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Notes from a Pedal Assembly Rebuild

 
Old 03-25-2012, 06:58 PM
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bruce7
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Default Notes from a Pedal Assembly Rebuild

Notes From a Pedal Assembly Rebuild

I took delivery of my '97 993 coupe April 2011 with 43k miles on the clock.
In July I took my annual 3600 mile driving vacation trip from L.A. to Missouri and back,
passing through about 10 states and every different type of terrain. It's a fantastic
way to spend time with the car you love. Anyway, the second day out the clutch
pedal began to not fully return. When I got back I began to research this problem and
learned about the clutch "kinematic" lever issue. To eliminate the possible cause
of air in the clutch hydraulic line, I bleed the clutch a couple of times but it didn't fix the
problem. So I gathered the parts to rebuild the pedal assembly. After about 2 months
of elapsed time, I finally got it all straightened out and now it works perfect. Along the way
I made some notes that I wanted to share since someone else may encounter a similar situation.
It's one of those rare days when it's raining here in L.A. so I finally sat down to write this up.
I'll just hit the highlights since this rebuild has been covered here and elsewhere before.

Accompanying photos and figures can be found here:
https://picasaweb.google.com/bruce.c...CIO06cK6laz2Kw


1. Beware of Defective Clutch Levers

I'm not talking about the one already in the car. I mean the brand new one you just got from Porsche parts.
Yes, it's true. My first replacement clutch lever was defective and led to a lot of rework at my expense since I did
the work and not Porsche. Porsche did refund the cost of a second clutch lever, but the time and materials
is not covered unless a Porsche dealership does the work. (Sunset Porsche did good by me and I got the refund
in 2 weeks after submitting the defective lever.)

What was the defect? The lever has a toothed ring gear that is welded into it. It enables the lever to slide onto the
clutch pedal shaft. It is keyed so that it is positioned properly and can only go on one way. Well, the gear was rotated
by one tooth. The result was that after installation of the pedal assembly, the clutch pedal was lower than the brake
pedal by about 1-1/2 inches.

This may not be as rare as you might think. There is a post on here where someone reported the exact same issue.
Following pedal assembly reinstallation the clutch pedal was not at the correct height.
(See https://rennlist.com/forums/993-foru...dal-lever.html)

That problem was never answered as to what was the problem. The gurus were stumped. Well, I think that cold case has now be solved - it was a defective clutch lever. When you look at the mechanics of the assembly, there really is no other way to explain it.

So the lesson here is not to assume anything when you get a replacement part. Look it over very carefully to see that it
matches the old part. Also, this could have been detected during bench assembly if I had known what to look for. If the
two pedals heights don't match up, something is wrong.


2. Causes for Failure of Clutch Lever

The clutch lever has had 3 iterations and the current part number is 993-423-519-03.
This is the part I took off my car that failed so it is not perfect either. I think they just gave up.
In looking at the visible wear, it seems that there may be alignment issues and/or lubrication
issues that lead to the failure.

The clutch master cylinder plunger doesn't line up perfectly with the bottom lever attachment rod.
The plunger has some side play to account for some misalignment but I noted some wear on the side
of the lever.

The two small "levers", which the PET calls them, that connect the top piece of the clutch lever to the rocker (a white plastic
part that rotates on a shaft where the return spring lives), also do not line up perfectly with their attachment point
and considerable wear is evident on the face of the clutch lever.

Over time, the binding that these misaligned parts would cause could keep the clutch pedal from returning fully.

Lubrication could help forestall eventual part failure.

During assembly, I used a grease found in the PET for the 996 to lubricate pedal assemblies. The part number is 000-043-203-37.
I believe it to be manufactured by Castrol and is know to them as Castrol Optitemp LG 2. The shop manual says to coat all bearings
and slide faces with a Teflon-compatible low temperature grease. The Castrol product satisfies this requirement but is not available to the public. It is only sold to auto manufacturers, so you have to get it from Porsche. There's enough in one tube to probably lube every 993 ever made. Here is a product data sheet:
http://www.dcproducts.com.au/Castrol...ts/LG2-tds.pdf

OK, that's great during assembly where you have access to apply the grease, but what do you do after the pedal assembly is installed
in the car and let's say it's a year down the road and you want to re-lube the assembly?

What I plan to do is use Wurth HHS-K spray lubricant. It has good properties, is easily available and has a permanently attached straw that makes for ease of use.

Bottom line though is that the pedal assembly didn't appear to get the necessary development it deserved. The misalignments should
have been dealt with and eliminated. Perhaps Heim joints could have solved the problem. Even with the latest version and periodic lubrication it may be necessary to replace it again.


3. Do Final Assembly in Car

The shop manual says to refit the complete assembly back into the car and connect everything up. I found this impossible. Maybe it
is just my car, but I've had the pedal assembly out and back in on two separate occasions and I could not get the clutch master cylinder
threaded to the outlet pipe. This operation couldn't be any more awkward. You have to lie stretched out with your arms over your head,
and blindly try to thread the bolt into the master cylinder with one hand. It seems you are fighting 2 or 3 opposing forces. It was also
between 90-100 degrees that day and my frustration level was beginning to boil.

