Technical Any master cylinder gurus out there?

Still having issues with the hydraulic clutch. I truly believe it's the master and not the slave. '62 Chevy truck master. I disconnected the hydraulic line from the master and depressed the clutch pedal. Shouldn't a steady flow of fluid stream out of the port? Mine just shoots out a short burst and then air. I've thoroughly bench bled the master. Here's a shot of the innards.....................



These have already been swapped side to side. Note the residual valve and rubber gasket at the top on the right side. That is currently on the right side which is the brake side. Originally, it was on the left side but I swapped it to the right side. Both M/C bores are 1-1/8" and are identical. Also, the M/C internals are identical except for the residual valve and rubber gasket. Again, I don't have a steady stream of fluid coming out of the port when I depress the pedal. Looking for ideas/answers.

 

If you can keep fluid in the bore, before you try to squirt it out, then it should shoot a steady stream. But it's probably running out before then? there's nothing to keep it in the cylinder, when the hose is disconnected

how are you bench bleeding it?

 

I can't help you from here-
But isn't amazing that those $1.25 rubber cups actually keep us from killing our damn selfs

 

Are the bypass ports in the same location in both bores ? Also, if you still have the original pistons, compare the length. Make sure the pushrod is "loose" in the piston, not binding.
The problem sounds like the bore(s) aren't refilling on release.

 

Might to have both threads together.
Something is odd about the clues- "extreme leg pressure"
1/2 the movement
Little fluid
I'm having troubles reconciling all of that together with the apparent issue.

Extreem pressure goes to bore size too large and a loss of mechanical advantages.

1/2 the movement goes to bore size to small or air in the system but the extreme pressure kills that notion.

Little fluid being displaced goes to air in the master or piston not returning to allow filling of the bore. But again the extreme pressure kills that one as well. Apparently it's enough fluid to get 1/2 the clutch fork movement needed.

Things sorta point towards some mechanical bind issue as being at least part of the problem

 

OK, bought a brand new master, swapped the innards and installed it. Now I seem to have a steady stream of fluid shooting out when depressing the pedal however, the pedal depresses about 3" with minimum pressure (maybe that fills the slave) and the final 2" moves the clutch fork but that final 2" takes a lot of leg pressure. I know the '88 TC slave bore that I currently have is a good 1/4" smaller than the master bore so it looks like I'll be a adapting a '62 Chevy truck slave. I don't know if there's much I can do with the pedal pivot point. Pedal assembly is from a '70s El Camino.

What do you guys think? Does the first 3" fill the slave and the extreme pressure in the final 2" is caused by the small slave?

 

The slave cylinder should stay full as it can be, with it retracted. Is all your linkage as it should be?

 

The slave cylinder should be moving pretty much as soon as the pedal is moving. The system is closed - there's no filling up, just building pressure, and that should be almost instant (the fluid doesn't compress). Might there be a ton of slack between the slave and the arm?

Chris

 

Couple things; while you are installing the Chevy slave cylinder you need to added a return spring to the throw out arm as well as making the pushrod "fall-out proof", also probably best to lose that skinny #3 hose and switch to 1/4" for proper flow, and when bleeding be sure to let the piston return fully (many times they are slow to return initially) each time before stroking again.

When done the slave will start to extend immediately and the only play felt should be the clearance between the throw out bearing and the pressure plate fingers.

If the pedal effort is still high, go back and make sure your pedal ratio is in the 6:1 area; not sure how a '70s El Camino manual clutch pedal translates into pushing the truck master.

Done quite a few of these with no problem.

Good luck on getting this sorted out; sounds like you are well on the way.

 

Rich B. I'm getting the 'fall out proof' slave pin but the throw out arm return spring is confusing me. If this were to depress the slave pin that would create freeplay that would need to be taken up before the bearing would meet the clutch fingers, and which sounds a bit like what's happening? I'm assuming the slave is a pusher, but thinking about it I'm not seeing it any differently were it a puller?

Chris

 

Perhaps the first 3" is taking up the free play and the last 2" is the pressure plate spring. 1/4 bore difference makes a huge difference in mechanical advantage,

The pedal ratio - measureing how far the pedal pad moves to the floor and how far the rod moves forward Ito the master.
'70 Chevy had a Zbar to operate the fork and those bars were not 1:1.
Also measure the full stroke on the master cylinder.

 

The pushrod from the slave to the release arm should have a threaded adjustment.

 

The return spring should run from the throw-out fork to someplace convenient forward and be strong enough to push the slave piston retracted fully; it also keeps the throw-out bearing off the clutch fingers when the pedal is released.

Crude drawing explaining this stuff.

 

Throw-out forks are usually hardened; may be tough to modify in place. Could also mount the slave further forward and use '40 Ford master cyl push-rod and a cut off bolt as an adjustable link that would push on the existing dimple in the arm. The return spring is doubly important in this case as it also needs to keep the rod from "dropping out".

