Clacking From Right Rear - What Can it Be?

[johnjr]

My 78 SC has developed a clacking sound coming from the right rear area. It started out as a noticeable (but not loud) clicking when I would lift off the accelerator. The speed of the clicking would decrease with a decrease in engine speed, and seemingly disappear on acceleration.

I originally thought the sound was coming from underneath, and hoped it was a chattering clutch. Armed with this optimism, I adjusted the clutch cable and, while I was under there, checked to make sure nothing had worked its way loose. Everything seemed okay. When I took the car out after the clutch cable adjustment, the clicking had disappeared. Or so I thought.

A day or two later, the sound was back. It has now progressed from a clicking to a louder clacking. A friend of mine rode along to hear the sound, and was able to locate its origin as the right rear wheel area.

Now, the sound is very audible from outside the car and is still variable with the engine speed, but I can now hear it even on acceleration. The sound disappears entirely if the clutch is depressed and if I am coasting in neutral. I've made an appt with Steinel's already, but I would appreciate any input on a likely diagnosis. Thanks! Oh yeah - the car has just under 105K on it, and is my daiily driver.

johnjr
78 SC Targa

[jmohn]

CV joint?

Jerry M
'78 SC

[randywebb]

check all 4 sets of CV bolts

while still under there, spin the wheel and listen

if nothing found, take both rear wheels off and look around

[johnjr]

If it was a CV joint, would it make the noise when coasting in neutral? When I'm coasting there's no problem - only when I'm in gear (any gear).

[spooldup]

One of my 911s did the same thing,after replacing both axle assys. wheel bearings,swapped out wheels/tires from another car and all that $ spent-it was a dry limited slip that was cured by getting the trans up to temp and putting fresh gearbox oil in and driving the car regularly it went away.Cant say thats what your problem is but oil is a lot cheaper and easier to do than all the other work I performed!

[Grady Clay]

All good suggestions.

First thing is to get under there and check that all the CV joint bolts are tight. If one comes loose from the transmission or hub while driving – bad things can happen.

If the CV joint is failing, the worst is you get towed home.

Best,
Grady

[ed martin]

In the past while I was dogged by this confounding problem, I did a number of searches in an attempt to diagnose my problem. One post that comes to mind is Recales differential diagnosis. To date I believe the problem remains unsolved.

As I was driving there was a super annoying clunking sound that was coming from...?! My first instinct was to suspect the CV joints, particularly the ones near the transaxle case. I needed to replace my first gear syncro and do an engine drop so I figured this was a good time to take care and diagnose the problem. Once I had everything apart I noticed that the suspect CV joint surfaces on the inner and outer race were completely shot, a lot of pitting. So problem solved! Or so I thought.

Once I had the transmission and the assembly back in the car(83 SC Targa) it was time for the test drive. To my relief the first and second gear syncros that I had replaced were functioning flawlessly, but as I gained speed, there it was, that horrible clunking noise. Back to square one.

One of the lessons learned in this whole experience is that you just can not tell where the noise is coming from by simply driving and listening. At times it would sound as if it were coming from the center, other times I could swear it was coming from the right rear, and then there were times that I suspected the left front bearings. The way the car is constructed, the noises are just transmitted and reflected in a way to make finding the source impossible. I even tried jacking the car and spinning all the suspect areas. None seemed to make any noise. It only seemed to make noise when I was in the car and at higher speeds and under load.

To make a long story short, here is what I discovered. Found out that by removing the tire and the transaxle to the bearings it was a lot easier to find the problem. What was not evident by spinning the bearing when connected to the transaxle, even with the tire removed, was extremely evident once I removed the transaxle from the bearing. With the tire and transaxle seperated from the bearing(which seemed to dampen the noise), and by spinning the bearing by hand, the problem and the offending noise was now very evident. That is to say that the noise was clearly coming from the bearing. So to clearly diagnose the rear bearings, or to at least eliminate them as a suspect, I would highly recommend this proceedure. If the problem is not evidenced here at least you've reduced it to the CV joints or the transmission.

In my searchs it seems that more often than not the problem is with the rear bearing though, as was my particular case. By the way, when I replaced the rear bearings, the new bearings when you spin them in this manner make no noise whatsoever, so if your bearing makes any noise chances are it's probably no good.

[johnjr]

Thanks for all the replies. I will check the CV bolts tonight. From Grady Clay's post, I assume I should not continue driving, right? To check the bolts, do I just jack up the car, put in the jack stands and put a wrench on them or is there some special way I should know about?

Thanks again.

johnjr
78 SC Targa

[kepperly]

Check to see if the right side torsion bar mount has torn loose,
another rather common problem.

keith epperly
87 slant nose turbo look carrera cabriolet

[johnjr]

Well, I checked all the CV bolts last night - both at the transmission and the wheel. Everything was tight. I then tried to see if the axle itself was loose at either end by manually trying to move it back and forth/up and down. I also tried checked to see if there was any loosness in the wheel. Everything seemed fine - no free play in the axle ends or the wheel.

