Dual 7" Servo

[denniswpearce]

Very interesting Peter, but it highlights yet another difference to my Sportster as my pedal lined up perfectly to sit within the clevis pin.
Just wondering how many more ways my car differs from everyone else's.
Wish I had the dedication to stop and take pics at each step of the way.
Nice job though.
As I have discs all round I do not have the restricter, I have looked.

[peterux]

Originally Posted by denniswpearce

Very interesting Peter, but it highlights yet another difference to my Sportster as my pedal lined up perfectly to sit within the clevis pin.

Whoever built your car probably modified your pedal box to line up the brake pedal with the servo. I know Mike and Robin had already done this and possibly others. I just followed the Marlin design which is not very aesthetically pleasing. My problem is that to get the brake pedal bolt out, I'll have to take the whole pedal box out (or cut a big hole in the side of the chassis?) which means disconnecting and re-bleeding the clutch, etc.

Maybe a winter project when I have nothing else left to do

[Grey V8 Pete]

Originally Posted by peterux

Whoever built your car probably modified your pedal box to line up the brake pedal with the servo. I know Mike and Robin had already done this and possibly others. I just followed the Marlin design which is not very aesthetically pleasing. My problem is that to get the brake pedal bolt out, I'll have to take the whole pedal box out (or cut a big hole in the side of the chassis?) which means disconnecting and re-bleeding the clutch, etc.

Maybe a winter project when I have nothing else left to do

I also have the bolt tack welded to the pedal on my Hunter. I fitted the dual servo / clevis assembly before I tightened the 4 servo securing bolts. That way there was just enough clearance at the servo nose to allow the clevis to slip over the end of the bolt. I also have an access panel that I cut in the side of the bulkhead a while ago to do a mod on the steering bush so that was a real benefit. I also put a spacer (large nut) between the jaws of the clevis to prevent any distortion of the legs. Peter.

[Mike]

Originally Posted by denniswpearce

Very interesting Peter, but it highlights yet another difference to my Sportster as my pedal lined up perfectly to sit within the clevis pin.

Dennis

I have borrowed John's Servo kit to check how the kit can be fitted: the input shaft will move through an arc of +/-15mm left to right. Therefore it should correctly fit on to the brake pedal even allowing for Marlin's sloppy engineering tolerances. I suspect Peter has taken the easy option to repeat the way he fitted the Metro servo off a tack welded stud.

Although I have modified my brake pedal to move it 50mm towards the transmission tunnel, and therefore added a dummy brake pedal in the original position, the attached shows the clasp fitted as its design originally intended.




My modified brake pedal, moved 50mm to the left, with the dummy pedal/arm in the original position



The very sharp eyed will see the original hole in the original pedal to the left of the dummy pedal/clasp fixing.
(I also added a plate to the pedal to activate the brake light switch)

[denniswpearce]

"nothing else left to do" I don,t think think so, there is always something to do.
Although my brake pedal lines up, there is a slight angle on the cutch operating rod, you only notice it when you are on your back with your head up close and personal with it in the footwell.

[denniswpearce]

And we let you guys loose on the roads in a fast sports car.

Well it beggars belief.

[GreatOldOne]

Hey, they're ok Dennis.

It's just skid pan Cundall here that you have to worry about...

[peterux]

Originally Posted by denniswpearce

And we let you guys loose on the roads in a fast sports car.

Well it beggars belief.

[Grey V8 Pete]

Originally Posted by denniswpearce

And we let you guys loose on the roads in a fast sports car.

Well it beggars belief.

Age and stealth will overcome youthful exuberance! ;-)

[peterux]

This picture shows the Marlin designed geometry of the standard Sportster pedal box as supplied in 2004. (Viewed from below)


Trial fitting brake servo on pedal box by marlinpeter, on Flickr


You can see that the servo is set at an angle to allow for the pedal to sit to the side of the servo actuator. As the pedal is depressed the servo actuator moves more or less parallel to it central axis. At the time of this part of my build, I queried this with Marlin (by sending them this photo) and they confirmed it was assembled correct. I'm not saying it is elegant but this is how it was designed.

I have just replicated this same alignment in my servo replacement. I think if I centralize the pedal in the clevis without modifying the pedal box, it may damage the servo by forcing the actuator too far to the left.

[peterux]

After days of waiting for the weather to improve I finally bit the bullet and got out there in the rain today to bleed my brakes.

