Lotus Elan

Metallic rattle

PostPost by: 2cams70 » Mon Apr 08, 2019 11:50 pm

Is your car fitted with the 4 speed Ford box or the 5 speed Leyland based box? On the Ford 4 speed the gear on the mainshaft driving the speedometer is steel and not plastic.
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PostPost by: Harvey » Tue Apr 09, 2019 12:32 am

It's the Ford four speed. I'm sure you're right and that I am confusing it with the plastic gear that lives in the speedo angle drive.
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PostPost by: alanr » Tue Apr 09, 2019 8:01 am

I certainly would not go shortening the Propshaft!...Do not do it!
If as you say the propshaft yoke is bottoming out and hitting the mainshaft then something is wrong with the location of the engine/gearbox or differential not being mounted in the correct place in the chassis. Lotus I am absolutely sure certainly did not build your propshaft too long!
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PostPost by: Craven » Tue Apr 09, 2019 10:55 am

2cams70,
Later 4 speed gearbox has a plastic ( Blue ) mainshaft speedo drive gear.
speedo-gear.jpg and
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PostPost by: Harvey » Tue Apr 09, 2019 5:52 pm

Alan,

I feel certain that the prop shaft is original to the car ('71 Plus 2S). I've owned the car for 20 years and in that time have driven it about 30,000 miles. The only potential change in the distance between the diff flange and the end of the main shaft would be attributable to the fitting of a Spyder chassis back in 2004. Thousands of trouble free miles have been logged since then. Engine mounts and diff torque rod rubber bushings are all good and the torque rods are tightly secured allowing no diff movement forward.

Why then, was the main shaft pushed forward into contact with the input shaft with enough force to displace the main shaft snap ring? A possibility posed by my mechanic is that the prop shaft is too long and somehow allowed the yoke to apply pressure to the end of the main shaft. While the yoke does not have as much clearance as my mechanic would like to see or that of an Elan I measured, the difference is small and still leaves almost 1/2" of movement when fitted before the yoke contacts the rear of the main shaft.

However, as I have tried to explain above, I cannot take a chance that the yoke might, in the future, come in contact with the main shaft. Since I am going to have the prop shaft balanced anyway I might as well have it shortened to make sure the prop shaft is beyond reproach. Even shortened by 1/2", the yoke still has plenty of support in the tail shaft. Moreover, I'm adding lightness to the car.

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PostPost by: joe7 » Tue Apr 09, 2019 7:17 pm

I don't think the prop shaft displace the circlip. Its more than likely the force on the circlip because it was installed incorrectly. If the circlip, which is tapered, isn't properly fitted into the beveled groove on the mainshaft it has a natural tendency to dislodge. How do I know? Because the 2 that I rebuilt had the circlip installed backwards.
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PostPost by: Harvey » Tue Apr 09, 2019 8:12 pm

Joe,

I hope that's the case because I have been assured that it is fitted correctly now.
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PostPost by: rgh0 » Wed Apr 10, 2019 2:16 am

If the gearbox output shaft is accidentally hit while handling and fitting the gearbox into the car that could also dislodge the snap ring especially if it was fitted incorrectly in the first place.

If the gearbox is installed attached to the engine and it accidentally swings and hits the chassis during the installation this sort of problem could arise.

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PostPost by: Harvey » Tue Apr 16, 2019 7:03 pm

Rohan,

Thanks for advancing a theory I hadn't thought of. However, I just had a chance to discuss this with the mechanically experienced guy who was handling the tail shaft under the car during installation of the engine/gearbox and he assured me he was being very careful to make sure the end of the shaft did not impact the chassis. Thus, it is still a mystery as to why my mainshaft snap ring was displaced and mainshaft was in contact with the input shaft when the gearbox was disassembled.

I will return to this conversation after I get the prop shaft shortened and get the car back on the road.

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PostPost by: gavk » Sun Apr 21, 2019 9:49 pm

Andy Hay

Very long thread so forgive me if you've solved your issue or someone has posted this already.

I had a similar sound occuring under similar circumstances, I found it was a screw up collar on my propshaft.

See my thread for photos and details:
viewtopic.php?f=37&t=40196&p=280280#p280280

Hope for your sake that it's the same issue, Easiest of fixes, Jack car up, tighten by hand, job done!

Please bear in mind that my car has an MT75 gearbox so your propshaft may not have the collar in question, other members may be able to advise.

