Lotus Elan

Metallic rattle

PostPost by: Harvey » Fri May 31, 2019 6:45 pm

Richard J

Even further proof that the Fidanza flywheel is not at fault and with an engine that more closely aligns with mine than Rob's Zetec. I wonder if your differential has as many miles on it as mine?

I forgot to mention in my last post that I replaced both drive shaft U joints which did nothing to abate the rattle/chatter. After changing so many components chasing this noise I feel a bit like Thomas Edison who said, "I have not failed, I've just found ten thousand ways that won't work" when inventing electric lighting.

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PostPost by: 2cams70 » Sat Jun 01, 2019 1:01 am

Harvey wrote:My muffler is a stainless steel stock item that has been on the car since I bought it in 1998. It is very quiet and I do not suspect it as a source of the noise. My doubts also rest upon the fact that the noise appears to be coming from forward of the shift lever.Since my post yesterday I spoke with Ken Gray of Dave Bean Engineering about the rattle/chatter on overrun. He said another possible source of the noise is worn differential crown wheel and pinion components. My car has 122,000 miles on those wear items so it is possible those parts need replacement.


For the little time and effort required it's well worth checking the muffler for a loose baffle. The muffler can be quiet otherwise despite a loose baffle or centre tube. I have come across it quite often in cars.
122,000 miles is not high for the Ford diff. If it hasn't been used for racing and hasn't suffered from oil leaks or abuse it's usually very reliable. The only thing that is prone to happen is that the collapsible spacer looses tension over time and the pinion pre-load is lost. It usually results in a diff that whines and not the symptoms you describe. Earlier (pre around 1975) spacers were made of thinner material and more prone to this than the later thicker upgraded type. Most problems with the diff are the result of incompetent people fiddling with it! Noises can travel in a car and it is often very difficult to identify the exact direction it's coming from. A stethoscope to poke around with could be useful however.
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PostPost by: Harvey » Sat Jun 01, 2019 5:22 am

2 cams 70,

I apologize for prejudging your suggestion that the muffler may be at fault and will check mine tomorrow. I also thank you for trying to help me solve this noise issue that plagues several of us posting on this thread. Anything is worth a try at this point as I am literally grasping at straws to identify this noise.

My car has not been raced and for the past 50,000 miles since I have owned it the diff has always been kept full of clean Redline diff oil. It does not whine. It is comforting to think that the crown wheel and pinion are not in need of replacement at 122,000 miles because I view replacing them and getting them lined up properly in the same league as rebuilding a gearbox. Because my car has been off the road for about 18 months I am not keen about another delay in enjoying the car by pulling the diff and sending it off to a specialist to rebuild.

You mention using a stethoscope to aid in finding the noise. I'm not sure how helpful this would be because the rattle/chatter will only occur when the car is on the road. Revving the engine to 4,000 rpms in neutral and then backing out of the throttle will not produce the noise. Nor will running the car up to 4,000 rpms in fourth gear and then lifting off the throttle while the car is on jack stands. There is something about the car being under load that creates a harmonic on overrun when decelerating from 4,000 down to 3,000 rpm.

At this point the untested theories regarding the rattle/chatter are: (1) A lightweight flywheel; (2) A muffler with a loose baffle; and (3) a worn crown wheel and pinion. I'll check the muffler tomorrow but theories one and three will remain untested for the near future.

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PostPost by: Richard J » Sun Jun 02, 2019 8:29 am

Hi Lee and others,

To add a little more to my earlier post, I think there is some merit to the comments about muffler/silencer resonance and to diff condition. I don't think it's the source of the noise itself, but it does contribute to the frequencies that the gearbox is rattling in harmony with.

I recently found that the two bolts that fix the rear silencer hanger to the body (inside the boot/trunk) were seized tight, but in such a position that the bracket could vibrate against the underside of the body. I didn't notice it before as they appeared tight and the weight of the exhaust system meant that there seemed to be no play when I checked under the car.

Now that I've ground them off and replaced with new and properly tightened bolts, the rattle hasn't gone away but it appears over a much narrower rev range. It is still usually in top on the overrun, and it always happens when there is other resonance (not really a vibration more of booming noise) coming from the rear of the car when I lift off. The rattle is still the same noise and coming from the same place - forward of the gearlever.

I am no gearbox expert - but it's really like something is loose and rattling in harmony/resonating with the overrun "boom" from the rear). I never get it when the gearbox is cold, it has to be warmed up first and a recent change to synthetic oil in the gearbox also delayed its onset and has also reduced the rev range over which it appears, so it seems to me that is it is component that sits in the gearbox oil.