First problem was the valve in my 'one man' bleeding kit was 'bleeding' knackered so had to take a trip to Halfords for a new one.

Following the bleeding of all four brakes, I went for a short road test, limited a bit by the poor weather. Even in that short trip I can confirm I now have a remarkable braking system. Absolutely superb feel and performance! I nearly went through the windscreen on first application and was able to lock up my front wheels and skid doing an emergency stop on a wet road from about 35mph.(with my almost new Avon tyres!!)

The RPV (only fitted because I have drums at the back) works very well taking up all the free travel of the rear drum brakes. Unfortunately, it works a little too well as I found after about 5 miles it was causing the rear shoes to bind a little, even when the brake pedal was not pushed. An interesting experiment, but it has now been removed.

It's all piped up again so I will need to bleed the back brakes again before futher road testing.

Thanks again to Jason and to Mike for bringing us this superb upgrade. (And everyone else who helped out testing the solution)

[denniswpearce]

I almost forgot Jasons......... ahem........ incident. So I will add him to the list as well.

If I manage to get my machine to Stoneleigh then make sure all you guys are at one end of the line and me at the other end.
I will bring some spare specs for you all

[denniswpearce]

Nice going Peter, welcome to the Sportster club with good brakes.

Hope you managed to get your slimline figure down into the footwell ok.
Presumably your brakes have the same feel as everyone else,s, longer travel and progressive, a really good feel to them, unlike my daily runabout which is instant and a very short travel.

Hats off to you for doing it in this weather though.

[peterux]

Originally Posted by denniswpearce

Nice going Peter, welcome to the Sportster club with good brakes.

Hope you managed to get your slimline figure down into the footwell ok.
Presumably your brakes have the same feel as everyone else,s, longer travel and progressive, a really good feel to them, unlike my daily runabout which is instant and a very short travel.

Hats off to you for doing it in this weather though.

I would describe them more like a new prodcution car with instant braking with less pedal travel than I had before.

Maybe it's the impact of the RPV that I have now removed.

But i'm not going out today in this.............

[peterux]

The weather was great down here in the South-East today so I was up and out bleeding my brakes. No problem with the brake bleeding so I took the opportunity to fix a small exhaust leak at one of my joints while I had the wheels off.
That all done, I was back down in the footwell to reset my brake light switch which has always a bit over sensitive. All done by 11am so off I went for a test drive.

Well by the time I was back my rear brakes were binding so much that I didn’t need to apply the handbrake and the air was full of that pungent burning brake smell : (note the RPV has been removed)
( I also had a run-in with a stationary speed cop while I was 'giving the new engine some beans' but luckily he was so interested in the car he didn't clock me . He seemed more concerned about my non-cancelling indicator. I stopped for a chat because he shouted at me as I went past!)

Anyway, back to the brake problem. The rear brakes would release if I hooked my toe under the brake pedal and pull it up? Not recommended.
I checked it wasn't my pedal fouling on anything. The only thing I could think was that my plunger extension inside the m/c was too long, so off it all came again, shortened it by about 3mm to ensure a little gap and more bleeding all round. (by now I was like a one man F1 pitstop team!).
Another test drive (avoiding speed trap).......and yup, you guessed it still no improvement.
So next I moved the m/c away from the servo by three washers (about 5mm) creating an even bigger gap between the servo plunger and the m/c piston.
Another test drive showed a significant improvement but now my pedal is not returning to it’s highest position without some encouragement. The braking point is also now much further down the travel so it does not feel so safe.

I think I need a strong return spring to pull the servo actuation rod back out of the servo to allow the rear brakes to release. Any other ideas welcome.

Anybody know any good spring suppliers?

[Mike]

Originally Posted by peterux

The weather was great down here in the South-East today so I was up and out bleeding my brakes. No problem with the brake bleeding so I took the opportunity to fix a small exhaust leak at one of my joints while I had the wheels off.
That all done, I was back down in the footwell to reset my brake light switch which has always a bit over sensitive. All done by 11am so off I went for a test drive.

Well by the time I was back my rear brakes were binding so much that I didn’t need to apply the handbrake and the air was full of that pungent burning brake smell : (note the RPV has been removed)
( I also had a run-in with a stationary speed cop while I was 'giving the new engine some beans' but luckily he was so interested in the car he didn't clock me . He seemed more concerned about my non-cancelling indicator. I stopped for a chat because he shouted at me as I went past!)

