Dual 7" Servo - Page 15

Grey V8 Pete · #1 24th January 2012, 23:36

I finally managed to remove the Metro servo today after a 3 hour struggle. Even with an access panel in the bulkhead the nuts are almost inaccessible and as always the worst one to access was the rusty one!

I had a couple of raised eyebrows about build quality when I found that the spigot diameter of the master cylinder had been hand fettled on a grinding wheel to make it fit the servo hole. Vacuum seal was by silicone sealant only! Also the packing piece in the master cylinder piston hole was a ground down nyloc nut (see pics).

Master cylinder has 23 on cast boss not 22 as previously mentioned. My fulcrum bolt has its head welded to the brake pedal so I am stuck for now with using the same offset setup with the new clevis. I shall put a spacer between the legs to give it some support when the nut is tightened. I will also re-use the offset packing washers to keep the servo in line with this horrid compromise set up.

The servo holes in my pedal box are so near the bottom edge that I will have to extend the holes inwards and upwards, not downwards. There are also two D-shaped cut outs underneath for spanner access, so that area is further weakened already (see pics). As the 5mm pitch difference only equates to a 2.5mm offset I am sure there will still be clearance under the bonnet when the master cylinder is rotated to get the rigid brake pipes exiting sideways & downwards.

Mike. Regarding your comments about fitting large washers I am thinking that if the dual servo is more “powerful” than the old one, so less pedal “push” is required, there should actually be less load on the pedal box but there will be a greater force (from the servo) acting between the servo and the master cylinder? Peter.

Mike · #2 25th January 2012, 08:30

Peter

I've sent a PM

Mike

Grey V8 Pete · #3 25th January 2012, 10:44

Mike. Thanks I've just replied :-)
Peter.

jeremy · #4 25th January 2012, 13:13

Fitted the servo today, slight fettling of the holes as previously described.When i fitted the clevis, I had measured it's length in comparison to the metro, in my case 13 cm from mounting face to centre of clevis mounting hole, and locked it.When I squeezed into the footwell luck would have it that the clevis was sitting with the pedal in it's groove and mounting hole matched so slipped in the retainer...job done.What's even better is that I didn't need to change my pipes to the master cylinder as I was able to undo a few shallow curves from my initial set up to allow for the extra length of the set up! I have kept the m/c in the same position as I had in the metro system as I have a remote reservoir and this made the pipe fitting easier.SMOOTH........just to confirm, there doesn't need to be an air tight seal with the M/c and the servo? The ford m/c has that little NIC in it's mounting plate.

Mike · #5 25th January 2012, 13:25

Another satisfied customer!
When will you be able to take it for a test drive, and report back?
Mike

Quote:

Originally Posted by jeremy

Fitted the servo today, slight fettling of the holes as previously described.When i fitted the clevis, I had measured it's length in comparison to the metro, in my case 13 cm from mounting face to centre of clevis mounting hole, and locked it.When I squeezed into the footwell luck would have it that the clevis was sitting with the pedal in it's groove and mounting hole matched so slipped in the retainer...job done.What's even better is that I didn't need to change my pipes to the master cylinder as I was able to undo a few shallow curves from my initial set up to allow for the extra length of the set up! I have kept the m/c in the same position as I had in the metro system as I have a remote reservoir and this made the pipe fitting easier.SMOOTH........just to confirm, there doesn't need to be an air tight seal with the M/c and the servo? The ford m/c has that little NIC in it's mounting plate.

GreatOldOne · #6 25th January 2012, 13:45

Quote:

Originally Posted by jeremy

just to confirm, there doesn't need to be an air tight seal with the M/c and the servo? The ford m/c has that little NIC in it's mounting plate.

Correct - no need for a seal. The servo is sealed internally, around the output rod. I have no rubber / gasket between the adaptor plate and the servo, or the master cylinder and adaptor, and it works just fine.

oaktree11 · #7 27th January 2012, 21:10

Just a question about removing the output shaft to fit an extended one, does it just unscrew? Mine rotates but does not unscrew and there does not appear to be a locking ring? Am i missing something? John

Grey V8 Pete · #8 28th January 2012, 12:50

Hi John. Attached photo shows the plunger unscrewed from my actuating rod. To do this I fitted the servo assembly loosely into the car, then wedged the pedal down so the plunger protruded out of the housing. Then with a 6mm and 10mm ring spanner I undid the locknut and removed the screw. It wasn’t very tight.

Note! Only use spanners. Don’t attempt to grip the plunger itself with mole grips as it is a vacuum seal surface for the centre rubber seal.

As I don’t have a lathe I am using a pillar drill and ingenuity to make a longer extension plunger to replace the removed part similar to GreatOldOne’s Thread 353 Page 18, but with the 10mm diameter part made separately with a 6x15mm deep threaded hole in it. This will accept a 6mm x 40mm thread cut from a high tensile bolt to maximise strength. The two will be secured together with thread lock liquid. I can use the original lock nut when fitting to the servo rod. Peter.

Quote:

Originally Posted by oaktree11

Just a question about removing the output shaft to fit an extended one, does it just unscrew? Mine rotates but does not unscrew and there does not appear to be a locking ring? Am i missing something? John

denniswpearce · #9 28th January 2012, 09:15

John, I don,t think it is meant to be removed it can only be adjusted minimally as discussed in previous posts and may need you to make a modification as shown in one of Jasons posts (greatoldone) so that the two operating faces marry up. As Jason has said to me "In an ideal world and with all parts from the same manufacturer then all surfaces will marry up, but........we have a kit car and even then no two are the same"
The servo unit is a sealed one unlike the metro unit.
Hope that helps.
But check out Jasons previous posts for a solution, not the only one I am sure.

oaktree11 · #10 28th January 2012, 17:23

Thanks Peter and Dennis. I see how it all works now and have removed the output shaft.
Obviously, the lathe solution is ideal but we dont all have
access (actually i do own one, a Myford Super 7 but no space for it - its all full of car bits!) and I think Peter's idea is sound. This is not an area with huge loading but obviously it IS safety critical so wants to be well engineered. Actually, with the spacer plate in place the shaft will almost adjust enough for me....but not quite!

