Getting Desperate - Please Someone Help - Suspension Knock!

[revilla]

Long-running thread here detailing my attempts to track down a nasty knocking from my rear suspension. I now know exactly what the noise is but I'm still stuck for understanding WHY and WHAT TO DO. Decided to start a new thread as the old one contains so many red herrings from before we knew what the cause was.

 

As shown here the inboard edges of my brake calipers contact the front Watts link arms as the suspension travels up and down.

 

The above photograph was taken with the car on axle stands, the rear right shock disconnected at the bottom and the rear right side of the axle jacked up slightly to simulate compression over a bump. As the wheel rises the caliper hits the Watts link arm. In the pitcure it is hard to see but it's not just close, it is actually hitting. You cannot slide a piece of paper between them.

 

As you can imagine this gives rise to the most awful knocking and rattling.

 

A few notes:

 

1) Nick Potter who originally tracked down what was knocking filed the caliper body a little, which has reduced but not really cured the problem. At least is shows we are on the right track.

 

2) The Watts link bellcranks are fitted correctly, displacing the arms inwards and away from the calipers.

 

3) All bushes have been checked over by Nick Potter and found to be pretty much as-new. There is no excessive play anywhere. This does not occur due the de Dion moving side to side, contact occurs with simple up-down movements.

 

4) I have checked the presence and fitting of all spacers etc. carefully against the build manual. Everything appears to be assembled correctly.

 

5) My de Dion ears are stamped "1.5". I'm guessing this means 1.5 degrees of camber? They do appear to taper towards the top which will make this issue worse, but no idea whether these are the standard parts.

 

I have heard that this situation can occur when the pads are well worn, however I have 7mm of friction material remaining which must mean they are close to the thickness of new pads.The part of the caliper which hits the arms is a contiguous solid peice with the part which presses against the back of the OUTER pads - so as the pads wear this part of the caliper body will indeed move INWARDS making the problem WORSE.

 

I have absolutely no idea why my car should be doing this when other people don't generally seem to suffer, nor do I really know the best way of fixing it.

 

Possible fixes (maybe some stupid, comments appreciated) which have flashed across my mind are:

 

1) Putting new pads in every time they wear down to 7mm (very inefficient, can anyone tell me the thickness when new, pads are these?).

 

2) Getting someone to water-jet cut some shims in the same shape as the pad backplate. I could then shim the outer pad to move the caliper outwards. I haven't yet investigated costs for this or whether there is room to shim it with fresh pads (can anyone tell me anyone who could do this?).

 

3) Adding a washer to the 6mm spacer between the caliper and de Dion ear to move the whole caliper outwards, although about 1mm is all I could move it by to avoid the caliper body touching the disk.

 

4) Further filing of the caliper body after checking the internals to make sure it is safe to do so.

 

5) Maybe replacing the aluminium plate between the de Dion ear and the de Dion tube with something slightly thicker to very slightly shim the whole hub and brake assembly outwards by a mm or two.

 

To be honest before bodging it I really wish I could find an explanation for WHY???? when eveything looks to be the correct parts assembled correctly.

 

Please help, this one is driving me mad!

 

[Wrightpayne]

As I said in my other post, I'd be on the phone to Caterham. Doesn't matter its a 2003 car if it is a design error.

 

 

If it were mine I'd stick some new pads in it to buy you some time whilst you consider the options. You could always open some Sierra pads in Halfords and measure the friction material thickness.

 

I would also try and find a local SV owner with the same set up and go measure everything side by side to see that the watts pick up points, camber etc are all the same and that all the components are the same.

 

 

Ian

[Pendennis]

Suppose you could shim between tube and ear, but something isn't right.

Is the disc central to caliper?

[revilla]

@Wrightpayne - Yes I guess you are right, I'll have a word with Caterham Mids, they are only 20 minutes from my house anyway. Just a bit disappointing because I bought the car to enjoy doing my own maintenance and I don't like to admit defeat, but if there is something wrong from a design perspective I'm never going to find the fault. The car was originally kit built and from what I can see it was actually built over a long period of time. I just wonder if maybe something changed during that time and my car has a mix of pre- and post- bits that don't quite go together.

 

@Pendennis - Yes the disk runs true exactly in the centre of the caliper slot.

[Pendennis]

Surely then, if your watts linkage is installed correctly the DD tube is too short for those radial ears

[revilla]

@Pendennis - Yes to be honest that was the logical conclusion in my mind, but I wasn't aware they made different length DD tubes, I thought they all came off a jig at the same length. If you know anything about different length DD tubes please fill me in. To be honest when trying to track this down, another problem I found was that the top edges of the springs were catching on the inner walls of the turrets. I managed to get clearance for them by very slightly reshaping the turrets but again it was unexplained - unless the DD tube was too short! Have you any idea what the correct "standard" length for the DD on an SV should be?

[Pendennis]

No I don't and am not aware of varying lengths either. I could measure mine for you, but how wide is yours?

Interesting about the springs catching turrets, how much of a gap do you have between the DD tube and the diff? Is the caliper catching the recessed section of the trailing arm linkage?

[revilla]

I'll try to measure mine tonight. I'm not sure if it will be easy to get a tape measure straight from one side to the other but I'll see if I can measure anything meaningful. I will try to measure the actual DD length (i.e. between the inner edges of the ears) and the length including the thickness of the ears too.

 

If you could manage to measure yours for me that would be very helpful. I presume yours is an SV too?

 

I can't remember how much clearance there was between the DD and the diff but it was one of the things I checked when trying to find the knock and it was certainly well clear, and yes it is catching the recessed section of the trailing arm. It's the casting immediately below the coil of the handbrake spring that catches as it sweeps up past the recessed section (which I presume is recessed supposedly to clear it).

