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Old 09-02-2020, 01:28 AM   #1
Sketchysedan
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Default Hydraulic clutch bleeding

Just installed a spec stage 3 clutch in my 740 turbo. I’m using a new clutch, new clutch fork and new slave cylinder with a flat flywheel. When using the factory rod on the slave cylinder, after bleeding, the piston over extended and the seal blew out of the slave. I made a longer rod and bled the clutch again, and it seems to hold pressure. The only issue is that the clutch grabs all the way at the top of the pedal throw and slips in anything but first gear. The clutch feels firm and I am getting clean fluid and no air when I open the bleeder. What should I do next? There is not much tension on the clutch fork with no pressure on the pedal, I don’t understand why it is slipping.
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Old 09-02-2020, 01:52 AM   #2
283SD
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New rod too long? Is there any free play or is the rod/arm tight in the slave cylinder?
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Old 09-02-2020, 01:59 AM   #3
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You need to adjust the pivot point of your clutch fork. Is this with a stock M46 car? Could be that the stack height of the pressure plate fingers is lower than stock.

Yay 80/20 aftermarket parts!
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Old 09-02-2020, 02:26 AM   #4
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no, it was a factory b230f/aw70 that now has an ft and m46. How do I adjust the pivot point of the clutch fork? I was having the same issue when I had the stock clutch installed, but assumed it was because the clutch fork I was using was cracked and worn on the pivot. I replaced the clutch fork and slave and same thing is happening. There is no play between the clutch fork and slave cylinder- I used a section of threaded rod and two jam nuts to make an adjustable rod. If I make it shorter, the piston pushes out of the slave. Any adjustment I make has no effect on clutch feel- there is always the same tension on the clutch fork, the only thing that changes is the “neutral” position of the piston. This is why I am confused on how to adjust it.
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Old 09-02-2020, 11:48 AM   #5
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Is the Spec clutch listed as applicable to the flywheel you are using? Has the flywheel been resurfaced? You definitely have a stack height issue, which moving the pivot point would compensate for. Extending the rod is not the solution as you have found. If you try driving the car & shift w/o the clutch mechanism (just rev-match), and it slips under load, you definitely have an overall problem with the clutch/flywheel setup.

Spec is really iffy in terms of quality/consistency. I have used a range of stage III setups (on whiteblocks) with sprung, unsprung discs, and never found them to be satifactory under all driving conditions.
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Old 09-02-2020, 12:01 PM   #6
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Stage 3 being a ceramic puck clutch?
If so, those don't have a lot of modulation to them. More on/off, with squealing in between those if you slip them a lot.

If it's slipping:
Did you clean everything with brake clean before assembly?
Is the FW resurfaced?
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Old 09-02-2020, 12:20 PM   #7
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Quote:
Originally Posted by Harlard View Post
You need to adjust the pivot point of your clutch fork. Is this with a stock M46 car? Could be that the stack height of the pressure plate fingers is lower than stock.

Yay 80/20 aftermarket parts!
Yes, or if it is too high the belleville spring goes over-center, so to speak, and the clamping force is weak.

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Originally Posted by Sketchysedan View Post
no, it was a factory b230f/aw70 that now has an ft and m46. How do I adjust the pivot point of the clutch fork? I was having the same issue when I had the stock clutch installed, but assumed it was because the clutch fork I was using was cracked and worn on the pivot. I replaced the clutch fork and slave and same thing is happening. There is no play between the clutch fork and slave cylinder- I used a section of threaded rod and two jam nuts to make an adjustable rod. If I make it shorter, the piston pushes out of the slave. Any adjustment I make has no effect on clutch feel- there is always the same tension on the clutch fork, the only thing that changes is the “neutral” position of the piston. This is why I am confused on how to adjust it.
The arm being cracked only matters for disengauging. The cover (pressure plate) is what clamps, and is best at the spec height. If the disc is too thin or too thick, no clampy. oil on surface, slips no matter how much clamping. Etc.
You had an issue before, of course it is still there.
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Old 09-02-2020, 12:21 PM   #8
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Originally Posted by lookforjoe View Post
Is the Spec clutch listed as applicable to the flywheel you are using? Has the flywheel been resurfaced? You definitely have a stack height issue, which moving the pivot point would compensate for. Extending the rod is not the solution as you have found. If you try driving the car & shift w/o the clutch mechanism (just rev-match), and it slips under load, you definitely have an overall problem with the clutch/flywheel setup.

