Clutch???

[mark elder]

Rick
There has to be 'some clearance' between the thrust bearing and the clutch cover fingers. If not, then you are always slightly 'riding the clutch'. The amount of clearance can be debated but I would be happy with anything from 2mm to about 5mm. I aim for 3mm.

So to check it, install the throw out bearing etc and ensure that the piston/thrust bearing is pushed back so that it is fully in (2 strong thumbs should be fine).

Measurement one is the amount the front face of the thrust bearing is 'inside' the bellhousing. Put a long straight edge (say 600mm) across the bellhousing face and use a second ruler and measure back from the reference face to the front of the bearing. For a VD its often a number like 100mm but every car is different.

Now the tricky bit. You need to measure the amount the clutch cover fingers are away from the back of the block (the face the bellhousing bolts to (its the same reference plane)). The fingers are sort of a bit deeper than the outside of the clutch cover. So the measurements are in 2 bits. Put a straight edge across the back of the cover and use a second ruler to measure forwards to the back of the block. Then measure the distance from the same straight edge to the cover fingers. Take this off the first measurement. So if its 100mm from cover to block and 5mm from cover to fingers, then the fingers are 95mm away from the block.

So in this example the fingers are 95mm further back than the block and the thrust bearing is 100mm from the block. Net clearance is 5mm.

[Steve Demeter]

Yep and I did it exactly like Scotty told me to when I put it back together last week.

[Steve Demeter]

I got my new master cylinder today. Installed it, bled it ( using my handy Mighty Vac) and while pedal was firm right at the top, pressing it all the way down to the stop set where it was prior to all this did not produce release of the clutch. Had a friend help and bled with the "down open screw close screw release pedal" method and same results.

Slave cylinder, throwout bearing, pressure plate are new from Scott Young as well as he rebuilt the clutch cover. Disc was already new. Clearance from TO bearing to fingers (to where the bearing would contact them was measured by 2 people at 0.180".

Master is new as after rebuilding old one had some concerns about it not wanting to return. Test of assembly with "old " master showed that the slave did extend when the pedal was pushed.

I am at a total loss??


Anyone got any suggestions.

The next thing is to split the car on Friday as I am exhausted and my back is killing me. The only thing that even remotely comes to mind is that the TO bearing somehow " collapsed" . But remember this assembly has never been rotated except for turning the axles by hand to see if the clutch had released.

[DaveW]

Did you try readjusting the pedal stop? With new parts and maybe more TO brg clearance it may just need more pedal travel to release.

The old damaged slave may not have been retracting completely and that also could have resulted in less pedal travel necessary than with the new parts, etc.

[BorkRacing]

I had a similar problem.
The cause was overthrowing the slave. I had missed the release point and the clutch was grabbing again.
Solution was to very carefully back off the pedal (using a clamp for consistency) until the clutch released.
For my car with a Tilton internal slave the window of just enough pedal and too much was 1/2" pedal travel.

Also how much force are you applying to the wheels to see if the clutch has released?
Some time the initial few revolutions of the disk against the clutch surface are very tight.

Just some food for thought.

[Steve Demeter]

We did check for release throughout the throw of the master. I used a C Clamp to slowly depress the clutch pedal while my helper kept trying to turn the rear brake discs with the car on stands. The main reason was to make sure not to overtravel the diaphragm springs and to hopefully find the release point and reset the stop properly.

Scotty called me late last night with an idea that is very long to explain (at least it is for long winded me) but if it turns out to be the solution I will post to let everyone know after I split the car tomorrow. Wife unit had other plans for me today...

[Steve Demeter]

After trying everything it seems known to man and somethings not known it finally worked last nite. Thanks to Rex Gunning and Scott Young for pointing out the obvious that we had not tried in our confusion between the forest and the trees.

"Put it on it's feet and get in and push the clutch in"

Guess what the first try did not work, so adjusted the pushrod on the master out and lo and behold IT WORKS..

So if anyone ever needs an example of being lost in the woods for something silly, feel free to use this.

[mark elder]

At this point I am a bit lost. Are you saying the pushrod was too long and when your foot was off the pedal there was no free play. Therefore fluid could not 'return to the reservoir' after you had pushed on the pedal?

[DaveW]

At this point I am a bit lost. Are you saying the pushrod was too long and when your foot was off the pedal there was no free play. Therefore fluid could not 'return to the reservoir' after you had pushed on the pedal?

He could not get it to release. It was not stuck with the clutch disengaged. As I surmised in post #44, the master pushrod was likely not depressed far enough and so, if I'm understanding correctly, lengthening the pushrod fixed it..

[Steve Demeter]

Absolutely correct Dave.