Finally, I thought, let's see if I can get the master cylinder started and threaded on it's own. So I took it off, threaded it halfway with ease
and verified that worked. Then I wondered if I could just slip the rest of the assembly in there and finish the install. Lo and behold, it worked! It was so easy I couldn't believe it. So if you are having trouble getting the bolt threaded due to tension in the clutch pipe or whatever, try this idea it might work.

Related to doing final assembly in the car is this one other tip. Screw the brake light switch in after you have everything else in and bolted down. The first time I put the assembly into the car, I snapped off the brake light switch and had to special order it. There is plenty of room to put it in after the fact.


4. By-Pass the Clutch Interlock Switch

The clutch interlock switch is in the way to get to the master cylinder bolt on the left side. So you need to have it off when doing
final assembly in the car like described above. But why even put it back on?

I first became aware of this tip while talking with Steve Weiner. He suggested by-passing the clutch interlock switch. Then you do not
need to put your foot on the clutch when you start the engine but more importantly it saves wear on the crankshaft. This tip can also be
found on this forum. (See https://rennlist.com/forums/993-foru...il-switch.html)

And recently, in "911&Porsche" magazine, in the March 2012 issue, on page 106 this advice is repeated. This was in connection with diagnosing crankshaft wear on a Carrera 2.7 RS. I'll quote it here for those without access to this issue.

"..starting the engine with you foot on the clutch, especially from stone-cold. That always puts lots of additional load on the thrust bearing, and until the engine is running there is very little oil in the area to lubricate it. And obviously, that's worse the stronger the springs inside the clutch. Thrust-bearing wear on an air-cooled 911 crank occurs not, as you might expect, on the face nearest the clutch, but on the opposite side of the same journal. This is because the clutch tends to pull the crank towards itself when you operate it. It's not an uncommon problem in older engines, but can usually be avoided with care."

Here's what I did. I took a tie-wrap and closed the switch contact. I then took some gaffer's tape and wrapped the entire switch up and
pushed it under the assembly out of the way.



5. Bolt the Pedal Assembly Down to a Bench

When working on the pedal assembly, I found that bolting down the assembly to a "bench", in my case an empty pallet,
made working on the assembly easy. The shop manual suggests using a vise, but I didn't have access to one and now I think
this is a better idea. A combination of washers and nuts leveled the base and the space between the pallets actually helped since
the bottom of the assembly is not flat.


6. Careful with the Rocker

This is soft plastic and easily broken. The return spring is powerful and if you're not careful you can ruin the rocker when the
auxiliary tool is in the rocker.

I don't know why they made this out of plastic, unless it was noise or maybe just cost.



7. Final Tip - Remove the Heater Tube when Bleeding Clutch

Removing the left-side heater tube is easy and really helps to gain access to the clutch bleed screw.
It's a good time to also clean it and make it shine. Nicer then the next time to bleed the clutch.


OK, so there you go. Would be interested in what your thoughts are on any of these points?

-bruce
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Old 03-25-2012, 09:35 PM
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AOW162435
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Very nice writeup, Bruce.


Andreas
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Old 03-25-2012, 10:23 PM
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Bruce, thanks for the info. The picture of the pedals shows you have some kind of extension on the gas paddle. Can you tell me what that is. I have had my car about 2 months now and the gas pedal is lower to the floor than the brake and it is impossible to heal/toe. I would love to know what you have. thanks
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Old 03-25-2012, 11:46 PM
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Great writeup.
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Old 03-26-2012, 01:28 AM
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wow, that must have been a bear to replace that white plastic piece.
some wood stain will make the plywood floorboard look beautiful. mine is so pretty now I didn't even put the carpet back in place.

996scott-while bruce's gas pedal solution works, notice in figure 4 how many threads are left on his brake pedal adjustment. lots of pedal clusters are set up so the clutch and brake pedal are even, for looks or feel or whatever reason.
on our 993's there is tons of adjustment for the brake pedal, just 3 turns will make a huge difference in the alignment of brake and gas while braking.
remember to adjust the brake light sensor when you move the brake pedal.
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Old 03-26-2012, 08:27 AM
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Great write up. If you own a 993 long enough . . . . . .
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Old 03-26-2012, 09:24 AM
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Garth S
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+1 on the write up ...

