Converting to hydraulic clutch. Questions/Advice

[Rob Board]

I wish to start amassing parts to convert to a hydraulic concentric clutch in my 1.8k 6speed 140 BHP k. (wet sump), with uprated Ap clutch. Doing a search reveals best option for m/c is 5/8"?? (As advised by PC) I have a few ideas for suppliers("super clutch" for the concentric bearing assy, and maybe "Burton, or D/T for m/c".

Buta few Q's.

1.Why is 5/8" m/c recommended?

2.From what vehicle, or what make is the m/c that would best fit, or do I buy an SV m/c from CTM. If so ££££?

3. Any further advice/pitfalls/tips greatly received.

Hopefully be able to pick up most bits at the next Autosport show.

Thanks in advance Rob.

[Jason Plato]

What benifits will the hydraulic clutch provide on the K over the cable and present CRB ??

 

Dave

[Rob Board]

Dave.

Using a concentric clutch enables me to ditch the current CRB and pressed steel release arm. IMO a worthy upgrade given the problems I have had with this in the past (as have many others), although to be fair since Caterham have fixed it under warranty, it has been faultless!! (Kiss of death). In addition pedal effort and response should be improved.In short I just feel it would be a good way of "modernising" the clutch assy, and improving longevity/reliability of the CRB.

Cheers Rob.

[Chelspeed]

1 You need to look at the clutch throw you want, for AP 5 1/2 inch it's 3.8mm max. Work out the effective area of the slave cylinder (area from OD minus area form ID). Measure the pedal throw and then work out which master cylinder diameter is closest. Or copy someone else who has done the sums (PC no doubt) or who just guessed at 0.7 inch then changed to 5/8 when it was too much travel (me!)

 

2 Get a titan slave from Burton's or SBD, these come with adaptors to fit Ford 4 or 5 speed boxes, and therefore Caterham 6 speed, Quaife sequential, Elite (I think) etc etc which use the same gearbox nose piece.. If you get a saab hydraulic slave, the one generally used and copied by AP etc, then you will need to engineer an adaptor to fit it on the front of the gearbox.

 

3 Tips! Use male - male adaptors and female fittings on the pipes, the banjo and copper washers are rubbish compared to adaptors which seal on the tapered ends. See also below on the same subject....

 

Make sure the hydraulic connections are 110% before putting the engine in, it's not like the brake calipers where you can just tweak them up a bit if they weep when you try driving it, it's engine out again. Also difficult to check them under pressure until the engines in as there's nothing for the slave to push against until then at which time it's too late.

 

I made a jig (posh name for a bit of angle dexion) to hold the an old clutch plate in the right place against the bellhousing so that I can exercise the slave at near full pressure to check for leaks. No problems since then.

[John Vine]

improving longevity/reliability of the CRB

Rob,

I know we (and others) have discussed this elsewhere on BC, but, for the benefit of new readers, the best way to do this with the standard CRB is to make sure that there's sufficient pre-load (in the range 80-120N). The standard CRB is a tough and long-lasting mechanism providing it's set up with the correct pre-load. In my experience, however, the standard clutch-pedal return-spring design (at least, in my car) does not achieve this (generating a pre-load as low as 15N).

 

(Note to self: Must complete the promised article on this subject for LF!)

 

JV

[JP]

How do you set the pre-load?

[Rob Board]

Chelspeed,

Many thanks for the input. I shall try and work out the required m/c, with regards to travel of the crb, after speaking to a few manufacturers. One consideration os ensuring I do not ahve too much travel, or a pedal stop, so that the bearing does not pop off the end of it's housing. All things I am sure that will be fun??? to sort when th time comse.

Cheers Rob

 

 

Edited by - Rob Board on 2 Nov 2003 16:41:53

[John Vine]

JP,

What a good question! Basically, there are two ways: either shorten the existing clutch pedal return spring, or replace the existing spring with two new ones (the method I used). Either way, you'll need to measure the force applied by the spring (say, by using a spring balance). Then you either (1) shorten the existing spring in stages until you get the force you want (you'll have to make allowances for the angle of the balance and the mechanical advantage of the spring/cable), or (2) instal new springs of the correct length so as to generate the required force.

 

You'll find more info here.

 

JV

 

Edited by - John Vine on 2 Nov 2003 17:13:40

[Peter Carmichael]

The recommendation for 5/8 was made for use with slave cylinders based on the Saab piston dimensions, such as the Quartermaster. 5/8 is the smallest size available and is still too large to give a reasonable pedal effort with such a mechanism. The car is drivable, but "horrible" - this is why my pedal box is modified with a new pivot point and I use a cut down standard ratio pedal to get the pedal weight right.

 

This also gives more than the 4mm travel permitted for the Quartermaster clutches. I fitted a pedal stop (fancy name for a bit of ally tube) "inside" the master cylinder. This is very discreet and assures proper pedal travel regardless of any pedal adjustments.

 

The concern is not to prevent the CRB piston falling off the end of the mech, but to avoid damage to the clutch diaphragm springs from over-actuation.

 

A burtons mech may require a different master cylinder diameter.

[Rob Walker]

John,

 

I am not sure that increasing the CRB preload has worked. I liased with Nick Green and borrowd his spring gauges and incresed my preload with the addition of one extra spring onto the clutch peddle giving me around 80N but on splitting my engine and box two weeks ago I was dissappointed to see that most of the grease had been thrown out of the CRB and the bearing felt very loose. The car had covered less than 1500 miles since the bearing had been replaced. I doubt the bearing would have lasted another reason.

 

Rob

[Chelspeed]

> 5/8 is the smallest size available and is still too large

 

Peter - AP, from some time earlier this year, brought out 14 and 15mm versions of some of their master cylinders, I know they do them in the short ones, CP2623.

