Cable Operated Clutch
The clutch pedal mechanism from the donor vehicle, sierra or granada will operate with a self adjusting quadrant mechanism. This will auto adjust as things settle and stretch over time to keep the clutch working. The standard mechanism is likely to have a red quadrant. The quadrant is a toothed piece that the cable fits over, the teeth grab other parts of the mechanism to adjust. A common problem is that there is not sufficient movement of the cable with this red quadrant and so it should be replaced with a larger radius quadrant which increases the amount of cable movement for the same amount of pedal movement.
The replacement is part number 91AB7L609AA. If you get if from a ford dealer it will be white, if you get it from another motor factors place it could be another colour.
The picture below shows the original red quadrant and the replacement black one, you will notice that the cable fixing point is further from the centre. If you're not sure which one you have, take the measurement as shown, on the original its around 45mm, on the new one its 55mm.
Cable Bulkhead Tube
where the clutch cable passes through the bulkhead you will need to place an tube fixed to the engine bay side of the bulk head to take up some of the slack end between the cable sleeve and the end that fixes to the pedal. Pilgrim will supply a tube for this with a bracket to attach it. You might find this needs to be trimmed or extended to get the correct tension in the cable to avoid running out of self adjustment. A modified (improved :) tube is shown below.
Cable operation with Lt77 gearbox.
The rover LT77 was intended to be used with a hydraulic set up, so you will need to modify it to accept the cable. This is pretty simple, you drill a hole through the end of the clutch arm that the cable nipple can just pass through, then out the back of the bell housing, here you attached a plate with a slotted hole that can be passed over the cable and bolted in place. JRV8 can supply and advise on this plate.
Here its is in place on the back of the gearbox.
At the front the cable passes through the cover plate and a gromet has been added to project it.
the action of pushing the pedal now operates the clutch by pushing the cable outer into the clutch arm, the inner cable is stationary as its fixed to the gearbox.
Converting a Sumo to Hydraulic Clutch
One way to prevent the problems with the standard clutch set up on a Sumo is to convert to hydraulic. Clutch cables are known for breaking in sumos and are tricky to change, especially at the side of the road, this is caused mainly as the cable has to have a number of tight bends in it to get from the pedal box to the gear box, this coupled with heavy clutch springs and sometimes making use of "used" clutch cables makes them unreliable. Additionally the cable operated clutch can be fairly stiff, so if you like something a bit lighter this is how to do it.
The below details show the process for a set up with a Sierra pedal box and rover Lt77 gear box, but as nearly all Sumos use a sierra pedal box and 90% of the work is at the pedal box end then this should be helpful to most builders.
Before you start this, its worth pointing out that this not an easy mod, working in the footwell is extremely tricky due to the lack of space and the access, you will spend quite some time with your head in the foot-wells and there will be scraped knuckles and swearing, so don't expect to complete this job in a few hours. You will need basic metal working skills and access to a welder.
Parts - Gearbox end
- Slave cylinder - fits to the gearbox - these are standard parts for your gearbox, obtainable from Rover specialists, JrV8, ebay etc. Should be around £25. If you are using a 0.625 master cylinder (see below) you must get a 3/4" slave cylinder, this dimension is the internal bore of the cylinder.
- Pushrod and end - This is what connects the slave cylinder to the clutch arm and pushes it forward. Again available from Rover parts specialist, JRV8, ebay, but there is a cheaper alternative if you happen to have a spare Rover engine valve pushrod and a drag link end, see below for details.
Parts - Pedal box end
- Master Cylinder - available from a range of suppliers in various sizes and qualities, the one shown below is from Compbrake the 0.625 was used costing £18.95.
- Clevis Bracket and Pin - used to connect the pedal to the master cylinder - again from CompBrake for just £1.95.
- Reservoir - a large one is available again from Compbrake, but the photos below show a far smaller item used, this was a motorbike brake reservoir from ebay, about £3.
- Pipe to connect reservoir to Master - depending on where you fit this, about 50cm should be plenty, ebay etc for a few pounds.
Parts - connectors
For the conversion detailed below various connectors were bought from a company called RaceParts UK Ltd, these guys are extremely helpful. These bits were ordered (part numbers shown, prices as at Dec 2008):
- 1.5m of dash-4 stainless steel braided hose (RTH-4) - £10.82
- 1 * dash-4 banjo with 3/8 hole (HETBAN-3-4) - to fit into master cylinder for connection to slave - £12.63
- 1 * 3/8 banjo bolt long (775-03LP) - for use with above - £1.25
- 2 * 7/16 copper washers (rtw481) - for use with above - £0.38
- 1 * 7/16 to 5/16 push-on hose Adt C/W (RTA800) - push fit connector for master to connect reservoir pipe to - £3.53
- 1 * -4 Bulkhead (443-04P) - this is the connector that goes into the back of the slave and can be seen below - £13.31
- Bracket - this is the tricky bit - connecting a sierra pedal box to the master cylinder is a challenge and this is where you need to start making things. The master cylinder firstly needs to fit into an accurately cut plate with the correct size holes, you could make this yourself, or if you want to save quite a bit of time, try TonyM from the Cobra club who is able to supply pre-cut/drilled brackets for the master cylinder for a very good price.
So, with a few other odds'n'sods (welding gas, nuts/bolts, postage etc) this entire project cost around £100.
Modifications - Gearbox end
First remove the metal plate you will probably have covering the front of the bell housing, this is easily done from under the car. If you have a cable fitted, remove it and any cable holding plates you may have on the back of the bell housing. BE VERY CAREFUL not to disturb the clutch arm inside the bell housing too much, if you wiggle it too much it may fall off and then you will need to drop the gearbox to get it all back together.
