Dragging clutch after replacing clutch/pressure plate (3.2)

[sid86]

Click here to read the outcome: http://forums.pelicanparts.com/porsche-911-technical-forum/913875-dragging-clutch-after-replacing-clutch-pressure-plate-3-2-a-3.html#post9307221


Hi all,

Some facts
- 911 3.2
- 915 gearbox, first generation (around ±1974 if I remember correctly)

So after spending a ton of money on parts and labour, the car feels worse than before...

Previously the car shifted hard to first gear (grinding), which was because of a worn synchro. Other than that, the car shifted fine.
I decided to have the engine and gearbox pulled out. I brought the gearbox to a specialist who only does these 915 gearboxes. Because the clutch was about half way, my mechanic recommended to install a new one since everything was already open. And because everybody loves upgrades, I decided on a lightweight pressure plate as well (SACHS)... To make things complete, I had the flywheel smoothened because of some burn marks (which was done nicely), and the whole package (flywheel, pressure plate, clutch) was balanced.

Two weeks ago everything was installed. Right from the start it was hard to get into first gear. Other gears were easier once driving. Warm/cold gearbox oil makes no difference. I replaced the new Swepco oil and filled the gearbox (with all new synchros, new bearings, new gaskets, etc etc) with Kendall: no difference. I bought a WEVO linkage: no difference. The adjustment of the coupling was to be blamed, but after fiddling around with it for days...: no difference.

So last Monday I was fed up and gave the guy who did the gearbox a call. He immediately invited me to his shop so he could have a go. After a couple of rounds about the block the conclusion was simple: gearbox is fine, the clutch is dragging. When the gear is in neutral, the clutch pedal is pressed, and quickly after that 1st gear or reverse is selected, you can hear the gears grinding.

About 1 out of 20 times, 1st gear can actually be selected, although it being difficult. It's easier to select 1st gear when still rolling (for instance to a traffic light).

After this long intro the question now is: what could be causing the clutch to be dragging? What could we have missed during installation? Any experience with dragging clutches on a 911 3.2 with 915 gearbox?
Any help would be much appreciated, because after 2 years of work I now dropped it of at the painter and am not to eager to drive it back home once it's finished!

More facts
Clutch cable was replaced a year ago, no problems since
Gearbox completely revised
New clutch fork (old one was worn)
Kendall gearbox oil
New SACHS clutch and lightweight pressure plate (article number 88-3082-999-746-M410)

[strictly]

clutch shaft operating bushes? Presumably checked/replaced at the time of the clutch fork.

Does the operating arm move freely on the fork shaft, the one thats designed to "slip", not the little one? If thats binding that would create drag. I presume the clutch cable itself has the correct adjustment

have you done any work on the pedal box? new bushes? clutch pivot pin broken? What does the clutch pedal spring look like (the one by your foot)?

I think you need to disconnect the cable from the bottom of the geabox, confirm the operation at the clutch pedal, then check how the main operating shaft "slips" the one which the helper spring attaches too (under gearbox, you will have to remove the circlip, and pull the little one off). while your are there pull on the clucth cable and let go, a few times to feel feel how the cable mechaism is (i,e drag or free to move). Then readjust the clutch cable to factory spec.

If it all seems normal then its inside (i.e clutch/fork/clutch shaft bushes)

[yelcab1]

Did you measure the minimum thickness of the Flywheel?
Minimum thickness of the pressure plate?
Minimum thickness of the clutch plate, was this OEM, Porsche, or something else?
Did you adjust the cable to specs? and then tighten the freeplay a little?
Good idea about the pedal box...

I would personally go back to the stock pressure plate

[sid86]

Thanks for the pointers, much appreciated!

The clutch cable was adjusted to 1mm free play, but made no difference.
No work was done on the pedalbox. The clutch pedal goes all the way to the bottom.

I don't think the clutch shaft operating bushes were replaced, but I would have to check the invoices.

I brought the flywheel, clutch and pressure plate to a specialist to have them balanced. I presumed, also because most parts were new, that they would have been measured. But aren't the flywheel plate and pressure plate more likely to be too thick instead of not meeting a required minimal thickness?

The clutch plate and lightweight pressure plate are new SACHS parts.
The flywheel is standard Porsche.

check how the main operating shaft "slips" the one which the helper spring attaches too (under gearbox, you will have to remove the circlip, and pull the little one off).

Do you mean disconnect the helper spring mechanism, and see of it make a difference? Because of my limited knowledge of the English language I don't seem to understand the underlined part. Thanks again for the help.

[yelcab1]

Here is how I would test it.

If the gear box can be shifted on the bench, or with the engine off, into all gears smoothly, then the gearbox is fine.

Then, if the gear box can be shifted with the engine idling clutch cable depressed fully, into all gears, then the clutch engagement while the car is standing still is fine.

If the gear box cannot be shifted into certain gears while the car is moving, then you have to look for dynamic reasons for why the gearbox and shifter mechanism is out of alignment, such as engine mounts, shift linkages, bushings.

I think your problem is that 1st gear is hard to get into even standing still. This points to a clutch fully disengagement problem. Several possibilities:

Cable related: stretched, broken, misadjusted, guide tube messed up inside tunnel. There is a travel specification that you can measure to eliminate this as a problem.

Clutch components: Clutch plate too thick, pressure plate too weak,

Installation issues: Something was misaligned when the whole thing goes back together.

Some of these problems require removal of engine to fix.

