Clutch keeps losing pressure.

[ramen tamer]

Hey, y'all. 

I have this chronic issue where, if my car sits for a couple days, it seems like I get air bubbles in my clutch.  I generally just bleed it and top off the reservoir.  But, it just happens again shortly down the line.  Sometimes it takes months for the issue to resurface, sometimes just weeks.  Always after it's had a day or two of not being driven.

 

Anyone have any idea what's causing this and how to permanently fix it?  I mean, I can just keep bleeding the bastard, but it's annoying when I'm trying to go to work and have a surprise maintenance issue to deal with.  Then I got slippery Dot 3 hands all day.  Obnoxious.

[Stoffregen Motorsports]

A car that sits for a long time between drives can accumulate moisture in the hydraulic fluid. That moisture can cause corrosion in the steel/iron slave cylinder and that buildup of junk can cause the seal to fail.

 

I bet if you disassembled your clutch slave you would find a buildup of crud. Usually all you need to do is clean it out and reassemble the slave and flush the old fluid out.

 

Let us know what you find.

[ramen tamer]

Thanks!  I'll dig around in that. 

 

I think the car sat a lot before I started using it as a daily driver.  So, I think you might be onto something. 

[datzenmike]

You don't mention any leaks. The system is under strong pressure in use and slight positive pressure at all other times. If you loosen the bleeder, fluid siphons down hill from the reservoir. So for air to get in, fluid must be getting out.

[Stoffregen Motorsports]

It's not under pressure when it sits.

 

My 320 had a similar issue with the rear brakes. Nothing leaked, but it did suck air from getting crud in the wheel cylinders. The crud was like a slightly crusty sludge. I cleaned them out and installed a 2 psi residual valve and never had a problem again. You can't install a residual valve on a clutch though...

 

Another spot it could be sucking air is at the pedal. Many people don't notice fluid leaking down their clutch (or brake) pedal, and the carpet usually hides it. If it's leaking there, you need to rebuild the master, or get a new one.

[datzenmike]

Not under much pressure but under the vertical weight of the fluid above the slave. I've never yet had to pump the clutch to bleed it. Open the bleeder and it runs out. I can't see air finding it's way in against that. Again, leaks were not mentioned. If there was wetness anywhere that might be different.

[Stoffregen Motorsports]

Sometimes the rest of the vehicle is so dirty that leaks aren't even apparent.

 

I hate dirty drivetrains.

[datzenmike]

1 hour ago, Stoffregen Motorsports said:

 

 

I hate dirty drivetrains.

 

[Thomas Perkins]

Maybe the seals in your clutch master cylinder are bad.Is the fluid like black and not yellow.I got mine from Autozone and never have to buy another one ever.They are 19.99 here. I would replace it and disconnect line at slave cylinder and drain all the fluid and install new brake fluid.Also get a slave cylinder for 16.49 and check the hose at the slave cylinder.I replaced mine not long ago.Oreilly's have them for 10.49.For 11.99 more get a clutch switch that goes on your clutch pedal,same as break switch.

[datzenmike]

I don't know... If the master seal is bad and it can't push fluid it must be getting squeezed back behind the seal on the pedal side. If that's the case fluid would eventually drip down on the carpet and the reservoir would need topping up.

[Thomas Perkins]

Mine was leaking and getting my carpet wet.I replaced everything .I first thought it was the Slave cylinder,I replaced the slave cylinder,hose that is connected to it cause hose was coming apart and clutch master cylinder,had warranty to all except hose and it is fixed,that was a good time ago.The clutch master cylinder didn't leak real bad.Also put a new Nissan boot at the slave cylinder that goes into the transmission.

Edited December 25, 2021 by Thomas Perkins

[ramen tamer]

Sorry for disappearing on y'all.  I've been busy, but I'm back with answers and updates.

 

Anyways, like Mike said, when I open the bleeder, fluid freely leaks.  So, it's not sucking air bubbles in. 

 

In between when I made the topic and now, I only just got the chance to poke around in the car.  I was fixing a minor, possibly major later, electrical issue and started up the car to see if it still shot sparks at me.  It does not.  So, I thought I might pop off to the store and get some beers.  No clutch, again.  That's to be expected, so I opened the bleeder and topped off the master.  This is always how I get the clutch to work after it sits a while.  But, it still didn't work.