I've had the car since '83, so I know the diff is in fairly original condition,(although it is firmly mounted) and has not had any recent work, so it is definitely possible that it is a source for the overrun/lift off resonance and booming.

So I haven't cured it, but the oil change and bracket fix have reduced the occurrence.

For those of you that haven't already heard it - this is the noise:

https://1drv.ms/u/s!AsOq-jbOtbQkguN1qnG4WKoEWpHt8Q

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PostPost by: h20hamelan » Sun Jun 02, 2019 3:29 pm

I have used a similar one for my trucks, lorries. Haven?t put in on an elan as yet

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PostPost by: Harvey » Mon Jun 03, 2019 11:09 pm

2cams70

Over the weekend I rapped and tapped the muffler but heard nothing loose. I now have a more serious problem with an inability to shift into second gear without gear clash. Probably a synchro problem which will require yet another engine out drill. To avoid thread drift I will now sign off.

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PostPost by: Harvey » Wed Feb 12, 2020 11:17 pm

Eight months have elapsed but I'm finally back with some new information. All of you who have responded to this thread suggesting that the snap ring on the gearbox mainshaft was the source of my shifting problem and rejecting the theory that the propshaft sliding spline pushed the snap ring out of place can pat yourselves on the back because you are correct. During the hiatus between my posts I took the gearbox to a shop that prepares vintage cars for racing (including Lotuses) at the Sonoma Raceway. The mechanic disassembled the four speed gearbox and found that the snap ring fitted was too thick and not seating fully in its groove. He machined it down so that it now seats firmly.

The car is back on the road and shifts beautifully. However, the chatter on overrun is still there. I have attached a short audio clip of the sound. The noise you hear is coming from forward of the shift lever with the center console off the car. I put the car up on a lift at the local tire shop and was able to duplicate the noise by running the car up to 4,000 rpm and then bringing the revs down to 3,000 rpm by left foot braking. The technician under the car discovered a bad inner bushing in one of the rear wishbones and movement in the diff due to slack in the torque rods.

I had the bushing replaced and fit new torque rods and poly bushings to stop movement of the diff when on and off throttle. Neither made any difference. I have noticed that with the engine on and the gearbox in neutral I hear a rattling noise that disappears when the clutch pedal is depressed. I believe this is being caused by the T/O bearing resting on the clutch fingers and spinning with the engine. As I noted in an earlier post, I replaced the external clutch slave cylinder with an annular concentric slave cylinder made by Tilton. According to Tilton the T/O bearing is supposed to rest lightly on the clutch fingers when the engine is turning. Perhaps this is what I am hearing on overrun although I also had the chatter before I fit the Tilton clutch slave setup. I think the chatter may also be more evident because of the magnesium bell housing I have fitted to the car. An iron bell housing may do a better job of damping clutch noises.

So this is the end of the story for me, I'm not going back to my iron bell housing, I'm not going to fit a stock flywheel, and I'm not going to give up my concentric clutch slave cylinder because the car shifts beautifully with a very short movement of the clutch pedal. In short, I'm not going to again pull the engine chasing the chatter. I'm just going to add some additional sound proofing under the center console and tune it out.

Thanks again to all of you who weighed in on this thread with recommendations and helpful ideas.

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PostPost by: 2cams70 » Thu Feb 13, 2020 5:05 am

Seeing you've checked almost everything else have you checked the crankshaft for excessive end-float?
Particularly as the engine was recently rebuilt the thrust washers may have been installed the wrong way around.
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1980 Ford Escort 2.0 Ghia
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PostPost by: Harvey » Sat Feb 15, 2020 5:38 am

2cams70 Welcome back to the thread and thank you for continuing to offer solutions to the metallic rattle or chatter I call it on overrun. I tried to attach an audio clip to my last post but was unable for reasons I don't understand.

I went back to review the notes I made when the engine was rebuilt and the Formula Ford "stroker" crank was installed. I had a Lotus experienced mechanic helping me with the rebuild when the thrust washers were fitted and he assures me the washers were installed correctly and that the crank end float was within specs.

The chatter continues to be heard from forward of the shift lever and I'm fairly confident that it is coming from within the gearbox even though three different mechanics have disassembled the gearbox and could find nothing amiss apart from the snap ring issue that is now solved. I think the only solution is to fit a different gearbox. I had a Voigt T9 five speed gearbox on order for two years before giving up when delivery still could not be determined. I will be looking for other five speed alternatives in the future but for now I'm just going to drive the car and tune out the elusive chatter.

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