (Oh, alright, it had a film of motor oil on it, but I don't lose fluid) <span style="font-style: italic">check</span>
Hose: untouched, but isn't restricting clutch movement in any discernible way. No <span style="font-style: italic">check</span> yet.

WTF else????

Starting to feel like composing a Craigslist ad. "Cool TR3 -- Needs a little work."

OR -- and this is a better idea -- convert the car to cable operated clutch! I'll bet I could cobble something together.

TexasKnucklehead
09-05-2012, 02:36 PM
I'd scratch the craigs list and cobbling ideas before you start regretting it.

There is a clevis adjustment on the rod at the slave and one on the master. Is it possible you are over stroking the M/C? When the pedal is the whole way in, the piston (and seal) could be forced against the bottom of the M/C. Maybe it has nothing to do with your issue, but it's worth a look.

Geo Hahn
09-05-2012, 03:49 PM
Have you rebuilt the master cylinder? If a slave fails it will leak but most M/C failures I have had presented no leak, just marginal or ineffective performance.

What has failed on those has been the little seal at the end of internal bits. This one:

https://i1214.photobucket.com/albums/cc499/Ahwahnee18/TR3/M-C-1.jpg

I think it works like a check valve and when it fails some fluid gets past it and back to the reservoir.

Moseso
09-05-2012, 04:40 PM
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I think it works like a check valve and when it fails some fluid gets past it and back to the reservoir.[/QUOTE]

Exactly right. And then you get no (or reduced) pressure down the line to the slave. Sadly, not my problem. My problem is air getting into the system from somewhere. When freshly bled, and not full of bubbles, The clutch operates just as it should. Then it gulps down some more air -- and doesn't operate at all like it should.

And, yes, the master cyl. was the first thing I rebuilt -- just last summer. I've got another kit on the way.

(Knock wood, knock wood, knock wood -- I can't even believe I'm saying this out loud) I'm sure glad it's the clutch doing this, and not the brakes!

Moseso
09-25-2012, 11:09 AM
About three-or-four weeks ago, I bled the clutch, got in the car -- and didn't even make it 1/4-mile before losing my clutch pedal. So I put the car in the garage and waited -- first, for parts and, second, for time to work on it.

Yesterday, I got around to it. First, I replaced the cover gasket on my leaky rear axle. I think I got it this time...

Then I drained the clutch hydraulics. I looked at the hose to see if it had the problem that Randall describes. Nope. It looks brand-new -- which it pretty much is. So, with nothing else left to work on, I threw a new seal kit into the master cylinder. Nothing looked amiss inside there -- good looking seals, shiny bore -- but, what the heck, a seal kit is cheap enough, and it's just not that hard a job to do.

Becky wasn't around to help me bleed the system, so I thought I'd try to "gravity bleed" it, as I've read about here. Boy, howdy! Does that ever work slick! I just put some fluid in the reservoir, crawled underneath and opened the bleed valve, and, after about a minute, there was fluid running out of it. I closed it up, thinking, "If I actually have a clutch, I'll be a monkey's uncle." When I climbed in and pressed the pedal, it felt fine-and-firm. Ook, ook!

So far: yesterday's test drive and this morning's ride to work, the clutch works just fine. It worked fine like that for a year, after the last time I rebuilt the master -- and then began sucking air again.

I STILL have no idea how this failure occurs, but I think I have proven that, if you just tear the whole system apart and rebuild EVERYTHING, you have to at least be touching the cause.

mrv8q
09-25-2012, 02:59 PM
Congratulations! Persistence pays off!