Thanks

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PostPost by: Harvey » Thu May 30, 2019 11:43 pm

Gavin,

Thanks for your suggestion but I have the four speed gearbox which does not have a collar.

Sorry for the long delay since my last post but health issues have kept me from working on the car. Against the advice of those who have posted to say don't shorten the prop shaft I had it shortened by 1/2" and balanced at the same time. I now have a full inch of sliding yoke extending beyond the gearbox tail extension. I don't really think the prop shaft was too long but to put to rest any doubt I had it shortened.

This thread started by a member hearing a metallic rattle on overrun. On January 29, 2019, Richard J posted an audio clip of his car making a rattle/chatter sound on overrun. I have been chasing that noise in my car for the past couple years and have removed and replaced the engine and gearbox three times in an attempt to end it. My latest attempt to end the rattle/chatter involved replacing the standard clutch external slave cylinder and T/O bearing clutch release lash up with a Tilton concentric slave cylinder similar to the one used on Alan Voigt's T9 five speed kit.

Yesterday I had a chance to road test the car. It now shifts better than at anytime in the 20 years I have owned it. The Tilton slave cylinder makes the clutch release noticeably lighter. However, the rattle/chatter on overrun is still as loud as ever and, with the center console off, is considerably louder than the noise heard on Richard J's audio clip. the noise is heard in all gears but is most evident in fourth because it takes longer for the car to lose rpms in that gear when decelerating. It starts at about 4,000 rpm and stops at about 3,000 rpm. I have gone through every component of the drive train in an attempt to end this noise but have failed at every turn.

I am out of ideas about how to diagnose this problem. However, there is one theory advanced by a knowledgeable clutch/gearbox specialist who posts on YouTube, Paul Cangialosi, that i haven't yet explored. When I explained my issue to him he stated that the noise is being caused by the lightweight (8 pound) aluminum Fidanza flywheel I'm running. He said the flywheel lacks enough mass to keep the input shaft loaded during deceleration and that it is the oscillation of the shaft on overrun that is causing the noise.

The Lotus parts supplier I purchased the flywheel from says he has never heard of this problem from other customers and he has sold dozens of Fidanza flywheels. Research reveals that a stock Elan/Plus 2 flywheel and ring gear weighs between 14-16 pounds. Thus, I ask readers of this post whether Mr. Cangialosi's theory offers a solution to eliminate this annoying noise? Having pulled the engine out three times in the past 18 months I am going to live with the noise for now. If the engine has to be removed for another reason in the future I then will have to decide whether the trade off between peace and quiet on overrun and improved acceleration with the lightweight flywheel warrants testing Mr. Cangialosi's theory.

For now I'm just going to enjoy driving my Plus 2 again.

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PostPost by: prezoom » Thu May 30, 2019 11:53 pm

I have a Fidanza flywheel on the Zetec in my Plus2. No noises like you describe with either the semi close or the current close ratio gearbox in the car. The flywheel should be close to the same weight as the one for the TC. However, the clutch cover and the driven disc are larger than the TC.
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PostPost by: 2cams70 » Fri May 31, 2019 12:59 pm

This post must hold the record as the longest one remaining unsolved!! I know the exhaust has been mentioned before but did you check the mufflers for loose internal baffles? Sometimes you can detect it by striking the muffler with a rubber mallet (or fist depending on mood!) and listening for a rattle from within.
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PostPost by: Richard J » Fri May 31, 2019 6:26 pm

My drive train is completely standard - so I don’t have a lightened flywheel. So in my case, which I’m pretty sure is the same as Lee’s, this isn’t the cause of the problem.

Listening to my noise again it does seem that it is at least exacerbated by other resonance that goes through the car when lifting off. But it really sounds like it is coming from the front end of the gearbox. Will go and listen again..
Last edited by Richard J on Fri May 31, 2019 9:27 pm, edited 1 time in total.
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PostPost by: Harvey » Fri May 31, 2019 6:37 pm

Rob,

Sorry I missed you at the WCLM but I did get to see your lovely car. I was only there for the concours event.

Even though your engine is different than mine it tends to disprove the theory that the Fidanza lightweight flywheel is at fault and the source of the annoying noise.

2cam70,

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. I have been told that worn prop shaft U joints can transmit noise forward along the drive train to make it appear as it the noise is forward of the U joints themselves. Perhaps the same could be true for worn differential components. I haven't researched differential problems on this website but maybe the answer lies there. I will do so now and welcome responses from others regarding this theory of the noise.

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