[Jonathan Kay]

Quoting revilla: 

I'll try to measure mine tonight. I'm not sure if it will be easy to get a tape measure straight from one side to the other but I'll see if I can measure anything meaningful. I will try to measure the actual DD length (i.e. between the inner edges of the ears) and the length including the thickness of the ears too.

Could this be done by dropping plumb lines to the ground and measuring between the marks on the ground?

 

Jonathan

[revilla]

Jonathan that does indeed sound like a very intelligent suggestion (as yours usually are ) thank you.

[Pendennis]

Ah, missed the SV bit

Sorry mine's an S3, can't imagine for one minute that an S3 DD tube would be on your car, but suppose you best measure to check.

 

Also, have you checked to see if trailing arm length security centres are as the manual, thus bellcrank is vertical

 

Is it knocking both sides? Thus do you have same clearance issues either side? If not, the A frame is pulling tube off centre

 

 

 

Edited by - Pendennis on 1 Jul 2013 18:17:42

[mav]

An s3 tube in an SV chassis would be easily identified. Do the tube end protrude past the outer chassis rail? If yes then you have the SV tube, if not, you don't.

 

See http://www.martinarichards.ukfsn.org/pictures/sv_watts_2.jpg

[revilla]

@mav - by "easily identified" I think what you are basically saying is that if I have an S3 DD tube in an SV, there wouldn't be anything sticking out to attah the wheels to? In which case I definitely have an SV tube! To be honest mine looks pretty much the same as your picture but something is out by millimetres somewhere.

 

It is quite easy to get a tape measure straight across the back face of the DD tube. I make mine 1264mm from flange to flange (i.e. up to but not including the aluminium "ears"). I'll put a separate thread on simply asking if anyone can measure an SV DD tube for me for comparison.

 

As well as talking to Caterham I think I'll give Bruce at Arch a call tomorrow. I think if there any funnies or if there have been any minor design changes, he would know.

[6speedmanual]

Is the leading linkage of the Watt's linkage actually straight?

 

Where the recesses are pressed in it is easy for the link to take on a curve which may not have been checked or straightened at the factory or after a bump?

 

At any rate, if it is just millimetres you are looking for, the link could easily be made to curve fractionally away from the caliper without affecting its function.

 

Heavy hide mallet on bench should be able to introduce the necessary adjustment without denting the tube or even damaging the powdercoat.

 

Peter

[mav]

I will try and measure mine tomorrow if I get chance and nobody else has beaten me to it...

[Mucus72]

Hello. Don't know how far you have got, but I have a 2003 SV in Loughborough, and if I can help with your investigations I would be happy to...

[TBKBABABTIM]

Happened to come across following while searching for something completely different here

[revilla]

@Martin - Thanks.

 

@Marcus - I'm only 10 mins from Loughborough in Burton on the Wolds. Sounds like our cars should be pretty much the same - I would really appreciate a second pair of eyes on the problem and if we could put the two cars side by side we should be able to track down what is different. I'm away at the weekend but on holiday (at home) next week - or if you wanted to come over one evening my Indonesian wife would be happy to cook up some oriental treats for a bit of dinner!

 

Drop me a BM and let me know what would suit you.

 

 

[revilla]

@TBKBABABTIM - Yes I had seen that thank you. I understand that they can come close when the pads are well worn, but mine are knocking hard on almost new pads!

[6speedmanual]

I have a vague recollection that when the SIII deDion was substantially redesigned it pick up a fractional increase in length (???) Was this reported/mentioned in the dd failures thread?

 

If this is true, was the SV axle length also increased?

 

Peter

[revilla]

OK - Finally some answers!

 

I measured up my de Dion tube last night at 1264mm and called Bruce at Arch Motors this afternoon, who kindly measured up a brand new one for me while I was on the phone and also got 1264mm, so we can discount problems with the de Dion length.

 

He put me in touch with Rob Singleton at Boss Racing, who I phoned today.

 

Rob tells me that from his time at Caterham, this was a recurring problem with SVs and he was aware of several cars having to change brake pads after only 2mm of wear! It appears to be a design flaw, basically a miscalculation when scaling the S3 up to the SV design which leaves the calipers very close and with very little scope for manufacturing tolerances, so if you do get one where the tolerances combine to put things a bit closer together they start to knock after only minimal pad wear (as the caliper bodies move inwards as the pads wear it gets worse).

 

The solution is to shim between the de Dion tube and the ears, which is something he has had to do on a number of race cars too (although more often to accommodate wider wheels rather than to fix this issue). There are two ways to do this:

 

1) If you only need a couple of millimeters, simply add in a couple more of the aluminium gasket/spacers already used to cap the de Dion tube.

 

2) If you need a bit more, say 5mm, get an aluminium plate cut to the same design as the spacers but in thicker material. In this case, slightly longer bolts will also be needed.

 

Rob has kindly agreed to have a word with the engineering shop that cut his plates for him to ask them if they can cut me a couple more, if not I'll get Bruce to send me a couple of the aluminium gaskets and get some thicker plates cut myself. I'm quite happy to pull the back apart and fit them myself.

 

Hopefully that will do the trick.

 

Thanks everyone for your input, it's been a long road to understanding what is causing this but I think I'm on the home straight now and looking forward to smooth and rattle-free driving. At least the problem has been seen and fixed before. Thanks also for the various offers of assistance but hopefully I should be OK on my own for now. Will post back here when all is sorted.

[Jerry Auton]

As another SV owner am pleased to hear that you have finally found the answer to this one. I have learned some more about SV's from your process, so thanks for that

I had a nasty creaking from the n/s rear for some time which turned out to be a Watts linkage rod end. Now happlly resolved thanks to SM25T