 

So, I tried to do a proper bleeding.  With the assistance of my loving wife, we bled the clutch for what was about two whole master cylinder reservoirs worth of dot3.  Step, open, wait, close, release...repeat.  The entire time, the fluid was coming out very frothy and my wife would consistently report that there was no increasing pressure on the clutch pedal.

 

SO!  I decided to put in an order on rockauto for a new hose, master cylinder and slave cylinder.  Figure, I might as well get the whole damn set in case there are multiple issues.  After that, I went poking around the car some more, because I wanted to see why the fluid kept frothing.  I saw what I think is the problem and it should be pretty easy to fix...

Y'know the rubber seal on the master cylinder on the driver's side of the firewall?  Yeah, I ain't got one of those.  Don't know where it's gone, but it is gone.  I know that it used to be there in some capacity.  I seent it.  I'm guessing that without the seal, the little plunger in there is pulling in a bunch of air and that's why I can't get any pressure on my clutch.

To test this theory, I'll replace the master cylinder first and do a little test before replacing the slave cylinder.  I like Stoffregen's theory and even if it isn't the current issue, I'm sure it will be, soon.  And then I'll test again before replacing the hose.  My hose seems fine, but I already bought the new one, so I might as well use it.

 

Cheers!

[ramen tamer]

On 12/23/2021 at 12:09 PM, Thomas Perkins said:

Maybe the seals in your clutch master cylinder are bad.Is the fluid like black and not yellow.I got mine from Autozone and never have to buy another one ever.They are 19.99 here. I would replace it and disconnect line at slave cylinder and drain all the fluid and install new brake fluid.Also get a slave cylinder for 16.49 and check the hose at the slave cylinder.I replaced mine not long ago.Oreilly's have them for 10.49.For 11.99 more get a clutch switch that goes on your clutch pedal,same as break switch.

 

Can confirm that the fluid is black.

[Stoffregen Motorsports]

The boot on the master inside the cabin is only a dust boot and does not seal any fluid or air, so replacing the boot won't fix the problem. Did you notice if there was fluid leaking inside the cab?

 

Black fluid is a sign of serious crud inside the system. If it's black at the reservoir, then the inside of the master is likely the problem.

Edited January 24, 2022 by Stoffregen Motorsports

[ramen tamer]

Ah.  Didn't know it was just a dust cap.  I'm fitna replace the whole master cylinder anyways.  Figured if it was a little crummy, fixing part of it won't do.  Might as well fix the whole thing so it doesn't just break in another month.

 

I haven't noticed any fluid in the cab, but I rarely look at my feet.  I can go pump it a bunch of times and see if anything happens.  Though, there's so little pressure in the system right now, that I'm not sure I'd get a leak even if I tried.

 

Yeah, it's black in the reservoir.  I'm going to replace everything, though.  Master, hose and slave just to make damn sure I solve the problem.

[banzai510(hainz)]

hoses dont go bad I would just replace what is needed esp if a stock clutch. you might introduce more proplems but buy it as a spare if needed now while the parts are for sale

Edited January 25, 2022 by banzai510(hainz)

[Stoffregen Motorsports]

Hoses do go bad. They swell up on the inside and can trap pressure or restrict flow, or both.

 

With the entire parts package costing only about $150, I'd replace everything. And flush the hard line while you're at it. No sense chasing a problem when you can have an all new system for less than a couple hundred bucks.

[datzenmike]

Seen a brake flex line go up like an aneurysm under load. Easy enough to check, just watch it while someone pushes the clutch.

[Stoffregen Motorsports]

Sometimes you can't see it.

[datzenmike]

You'll see it swell if it does.

[Thomas Perkins]

Maybe it's the way you are bleeding it.You may be letting air back in.I use a one man bleeder kit from Autozone.The container has a magnet on it and stick it high up so air can't go back in it and you can do it your self.Black fluid is caused by the rubber gasket deteriorating from the master cylinder.https://www.autozone.com/test-scan-and-specialty-tools/brake-bleeder/p/oemtools-one-man-brake-bleeder-kit/46839_0_0. When I did mine,I replaced everything and have a lifetime warranty on it and never have to buy again,except the hose.I get most of my parts from Autozone cause of the lifetime warranty.

