Rear Suspension Knocking - FINALLY SOLVED!!!!

[revilla]

I suppose it's possible but they don't look like they've been pushed in at all. The springs are really chewing chewing quite hard into the metal of the panel not just touching, it's quite hard to see from the pictures but I would say it has ground it's way through about half the panel thickness so I would really like to understand what is happening.

 

What I really don't understand is that the scrape marks in the panel suggest that the lip on the spring is scraping up and down by about a centimetre, but it's at the very top of the spring which shouldn't move vertically at all unless the top bush was completely shot, however the bushes on both sides looks fine.

 

Edited by - revilla on 6 May 2013 10:02:38

[charlie_pank]

Is the suspension bottoming and/or topping out? The spring should always be in compression, the only way it could move relative to the damper-end is if it tops out then crashes back down again

 

[Jonathan Kay]

I know it's clonking now, and that there are marks on both the spring and panel, but are you sure that they are fouling now and not at some time in the past when the configuration was different? Could you put a piece of masking tape on the panel and confirm that it gets marked?

 

Jonathan

[sparky]

This may have been mentioned? But I've missed it.

When I installed my spring damper units, the manual was very specific about the SPRING being the correct way.

Just random thought is the spring tapered? Maybe?

It would be worth having a measure up with the vernier first. If they are anything like motorcycle shock/fork springs its minimal but can make a huge difference.

 

 

Edited by - sparky** on 7 May 2013 08:44:21

[Bio]

Just looked at my build manual from 1999 and it shows the rear damper mounted with the piston at the top and progressive springs with the more open coils at the top also.

In your picture the spring does not seem centred on the top collar. Have you got progressive springs mounted upside down 🤔

When I fitted adjustable platforms to my Billies I seem to remember having to move the lower platform clip up to the next groove and fitting one or two spacer washers between the damper eye and Dedion.

 

John

[revilla]

Thanks everyone for you helpful input, appreciated as always.

 

@charlie_pank - If I jack the car up by the rear chassis until the wheel lifts, with the damper at full extension, or when I remove the damper from the car, the spring is still very firmly under compression, so I guess it's not "running out of spring" as it were.

 

@sparky** & BIO - You may well have a point here. If you are absolutely sure of this, then it would appear that my dampers are fitted correctly but my progressive springs are upside down, as they have the more open coils at the bottom! A bit confusing because the various photographs I managed to Google of Caterham rear suspension seemed to favour the more open coils at the bottom, but there weren't many and they could have been wrong too. If there is any element of taper to the springs, even slight, then it could well make the difference. I will try turning them around and see if they fit any better against the top seat, i.e. without projecting as much as they do now. When we did a flat floor on my car we were limited in how much we could raise the back end as we found that my dampers only had the one groove machined in for the spring seat circlip, but looking at the bottom mount everything looks like it should clear the de Dion OK, maybe with one more washer to be 100% sure.

 

@Jonathan Kay - When I turn the springs around as above I will indeed put some tape to see if there is still any contact, that's a good idea, however I'm fairly sure the scrape marks were fresh and new, it gets quite dirty under the wheel arch but the scraped areas were absolutely clean shiny silvery aluminium, not even surface oxidised. I was also thinking of removing the shock and sticking a lump of blu-tack on the scrape, then refitting the shock and removing it again. That way I should be able to see from how far it has pressed the blu-tack flat how much static clearance there is, so if there is any future contact I can at least know how much it is down to a statically tight fit and how much of it is down to lateral movement.

[Fishy Dave]

Hi Andrew,

Thanks for your e-mail and the chat on the phone and sorry I hadn't seen this thread until now. I obviously feel some concern and responsibility having worked on your car with you.

I read back through my notes and remember we removed a damper on one side due to the two spring platforms being locked together. The spring went back on the same way around as removed and all was well, and the flat floor set up continued.

I have checked both build manuals (photos) I have here and compared it to a local Severners SV and sure enough the springs are the wrong way up, just as BIO and sparky suggest. Neither of my build manuals seem to mention which way up the springs should go, is this because they are already assembled as complete units in a kit?

The odd things for me is that it must have been like it from new so am surprised the orginal owner or Caterham didn't check this. I remember you saying the previous owner had set the suspension to be that low, although I can't see why he would change the springs over?

One of the things we rectified was the total ride height, in particular at the rear, which was far too low and only gave 4mm rake. It's maybe this change of height and so angle which has caused the spring to contact the metal panel, where there was previously just enough clearance or an unnoticeable amount of rubbing.