[sid86]

That's a nice systematic approach yelcab1, thanks for sharing. I will certainly strongly suggest the garage to take this approach, even though the clutch cable, pedalbox and other linkages seemed fine before.

Update in about 2 weeks I hope.

[john walker's workshop]

Nobody has mentioned the cable sheath adjustment for where the clutch engages and releases using the pedal. There are two clutch adjustments. One for the clearance between the two arms on the transmission and one for pedal engagement point.

[brianlay]

I agree with John.

simply needs proper adjustment.

[gomezoneill]

I just installed a lightweight pressure plate and had the same issue. The cable adjustment had to be tighter than the 1 mm arm freeplay. Tighten up the cable just a small amount and you'll be fine. The lightweight plate also makes the depressing of the pedal about twice as hard to push to the floor. Wished I'd never used the lightweight plate the original would have been more comfortable to drive.

[sid86]

Thanks John and brianlay, I never heard of that adjustment point!
Could you provide a little more info on where to find it?

@ gomezoneill: did you install the same SACHS part? To be honest, I can't feel any difference pressing the clutch pedal... but also no noticeable difference in revving. It's the 'worst' decision I made on the car concerning buying new parts I think only in combination with a new lightweight flywheel it would have made an 'improvement'.

[brianlay]

A summary of the procedure can be found here.
Porsche 911 Clutch Adjustment | 911 (1965-89) - 930 Turbo (1975-89) | Pelican Parts DIY Maintenance Article

Figure 3 shows the threaded sleeve of the clutch cable with the adjusting nuts. With those nuts loosened, pull the cable sleeve back away from the transmission and get all the slack out of the cable. It helps to have an assistant hold the pedal all of the way up against the stop.
now move the forward nut on the sleeve to hold that slack and then tighten it further to reduce the gap between the levers by .2mm.
tighten the rear locknut on the cable sleeve to hold the cable in place.
Finish by checking the total cable travel and adjusting the pedal stop to limit travel to 25mm



Once

[sid86]

@ brianlay: thanks! I thought at the pedalbox, but this makes sense. I will check it!

[Quinlan]

Originally Posted by brianlay

A summary of the procedure can be found here.
Porsche 911 Clutch Adjustment | 911 (1965-89) - 930 Turbo (1975-89) | Pelican Parts DIY Maintenance Article

Figure 3 shows the threaded sleeve of the clutch cable with the adjusting nuts. With those nuts loosened, pull the cable sleeve back away from the transmission and get all the slack out of the cable. It helps to have an assistant hold the pedal all of the way up against the stop.
now move the forward nut on the sleeve to hold that slack and then tighten it further to reduce the gap between the levers by .2mm.
tighten the rear locknut on the cable sleeve to hold the cable in place.
Finish by checking the total cable travel and adjusting the pedal stop to limit travel to 25mm



Once

This is what I went through very recently. I wasn't getting all the slop out of the pedal using the 15mm adjustable nuts, since I didn't have the clutch pedal propped up to the very top.
One thing to be aware of - if you have an aftermarket cable (as opposed to genuine Porsche) it might have to be shortened by about 1-1.5 cm at the pedal end. I compared my old cable with the new, and that was the difference in length. If you don't shorten it you won't have enough room to adjust the clutch - it will drag.

[sid86]

I had this cable installed, but no idea if it is original Porsche...

http://www.rosepassion.com/nl/cat/porsche-911-74-89-1979-3-0sc-coupe-manuele-bak-5-versnellingen/M158/koppeling-en-vliegwiel/koppeling/B1524/pedaalas-ontkoppelingskabel-rubber-pedaal/I1896/kabel-koppeling-stuur-links/P31234

[sid86]

The supplier of the cable just confirmed that it's not an original porsche cable, so I will surely check the slack once I get the car back from the painter...

[sid86]

I picked up the car this morning. A new original Porsche clutch cable was fitted. However, no improvements...
When pressing the clutch and immediately shifting into first gear or reverse, you can hear the gears grinding.
When you press the clutch, wait 1 second, and then try the select first or reverse, there is no grinding
I guess I will have to check the slack myself.

[jlex]

Originally Posted by sid86

I picked up the car this morning. A new original Porsche clutch cable was fitted. However, no improvements...
When pressing the clutch and immediately shifting into first gear or reverse, you can hear the gears grinding.
When you press the clutch, wait 1 second, and then try the select first or reverse, there is no grinding
I guess I will have to check the slack myself.

That's the way my '85 always acted.... needed a pause between shifting to allow a smooth shift to the next gear.... that's normal for the 915, right?
In fact, the manual itself says "before shifting into reverse, the clutch pedal must be depressed for several seconds..."
The G50 in the '88 I now have is much smoother & a more enjoyable drive. JMO.

[yelcab1]

Reverse has no synchro so a second wait is to be expected. First gear dog teeth is different from other gear, I hope the rebuilder used the right one. In any case, a bit of a wait before shifting into first is not a deal breaker.

[brianlay]

Still needs to be properly adjusted

[BGCarrera32]

Originally Posted by john walker's workshop

Nobody has mentioned the cable sheath adjustment for where the clutch engages and releases using the pedal. There are two clutch adjustments. One for the clearance between the two arms on the transmission and one for pedal engagement point.

Yup cable adjustment. ^^^^

Get the car up in the air and have your wrench walk you through the clutch arm adjustment process he used and check everything against a Bentley manual or the Pelican Parts book.