FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: jayb on September 14, 2017, 05:11:21 PM
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So, I've got about 1000 miles on my 68 Mustang now, with the 428 CJ (my former dyno mule), and the T56 Magnum transmission. I got the complete transmission setup from American Powertrain. The T56 is wonderful, shifts like a dream, all the gears are easy to find, etc. etc. However, my clutch is behaving strangely. I have the hydraulic clutch master cylinder and hydraulic throwout bearing that came with the kit, they installed and bled fine, and mounting the master cylinder was no real problem. However, from day 1 with this combination, the clutch pedal has been sticky. When you try to release the clutch pedal from the floor, it comes up about a third of the way feeling normal, then it seems to stick. If you then start letting off the pedal pressure it will not move at first, but when it hits a certain foot pressure level it will suddenly pop up to about two thirds of the way up, and then stick again. Again, to get it to move you have to release the pedal pressure. Then, since you have started releasing some of the pressure it comes up too fast and engages with a lurch; you can't control it. Seems to do it more when it is cold, but the issue is present all the time. Makes pulling away from stoplights or stop signs rather problematic.
After I got the car put together and this problem persisted for a few hundred miles, I concluded that it must be a clutch pedal or linkage issue. I took it all back apart, and made sure to lube the pedal cross shaft where it goes into the pedal tree, and replaced the plastic bushings in the pedal tree. But the old bushings looked fine. There didn't seem to be any binding on the rod from the pedal to the clutch cylinder, but I made sure that the rod cleared the firewall properly, and that there was no binding where it connected to the pedal. After going through all this, there has been no change; the problem is exactly the same.
This clutch is a dual disc McCleod diaphram style clutch. Is it possible for the fingers to stick on these things, or is this something that can be encountered with a hydraulic clutch setup? Could this be an adjustment issue? I'm beginning to think I should have put an automatic in this thing... >:(
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Twin disc or dual friction?
If it's a mechanical linkage and a diaphragm plate, you could be overcentering the pressure plate.
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Sorry, I just looked up the sales order and it says the clutch is a Science Friction Atomic Twin SFAT26AF clutch, 950 ft-lb rated, Ceramix discs. Two clutch discs with a floater plate.
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Never heard of them.
I jumped the gun on overcentering. Just reread and saw it's all hydraulic. Less likely to do it with hydraulics.
Have any return springs anywhere?
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Is it a slave cylinder or a hyd. t/o bearing?
I've had slaves that acted like that. (import)
With the bleeder open you could feel the stroke wasn't smooth.
should be the same for the master.
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Never heard of them.
I jumped the gun on overcentering. Just reread and saw it's all hydraulic. Less likely to do it with hydraulics.
Have any return springs anywhere?
Great, I've got a brand X clutch ::) No return springs, in fact I took out the over center spring in the clutch pedal assembly because I thought that might be causing the problem. Didn't help.
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Is it a slave cylinder or a hyd. t/o bearing?
I've had slaves that acted like that. (import)
With the bleeder open you could feel the stroke wasn't smooth.
should be the same for the master.
It's a hydraulic throwout bearing, not a slave cylinder. I may try opening the bleeder and working the pedal back and forth, at least that would eliminate the master cylinder from consideration if it felt smooth...
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I would have bet it was the bushings, could the throwout bearing be coking or the middle plate in between clutches. Is the pedal pressure smooth going in. Installed like the same setup in a 69 chevelle with a TKO was very smooth. Now the one that he gave me made rattling noises when doing small menuvuers and he said he got the one with out the bushings that keeps the disc from rattling around, does yours maybe have those bushings inside and something is getting in the way.
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Jay -
Do you have that big clutch assist spring attached to your clutch pedal under the dash? That could be the culprit. Your setup may require lower pedal effort than stock, so the spring may be too strong. Try taking the spring off.
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Pedal pressure is smooth going in, just sticky coming out. I can't recall if there are bushings in that center plate or not...
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Did you set up the depth of the clutch release bearing correctly?
