Lotus Elan

Bang/clonk noise, followed by no drive

PostPost by: Rich135 » Thu Dec 28, 2017 11:32 am

Hi All

I would appreciate any guidance before I get under the car and start taking things apart.

Just as I was pulling onto a roundabout, letting the clutch out in 1st gear (not a racing start or anything silly) I heard a bang/clonk noise underneath and I lost all drive. I let my 12 year old son steer while I pushed the car to the side of the road (he loved that!).

Luckily I was close to home so a couple of petrolhead neighbours came and pushed me home, and after checking, the clutch and gearbox are fine, as the propshaft is still spinning into the rear diff, but neither rear wheel has any drive. There aren't any strange noises coming from any parts (diff or rear drive shafts).

Where should I start? I am assuming the rear diff has a problem, but if a drive shaft had gone on one side would that cause me to lose power to both rear wheels? I believe I have CV joints, not donuts.

Many thanks for any help.

Rich
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PostPost by: rgh0 » Thu Dec 28, 2017 11:52 am

Most likely a broken diff output shaft. if one breaks inside the diff which is common on pre 1970 cars then you loose drive to both wheels unless you have a LSD

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PostPost by: gus » Thu Dec 28, 2017 2:00 pm

yup diff output shaft, I see a diff removal in your future. You should replace both, clean the little shaft bits out, bearings, seals, off you go.
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PostPost by: Rich135 » Thu Dec 28, 2017 2:25 pm

Thanks both. After doing a bit of research on here, I tend to agree with you both. My garage is too small for me to jack it up in there, so I will do that outside when I next get a chance and check by spinning one wheel at a time first, then see if the other spins.

I will replace both if only one is broken. Good winter project :shock:

Thanks again.
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PostPost by: Coupe » Thu Dec 28, 2017 4:41 pm

Same happened to me - replaced with TTR steel billet shafts.
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PostPost by: Rich135 » Thu Dec 28, 2017 6:40 pm

Thanks Coupe, I will look at them when I rebuild, even if that isn't the problem.

So far I have the CV joint off of the drivers side shaft and the shaft spins and sounds like it's moving cogs inside the diff casing. It won't pull out either, so I am guessing that one isn't broken (yet). i will try to do the passenger side next week days (won't get a chance over the weekend).

Rich
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PostPost by: gjz30075 » Thu Dec 28, 2017 7:01 pm

It won't come out until the big circlip is out. Even then, it may take a puller of sorts to pull it out, due to
bearing fit.
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PostPost by: Rich135 » Thu Dec 28, 2017 7:05 pm

Ah, ok thanks Greg, I will clean it up and see if I can find the circlip.
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PostPost by: RichardHawkins » Fri Dec 29, 2017 9:09 pm

Rich,

Do make sure you clean the diff case and components thoroughly. You don't want bits of shrapnel left inside to ruin the gears and bearings. When I took my diff apart there were bits of debris left from a previous failure which may have accounted for the premature wear of my crown wheel and pinion.

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PostPost by: gus » Fri Dec 29, 2017 10:51 pm

Coupe that is an atypical break

usually they break where the splines leave the diff

that also appears to be a 'fat' shaft which usually do not break
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PostPost by: rgh0 » Sat Dec 30, 2017 12:46 am

gus wrote:Coupe that is an atypical break

usually they break where the splines leave the diff

that also appears to be a 'fat' shaft which usually do not break


While the break at the radius of the shaft to the outer bearing is less common it does happen . The failure where the spline leaves the diff is most common and twisted splines at this point can be observed in most pre-1970 cars with the original early shafts even if they have not progressed to failure yet.

I have had one of each type of failure in my Elan until I got better quality billet shafts fitted back in the early 80's

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PostPost by: Davidb » Tue Jan 02, 2018 6:48 pm

How often do the outer 'spindles' break? On a road car?
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PostPost by: Famous Frank » Tue Jan 02, 2018 11:40 pm

The outer axles break right after you say they never break.

Actually, I have seen the outers break only once on a road car that had skinny no grip original type of tires. Once you put sticky tires on or head to the track for a few hot laps, your percentages go way down.

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PostPost by: seniorchristo » Wed Jan 03, 2018 4:05 am

Gus
I don't think that is a "fatter" shaft. It looks like the splines taper down to the shaft. "Fatter" shafts ,as shown on the right, have shaft diameter the same as splines. :)
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PostPost by: alan.barker » Wed Jan 03, 2018 10:23 am

It seems with CVs it's a good idea to have the latter shafts. This could be a plus for running rotoflex :wink:
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