Hi all, Very first thing to get right on this Merc I just bought a week or so ago is to get the clutch reliable. Right now (seller told me this when I bought it so it wasn't a surprise) the clutch will work perfect for usually 30 or so shifts, and then all of a sudden you go to shift and the clutch goes right to the floor and it's stuck in gear. Pump the clutch 5 or 10 times and you're back in business for another 30 shifts or so. So far I have bled the system two different ways, both times with the front end jacked up so that the master was tipped back, for air to rise up and out the front of it. First I did the "pump it up and crack the bleeder" method. My lovely assistant would pump the clutch 5 times, I crack the bleeder till flow came to a crawl, close bleeder and repeat. Did that probably 10 cycles or so. That didn't change anything, so I then "bench bled" the master, still installed in the car, but ran a temporary line from the master right back into the reservoir. Watched that while my lovely assistant pump the clutch about 40-50 times. Probably overkill but I wanted to be sure! I saw a few tiny bubbles but nothing major. Then reconnected the permanant line to the slave cyl and sucked about 80% of the reservoir out the bleeder screw to get any air out of the line. Again this did not change a thing. I also saw on youtube a method of sticking a line in the hole at the bottom of the reservoir and sucking that out until there is no air. So I tried that method, but my reservoir has two holes in the bottom of it, not one. I tried both but I was not really able to suck anything out of either one. I was using a small cone fitting on the end that fit nicely in the holes, but I really couldn't get that method to work for me. What gets me is I would think that if air were in the system, the clutch would feel pretty much the same every shift. What would make it work perfect for ~30 shifts, and then not work at all until it's pumped up a few times, then perfect for another 30ish shifts? Thanks for any help!
Sounds more like a problem with the master cylinder. I would take it off strip it down see if I could see something wrong with it, even if I couldn't I would certainly fit new seals.
Are you sure its not just sticking when you push it down? Then the pumping action may just cause it to "release" from the stuck position and resume normal operation. When it sticks down, does the clutch stay disengaged.....or does it stay down and the clutch is still engaged?
sounds like when it fails, it is not releasing the clutch. I second the guess that the master cylinder is defective. But first, make sure the pedal has the correct free play, and return springs are doing there job, and nothing is binding.
"sounds like when it fails, it is not releasing the clutch" Exactly squirrel. It is definitely a hydraulic issue and not mechanical. It will be working fine for a while, then all of a sudden there will be zero pressure, or resistance on the pedal. Then you start pumping the clutch, and as you're pumping the clutch you can feel the pressure build up a little more until after 5 to 10 pumps you're back to full pressure and back to working normally for a while until about 30 shifts later when it repeats.
Oh, and to answer your question Ekimneirbo, when this happens, the clutch does not stick down. It will come back up if I take my foot off, it's just a matter of no pressure on it, and the clutch is engaged when the pedal is down and the shifter is stuck in whatever gear I had it in until I pump it up to get the pressure back.
If you know what master cylinder it is I'd just get a kit for it, hone it out and go again. And probably rebuild the slave cylinder to boot. I fought the brakes on an OT van that we had for weeks until I finally figured out that one of the flair fittings was allowing air to be sucked back in the system. It did pretty much the same as you experience. Worked great for a number of stops and then the brakes got mushy but no visible fluid leaks. That may not be the issue as it sounds like it is happening too fast meaning that the master cylinder cups are most likely letting air in.
I remember many years ago there were problems with diaphragm clutches that got pushed "over center" and they stuck that way for a while. I wondered if the clutch itself was malfunctioning and not providing any resistance to the hydraulics. Does your hydraulic system lose any fluid when the problem occurs? Look in the reservoir and see what the fluid level looks like while the clutch is stuck. It sounds like fluid may be bypassing internally as if a chip of metal might be moving around inside and ocassionally getting caught in a seal.......then coming lose and randomly catching again later.
I think those problems were due to the "overcenter" assist spring in the pedal assembly, and the diaphragm clutch not having enough spring pressure to make it return. But I could be wrong. Anyways, let's see how he does with rebuilding/replacing the master cylinder on this on, after checking all the other possible problem areas. Getting stuck doesn't seem to be his problem?
I had that same trouble on a Semi I had that I used to pull my camper.. Won't bore you with the details, but after months of frustration, I told them to pull everything out and replace it.. Problem was in the hydraulic clutch area....it would work fine, till it got very warm, then act up. Cleaned everything, put in new hoses, and never had another problem..
I think you are probably right. Its been a looooong time ago and I was thinking when diaphragm clutches first came out they had to redesign (add counterweights ?) and maybe alter them slightly because they were sticking at high rpms. But like I said, that was a long time ago. I guess the next logical question for the OP would be to ask if it is a diaphragm clutch or not. Kind of a moot point if it isn't a diaphragm.
Not knowing how your set is made up, I'll add this on top of checking master. There have been issue's with late model cars having clutch's not releasing properly. Do you have a hard line to slave from master or a flex line?
In that case the clutch should be stuck in the released position not stuck in gear(which I assume means the car won't stop). A clutch cylinder should not have a check valve in it so the fluid that is in the slave cyl and line will flow back to the master by the pressure exerted by the pressure plate pushing it back. This also why you most often do not see return springs on hydro clutches as it pushes the slave cylinder too far back and you have to pump it to get the slave piston out far enough to be in proper adjustment to release the clutch.
I run a hydraulic clutch in my car, clutch is an 11" Zoom diaphragm. I removed the assist spring at the pedal assembly. I use an AFCO stock car 32" braided line from the master to the slave. Don't want to jinx myself but it works great and I have close to 12k miles on it. I would check for a bind in the pedal linkage first. Also at the release arm.