 

OK, I've got the master figured out and I got a '62 slave. The '62 slave's bore is maybe 1/8" larger than the TC slave bore. I don't think that's gonna make that much difference. Pretty sure the problem is the pedal ratio. After doing some calcs the ratio for both brake and clutch is............drum roll please.............2:1! Hahahaha! The whole pedal assembly is integrated into the cowl cage and although it could be done, it would be a major PITA to modify! So..........thinking outside the box, maybe dump the firewall master, fill the holes in the firewall, retain the TC slave and install one of these on the floorboard.

http://www.ebay.com/itm/Basic-Pedal...d=192108524306&_trksid=p2047675.c100752.m1982

At this point, I just wanna get this thing on the road! Comments, suggestions, opinions, please?

 

Just for kicks, it you have a flex hose attached at the slave, it may be plugged damaged.

 

Nope, one of the first things I checked. The slave is full.

 

2:1 pedal ratio? Are you sure? The pic of the master on the firewall doesn't seem to indicate that unless the pivot point was right up at the top of the cowl. At you sure you've got your ratio logic and measurements correct? Pics would help, and might be an education!
If you can cut and weld I'd bet fixing what you have is possibly easier than the setup you've linked to. To make that racecar type stuff work you need sufficient space to have enough legroom, or you'll be looking to operate the pedals with you knees!

Chris

 

64-72 Chevy chevelle clutch pedal.
2:1 ratio would put the rod pivot at mid point in the pedal. Not the case in the pic

 

The pivot point is the shaft up top where both pedals attach, correct?
Measured from that point to the center of footpad is 12-1/2" (A).
Measured from that point to the attaching stud for the pushrod is 4-1/4" (B).
A/B=2.94 or roughly 3:1

The brake pedal measures 9" and 4-1/4" respectively. A/B=2.11 or 2:1.
Am I measuring it correctly? BTW, I don't have that 90* bracket hanging off the clutch pedal.

Horrible pics......................

 

That's not a chevelle pedal, not that it matters any because what you have there ain't working set up like that. It's like the pedals are backwards or something.

Here's a set from a 73-87 Chevy truck.
The pedals are relatively straight, mounted with swing pivot away from fire wall and rod pivot close to top pivot.

 

Are you any good a drawing?
See how this one is drawn?
Draw yours up as is now. Throw some dimensions in there and that might help a bunch.

What's important is the -
master stroke
Pedal pad stroke
Distance from pivot to rod and pivot to foot pad
The shape of the pedal's arm

 

The guy I bought it from at the swap meet said GM G-body. He thought maybe El Camino. Maybe it's a later version.

Lookin' at your first pic got me thinkin'.
How about if I weld a 90* bracket (kinda like the one in your first pic) towards the top of the pedal only flip it upside down and facing forward. Wouldn't that place the pushrod pivot point higher and closer to the pedal pivot point theoretically raising my pedal ratio. Not sure...........I failed geometry in high school! Am I making any sense?

 

Just saw your second post. I've got an appointment and gotta go. Be back in a few hours and I'll try to post some dimensions.

 

OK, my drawing sucks so I'll go with pics I have. To answer your questions:
Master stroke = about 3-1/2"
Pedal pad stroke = also 3-1/2"
Distance pivot to rod = 4-1/4"
Distance pivot to foot pad = 12-1/2"
Shape of pedal arm - second pic. Best pic I've got.





The whole assembly looks a lot like your Chevelle pedal assembly pic. Not identical, but close.

[/QUOTE]

 

The master cylinder needs to stroke 3-1/2" ???

If you had it on the bench,
how far does the master cylinder's piston move from resting to fully bottomed out?

 

In the shitty pics, it looks like the clutch pedal has a goofy banana bend at top?

More like this


Note how the leverage is applied and the orientation of the master. Also note the rod attachment position in relation to the pivot.

Does your clutch pedal have that goofy bananna bend? I see it has holes very near the pivot. Both brake and clutch pedal. I'll bet you lunch that's the holes for rod attachment to get the proper pedal ratio.

 

From the looks of your pictures, it also appears that your master cylinder is mounted too low to be able relocate the pedal push points enough to correct the pedal ratio.

The rod needs to be at 90 degrees to the master at the mid point of stroke, other wise it can bind in the piston, either when released or at full stroke.

Kinda hard to see in the picture; but the push-rod is really close to the top of the hole in the piston with the pedals in the released position; and it will be close to the bottom of the hole when the clutch pedal is depressed.

Hate to say it; but it looks like your pedal/master set up needs more than a little rework.

 

My bad! The bore is 3-1/2" long. The stroke when filled with fluid is probably 1" or less.
The pedal has kinda a funky bend in it too.

I'm obviously gonna be doing some work on the pedal assembly so I pulled the master, dash and cowl off today so I can get to it.





You can see the two holes for the pushrod just below the pivot. Brake pedal has 'em too. I think what I'll do is weld on some steel plate and extend the mounting bracket down a couple of inches. Then, drill a hole and run the whole pedal pivot about 2" lower. At that point, I can utilize the factory holes for the pushrods, keeping the rods parallel to the master and that should give me the good 6:1 ratio. I'll probably have to cut the pedals, remove 2" and reweld also. Hopefully, that'll do the trick!