Agree with your points on lube - and that the latest iteration of the kinematic lever assurance of a cure.
My clutch pedal occasionally hangs up upon release for a fraction of a second, and then snaps up with an audible "sproing" of the return spring - or is prompted to do so with a feather light tap of the toe during the release ( ingrained reflex).
I've cleaned the pivots, etc in past - and have a complete spare assembly - both of which have the latest lever p/n: this time in, the plan is to thoroughly spray each contact surface with a high tack synthetic grease ( Wurth HSS 2000) that has a good 'creep' factor for penetration ..... and plan for success.
This is an issue fully contained within the pedal assembly, at least in my car: the clutch clearly engages/disengages correctly, so no concerns there - just a sticky pedal return.
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Old 03-26-2012, 11:08 AM
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Originally Posted by bruce7 View Post
Beware of Defective Clutch Levers

I'm not talking about the one already in the car. I mean the brand new one you just got from Porsche parts.

What was the defect? The lever has a toothed ring gear that is welded into it. It enables the lever to slide onto the
clutch pedal shaft. It is keyed so that it is positioned properly and can only go on one way. Well, the gear was rotated
by one tooth. The result was that after installation of the pedal assembly, the clutch pedal was lower than the brake
pedal by about 1-1/2 inches.
Looking at your pics, you replaced an -03 lever with a new -03 lever.

I have my pedal assembly apart waiting for some parts to come in. I just compared my original kinematic lever (yellow chromate type plating) to my new -03 kinematic lever.

Stacked upon each other so that the keyed spline lines up, the bottom edge of the kinematic levers line up.

I really can't see any major differences other than possibly the small hole is shifted ever so slightly and the two welds (the original had an offset stamp to raise the contact point) and a small plate welded to the new -03 kinematic lever.
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Old 03-26-2012, 11:41 AM
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Originally Posted by bruce7 View Post
The two small "levers", which the PET calls them, that connect the top piece of the clutch lever to the rocker (a white plastic part that rotates on a shaft where the return spring lives), also do not line up perfectly with their attachment point and considerable wear is evident on the face of the clutch lever.
That wear, no matter how well lined up everything is, will happen because those two levers (intermediate piece as Porsche calls them) are under compression and will want to "buckle" as the clutch pedal is depressed.

With only a couple of pins (bolts as Porsche calls them) and retaining clips (locks as Porsche calls them) to sandwich the white plastic part and kinematic lever with those intermediate pieces, there is enough play to set up slight angles while they are in compression...so those parts are going to rub and wear slowly.

Talk about an overly complicated system. I guess they have that big spring in there and levers to generate an over-center condition when the pedal is fully depressed...sort of a power clutch system.
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Old 03-26-2012, 01:27 PM
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bruce7
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Originally Posted by 996scott View Post
Bruce, thanks for the info. The picture of the pedals shows you have some kind of extension on the gas paddle. Can you tell me what that is. I have had my car about 2 months now and the gas pedal is lower to the floor than the brake and it is impossible to heal/toe. I would love to know what you have. thanks
Hi,

The gas pedal extension was on the car when I bought it. I've left it on but have thought about taking it off. It looks like they took another pedal and stacked them. Here is another picture with more detail.

-bruce
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Old 03-26-2012, 01:43 PM
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Originally Posted by k722070 View Post
wow, that must have been a bear to replace that white plastic piece.
Hi,

Actually, replacing the rocker was pretty easy. Here are a few extra pics to help explain. Following the shop manual, you use a pair of brake pincers to remove
and install the spring/rocker assembly. I used the crescent wrench shown in the background to lay across the back of the block to spread the load. Removing it was easy for one person, but reinstalling it requires 3 hands, I had to get someone to insert the auxiliary tool (I used a clevis pin) while I compressed the spring.
The rocker and lever combination is assembled together and then installed onto the clutch pedal shaft as a unit. It is easy to lube the sliding faces at this point rather than later due to the closeness of all the pieces.

-bruce
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Old 03-26-2012, 11:50 PM
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That pedal is pretty crazy. It does look just like they bolted one on top of the other. Looks a little funny, but if you decide to get rid of it let me know. I would give it a try.
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Old 03-27-2012, 12:03 AM
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Saved as a reference for when I need to do this. Thanks, very nice job.
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Old 03-27-2012, 12:17 AM
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How long does it take you to pull out the pedal box now?

Great to know on the parts, this is on my list for the 95.
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Old 03-27-2012, 02:34 AM
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Nice Work! A couple of comments:

1 - Bypassing the clutch switch will disable the cruise control, correct? (not that many of use do that anyways).

2 - I have done perhaps 6 of these now, I usually leave the clutch slave cylinder attached in the car, and disconnect the rest of the assembly and pull it all out. I have done it the other way as well, usually if I am replacing the slave. Both are a pain but both are possible. It does take some contouring to work in the pedal area ( and I am 6' and 225 lbs).

3 - Interesting comments about starting the car with the clutch engaged causes some thrust bearing wear - I had not thought about that, good comment!

4 - i also do not remove the vent tubes if I bleed the clutch - not sure why these would be in the way. Mind you, I bleed on a lift so that might make some difference. I have a system with a jug hung on the cross member, and a long clear plastic tube from the bleed nipple. I then use pressure to bleed the clutch, but slowly since you do not lose much fluid in the reservoir before you will start to push some air.
Cheers,

Mike
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