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It is your car showing you it's unhappy that you didn't just go with a factory Z bar and heim joints :) and it will continue at least until you stop threatening it with a slushbox LOL
Seriously, it sounds to me like one of 3 things: a bad hyd TB, a kinked or damaged line, or maybe a bad master cylinder. I seriously doubt it is the clutch itself. I think I'd be leaning toward the TB, but, I'd probably reverse the line and see what happens first for laughs in case it's acting like a check valve
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I set the depth of the throwout bearing as described in the instructions, something like 0.090" gap between the face of the throwout bearing and the clutch fingers. Maybe I should get in there and try moving that around some. The line isn't kinked at all, its a braided steel line and is nice and smooth all the way into the bellhousing. You'd think with all the automatic cars around here that clutch would get wise and shape up... ;D
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Just saw this about magnum T56 gearbox's and twin clutch plates (One other thing you’ll need to look at is the stack height of the clutch assembly. This is the thickness of the assembly when it is bolted together. Some twin-disc setups are thicker than stock clutch assemblies, and if this is the case in your application, you may need to trim the bearing retainer on the input shaft of the transmission to prevent it from pinching the clutch discs to the flywheel)
According to some gap should be 0.15-0.20"
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Jay on Mercedes with hydraulic clutch there is the same
kind of "rat trap" spring on the clutch pedal as Ford have
And sometimes when the master cylinder goes bad like rusty
with piston sticking to the bore there is exactly the
problems you describe
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Maybe listen to the Master and slave if you can with a Stethiscope and see if one of them makes a bunch a noise in the spot it acts up
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I have a T56 with a Ram hydraulic bearing and twin disk RXT in my 68, it was very hard to get bled but once I got there it has been working great. I do remember having to have to change the trans snout to get it right.
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I hate hydraulic clutches. So much so that I converted my Ranger to a cable. They just don't give a positive feel.
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Jay, what does your setup use for a spring setup to return the TB to original position? Are they external to the throwout bearing, or does it just relax on it's own? Is the master and throwout bearing a matched pair, or did you pick them?
I wonder if your design has some extra resistance and needs a little more spring pushing back through the master cylinder?
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If no one has mentioned it, make sure the TO bearing isn't binding on the extension.
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Just to make sure....there isn't any kind of fluid return regulator on the hydraulic line right? The car I drive to work every day is an Acura TL, I got it in the 6 speed manual, it has a hydraulic clutch. I was having issues with erratic clutch behavior. After looking online for a while I realized that they put a regulator in line to help pedal feel and not let bad drivers release the clutch too quickly. It's a common piece that people have problems with. I bought some Honda tuner guys kit 8) that eliminates the fluid regulator.
Not sure if your setup has one...but this is my one experience. And the symptoms don't sound too much different than yours.
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In the interest of keeping things simple I'd just try to bleed it again. It really sounds like there is some air in the system.
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I suppose another thing to check is that the t/o bearing is the correct diameter for the clutch fingers and not running off the edge.
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Any progress Jay?
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OK, to answer some questions, the throwout bearing returns on its own, unless there is an internal spring that I don't know about. The throwout bearing is solidly fixed to the transmission input shaft sleeve, and then expands towards the clutch fingers when the pedal is depressed. The throwout bearing and master cylinder were bought from American Powertrain in the same kit, so they are designed to work together as far as I know. The line from the master cylinder to the throwout bearing is direct, no check valves or anything in between, unless they are in the throwout bearing or master cylinder themselves.
So, here's a new twist. Sunday the wife and I took off for a car show about 50 miles away. This involved some freeway driving for most of the trip, where I was going between 70 and 80 the whole way. I had not yet put this kind of driving on the car, being mostly limited to around town driving and local roads up to 50 MPH. Sunday, after getting off the freeway, suddenly the clutch worked perfectly! No sticking at all. It worked great all the way to the car show. We didn't stay too long, only about 3 hours, and when we left the clutch still seemed to be fine. Back at home I parked the car, and after thinking about this I suspected that the heat buildup on the freeway was the reason that the clutch started working properly. Monday morning I got back in the car to run some errands, and sure enough, the sticking was back. However, this time, after about a 15 minute drive around town, it started working perfectly again.
It seems clear that there is some tolerance that is too tight somewhere, and heat buildup causes the parts to expand and start working normally. The throwout bearing is the primary suspect, I think. However, it may be that after some time it will wear in and the problem will disappear, because it seems to be improved after the trip on Sunday. I will have to drive it a little more to see if it really is better now. If it doesn't get better after another 1000 miles or so, I think I will probably replace the throwout bearing. What do you guys think, am I on the right track?
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I think you are on the right track something is sticking. Probably
wear in after some use
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Jay, I run into that very same thing with my brown truck. It has a McLeod single disk. When I'm in traffic and shifting a lot it starts to stick. Not stop like yours but I can feel it grab. I took it apart and champhered the front and rear edges of the throw out bearing made sure there was grease in the center depression and put it back together. It was better but not gone. I think you are on the right track also with heat expansion.
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I think it sounds as good as anything. I'd put some more miles on it, and if you decide to pull it, then look for dry spots or potential misalignment/off center components
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I think I feel your skepticism Ross.
Why would something made to work together like that succumb to heat expansion when that should be part of the formula? The only thing I can come up with is tight tolerances of new bearings used with older used sliders.
After I put mine back together and the problem was still there I figured I should have at least straight edged the slider.
Also thought about to much clearance and the bearing rocking but seems unlikely. Can't take anything for granted.
