Clutch pedal stiffness when hot

[TheSilverBuick]

And lasting more than 4 hours...

Now that's out of the way, this weekend I've been driving the Buick around town and the pedal more or less feels normal. It's not quite perfect, but I attribute that to jacking with the clutch fork pivot ball adjustment. It doesn't have the feeling of "it's going to break something" when I push the pedal.

What would cause the pedal effort to go through the roof while hot while at the same time allowing the pedal linkage itself (pedal to throw out bearing) to remain loose and unbinded?

I'm not so sure it's going to be a broken spring or something in the clutch set anymore, but I'm wondering with some heat if something is expanding and binding up? I'm still highly suspicious of the clutch set, namely the pressure plate.

It's coming apart one way or another and I'm changing the clutch set to a different brand, but want to make sure I'm not missing anything else while its apart.


Thoughts or experiences?

[TheSilverBuick]

I guess I'll add some details for those that might not follow my build thread =P

Buick 455, TKO-600, stock mechanical clutch linkage in a 1977 Skylark.

Clutch itself has well over 20,000 miles on it. Ran Drag Week last year on it, drove to the Oregon coast and back last July and towed my camp trailer to Bonneville last August, so it's regularly driven and used. I was about 800 miles into my trip when things went south and only about 4 hours/250 miles worth of driving that day.

[milner351]

mechanical clutch linkage?
so there's a rod from pedal to top of z bar, another at the bottom of z bar to the fork that has a pivot in the bell housing and the throw out bearing on the other end... right?

I agree that I would suspect the centerforce pressure plate only because I've heard lots of bad experiences about them.

If there was an issue with the mechanical clutch linkage - I would think you'd have found it on your initial inspection in Dan's garage.

[TheSilverBuick]

That is correct description of the linkage. I had no problem wiggling the linkage with my hand. Prior to screwing with the pivot ball adjustment I had about 1" pedal travel and about 1/2 to 1/4 inch at the throw out bearing. Watching the pressure plate and clutch disc through the fork hole of the scatter shield as Dan actuated the pedal, the pedal would stiffen up the moment it touched the pressure plate, it wasn't over centering and would pop back as fast as Dan would let up on the pedal, aka no slack in the linkage if the throw out bearing was hanging up. I removed the tension spring on the lower rod so if the throw out bearing was hanging up I'd expect the lower rod to drop out when releasing the pedal.

[hauen]

Most of the mechanical linkages have some kind of bushing on each end of the z bar; are they all in round, greased and happy? I'm not sure if your car would have brass or plastic bushes, but if they are the plastic ones and have have broken up, as they are wont to do with age, they might be grinding around and sticking when things start to heat up down there.

[TheSilverBuick]

Most of the mechanical linkages have some kind of bushing on each end of the z bar; are they all in round, greased and happy? I'm not sure if your car would have brass or plastic bushes, but if they are the plastic ones and have have broken up, as they are wont to do with age, they might be grinding around and sticking when things start to heat up down there.

No bushings or inserts. When I last had it apart I did weld on new material to the Z-bar and one of the rods then ground and cut back to a nice fit. I didn't directly WD-40 the pivot parts when they were bound up, but I'd be impressed if that bit of friction that is non-existent cold or the other 99% of the time can compound into bending the lower rod out. But I'll inspect for galling or something on the pivot points when I have it apart. Thanks.

[CDMBill]

I don't think its the linkage. Either the throw out bearing is binding on the shaft when things get warm or the Bellevue is hanging on the housing due to wear on stanchions.

[Beagle]

Centerforce? the one with the weights? What if the weights are getting hung up when they're expanded (heat)?

[TheSilverBuick]

Centerforce? the one with the weights? What if the weights are getting hung up when they're expanded (heat)?

Yup the one with weights. I kind of wondered the same thing. When pulled apart I expect to see some scuffing or damage to some of the weights if this is the case.

or the Bellevue is hanging on the housing due to wear on stanchions.

Huh?? Autocorrect or am I taking this statement too literal?

Drove the car to work today because winter is fast approaching. Which reminds me, I need to drain the water out of the system and replace with proper coolant. [/Hi-jack]

[NewEnglandRaceFan]

if it's expanding the weights I'd think the clutch is slipping, I could maybe see that happening if you just got through hot dogging it for a while..
you check the header temp as it passes the bell? you might be hotter then most as you have your efi so dialed in.. my bet through out bearing coming apart

[SpiderGearsMan]

towing with a manual trans ?

[TheSilverBuick]

if it's expanding the weights I'd think the clutch is slipping, I could maybe see that happening if you just got through hot dogging it for a while..
you check the header temp as it passes the bell? you might be hotter then most as you have your efi so dialed in.. my bet through out bearing coming apart

I got under the car immediately after trouble started and immediately after it bent the lower rod out and the bell wasn't unreasonably hot to the touch IMO (burnt my arm on the exhaust pipe a few times though). Headers still have paint on them too, so the exhaust gases haven't cooked the paint off heat wise. I was able to spin the throw out bearing with a long screw driver and it spun freely and without noise, nor does it make any noise when engaging the pressure plate while driving or on shift changes. It will be looked at, it also has around 20,000 miles on it.

towing with a manual trans ?

I have towed my little camp trailer to Bonneville and back on this clutch. Right now the trunk is just loaded up with gear; two mounted tires, tools, etc. Didn't have any slipping issues. I've driven vehicles with slipping clutches and this definitely wasn't the case.

[Leadsledcaprice]

Forgive my non-expertise in this, but I was wondering if maybe the input shaft might have a slight bend in it. I agree, that it shouldn't matter with heat or without. Maybe when the input shaft gets heated the 'bend' becomes more pronounced (metal expanding under heat). Thus, it would be like trying to slide your small wedding ring off your large, swollen finger, but is fine when cold since the bend isn't as pronounced and the metal is tighter.

Definitely a far fetched (and probably wrong) idea, but just and idea at that.

[TheSilverBuick]

I'll be looking at the pilot bushing (I installed a new one this year while the engine was out) as well as the input shaft sleeve the throw out bearing is riding on for scuffing, etc. The shaft itself should not effect pedal pressure, but the sleeve could.

[Leadsledcaprice]

Maybe the sleeve is expanding under the heat, and the throw out bearing is getting hung up.

Another weird one for you so you know you aren't alone: A friend of mine some years ago bought a Fox-body w/a 'built' motor, it ran well, scooted, and was a 5 speed car. My buddy noticed that there was a vibration in the shifter (and only in the shifter. Was not noticeable in the car unless you had it in gear with your hand on the shifter), and chased it for months. Clutch, flywheel, driveshaft, throw out bearing, diff trans even if I remember correctly.

Well, after a while, he wound up getting down into the engine for one reason or another, and discovered that one half of the motor had reliefs cut into the pistons for the valves, and the other half did not. And when I say half, I mean one side of the motor. Weirdest thing I've ever seen.