Having also looked on google for 'Caterham rear spring' I agree that most photos show the spring the wrong way up (the way it is fitted to your car).

A previous thread didn't raise any concerns about orientation - here

I think what you propose is correct; fit the springs the other way up and go for a drive and report back. Let me know if I can help in any way.

 

Cheers, Dave

[revilla]

Dave,

 

Thanks for taking the time to call me. I will swap the springs around and put tape on the marks on Sunday and see how things go. When I slacken off the adjustable collars I will count the turns so I can put them back exactly where you set them :)

 

Andrew

[sparky]

Taken from Downloadable build manual on CC web page. Version 05.2012

Page 137 section 9.6

Note 2

"insert a sleeve into the top bush of the damper unit (close coils of spring are at the top), align the ................................."

 

Hope this cures your issues, good luck.

 

[revilla]

Sparky** thanks for that but now I'm really confused because that's the exact opposite of what BIO said he found in his build manual! According to your description my springs are fitted the right way around after all :(

[sparky]

Whoops.. That's really put a spanner in the works.

Can you measure the diameter of the springs top and bottom.

My rear shocks are off the car I can measure them tomorrow if you want?

[revilla]

Yes please, measurements of the diameter of the conical seat at at the top end of the shock and an idea of how much wider the spring itself is than the seat would be really useful. In my photos you can see that the spring is quite a bit "fatter" than the seat. Thanks.

[sparky]

O/D of 78mm at most open end of coil spring

O/D of 78 mm at most closed end of coil spring

O/D of top spring seat is 70 mm

 

Have you got any end float in your 'A' frame bushes?

 

[revilla]

Sparky** thanks for that, I probably won't get time to pull mine off and measure them properly until tomorrow (two little toddlers demanding my attention and a wife sending me to IKEA!) but that does seem to confirm that they are not tapered at all. The springs being 8mm wider than the seat sounds about the same as mine too, I'll check them properly when I get a chance but protruding by about 4mm sounds about right. I guess the importance of putting the closed coils at the top must just be for reasons of unsprung mass, getting the heavier end of the spring on the "car" side rather than the "wheel" side. I don't think I have any movement in the A-frame bushes, but I'll check again when I jack it up. The bushes all looked sound, and a good violent shoving of the car side to side by the base of the roll bar didn't seem to induce any unexpected noise or slopping around. There's also no sign of the de Dion moving around when driving, i.e. no tendency to wander around at all, but I'll have another very good look tomorrow as lateral movement of the de Dion is the only thing I can think of.

[revilla]

OK here's the latest ...

 

Today I jacked up the chassis onto axle stands so the the deDion was hanging freely. Removed the wheels followed by both rear shocks, so the deDion was easily moved around by hand. Couldn't feel any lateral movement. Couldn't induce any clonks against the A-frame or similar over the normal range of movement. Couldn't find any other witness marks other than those I found before, except a possible light contact between the lower edge of the shock adjustable platform and a drilling through the deDion just above the skock mounting point (not sure if it's a mount for the rear anti-roll bar which i don't have?).

 

Measured the spring and cup diameters top and bottom with a vernier calliper, results exactly the same as yours Sparky**, 78mm spring O/D top and bottom, 70mm cup O/D.

 

Attached the shocks again by the top bolts only so I could swing the bottoms in and out to find how much movement was required to make the tops hit the panels. Answer - ZERO - THE SPRINGS WERE PRESSING AGAINST THE PANELS WHILE STATIONARY!

 

So, looks like its not caused by the unusual movement of anything, just some sort of misalignemnt, and although they really didn't look distorted the only thing I could think of was that the panels had indeed been pushed outwards somehow, or at least that I could fix it by reshaping them inwards a bit ...

 

AS SUGGESTED BY SFORSHAW IN THE FIRST REPLY TO MY POST - oh dear, thanks and remind me to listen very carefully to your advice in future!

 

So as suggested I've made up a rounded wooden former and used it to gently dish the panels inwards a little to give a bit of clearance around the points which were catching. Thanks to the leverage of the length of the shock, further checks now show that the deDion would now have to move by about 2cm to get anything to catch. I've attached some squares of duct tape over original marks so I can check that it is no longer snagging.