Interestingly enough the adjustment moved the top of the pedal about 2 inches toward the rear of the car. Now it goes over center in order to release the clutch.

Gonna have to move the dead pedall

[DaveW]

Absolutely correct Dave.

Interestingly enough the adjustment moved the top of the pedal about 2 inches toward the rear of the car. Now it goes over center in order to release the clutch.

Gonna have to move the dead pedal.

Glad you got it working. BTW, on my car, there is no room for a "dead-pedal." I just rest my foot lightly on the clutch pedal, which is fine since I use the clutch for every shift.

[DaveW]

Absolutely correct Dave.

Interestingly enough the adjustment moved the top of the pedal about 2 inches toward the rear of the car. Now it goes over center in order to release the clutch.

Gonna have to move the dead pedal

You might think about putting a spacer between the master flange and the bulkhead it attaches to. That would move things forward, and as long as you still have enough pedal and piston travel for clutch disengagement, that might help.

[Steve Demeter]

Dave I have thought about doing that. Would have to be awfully thick. About 1" to move pedal back to where it was. Like you said that might compromise getting enough pedal travel to disengage. That is going to be a winter project as it would also involve changes to the footbox for additional room for the master.

Wish I could figure out why so much more pedal travel is needed not than before..The assembled gap TO bearing to fingers is only 0.180". Scotty told me 0.200" is what he shoots for. Same flywheel, rebuilt cover, new pp, old disc, new slave, new master. I guess somewhere there was some lost motion.

[tlracer]

If the travel at the pedal/master has increased to get the same slave travel...is your new master cylinder smaller bore than the old one?

That would displace less fluid for the same linear travel, hence the slave would not move as far.

Increasing the travel - as you have done - would restore the same fluid displacement as the bigger master/shorter travel, allowing the slave to move further and so disengage the clutch.

[Steve Demeter]

Thanks.

Both new and old MC's are labeled 0.75. So I have to assume that without disassembling them that they are the same.

[mark elder]

Can you measure the old one and report. It is a start.
A difference in MC diameter is a very real possibility.. To me, it explains (almost) all.

[tlracer]

Thanks.

Both new and old MC's are labeled 0.75. So I have to assume that without disassembling them that they are the same.

Okay, taking it as they are the same bore, then something else has to be happening here. I would be looking to answer these questions:

1) For some reason the new slave requires a bigger fluid displacement than the old one to achieve the same linear throw?
2) Does the chassis have different pivot positions for the pedal and, if so, is it still mounted in the same one?
3) Did the new master come with a pushrod and, if so, is this the same length as the pushrod on the old one?
4) For the same linear movement, does the new master cylinder displace the same volume of fluid as the old one?

Point 1 has probably been covered-off by refitting the old master which, as I understand, gave the required slave throw for the expected pedal movement
Point 2 is probably a given, but worth just ticking off as not changed
Point 3 is possible if the new pushrod is longer, so setting the pedal in the 'normal' place meant the master was already partially depressed
Point 4 is worth testing as it could identify various causes - different bore, fluid leaking past the main seal, fluid leaking past secondary seal to the reservoir. For some checks it would be good to blank-off the master cylinder outlet as any significant movement of the pushrod would suggest a seal issue internally.

[mark elder]

Point 4 is worth testing as it could identify various causes - different bore, fluid leaking past the main seal, fluid leaking past secondary seal to the reservoir. For some checks it would be good to blank-off the master cylinder outlet as any significant movement of the pushrod would suggest a seal issue internally.

If you have a quick release in the line, then this is easily tested; disconnect and check the pedal; it should be like a rock.

[DaveW]

Additionally, the SAAB slave piston position is basically self-adjusting - it will take up any extra slop between the TO brg and the clutch fingers. I.e., it only retracts enough to zero the force pushing it back. This minimizes the amount of necessary slave-piston travel w/o causing any load on the clutch fingers while the clutch is engaged. So, unless the slave piston is extended so far that it binds or comes out of the cylinder, or pushed back so far that it bottoms, that should never be a source of extra master cylinder piston movement or lack of engagement. So one has to look elsewhere.

The 1/8" or so free-play used to set up the slave position vs the fingers must be done with the slave piston fully retracted. That optimizes its position preventing binding or over-travel to release the clutch.

So if everything else is properly installed I would suspect some air left in the fluid system. Does the pedal feel "spongy" at 1st press? If so it's likely a sign of air in the line or elsewhere. Is the SAAB bleed port at the top so it can bleed properly?