[DanB]

...and I've got a .5 inch Girling MC on my hydraulic (blackbird) set-up...

 

😬

 

Dan

[John Vine]

Rob (W),

Ouch! That's bad news indeed, especially after such a low mileage. Maybe the damage was already done before you upped the pre-load? Were you getting any squealing noises? I've done 4000 miles to date with my modified springs -- so far, so good (now I can expect it to go wrong tomorrow, I suppose!). I was chatting to Nick at Brands during the L7C trackday in September, and his CRB seemed to be in rude health then.

 

JV

 

Edited by - John Vine on 3 Nov 2003 16:53:45

 

Edited by - John Vine on 3 Nov 2003 16:54:18

[Rob Walker]

John,

 

The increased preload was applied to the bearing from new. The engine and box were removed for other reasons there was no indication that the bearing was deteriorating before the strip down. In view of how its been overheating and thrown most of its grease I doubt it would have lasted much longer before starting to make some complaining noises. The worrying thing is what to do now as all my previous CRB`s have failed by way of the bearing coming away from the plastic slider section with little or no evidence of loss of lubricant. ???????????// Have I made the situation worse by applying more preload, it would seem so ??????????/

[John Vine]

Rob W,

Hmmm.... A tricky one, that. It might be worth sending your CRB to INA for their expert opinion as to what caused the failure (I can give you a contact address if you need it). They were very helpful in my case. And, as INA pointed out to me, although insufficient pre-load is bad, so is excessive pre-load (which can lead to early CRB failure and damage to the diaphragm fingers). What did your fingers look like (if you get my meaning)?

 

JV

[Rob Walker]

John the contact / thrust face looks perfect. I have seen some wear on the faces of my previous CRB`s but they had done more milage 8000 and 4000 ish.

 

The Manufacturers number would be helpfull thanks.

[John Vine]

Rob W,

 

INA's address is INA Bearing Co Ltd, Automotive Division, Forge Lane, Minworth, Sutton Coldfield, West Midlands, B76 1AP. Their number is 0121 351 3833. I suggest you contact Stewart Davies, Applications Engineer, Engineering Division (I found him very helpful indeed). I'm assuming, of course, that your CRB is Caterham p/n AB57 (INA code F-202994). Good luck!

 

By the way, the classic signs of an overheated CRB are (1) a shiny and discoloured contact face, (2) grease visible between the bearing and the plastic housing, and (3) radial movement of the bearing housing around the plastic housing. Does yours match these?

 

JV

[Rob Walker]

John

 

Thaks for the info. Yep my bearing has the grease between the bearing and the plastic housing and the contact face of the bearing is very shinny but not worn.

[John Vine]

Rob W,

 

Hmmm... Doesn't sound good. But I'd be very interested to hear what INA have to say. Perhaps you could post the results here when you get them?

 

JV

[KayTee]

Just trying to get a grip on what I've been reading here.

I got the burton's set-up for a Ford Rocket box, and I have an AP twin plate clutch as well as a brand-new Girling 5/8" clutch MC. No return spring as of yet.

 

Will I need to fit a return spring working against my foot's force when pressing down the pedal, in order to keep the bearing from touching the clutch spring when I am resting my foot on the peadal while driving ? Does said return spring lift the CRB off the clutch spring ? Is said CRB supposed to rotate with the clutch at all times, as 'pre-load' seems to indicate ?

 

I suppose I'll be able to measure CRB throw before mating engine and gearbox, how much travel does the AP clutch need ? Pedal stop by adjusteable rubber knob ? (ooo-err!)

 

Gosh, this turns out to be even more complicated than I thought

 

Cheers ! - Karsten

 

 

[Chelspeed]

No it's not Karsten, don't worry. I think this pre-load discussion is for cable clutches.

 

If I'm understanding it correctly the pre-load is to hold the bearing against the clutch, not to hold it away, so the spring would be holding the pedal down a bit. Not against your foot's pressure but with the foot's pressure.

 

With hydraulic slaves the only thing that returns the bearing will be the clutch cover springs. So I think there will always be some preload on the bearing as there's nothing to move the bearing off the clutch springs.

 

Anyway I've never had a spring on my hydraulic clutch system and it's been fine through 2 clutches and about 4 release bearing set ups (changed due to upgrades never failures before anyone says anything).

 

Slave cylinder throw is on the AP drawing that comes with the clutch, it's 3.8 mm max on the CP6002 model 5.5 inch AP twin plate. Which clutch have you got? My pedal stop is a 10mm bolt through a nut migged onto the side of the pedal. From the master and slave diameters I worked out how much master cylinder movement would produce 3.8mm at the slave and set the pedal stop that way.

[richardhomer]

Dave Kimberley and I fitted a concentric clutch slave cylinder from Tony Tewsons Quarter Master company (01926 424609) to our hillclimb Caterham VX. Upon supply of exact dimensions Tony supplied a correct size mounting adaptor. Dave at Demon Tweeks can advise and sells the correct size master cylinder, 5/8 I think. Master cyl has been fitted to into standard pedal box alongside,but slightly higher than the twin brake master cylinders. As Peter Carmichael points out, it is neccessary to fit a positive stop to prevent overthrow- I think I used an 8mm x 130 bolt to do this and just set it by adjusting the stop to when the car could just be pushed when in gear and pedal depressed. The pedal pivot was not altered but a yoke was pivoted on the pedal to line up the operating rod with the master cyl. Works superbly with just the right weight and travel and is giving much more control over starts with very smooth take up compared with the cable.

Incidentally the Quarter Master twin clutch plates in the Sachs 5" clutch have given excellent service and little detectable wear with double drives for a season of hillclimbing. Just a pity the cam belt tensioner was not as reliable - but that is another and rather expensive story !

 

1.8 SV160 S7OMA