 

I've also shimmed the bottom shock mounts forward from the deDion tube with one extra (in addition to the one existing) M12 washer which should be enough to make sure nothing can knock at the bottom end without putting any great extra strain on anything.

 

While I was under there, there was a rubber sleeve around the handbrake line where it was tie-wrapped to the A-frame but the sleeve and tie wrap had slipped away from each other - it wasn't loose enough to have been knocking but to prevent chafing I tidied it up.

 

Weather permitting I've got a 6hr round trip to SBFS tomorrow, so a bit of a test. Will report back. If it's still knocking I think I've reached the limit of what I can do and I'll admit defeat and bung it in somewhere to be looked at.

 

Thanks to everyone who has chipped in with helpful suggestions, I'm fairly new to this and it's all a learning curve so much appreciated guys!

[Jason Plato]

are they 2.5" springs instead of the 2.25" that is std ?

[revilla]

Right ...

 

This is getting personal!

 

Took the car for a good (380 miles!) run yesterday. It's better, the suspension at the back is generally quieter, some of the more chattery noises have gone, but there's still the same clonk over potholes etc.

 

Now that the rest of the the noises caused by the springs rubbing the panels have gone, the clonk is quite clearly isolated and I'm still sure it's coming from the top of the driver's side shock. My thinking is:

 

- Both springs were touching the panels, probably just poorly shaped panels or panels that had been pushed outwards at some point.

 

- The passenger side (which is NOT clonking) spring was rubbing a small horizontal mark on the panel, pretty much the same shape as the bit of the spring that was touching it. This is as expected given that they were touching.

 

- The driver side (which IS clonking) spring was rubbing a much larger mark of the same sort of width but scraped up and down vertically. This implies to me vertical movement which is not occurring on the passenger side.

 

- I would not expect any vertical movement of the top of the spring unless a mount was broken (unlikely and would probably be obvious) or the top bush had failed.

 

So despite that fact that it looks OK I'm going to send my £3 or whatever in the direction of caterhamparts for one last spin of dice on a new top shock rubber bush. If that doesn't stop I will stick it into one of the Seven garages for them to have a good look over the whole rear suspension. If they can fix it - job done. If they can't find anything - guess I'll just have to close my ears.

 

[Eugene]

Is the off-side spring extended compared to the near-side, to allow for driver weight when setting up the handling?

 

You may find the shock is over-extended and is 'topping out' (the opposite of bottoming out) when the wheel drops down a pot-hole.

 

I have seen this before.

 

 

Edited by - Eugene on 14 May 2013 11:47:04

[Z3MCJez]

I have had clonking when suspension is unloaded and the spring comes free. This can be fixed by putting some small retaining springs in place under the main spring. These spend most of their lives completely compressed.

 

Jez

[sparky]

Off the side of this subject, do I have a potential problem?!

Or is it common...

Car fully suspended at rear sat on axle stands shocks fitted. The de-doin is touching the lower chassis tubes. Is this correct?

[Eugene]

Having a lovely live axle I can't comment on common or not, but it doesn't sound good to me!!!

 

[Fishy Dave]

Quoting Eugene: 

Is the off-side spring extended compared to the near-side, to allow for driver weight when setting up the handling?

 

Edited by - Eugene on 14 May 2013 11:47:04

 

Yes, the spring platform is higher on the drivers side. This shouldn't make a difference to the top of the spring hitting the inner bodywork though? It's a strange one

I wouldn't have thought a new bush in the top of the shock will be the answer, but it's not going to harm.

Will give you a call later on.

[Eugene]

No, it's not the shock platform hitting the 7 body, but the internals of the shock 'topping out'...

 

Basically, the shock reaching the end of it's travel as you have it already extended close to its limits.

 

Worth checking the amount of travel extension you have on that shock compared to the other?

 

[revilla]

Eugene - But if you see the photographs I posted earlier of the damage to the aluminium panels it is clear that the shock/springs ARE hitting the body panel.

 

Just thought of a bright idea to confirm whether there is movement in the top bush. I've not got an FIA roll bar, so the exposed bolt hole for mounting the FIA bar I believe is immediately above the top shock bush. If I fit a little wooden dowel or (anything similar which is a snug fit) into that hole and push it down until it rests on the top shock mount, then mark a line on it level with where it protrudes from the hole, any movement in the bush will knock it upwards allowing me to see how much it is moving.

[Eugene]

Ah - I though you had fixed them hitting the panels, but now had a knock that was different/had been masked by the panel knock???