Stymied, I decided to recheck the clutch cable, since the sound definitely got louder after I had adjusted the cable a week or so ago. I undid what I had done, and then readjusted. This morning when I drove to work, the clacking sound was gone. What gives? This is probably a stupid question, but why would the clutch being maladjusted cause the clacking sound in the right rear of the car?

Thanks for all your suggetions.

johnjr
78 SC Targa

[ed martin]

You probably had the cable too tight and you were and putting pressure on the throwout bearing.

[johnjr]

That must have been it - much better than all the horror scenarios that were running through my mind. Whew!

Thanks again.

johnjr
78 SC Targa

[Grady Clay]

John,

Great that the CVs weren’t falling off and good that the noise went away but that shouldn’t be the end of the story. 911s don’t make clicks or clacks without a reason. Usually it is more economical, satisfactory and safe to chase down the noise.

Let’s review the symptoms:

The clickety-clack is road speed dependent – the frequency changes with road speed not engine speed.

It is load dependent – it changes with acceleration, trailing throttle and disengaging the clutch.

Adjusting the clutch makes a difference – noise disappears.

IMHO these are usually mutually exclusive – the clutch is on the engine side of the transmission and is engine speed dependent. Road speed is on the differential side of the transmission.

Are you sure of these symptoms? This may mean you have to make the noise reappear. When you adjust the clutch, what is your procedure for lifting the car?

My next question is “is the noise gear dependent?”


This still sounds like a failing CV joint but that shouldn’t be related to clutch adjustment. Is the clutch now properly adjusted?

Best,
Grady

[johnjr]

Hi, Grady. Thanks for your interest in this issue. The clacking sound was definitely related to the engine speed rather than road speed. What I mean is that the sound did not decrease based on the speed I was traveling, but based on the decrease in rpm. I could tell that because I tested by traveling the same speed in different gears, and simply taking my foot off the accelator. If I was going 35 in 3rd, for example, the clacking would be slower than if I was going 35 in 2nd.

For lifting the car I put the jack under the sump plate ala Wayne's book. I then jack it up and put jack stands under the torsion bar ends just in front of the rear wheels. I then lower the car on to the jack stands, leaving the jack in place as a safety.

Finally, the noise is/was not gear dependent. It clacked in every gear - even reverse.

I "think" the clutch is now properly adjusted, but I have one of those rather cheapo micrometers. It does feel much easier to depress than it did when the clacking was going on.

Incidentally, I'm still taking the car to the shop to make sure everything is up to snuff. My confidence in my own mechanical ability is on the low side.

johnjr
78 SC Targa

[Grady Clay]

John,

Thanks for the detailed diagnosis. That is what it takes to solve these issues.

OK, so it is clutch related. Noise is with engine speed and changes with clutch operation and adjustment. Now the question is “What is the problem?”

Does the clutch release fully when depressed? That is, does it grind going into reverse after an appropriate pause with the clutch depressed when the car is stopped?

What is the history of the clutch? Could it be an original rubber center clutch?

When you were under checking, did you check the four engine-to-transmission nuts? (To check the 10 mm Allen one by the starter, you should disconnect the battery.) Are all four bolts that attach the engine-transmission assembly to the chassis properly tight?

Any other clues?

This is one of those situations where the noise shouldn’t disappear with a simple clutch adjustment unless something unusual is wrong.

Best,
Grady

[ed martin]

Grady, Is there a chance that with the cable being too tight, putting the fork in a position where it's perhaps just grazing a portion of the throwout bearing to make the noise, would that not be consistent with the described symptoms?

[johnjr]

Hi, Grady. There is no grinding when I put the car in reverse. The clutch seems to be doing its job. As far as the type of clutch, ie., old style or replacement, I was told when I bought it from the previous owner (five years ago) that the rubber center clutch had been replaced. There were no receipts to verify this, however, and the car had just 64K miles on it back then. It now has 105K.

I did check every bolt/connection I saw when I was under the car, and found nothing loose. I did not check the nut near the starter, however, because I didn't even know there was one there. Everything else appeared to be properly connected.

The only other clue I can think of is that I first noticed any sound when I was turning. It was a clicking noise as described in my first post that I noticed when I turned a corner or when going around a long curve, such as an entrance or exit ramp. The noise then progressed to appearing when I lifted off the accelerator to being audible when I accelerated to clacking nearly all the time under load. It disappeared completely when the clutch was depressed or when I was coasting in neutral.

Now that I readjusted the clutch, the sound is gone. Weird. Anyway, as mentioned earlier, I'm still taking it to the shop next week.

Thanks.

johnjr
78 SC Targa

[johnjr]

Well, the culprits were the CV joints. I took the car to Steinel's and it turned out that three CV joints were shot. Got the car back Saturday and it runs like a new car. Thanks for all your help.

johnjr
78 SC Targa