Like others, I believe you have a bad seal in your master cylinder. The way I have always checked them for a failing lip seal is to depress the pedal, then start letting up on the pedal slowly, very slowly. If you have a failing seal, the pedal will start to drop as you are releasing it. Works on both clutch and brake master cylinders.
The amount of help pouring out here is incredible and I appreciate all the replies!! I thought for sure I had it fixed yesterday when I found that the 3/16" line was connected to a 1/4" fitting at the MC with both mating surfaces pretty mangled. Thought for sure I had found the culprit. Replaced the last bit of the line with a compression fitting and a 3/16" factory flare and replaced the 1/4" fitting with a 3/16" one so all was 3/16", all mated correctly. "Bench bled" the MC (installed) and bled the line for the 3rd or 4th time, dropped her back down to the ground, started her up and went from 1st to 2nd to reverse in the driveway about 10-15 times, thought it was fixed, went for a drive and about a mile down the road did the same old thing.... The PO told me tonight that he believes that it is an '80s Ford Ranger system. I am now thinking just rebuild/replace it all. Not like it's a lot of $$. I'll have to see if it's worth rebuilding or just buy new units. To answer your questions- I can't answer if it's losing fluid because I have bled/replaced fluid so often since I bought it that it's hard to tell. I am not sure what a diaphragm clutch is but told it was a Borg Warner if that helps. About half flex and half hard line from the MC to the SC. I will try your suggestion jaracer before going further. Thanks again for all the help, much appreciated!!
So it's been over a month now since my last post on this and I think it's safe to say it's fixed. Just prior to my last post I had replaced the 1/4" fitting with a 3/16" one to match the 3/16" line, and replaced the last couple inches of the 3/16" line just so I'd have a new flare to mate with the new fitting. It acted up one or two more times afterwards which led me to believe I hadn't really fixed it (hence my last post), but for the last month, in which I've put on about 1000 miles, it has not acted up once. So maybe a residual air bubble right after the fix? But she's been good for long enough that I'm confident it's fixed and it is not losing fluid. Thanks again for all the suggestions and help!
cool, gonna add this tid bit. A strong enough spring to pull the slave cly back into position is a must. for mine anyway. Im using a diaphragm clutch with a hydo set up. 3/16 lines with a flex hose at the slave. no issues.
So fast forward about 8 months since my "it's fixed" post, and she started acting up again, and all of a sudden! Suddenly I had to pump the clutch like 10 times every other shift after months of no issues, so something obviously failed. Figured it's either a fitting or the slave cylinder, and considering the slave cylinder was God-knows-how-old, and since I had checked/fixed the fittings a few months ago, I went to my friendly Wolfeboro NAPA for a slave cylinder. They know me well and know that everything I need is for something really old, has no history, and will require alot of guesswork and the good old paper books. But God bless 'em, between my old slave cylinder in hand and the good old paper books, they found it in a few minutes. I installed it, bled it, and all was well for a couple days but today went to start her up and no pressure on the clutch! Pumped a few times, started her up, went for 10 miles or so of in-town driving with no issues. What do you guys think, is it possible I just need to bleed the slave cylinder again one more time? Is it possible for the system to suck air in from fittings above the slave? Or to put it another way, is there ever a vacuum in the lines? I assume any fine air bubbles in the lines would work there way to the reservoir and not be an issue, but maybe an air pocket formed in a high spot in the slave cylinder? Next thing I will try I guess is to bleed the slave again and see if there was any air in there. Or maybe it will never be an issue again. That's why new cars can't compete with the old ones IMO, old ones have character!
I bleed my clutch backwards. I disconnect the linkage at the slave cylinder. With the system full of fluid, I use a screwdriver and push the slave piston into its bore which pushes the air out at the master cylinder. No bleed screws needed.
Just want to add regarding bench bleeding a master cylinder, it needs to be done on a bench, not installed in the car, hence the term. The reason for this is that the pedal assembly may not be capable of achieving the full travel of the master cylinder and not fully bleeding all the air out of the master. On the bench, a rod can be used to ensure that the piston in the master cylinder can be moved its entire stroke. Just food for thought as he mentioned bench bleeding the master in the car. Sounds like air is being introduced into the system somehow or there's a leak somewhere. I had an OT truck with a leaky hydraulic throwout bearing that would act similarly when the fluid got low. I filled the master every couple days to keep it on the road for probably three years. LOL Put the car in the air and have your assistant work the clutch pedal a few dozen times and watch the linkage, clutch arm, slave cylinder, etc. Might be something obvious after careful observation.
I had all the problems you are describing with my 52 Chevy pickups hydraulic clutch. Turns out the rod connecting the pedal pushing on the master cylinder just wasn't quite long enough. I lengthened it out and have never had a problem since. I see these posts are a couple of months old but maybe someone can learn from this experience.
I think you must remove the check valve in the master cylinder to get the slave cylinder to operate .
Cars like Ford Mk2 Cortinas [Lotus etc] don't have a spring on the clutch fork. They had a long travel slave cylinder so it would "self adjust" as the clutch wore down [pushing the slave back further] Earlier Ford Mk1 Cortinas had a return spring and an adjustable push rod. On our O/T race car we were chasing our tail with a clutch not returning . It turned out to be Flap inside a poorly made braided hose.
Also see if the slave or tubing is too close to the exhaust and getting hot with the engine running. That could cause the slave not to work, kind of a vapor loc type of deal. If so install a heat shield.
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