Virginal 911 owner with a shuddering clutch

[UnSafe]

First, I'd like to thank all of the posters and Pelican Parts for contributing to a very nice forum. You've already saved my sanity and money.

OK, My wife's Grandfather had a '78 911SC with Targa top. Sort of a pet car, along with several other classic American cars. He passed away a year ago and left the Porsche to his only son (My wife's uncle) who lives in Oakland, CA, who feared that it would be stolen within days of it's arrival. We offered to buy it from him, and there you have it. Buford (Wife's Grandfather's middle name) is ours.

Buford has had restoration and repair work done, and supposedly had the engine (And maybe the tranny) rebuilt 3K miles ago. It seems to have all the usual 30 year old problems. Most I can work out, but a big one has me worried.

Since it's arrived, we've driven it about 50 miles, ran OK, sloppy and difficult shifting, but OK and a blast to drive.
After a short loop to the local lake, the clutch begain to shudder pretty bad on take off in 1st or reverse. Once hooked up, it does well, no slipping or shudder with acceleration..

I searched the posts and printed off the clutch adjustment tutorial last night and headed out to the shop to take a look today. The small, coil return spring on the clutch arm is missing, there's zero clearance at the arm adjusting bolt and a first attempt to adjust the Bowden tube made no difference.

I'm not sure if the sudden onset of the problem, the fact that it shudders while slipping the clutch into gear, but no apparent slipping once engaged, makes a difference?

Any ideas appreciated!

[SP2]

I am no expert, but I dropped my engine and replaced my clutch so I am familiar with the anatomy. When you take off from a dead stop it sounds like your clutch plate may be slipping on the flywheel. There might be some oil in there that might get better the more you drive the car and heat up thet clutch. The flywheel is constantly spinning as the engine is running. The clutch plate is what provides the friction to connect the engine to the transmission. Before you go replacing your clutch, try driving it a while. Just don't go too far from home in case it breaks down.

Welcome to the board BTW. Tradition has it that you post a photo of your new car! I am sure more knowledgable will chime in shortly.

[aigel]

The shudder is an indication that your clutch is not adjusted properly. If parts of the mechanism are missing, you will want to replace them first, then go through the adjustment procedure. The 101 projects book has an excellent article on it.

Good Luck,

George

[zipinitaly]

I had the exact same problem...the adjustment is in the rear of the car, the one that you need the .047" feeler gages for. Fixed mine...no problems since!

Good luck

[Lindz]

I have a similar issue but seem to have no shudder when the car is cold but after driving for a while it shudders a bit in first gear when engaging - would you think this is an adjustment issue as well?

[zipinitaly]

My car only had clutch chatter (shudder) when I "got on it" in first gear. Cold or warm, didn't matter. I had several other recommedations as to the problem, some very severe. The clutch adjustment fixed everything...

[Early_S_Man]

WE need pics to be sure that the omega spring is missing, but I believe you need to get a replacement and start the adjustment process after it is installed.

Too much slack in the Bowden cable [flex cable sheath usually covered in black plastic between firewall and transaxle mount that cable passes thru] will cause bad shuddering on takeoff. There need to be about 1" of preload on the Bowden cable.

[jmohn]

Originally posted by Early_S_Man
WE need pics to be sure that the omega spring is missing, but I believe you need to get a replacement and start the adjustment process after it is installed.

Too much slack in the Bowden cable [flex cable sheath usually covered in black plastic between firewall and transaxle mount that cable passes thru] will cause bad shuddering on takeoff. There need to be about 1" of preload on the Bowden cable.

Just want to emphasize Warren's comment. As he says, first be certain all the correct pieces are in place and properly adjusted, then, if you still have the problem, adjust the pre-load in the Bowden tube. I had this "shuddering" problem after replacing my clutch cable. I thought I had plenty of "pre-load" on the bowden tube, but I was wrong, it needs to bow up about 1 inch from it's "at rest" state. You may try adding some "bow" to the "bowden" and see if that helps. To do this, and get the proper adjustment at the clutch arm(s), you may have to adjust the location of the attachment clevis at the pedal end of the cable.

