Knocking from the rear when driving with passenger

[S2_Sandviken]

I have a bit of a tricky problem on my Esprit S2...

 

When driving with a passenger in the car I can hear a knocking sound from the rear, it is a rythmic knocking that follows the speed of the car and is more prominent in low speeds. Yesterday it seemed to fade after a while but then returned, note that it does not cause any form of vibrations or similar, just a knocking sound.

The UJ's are replaced not that long ago, same goes for the bearings, and I have also replaced the sliding pins on the calipers and checked for loose pads.

 

I have tried to provoke the car and put it under load when driving without passanger, but have not this far beeing able to recreate it. strange, isn't it?

 

Any ideas????

 

 

[gvy]

Anders,

I have no idea, so I hope someone will come up.

I have the same with my S2.2.

 

With a passenger and while turning slowly to the right I have this knocking sound ( It is speed dependent) When driving straight, I hear nothing, unless one time , when I was very heavy loaded ( passenger of 100+kg and car fully loaded with camping material (drive to lotus festival) I could hear it  when driving slowly straight .

I am still searching.

 

Geert

[gvy]

Hi Anders

Did you ever solve this problem ?

Geert

 

[marode]

Same here... I am also searching for that noise for about 5 years now, still have´t found it yet. Appears with a ( > 80kg) passenger and / or some luggage.

[S2_Sandviken]

Problem with the knocking solved, inner U/J, changed and no knocking anymore. Had to check the U/J when the car was still warm, could not notice the problem when cold, probably due to the grease getting thinner when warm ?

[gvy]

Same here.

Changing the UJ stopped the knocking sound

[marode]

I think I may have found the solution ten years after! The driveshafts have different ends! I just came across this question: https://www.facebook.com/groups/18682611768/permalink/10159999234381769/

For those without a Facebook account, see pictures. Tim mentioned the driveshafts differ from "early" ones with differences each side to "late" ones which have equal ends. Also the yokes seem to be different, see https://www.youtube.com/watch?v=JELroOpenkY (around minute 8). So the "knock knock" may be a result of mixing these up and then under certain angles the parts touch each other?

Edited April 26 by marode

[EXCEL V8]

I'll have a look at my Elite shafts to see if they are the same.  Thanks for that!

Pete

[Esprit2]

Close, but no cigar.   I’m a participant from the Facebook Group mentioned above, and I posted the following over there.

Sorry, but this gets long...

The original halfshafts had a 1.50” radius at one end, and a 0.75” radius at the other end.

The later halfshafts had 0.75” radius at both ends.

But that alone is not really the problem.

Inspect the “hollows” created by the radiused fillets, and you’ll see that ONE per end of the halfshaft is “slightly” deeper than the other three.   Not by a lot, but noticeable if you’re looking for it.   Subtle.

When assembling the halfshaft/ installing new U-joints, it is critically important that you align the end of the halfshaft with it’s mating yoke (ie, “flange yoke” on the inner end, and “stub axle yoke” on the outer end) such that the two “deeper” hollows (one per part) align with one another.   Together, the two hollows create enough space between the two yokes (one deep hollow on the halfshaft, and one on the mating yoke) for the grease fitting on the U-joint.

In addition, you need to replace the stubby grease fitting that comes on a new U-joint with a tall, slender one that gets the fittings “head” and hex-drive up, out of the crotch of the U-joint.   OR… your alternative is to use a U-joint that doesn’t have a grease fitting (lubed for life).   IMHO, the best of that category is the Hardy Spicer.   Or, similar but different, use a U-joint that has the grease fitting in one of the four cross-bar’s end cap.  Either way, there’s no grease fitting down in the crotch of the U-joint!!

All U-joints (of which I’m aware) that come with a grease fitting, come with a short, minimalist fitting that sits right down in the crotch of the U-joint.   Down there, as the halfshaft flexes, the “hollow” closes up until it pinches the grease fitting… “going solid” and making a “thump”.   Loading up the car with weight (bodies and junk in the trunk) causes the suspension to sag, flexing the U-Joints, until finally the grease fitting gets pinched, and goes “thump”.

Carefully aligning the two slightly deeper “hollows” during assembly, and installing a tall, slender grease fitting to get the “head” up out of the U-joint’s crotch will usually eliminate the possibility of binding on the fitting, and causing a thump.   But it’s up to you to be aware, and very careful during assembly.

Or, as noted above, use a U-joint that has no grease fitting.

Well, there is another option.   Replace the grease fitting with a small, Allen drive plug.   Either a grub screw (it all threads into the hole) or a ‘cheese head’ machine screw short enough that the threaded body is all inside the U-joint, and only the small Allen ‘cheese head’ is sitting on the surface of the joint’s crotch… way down in the gap.

In either case, greasing the U-joints will then involve removing the plugs and installing the grease fittings.   Then when you’re done, removing the fittings and replacing the plugs.   All that is easier with the back of the car up on stands, the rear suspension at full droop, and the halfshaft  rotated until the “open” side of the flexed joint is facing up.   That’s the biggest hole you’ll ever have in which to work.

Regards,
Tim Engel

Edited April 26 by Esprit2