Clutch Burn Smell but No Slipping

[RyCliff]

Hi All, 

Driving back to Manchester from the Lake District and noticed a strong clutch burn smell initially when driving below 50mph on an A road then again even stronger once we got to the other end of the motorway in slow/ stop start traffic. There aren't any symptoms of the clutch slipping as far as I can tell. I did have the roof on which I know exaggerates smells but this was no throttle acceleration from lights and a steady 60mph all the way on the motorway. The car was running a little hot, the temperature gauge pushing 90 once sat in traffic. 

I do have a rattly clutch cable which seems slightly slack as the rattle goes once a tiny bit of pressure is applied. It has been like this for at least 3 years now though and never had so much clutch burn smell. Is the car so light that there's no noticeable clutch slip at the point it needs replacing and I need to sort it? If so does anyone have a rough idea of costs for such a job?

Cheers in advance

[paul richards]

To check clutch set off in third gear. If it stalls no problem. 

[Tom_Arundel]

Seized brake piston?

[timb2117]

Clever Tom - yup that'd fit - some sort of drag on the car perfectly.

[RyCliff]

Thanks Paul, I'll try tomorrow when we get some dry weather again up here. I assume it should stall no matter how much I put on the accelerator? 

Good thinking with the brake piston. Only thing against that is when I had a brief stop on the hard shoulder around Bolton I didn't spot anything from any brakes. My last experience of a seized caliper at that speed was quite a lot of smoke and squeaking when stopping. Still will check them for any obvious signs that any of them are seized. I think it would be the rears if any so might try winding the pistons back a touch anyway. 

[SM25T]

With the rears, you have self adjusters inside the pistons. The only reason to wind back the piston is to make room for new pads. First heavy application of the brake pedal operates the adjuster again. Is handbrake over-adjusted ? Lift car and turn wheels by hand to check for free rotation. Feel wheels (not discs !!) after a drive to see if warm.

[7 wonders of the world]

if you've been dragging a brake for that length of time there will be noticable discolouration to the pads if not the disc too, the pads go light and brittle on the contact points. you will also find they are more worn when  comparing side to side

[Beagler]

Jacking car and spinning wheel will show a binding brake. Pads will need replacing if any adverse signs and discoloured discs will need checking for distortion and cracks.Might want to change brake fluid if its got that hot.

Dipping clutch on a steep incline will show slippage.

[aerobod - near CYYC]

A dragging brake will also be obvious when you stop after doing little braking, as the hub of the wheel where the brake is dragging will be much hotter (of course it is advisable to hold a hand near before touching, to avoid burns if it is really hot).

[RyCliff]

Thanks everyone for the notes on the dragging brakes. Quick look around the discs with the wheels on and there's no apparent markings I'd say are in line with a sticky caliper that's been dragging for that distance. 

However, setting off in 3rd gear with no accelerator pressure on a very slight incline is relatively easy for the car, slight dip of engine speed but nothing massive. This is a 6 speed though so does the same still apply with the shorter ratios? Next question will be anybody recommended in Cheshire area other than Oakmere? I'd go to Track V Road but getting there during the week could be difficult and am booked in at Three Sisters track day first week of July 

[Tom_Arundel]

Someone put a kipper on your exhaust manifold ? 

[RyCliff]

Haha that would be a much preferred problem to solve. The smell definitely resembled a clutch friction plate rather than a kipper unfortunately! 

[paul richards]

Is it a cable clutch? If so make sure there is some slack in the cable.

[paul richards]

You can get some strange smells if something has landed on the exhaust. 

[Wrightpayne]

Paul,

what do you mean by slack? The K series has the spring on the pedal to ensure preload on the bearing (a second spring is advisable - see John Vines thread)

Ian

[RyCliff]

There's definitely slack on the cable from the way things sound and the pedal feel. I suppose one other thing is there is quite a bit of transmission noise in neutral with the clutch lifted, I always assumed this is just typical of sitting alongside the gearbox with no sound insulation.

I'll take a look at John Vines thread for the extra preload spring. I'd imagine that should be a simple job. 

[paul richards]

Perhaps I could have given a better description. Yes you need a little pre load but you don't want pedal jamming and keeping cable a taught so that clutch is not fully engaged.

[paul richards]

The noise you are experiencing which goes away when clutch is depressed is quite normal. 

[RyCliff]

Cheers Paul. I see the original spring in the blog post is no longer supplied by Caterham but should be some alternatives out there.

There was a slight squeak of the clutch pedal at the point when the smell was bad, so could be looking at a clutch release bearing needing replacing. Not sure how much a new friction plate is but if the CRB needs doing then might as well get both sorted

[Wrightpayne]

I had a friction plate disintegrate - 2/3 of the friction material on one side let go. This was at quite a low mileage and no heavy use.

If the smell persists after a couple more outings and all other sources are ruled out then time to consider a clutch swap

[John Vine]

I see the original spring in the blog post is no longer supplied by Caterham but should be some alternatives out there.

Indeed, spring CQ13 is no longer available, either from CC or Redline.  Darren in Parts told me that the supplier had ceased trading.

I've searched all over for an equivalent spring, but have yet to find something similar.   The best bet may be simply to obtain a spring (or springs) of roughly the right size and spring rate, and then calculate how much modification is needed to provide the correct pre-load. 

Please let me know if you do find a suitable spring.  I'll then update my Guide.

JV

 

 

 

[RyCliff]

Hi John,

I've found product 9645 on the attached site. I can't seem to send a link to the exact product page but search 9645 in part number and it should come up. Spring constant is seems good at around 100N applied load with 20mm extension and free length is close to the 100mm of the one you purchased. 

They also sell them as single springs which is unusual! 

I haven't yet measured up the OD of the existing to make sure they're similar but will check that too before going ahead and feedback if it fits.

 

ETA

https://motioncontrol.metrol.com/tension-springs/extension-springs-with-loops.html

[SLR No.77]

Ryan, I'd still suggest investigating further a dragging brake, if there's nothing obviously wrong with the drive of the car it's much more likely brakes than clutch. 

Stu.

[John Vine]

I've found product 9645 on the attached site.

Sounds promising, but there was no site attached. (To do this, click the "link" icon and paste in the site's URL.)

JV

[Jonathan Kay]

"You can get some strange smells if something has landed on the exhaust."

...

"Ryan, I'd still suggest investigating further a dragging brake, if there's nothing obviously wrong with the drive of the car it's much more likely brakes than clutch."

...

In the absence of any clutch symptoms I'd also be looking for other causes. 

Can you get it up on stands for a look and a play?

Jonathan