Spec is really iffy in terms of quality/consistency. I have used a range of stage III setups (on whiteblocks) with sprung, unsprung discs, and never found them to be satifactory under all driving conditions.
What you are calling "stack height"..do you mean the disc thickness? Or are you referring to something else?
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Old 09-02-2020, 12:58 PM   #9
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Yes, the clutch is matched to the flywheel. Flywheel was freshly machined and everything was clean. The spec stage 2 in my 240 turbo performs great. I will see if it slips without pressure on the fork tonight. Since I am using a flat flywheel instead of a dog dish, do I need to move the pivot ball towards the front of the car and extend it?
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Old 09-02-2020, 01:13 PM   #10
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Washer or two under the pivot ball pedestal before you screw it on the bolt.
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Old 09-02-2020, 01:23 PM   #11
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Ok will try that tonight and update with results.
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Old 09-02-2020, 03:12 PM   #12
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Quote:
Originally Posted by mikep View Post
What you are calling "stack height"..do you mean the disc thickness? Or are you referring to something else?
Flywheel, Disc & PP. They need to be matched as a set. as I'm sure you are aware, any clutch kit for a specific application is designed to operate in a very narrow window - if the throw is - + what that is designed for, it won't work as intended, whether it be pedal position, over extension of the slave, PP fingers damaged, etc....
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Old 09-02-2020, 04:59 PM   #13
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Quote:
Originally Posted by lookforjoe View Post
Flywheel, Disc & PP. They need to be matched as a set. as I'm sure you are aware, any clutch kit for a specific application is designed to operate in a very narrow window - if the throw is - + what that is designed for, it won't work as intended, whether it be pedal position, over extension of the slave, PP fingers damaged, etc....
+1

In my case with Redblock hydraulic clutches, I like to have the fork positioned so that the pushrod is close to bottomed out at resting position.
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Old 09-02-2020, 05:18 PM   #14
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Originally Posted by Harlard View Post
+1

In my case with Redblock hydraulic clutches, I like to have the fork positioned so that the pushrod is close to bottomed out at resting position.
That's exactly how I set mine up.
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Old 09-02-2020, 05:44 PM   #15
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Anyone know if it is possibly to get the clutch fork and pivot ball out without pulling the trans again?
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Old 09-02-2020, 06:39 PM   #16
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It's possible. That mentioned, it's also kind of a pain in the ass.
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Old 09-02-2020, 08:21 PM   #17
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Quote:
Originally Posted by lookforjoe View Post
Flywheel, Disc & PP. They need to be matched as a set. as I'm sure you are aware, any clutch kit for a specific application is designed to operate in a very narrow window - if the throw is - + what that is designed for, it won't work as intended, whether it be pedal position, over extension of the slave, PP fingers damaged, etc....
Never heard it called that, just step height. Stack reminds me of a bike headset. Thanks.
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Old 09-02-2020, 08:46 PM   #18
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Doesn’t the slave cylinder piston overextending point to a different issue? Just asking because that also happened in my 122 with a Spec stage 3 clutch, factory 122 master, and 740 slave. I just assumed the two weren’t matched perfectly and was going to rig up a pedal stop to keep the slave from pushing the fork too far. Otherwise the clutch operates perfectly.
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Old 09-02-2020, 09:12 PM   #19
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Yes. That points to a pushrod or pivot issue.

I looked up clutch stack height. It pertains to automatics and motorcycles. I knew it rang a bell aside from steering head sets.
It does not pertain here.

Usually you have a step height (+-) for a clutch and cover pair. Mix and match means you need to measure the FINGER height with spec disc, then new disc, then add/subtract the step height.
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Old 09-02-2020, 11:17 PM   #20
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Ok guys. Just used two washers to space out the pivot ball. I can now use the factory rod included with the master cylinder, the piston is almost bottomed out in the cylinder when the fork is in its neutral position. However, the clutch still grabs all the way at the top of the pedal throw and the clutch still slips. What next? I’m still not understanding why it grabs so high up on the pedal throw.
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Old 09-03-2020, 08:43 AM   #21
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Quote:
Originally Posted by mikep View Post
Yes. That points to a pushrod or pivot issue.

I looked up clutch stack height. It pertains to automatics and motorcycles. I knew it rang a bell aside from steering head sets.
It does not pertain here.