Anyway, back to the brake problem. The rear brakes would release if I hooked my toe under the brake pedal and pull it up? Not recommended.
I checked it wasn't my pedal fouling on anything. The only thing I could think was that my plunger extension inside the m/c was too long, so off it all came again, shortened it by about 3mm to ensure a little gap and more bleeding all round. (by now I was like a one man F1 pitstop team!).
Another test drive (avoiding speed trap).......and yup, you guessed it still no improvement.
So next I moved the m/c away from the servo by three washers (about 5mm) creating an even bigger gap between the servo plunger and the m/c piston.
Another test drive showed a significant improvement but now my pedal is not returning to it’s highest position without some encouragement. The braking point is also now much further down the travel so it does not feel so safe.

I think I need a strong return spring to pull the servo actuation rod back out of the servo to allow the rear brakes to release. Any other ideas welcome.

Anybody know any good spring suppliers?

Peter
It sounds as though something is binding. My set up does not suffer this problem and I do not feel yours should either. Adding a spring is masking the problem.

You should only require a minimal gap between the servo push rod and master cylinder - definitely not 5mm.

The servo/master cylinder have a very strong combined return spring - remember how difficult it was to get the servo plunger to extend to fit he new M6 set screw and lock it off?
If your pedal is not returning something is seriously binding. It could also account for the rear drums binding too, rather than the new rear valve.

Have you over tightened the connection between the clevis and pedal? Try slackening it off. and see what it feels like.

(........and if you can get the bolt out of your pedal, fit the clevis around the pedal stem - sorry that was a bit tongue in cheek, but you know my views on the way it should be assembled - making sure the pin is not tight in the pedal due to the slight angle)

Mike

[peterux]

Originally Posted by Mike

Peter
It sounds as though something is binding. My set up does not suffer this problem and I do not feel yours should either. Adding a spring is masking the problem.

You should only require a minimal gap between the servo push rod and master cylinder - definitely not 5mm.

The servo/master cylinder have a very strong combined return spring - remember how difficult it was to get the servo plunger to extend to fit he new M6 set screw and lock it off?
If your pedal is not returning something is seriously binding. It could also account for the rear drums binding too, rather than the new rear valve.

Have you over tightened the connection between the clevis and pedal? Try slackening it off. and see what it feels like.

(........and if you can get the bolt out of your pedal, fit the clevis around the pedal stem - sorry that was a bit tongue in cheek, but you know my views on the way it should be assembled - making sure the pin is not tight in the pedal due to the slight angle)

Mike

Hi Mike,
thanks for the suggestions.

And yes, I agree that something is not right and different to others experience.

I can't find anything binding and I slackened off my pedal bolt completely. (It's now flopping about in the clevis) The pedal is not tight and I can't currently see how my mounting position could have this effect, but I will try it if I can.. I have convinced myself today that it is not the brake pedal causing this. The RPV is now removed so i'm back to how it was with the metro/bmw config.

With vacuum applied to the servo from the engine running, the servo input actuator does not fully return to its rest position until I turn off the engine and pump the pedal few times or pull it back. It's as if the vacuum is somehow holding the brakes applied until I pull it back manually or the input spindle is sticking? With the engine off, the pedal returns fully. My vacuum pipe is from the standard BMW source, like others have used.
I may be the only one with drum brakes but again, I can't think how this would cause this effect, except that my front brakes do seem OK so maybe this is the clue?

As you can imagine, it's hard to see exactly what is happening with your head stuck in the footwell.

Apart from a spring, I can't think of anything else to try?

BTW, I only drastically increased the gap between the servo and m/c to eliminate this as a cause. It did make a good improvement but it is, in your words, masking the problem.

Anybody else got any ideas?

[denniswpearce]

Clutching at straws but you used a M6 threaded tube over the main bolt that goes into the body of the servo, whereas most of us had nothing. Could that be fouling internally on anything ?

[peterux]

Originally Posted by denniswpearce

Clutching at straws but you used a M6 threaded tube over the main bolt that goes into the body of the servo, whereas most of us had nothing. Could that be fouling internally on anything ?

I have wondered about that, as well.
I haven't tried removing it (yet?), but I did operate the brakes with the nuts holding the m/c to the servo loose, in case it was causing the plunger to bind. That didn't seem to make any difference.

And now the rains back again tonight

[oaktree11]

Mike and Peter,

I am lying on my hotel bed having just arrived in Canada. I am away for 5 weeks so no worries with using my servo. I hope it helps.
John