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I do remember a somewhat similar issue on a Chevy clutch job. IIRC, the fork-end was for a big diameter t-bearing while the actual t-bearing was a small one, at least the flanged part that intersects with the fork's fingers. Anyway, as one worked the clutch pedal (mech linkage here) the t-bearing seemed to drag 1/2 way down the stroke, then release.
But, not quite the same thing nor heat related as in Jay's case. If it clears up after more driving, saving a lotta' work (!) I'll bet Jay finds witness marks later, leaving a clear trail of what exactly it was.
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The hydraulic T/o bearing don't slide it fixed and "telescope" in it self.
And how often have you got parts that was made to work together that
actually worked together ;D Or is it just me that live on the otherside of
the globe that get sent defect parts that someone living closer have returned
One thought is the T/O bearing right angeled against the pressure plate
if not you got a side loading that can make the T/O stick?
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I get that it's fixed Heo but does not the clutch side of it extend on the slider?
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I know that when I was building Cobras we used McLeod TO brgs like this one:
(https://static.summitracing.com/global/images/prod/mediumlarge/mcl-1430_ml.jpg)
They would ship with a rebuild kit. We were told that if they sat on the shelf for too long they would dry out. With this style, the bearing part still slides on the support sleeve even though the base is fixed.
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I get that it's fixed Heo but does not the clutch side of it extend on the slider?
Yes, it does.
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Hmm, the instructions I got with the hydraulic clutch kit didn't say anything about lubricating the tube that the bearing rides on. I didn't realize that the movable part of the throwout bearing slid on the tube; I thought it was contained with some kind of sleeve in the throwout bearing itself. Maybe I'll see if I can paint some oil or grease on that tube through the window on the bellhousing, and work it back and forth a few times to see if that helps...
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Jay, I think that would be wise to lubricate if you can. I cannot imagine they would give up indexing the bearing off the collar, otherwise the seal would have to be pretty stout to take the load when it meshes with the clutch, but it is speculation, it really depends on design.
Does that setup have you spot face whatever it pushes off of? Not sure if I am being clear, but if the back side was not pushing off a parallel surface it could introduce a side load, which could cause binding, then minimized with some slop fro heat. All theory, could be a sticky, I like that idea best, but bench racing here
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The problem with using grease and oils inside a bellhousing is that it becomes a magnet for clutch dust and friction material, which usually isn't good and will lead to more sticking, binding or wear. But I have no experience with hydraulic clutches either.
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Ross, the throwout bearing slides up against a flat face on the front of the transmission. If I recall correctly there are shims that go between the throwout bearing and the front of the trans to get it properly spaced to the clutch fingers. There is a set screw that goes into the sleeve to keep the throwout bearing from rotating.
I got the car up on the hoist and looked in the side of the bell, and with the diaphragm style clutch there is no way for me to get in there and grease the sleeve. I put a couple squirts of WD-40 between the fingers, but didn't want to use too much for fear of oiling the discs or attracting dirt as Doug mentioned above. Afterwards I went in and pressed the pedal about 20 times but it didn't seem to help any...
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I agree in theory with Dougs statement but I haven't found any real world crud driven binding after many years of stop and go commuting every day.
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I would not lube the bearing support. It'll just attract more crud and probably end up causing more wear and tear than if you left it dry. It needs to be smooth and dry and shouldn't have any issues.
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Hundreds of thousands of vehicles in all kinds of environments have had grease fittings that not only lubed the TB but also the surface it rides on.
However, it is of course your call
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Fun, ain't it??? ::)
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Found out something the very hard way. The production versions of these annular throw out bearings have seals incompatible with synthetic fluids. Some older transmissions, up to around the mid-90's were not rated for synthetic trans fluid and can bail out the fluid through gasket or seal leaks. This then contaminants the throw out bearing seal causing it to fail. Not sure if this applies to the aftermarket throw out bearings of this type.
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Hi, I have replaced a lot of hydraulic clutch systems and they work great, if someone can work the clutch so you can put a long feeler gauge between the through out bearing and the fingers to see if it is the clutch sticking or the slave/ through out bearing, I do not believe the through out bearing moves much on the sleeve other than for alignment purposes, somehow you need to find out if the through out bearing is retracting smoothly and the way is with a feeler gauge. Leny Mason
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My money is on a disc or pp. problem. That is where most of the heat is concentrated.
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Another quick update, I took the car out for a spin yesterday around town and as usual the clutch pedal was sticking in a few spots. However, after driving for about 15 minutes it smoothed right out. Again, before I went on the long trip at 70-80 MPH, it had never done that. I'm thinking about taking another couple long trips to see if just running at speed for a while will continue to improve the situation. Once the clutch pedal smooths out, the car is just a joy to drive with that transmission...