Depending on what your plate had had done to be before you may need to trim bits off to allow the slave cylinder to fit without fouling the plate, below shows a before and after of a plate (the original was supplied by JRV8 and had been modified to have a hole for the cable and a grommet). An extra piece of plate was welded and cut to keep the bell-housing completely covered, but allowed the slave to fit up to the bell-housing without sandwiching the plate. (probably a bit OTT)
Next you will need to find a way of connecting the slave to the clutch arm with a push rod. Parts are available for this but if you have the right bits laying around you can save a few pounds by making your own. The rod needs to be very stiff and strong and fit into the slave and have a ball shaped end at the other end to fit into the cupped socket on the clutch arm. A Rover engine valve pushrod is perfect for this, it has a nice bulbed end and can be cut to length easily. However, if you have previously had your clutch arm modified for cable use, its possible it has a hole drilled in it and so the push rod will be too small, to resolve this you can take apart a drag link end (as used in sumo suspension, lots in scrap yards) and get the ball joint out of it, this can then be drilled out to take the push rod and shaped to fit the release arm perfectly.
The length of the push rod needs to be pretty accurate to ensure you get good movement of the clutch arm. To do this, start with the push rod way too long, fit it into the slave then push the slave up against the bell housing with the ball joint fitted into the clutch release arm, push it until all the slack is taken by the spring inside the slave and you would start to move the clutch arm, now the gap between the front face of the bell housing and the slave is the amount you need to trim off the push rod + 1-2mm extra. Essentially you want the spring inside the slave to be very nearly fully compressed with everything in the at rest position, this will give you maximum travel when you press the pedal and the maximum ability to take up slack in the system when the clutch plate wears. If you put a depth gauge in the back of the bell housing through the hole the cable used to come out through, you should find the arm travels around 16mm when working properly.
Now its simply a case of bolting the slave to the bell-housing, there should be 2 threaded holes there already. (contact JRv8 for the correct bolts, sorry I don't know the thread size) The alloy used to make the bell housing is fairly soft so be very careful not to over tighten these bolts and strip the threads, use loctite and/or spring washers.
Here it all is fitted and ready to go:
Note that the bleed nipple is at the top to allow the air out easily.
Modifications - Pedal box
This is where the fun really starts, firstly remove the drivers seat and steering column, this will make access far easier.
Next disconnect the cable and remove it. Then remove the pedal box. You can also remove the extender tube you will have bolted to the bulkhead.
Now you can dismantle the pedal box, remove the quadrant, the spring mechanism and cable feed (metalic part shown below) as none of this is needed any more.
Now you will need to attach the master cylinder to the front of the pedal box (front being the bit at the back of the car) and connect the pedal to the master cylinder pushrod. Before you start welding you need to figure out where it all goes, and check it will all fit back into the footwell. It would be almost impossible to assemble all this outside the car and just slot it in, there is so little space in the footwell you need to be able to assemble as much as possible in situ. This is especially true in the Mk3 as this has a strut right across the footwell that s in the way. So start my mocking it all up using clamps and bits of card. Attach the master cylinder to the front of the pedal box using a small clamp and set it approximately as shown below.
This one has had a fillet of 2mm steel plate welded to the side of the bracket to butt up against the front edge of the pedal box for extra rigidity.
Here it is viewed from the front.
Now you can start on connecting this to the pedal. This is achieved by extending the pedal upwards so it reaches the clevis pin on the end of the pushrod. Start with some cardboard as a template, what you want to do is find the right angle and place on the extended part to drill the hole for the clevis pin, you need this such that the pedal movement takes the pushrod on the master cylinder from one end of its travel to the other fully while at the same time keeping it all as close to aligned as possible. What you must avoid is stressing the master cylinder by exceeding its max travel in any direction or forcing the push rod in or out at a nasty angle. Once you have found this, you can weld the extender in place.
The below example shows a piece of steel box section was used for max strength, but reduced down to fit into the clevis pin in the right place. (also a piece of hard stainless was welded to the faces to prevent any wear - slightly OTT)
When fully depressed the master cylinder push rod remains nice and straight, check that there is still a tiny bit of slack in the master cylinder at this point. The clevis pin can be wound in and out on the push rod to fine tune this.
Now its sort of there but it might all feel a bit floppy, so to stiffen the entire thing up, its a good idea to add some additional bracing.
Below shows a heavy (3mm) steel brace thats been added, this is removable as its bolted in place, the bracket is made from 2 pieces welded to fit into the pedal box.
here is the diagonal piece dimensions and it held in place before being bent and welded up.
You will notice in the photos many of the nuts have been welded in place, this makes a huge difference to getting all this back together again, captive nuts means you only need 1 hand to get the bolts started. Also to help with assembly in the footwell the clevis pin supplied was replaced with a nut and bolt as fiddling with a circlip in the footwell is tricky.
So, once you have all this done, its not just a case of giving it all a lick of paint and assembling and testing it.
The video clip below shows the finished pedal box in action, click the little HQ button on the video pane to get a better quality image, apologies for the music I was experimenting with Youtube features :).
Testing and performance
For a LT77 gearbox (the standard on Rv8's), the clutch arm should move around 16mm and you should find that the bite point feels totally normal, somewhere in the middle. If you find the bite point is too low you can measure the the arm movement by putting a depth gauge in the old cable hole and getting someone to press the clutch pedal. If you don't have enough travel you could have the wrong slave/master combination (see specs above) or air in the system and need to bleed the system again.
Once you've got all the bits installed properly and the air out, you should find the clutch is as light as any modern production car and very smooth.
Here are a couple of other peoples modified pedal boxes to have a look at:
Here is a picture of the clutch reservoir mounted on a small home made bracket, the pipe comes directly from the master cylinder in the footwell into the space next to the battery tray.