[Thomas Perkins]

Here is a story from my Archives.This happened many years ago.I got off Work and it was getting dark.I put my key in the 720 and pushed my clutch in and it went all the to the floor with no pressure and I said the slave cylinder went out.I called my wife and she came.While I was waiting,I thought maybe I can bleed it and it would hold till I got home and it did.I didn't have my one man bleeder kit with me but she brought it..Believe it or not...

Edited January 27, 2022 by Thomas Perkins

[DIY 1985]

When a slave cylinder is bad, there could be a bit of rust, some crud, and wear on the seal.  I could see how this could cap the system when the slave piston travels in one direction (pressure from the master).  The pushrod might also be pushing back at an angle, and not on the exact axis of the cylinder and piston.  Wouldn't the master create negative pressure when the pedal is no longer depressed, and until it travels to the point where its piston seal meets the fluid from the reservoir?  With negative pressure on the system, that could draw air in at a half-functioning slave cylinder?

[ramen tamer]

On 1/25/2022 at 9:58 AM, Stoffregen Motorsports said:

Hoses do go bad. They swell up on the inside and can trap pressure or restrict flow, or both.

 

With the entire parts package costing only about $150, I'd replace everything. And flush the hard line while you're at it. No sense chasing a problem when you can have an all new system for less than a couple hundred bucks.

 

Less than $150 for the parts.  I think it was $50 for master, slave and hose.  I didn't change the hose.  I'll just save it for later, like Banzai suggested. 

 

22 hours ago, Thomas Perkins said:

Here is a story from my Archives.This happened many years ago.I got off Work and it was getting dark.I put my key in the 720 and pushed my clutch in and it went all the to the floor with no pressure and I said the slave cylinder went out.I called my wife and she came.While I was waiting,I thought maybe I can bleed it and it would hold till I got home and it did.I didn't have my one man bleeder kit with me but she brought it..Believe it or not...

 

So, my issue is similar and it's been going on for some time.  Generally, if my car sat for a couple days, like when I'm not driving it over a weekend, on Monday, I couldn't shift.  I would just open the bleeder, let it drip and top off the fluid.  Then it would work all week.  Repeat next Monday.  It was weird.

 

23 hours ago, Thomas Perkins said:

Maybe it's the way you are bleeding it.You may be letting air back in.I use a one man bleeder kit from Autozone.The container has a magnet on it and stick it high up so air can't go back in it and you can do it your self.Black fluid is caused by the rubber gasket deteriorating from the master cylinder.https://www.autozone.com/test-scan-and-specialty-tools/brake-bleeder/p/oemtools-one-man-brake-bleeder-kit/46839_0_0. When I did mine,I replaced everything and have a lifetime warranty on it and never have to buy again,except the hose.I get most of my parts from Autozone cause of the lifetime warranty.

 

Oh, man.  Bleeding it after putting the new parts on took some effort.  I spent way too long under the car, with my wife on the pedal.  My shoulder is sore from opening and closing that damned valve.  I got it this morning, though.  I got one of those cheap $10 bleeder kits and just grabbed one of the little hoses and one of the little nozzles.  Then, I took a cooking syringe and sucked up some Dot3 into it.  Then crammed the nozzle into the hole in the master cylinder and pushed the plunger on the syringe down, forcing the fluid through the system.  It worked brilliantly.  A little too brilliantly.  Before I did all this fixing, my clutch pedal would have to hit the floor to engage.  And lifting it any amount would disengage the clutch and car would go.  Now, it's right at the top.  I lightly press the pedal and clutch engages.  And it doesn't disengage again until I'm back at the top.

Since I'm used to smashing the pedal to the floor, I have a lot of re-education before I do much driving.  Living in Seattle means steep ass hills everywhere, with stop lights in the middle.  I can't be fussing about trying to get car to go when I have a line of people behind me and I'm rolling backwards.

The e-brake trick would work, but really I just need to get used to how the car drives, now.

 

Cheers!

[ramen tamer]

The next project will be fixing, brake swapping and lifting my 620.  Which, if cursory forum searches are to be believed, will be really difficult and unpleasant.  So, see y'all in my next topic!