Good luck,

Jerry M
'78 SC

[Gunter]

Sounds like more than just an adjustment.
If the age of the clutch is unknown, it could very well be worn out meaning: Disc lining gone, rubber center shot?
A picture from underneath showing the levers and C-spring would help.

[Walter_Middie]

The above responses are most likely correct - however, a more remote possibility is that the bolts that hold the transmission and the engine together are not tight. You said it had recent work done on the engine and trans - so it's a possibility. I have seen this happen before, and it's easy to check.

[UnSafe]

Thanks for all of the replies to date!

To expand, my initial look underneath showed that it's the clutch arm coil return spring that's missing, not the "Omega" or circular spring. As far as preload or pressure on the Bowden tube, I set it so the rearmost lock nut is al the way to the end of it's threads, then tightened the forward locknut. No greater preload possible.

I checked the 4 engine to transaxle bolts. All tight. Still trying to figure out how to view more than a glimpse of the clutch pedal end of the cable. The cutout in the sheetmetal, to the right of the accelerator pedal is pretty small. Do I have to loosen/ disconnect the aft end of the cable to allow enough slack to adjust the front end?

Pics to illustrate:

My Honey, with Buford


The clutch arm, missing coil spring and zero clearance at the adjustment bolt


The Bowden tube adjustment. Looks like an old cable, if the rotten boot is an indicator of wear

[Zeke]

Forget pics of the drity trans. Get the girl out of the car and take your pics! She looks rather cute to me.
Oh, and we like car pics, too. It's sort of a rite of passage.

Now, AFA your clutch is concerned, any time adjustments are full out, that incicates a problem. You need to start a square one and make sure the arm and TO bearing are good and in adjustment. Then to the cable. Cables stretch and that's a sign it's about to break and leave you with the pedal laying on the floor. Now, you may also have a main seal problem and the disc just got oily on your trip to the lake. Look for oil. Don't down shift and let the clutch out to brake the car. Always rev the motor to match engine speed to ground speed before letting the clutch out. This can start a shuddering, too. I don't why that is, maybe sort of a grain on the disc.

[zipinitaly]

My problem was the clutch arm...I had zero clearance...and when I adjusted it out to the .047" that the book calls for, it fixed my problem.

[javadog]

Okay,

I see a few problems here. I wouldn't drive the car with the cable adjusted as in the picture.

First, I think a new cable would be in order here. If you want to drive the car before replacing the cable, do the following:

To adjust the "bow" in the tube, you want to adjust the cable length at the front, not the back. Adjusting it at the back just screws up the clutch adjustment.

Undo the cable at the back and remove it completely from the arm. Remove the pedal board at the pedals, disconnect the throttle pedal and get it out of your way. Flip the clip on the end of the clutch cable and remove the cable end from the lever. Make sure you catch the clutch pedal, so that the return spring doesn't pull it to the floor. Adjust the part on the end of the cable to lengthen the cable and still have adequate thread engagement. Tighten everything up and reinstall the cable, throttle and board.

Return to the rear of the car and set the clearance at the adjustment bolt to 1.2mm. Reinstall the cable and adjust it to get 1.0mm clearance. Enlist a helper (preferably the pretty lady in the photo) and have her push the clutch pedal all the way to the stop on the board. Measure something convenient on the cable, say the end, compared to some fixed point on the transmission. Have her release the cable and make the same measurement. Subtract the two. Adjust the clutch pedal stop on the board until you get a difference in these two measurements of 25.0mm.

Then, test drive the car and see if any further work is needed.

JR

[john70t]

Wouldn't hurt to put in some new Swepco trans fluid while you're at it(lol the disease starts), or check it.