[Lee Johnson]

[QUOTE=tlracer;643129] "Okay, taking it as they are the same bore, then something else has to be happening here. I would be looking to answer these questions:
|
3) Did the new master come with a pushrod and, if so, is this the same length as the pushrod on the old one?
|
Point 3 is possible if the new pushrod is longer, so setting the pedal in the 'normal' place meant the master was already partially depressed
|"


If the master cylinder is partially depressed too far (i.e., piston seal continuously isolates the fluid reservoir from the pressure chamber), then it seems no new fluid will get into the system during bleeding. This would potentially leave air in the system & insufficient slave cylinder travel while that air is being compressed. I don't think those symptoms have been reported, although lots of data & hypotheses are in this thread.

Lee

[tlracer]

Additionally, the SAAB slave piston position is basically self-adjusting...

Similar to other concentric slave designs, eg. Van Diemen, Swift, etc. no return spring, unlike Hewland external slave.

As you say Dave, any remaining air should show up as an initially spongy pedal, but I seem to recall Steve D saying the pedal is firm?

If, as I understand, the whole system is back to 'normal' using the old m/cylinder but, with the new one, the slave throw is reduced - unless the pushrod is adjusted longer - then the cause must be in the new m/cylinder?

[Steve Demeter]

The pedal is FIRM with the first push.
The to bearing to fingers gap was measured with the slave fully retracted.
The bore of the new slave vs the old one is not known at this moment. Old one was sent to Scotty. Will check to make sure.
Pedal pivot is in same hole on floor. But there a couple of alternates that might favorably rotate the pedal without sacrificing total pushrod travel.
Pushrod length are the same. PN initial install set the nut on the pushrod that jams against the rod end connected to the pedal the same distance from the mounting face of the MC new vs old. Had to extend it quite a bit to get clutch to release. About 5 turns on a 5/16-18 thread.

Thanks to all again for the ideas.

I just will keep reviewing them one at a time and trying out the new ones

[Rick Iverson]

The amount of clearance can be debated but I would be happy with anything from 2mm to about 5mm. I aim for 3mm.

Mark;

Do I understand correctly that there is a method to adjust the gap?

[DaveW]

Mark;

Do I understand correctly that there is a method to adjust the gap?

I did this with measurements from the bellhousing and block surfaces that bolt together. It's just add and subtract the various measurements to get the gap from the fingers to the TO brg.

[mark elder]

To adjust the gap; if too little gap then you need to machine something. You could machine the bellhousing (difficult) or take something off the TO bearing (easy); I think I took it off the back last time (measure and look twice; engage brain; cut once).

If it is too much gap, I have made a shim to go between the TO bearing and the bellhousing

[tlracer]

About 5 turns on a 5/16-18 thread

Thanks for the checks and clarification, Steve! I've copied the above as the increase needed in pushrod length is around 1/4" from this?

In a 0.75" master cylinder, that is a fairly small volume of fluid displacement...could that volume simply be variance between the operation of the old and new cylinders?

[Steve Demeter]

At this time I think ANYTHING is possible.

Not sure how to test that.

But to clarify even after rebuilding the "old" MC it would not operate the slave. IT was fried. Piston did not even return when holding it in one's hand.

Have confirmed that the old one is in fact 0.75 bore.

At this point not going to touch the new one til this winter. Too many things to go wrong. And I have experienced many of them the last few weeks

[Rick Iverson]

…..dead pedal

What is that?

[Fred Michael]

A dead pedal is a foot rest for your left foot

[BorkRacing]

What is that?

A pedal you push that brings Jerry Garcia music to you earplugs during a race.

Personally I use a heavy metal pedal because I tend to push hard at the end of a race.

[Rick Iverson]

a pedal you push that brings jerry garcia music to you earplugs during a race.

Personally i use a heavy metal pedal because i tend to push hard at the end of a race.

lmao

[tlracer]

Thanks for the checks and clarification, Steve! I've copied the above as the increase needed in pushrod length is around 1/4" from this?

In a 0.75" master cylinder, that is a fairly small volume of fluid displacement...could that volume simply be variance between the operation of the old and new cylinders?

Quick calculation, I make it 0.06 fl.oz (US) volume. I'm not too familiar with the Saab clutch though, so I don't know if that could be a 'normal' variation but is doesn't seem to be a huge amount...anyone?

[DaveW]

From a calculation I made several years back:

[tlracer]

Thanks DaveW - a 0.75" dia master has a piston area of 0.441 sq.in, so approximately half the effective area of the Saab slave shown in your calc.

That would mean a 1/4" piston displacement in the master would give a 1/8" displacement for the slave, assuming no air gaps and fluid at 100% incompressible.

[Steve Demeter]

Well made it through an entire weekend and not a single issue with the clutch. HOORAY. Thanks to all who offered ideas, advice, suggestions. A big shout out t6o Scott Young and Rex Gunning in particular who helped a lot off the forum.

Community will always figure the problem out no matter how goofed up the guy working on it is..