Usually you have a step height (+-) for a clutch and cover pair. Mix and match means you need to measure the FINGER height with spec disc, then new disc, then add/subtract the step height.
Thank you for your research - that is what we meant, sorry for using the wrong term. In anything but a stock setiup, it has to include the flywheel height though, since a modded/custom and/or machined flywheel will not necessarily be the correct specification for the clutch being used.
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Old 09-03-2020, 08:47 AM   #22
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Quote:
Originally Posted by Sketchysedan View Post
Ok guys. Just used two washers to space out the pivot ball. I can now use the factory rod included with the master cylinder, the piston is almost bottomed out in the cylinder when the fork is in its neutral position. However, the clutch still grabs all the way at the top of the pedal throw and the clutch still slips. What next? I’m still not understanding why it grabs so high up on the pedal throw.
You're still back to an issue with the step (stack) height with the clutch. Think about it. Yours is acting like a stock worn clutch - grabs high in the pedal travel (slipping extra). OR the T/O is already depressing the fingers & therefore preventing full clamping force of the PP. Last possibility is just it's a crappy Spec clutch, which is always possible. Either way, it's a problem with the clutch disc/PP & flywheel combination, IMO

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Old 09-06-2020, 03:09 PM   #23
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Hello All,

Although this probably won't address the OP issue, which by the way sounds like a 'total height / thickness of the flywheel / clutch disk / pressure plate combo', I thought it may help others that end up with a 'hydraulic clutch adjustment' issue'.

I just completed a AW-71L to M46 w/OD conversion in my 1994 940. The donor vehicle was a 1988 740. The swap had it's challenges but the two key ones were the OD relay wiring set-up (to be solved soon - workaround in place), and the hydraulic clutch set-up (solved today).

I installed a new master cylinder, hard line, flex line and slave cylinder to ensure no hydraulic issues. The flywheel was skimmed (disc and pressure plate surface), and a new Sachs clutch kit (disc, pressure plate, release bearing and pilot bearing. Upon bleeding the system I was VERY DISAPPOINTED to discover the 'bite point' of the clutch pedal was within ~2.5 cm (~1 ") of the floor. No amount of bleeding improved this.

So, I tried the 'washer under the clutch fork pivot'. A bit of a pain to do this with the clutch fork in place and unfortunately in my case the pivot unscrewed with the stud attached preventing me from removing it completely. I felt it was too risky to try to pull the clutch fork out so I had to resort to cutting a section out of a washer to create a U shaped spacer. Be VERY CAREFUL if you try this, it is very easy to drop the washer and fishing it out of the bell housing is VERY stressful - ask me how I know.

Upon testing the 'washer fix' I could not tell the difference between the original set-up and the washer fix. So, on to plan B; a threaded adjustment for the push rod.

I took a 90 mm (~3.5"), 8 mm bolt (~5/16"), a nut, fiber washer and acorn nut (aka dome nut). To avoid corrosion issues try to use stainless steel or zinc plated fasteners. Note - in hindsight a 100 mm (~4"), bolt will give a bit more adjustment range but make sure the threaded portion is long enough to ensure the adjustment starting point is roughly the same as what it is with the stock push rod.

The rounded head of the acorn nut will fit nicely in the existing relief hole in the clutch fork. I cut the head off the bolt and carefully ground a rounded taper using my bench grinder and drill press (with file and then sandpaper), to match the existing push rod. I then took the acorn nut and ground the domed end to create a hole just large enough for the threads of the bolt to pass through. Grind the fiber washer to be the same diameter as the nut - the later will be a lock nut for the acorn and the fiber washer as a spacer to allow two wrenches next to each other for easy adjustment / locking. The reason for the fiber washer is it allows easy grinding to ensure the diameter is the same as the lock nut (typically 13 mm), but less than the acorn nut (typically 14 mm).

Find a pair of locking pliers or other tool capable of clamping the hydraulic flex line. Insert a piece of cloth between the clamp and the hose to further protect it. Have this ready when you push the clutch fork towards the slave cylinder - it will require some effort. When you have moved it about 15 mm (~1/2"), clamp the hose, this will hold the slave cylinder in this position. You can now remove the existing push rod. Slide the bellows off the push rod.

Slide the bellows over the adjustable push rod and put a little grease on the tapered end of the push rod and a big blob on the clutch fork end. Install the new push rod and release the hose clamp. The slave cylinder will return to it's 'zero play position'.

You can now start adjusting the throw to allow better clutch engagement. In my case, it now grabs about 5 cm (2"), from the floor - MUCH better!!

I have a picture of the adjustable push rod and the 'installed' set-up. Unfortunately I couldn't attach them as I don't have a photo account anywhere. PM me if you would like a copy of the 2 pictures.

Hope it helps!
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