[UnSafe]

It keeps getting better, again thanks for all of the input.

I'm going to order a new clutch cable, helper spring and coil return spring, then dive into the pedal assembly removal or needed access to the front end of the cable after we return from our annual ski trip/ AKA medical conference.

I'm scratching my head over something and am not sure if it would contribute to the problem. The rear brakes drag somewhat. More than any other disc brakes I've worked on.

I pulled the rear wheels off and could barely rotate the rotors by hand. It doesn't appear to be the parking brake, as there's slack in the cable housing and I can work it on/off. I even marked the rotor w/ chalk, and yes, it rubbed off with one turn.

Normal for 911 brakes? Bad pad return mechanism? (Unfamiliar w/ Porsche terminology). Brake drag participating in clutch or shifting problems?

[Zeke]

Brake drag and clutch are not associated directly. Your hoses are probably bad, but you need to check the calipers, too. People around here change their hoses at a maximum of 10 years. They swell shut sometimes. No need to even let them get close to doing that.

Sounds like this car needs a top to bottom inspection and some service. You better take the fuel level sender off the tank and take a gander down there with a pen light to see if the bottom of the tank is still clean and bright. If you see rust, you're looking at some more problems down the road. Clean fuel lines and clean brake lines are a MUST.

Now, where are the pics of the rest of your car and your pretty GF??

[UnSafe]

Pics will have to wait until we get back

I'll screw w/ the brakes after a nose to tail inspection and "wallet biopsy" part ordering session. This thing's pretty, a blast to drive, but I'm having flashbacks of my old '65 VW Baja Bug thrasher as I look closer and find problem after problem...

Off to Breckenridge. The forcast says it's only going to be snowing for the last 350 miles of the trip there

[Gunter]

Unsafe:
Aside from getting a new cable, C-spring and coil spring, you need to ensure that the long release lever pivots freely on the cross shaft.
Disconnect the cable at the transmission end. Remove the small circlip at the end of the cross shaft, slide the short position lever off the splines. Now try and remove the long lever. It may be stuck and you'll have to pry it off.
I suggest strongly that you get the Bentley SC Repair Manual so you can learn more about your car like maintenance and adjustments.
When installing the new parts, use Moly grease on the pivot-points.
For the new cable: Remove the inner strand-wire cable from the sheath, lube with Silicon, re-insert and install/adjust per Bentley.
Your picture shows the adjustment screw at its end, so, I suspect that there is no more lining left on the disc meaning: It's getting close to the rivets and you'll need a new clutch.
You can try and place the small positioning lever back on the spline of the cross shaft one tooth off to get more adjustment with the screw but it may not work.
If the disc is at its end, no adjutments will help.
The levers look pretty rusty and haven't seen lube for a long time and that means the parts inside like the guide tube, release bearing and input shaft spline are most likely as dry as camel ***** in the desert.
If engine work was done 3k ago, it strikes me as odd that the clutch was not relaced and properly adjusted with a new cable.
A 911 is no fun to drive if things are done on the cheap.
It's not an old bug; it'll cost a few thousand $ to have this 30 year old race horse restored.
As for the brakes: The pistons in the calipers are frozen and will not retract. That means the pads are constantly rubbing against the rotors robbing you of HP. Pistons will freeze (rust) inside the calipers when not "exercised" (Stored for too long)
It means a caliper rebuild all around since the front is probably just as bad. Do a rebuild and also replace the rubber brake hoses if they look old.
You can try and free the pistons by taking the wheel off, pry back the pads with the help of large channel locks, then push the pistons back out with the brake pedal. Repeat this "exercise" 3-4 times and see of it helps.
Get the Bentley; you'll love it.
BTW: I am a "hands-on" ME with lots of experience and wouldn't steer you wrong.

Have fun and play it safe

[Gunter]

The adjustments should look something like this:



If the disc lining is finished, and/or the cross shaft is frozen, no adjustments can be done.