Another question! My MC has lugs that will take an M10 bolt. Has anyone fitted M10 machine countersunk bolts to the adaptor plate?

Thanks again, John

Grey V8 Pete · #11 28th January 2012, 18:57

Servo in at last and just trying the master cylinder in place to check the pipe runs. BUT I seem to have discovered an alarming latent error from build. My understanding of the Sierra dual braking circuit is that the single output pipe from the rear (primary) piston goes to the rear brakes where it divides at the axle. The two output pipes from the front (secondary) piston each go to one front brake. That way if the rear fails you still have the front brakes and vice versa. Does everyone agree? With my system the rear brake pipe goes to one of the front cylinder outlets! Pipes were identified to M/C before disassembly and lengths are different so not an eror by me. Would appreciate any confirmation / comments before I do some major re-routing of the m/c connections to correct this. Peter.

oaktree11 · #12 28th January 2012, 19:12

Peter,

That is a big no no IMHO. The split system off one chamber is always seperate circuits to the fronts and the single outlet goes to the rear to be "T'd".

If you think about it the way yours is plumbed you stand the chance of losing the rears and one front all at once which is a scary thought...

John

morris · #13 28th January 2012, 19:23

My solution to the problem of getting the servo push rod to work with the M/C plunger

The countersink M6 screw replaces the one supplied in the end of the servo pushrod but the little collet is retained to help prevent vibration slowly screwing it in further. I also had to grind the edge of the screw head a little to get it down to 10mm diameter so it will run smoothly up inside the M/C (compare with the unmolested screw above it)

The bullet was ground to shape from the shank of the M10 bolt I chopped out of the pedal box that was welded in as the accelerator pivot. It has a flat base for the screw to push on.

I had tried to use a much longer bullet with an M6 thread cut down the centre so I could screw some threaded rod in to mate with the servo directly but without a lathe and using a cheap clarke drill press, this is pretty difficult at this scale and I struggle to centre the hole, hence this solution.

It feels pretty solid when pushing the pedal.

One thing I have noticed with the new servo (even without the M/C installed) is that I get a slight clunk when you first push down and then it runs smoothly. it may be because my clevis pin is currently in loose as I'm going to replace with an M10 bolt but I wondered if anyone else had experienced this?

Grey V8 Pete · #14 28th January 2012, 22:43

Quote:

Originally Posted by oaktree11

Peter,

That is a big no no IMHO. The split system off one chamber is always seperate circuits to the fronts and the single outlet goes to the rear to be "T'd".

If you think about it the way yours is plumbed you stand the chance of losing the rears and one front all at once which is a scary thought...

John

Yup! That's what I thought. If the rears had failed it would have given me just one front brake = up the bank, or into oncoming traffic! Scary or what. Good job I found it now.

Attached is the servo plunger made on my small drill press today :-) Peter.

oaktree11 · #15 29th January 2012, 07:07

Peter,

At least it should not be too bad to put your braking system right.

Good job with the plunger - I might try to copy it this morning! - John

morris · #16 29th January 2012, 11:59

Pete (V8), that's essentially what I was trying to achieve but with the bullet bit being pretty much the entire length. You must have a better drill press vice than me as I can never get an accurate centre to do this kind of fine work. mine tends to push the piece out of alignment as you tighten it up

oaktree11 · #17 29th January 2012, 18:01

hmmmm am I being too simplistic or will and M6 bolt with the head ground to a button work just as well as a fabricated part. I had a bash a short while ago (until the cold got to me) and this is what it looks like. I will tidy it up tomorrow - I think it will work fine? - John

Servo with ground down 6mm bolt by oldpropuk, on Flickr

Servo output mod by oldpropuk, on Flickr

GreatOldOne · #18 29th January 2012, 18:15

Yes, that would work - it's essentially what I did with the trial servo. I just cut the end off an M6 bolt and re-used the spacer / cap I already had for use with the metro servo.

Top tip - if you want the head of the bolt to be symetical, mount it in your drill and spin it as you offer it up to the grinding wheel. I did this when I ground the head down on the carriage bolt for my iPod mount. Works great.

oaktree11 · #19 29th January 2012, 19:18

Goo, now that IS a top tip! Actually I used a spare drill chuck to hold the bolt in but i didnt think of actually spinning it in a drill, thanks, mkII will follow tomorrow. John

Grey V8 Pete · #20 1st February 2012, 21:08

Despite a whole succession of unscheduled events lately that have impinged on this project I have finally fitted the dual servo unit, and very smart it looks too! For anyone else who also has the older (straight) pedal box I can confirm that the packing washers are still required to offset the servo inwards. There is approximately 6mm total pack on each of the two outer studs. This still provides minimal clearance with the bonnet side panel junction which will need a bit of careful fettling to make it all clear. I have made a neat seal around the pedal box-to-bulkhead using black silicone sealant. I finally tracked this down at Screwfix (Cat No 90574). I have also made up a cover plate for the two access holes under the pedal box as none existed before and would have let engine bay fumes into the interior :-(

I have noticed that as there are two diaphragms (and presumably two separate in-line push rods) there is more pedal travel before the front actuating plunger starts to move, compared with the old Metro one. I have also made a new bracket to raise my remote fluid reservoir another 12mm higher to retain sufficient head above the front piston.
Peter.