Dual 7" Servo

[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

[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)

[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]

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

[mashtun]

Originally Posted by peterux

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.

It would be interesting to know if that's the same as others see. Might indicate a faulty servo unit if not?

Originally Posted by peterux

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?

Maybe you need a pressure reducing valve for the rear brakes? Mind you, I don't think those do anything when the pedal's not pressed...

Originally Posted by peterux

Anybody else got any ideas?

Is it possible to have too much vacuum? What would the effects be if so? I've seen minimum but not maximum vacuum levels quoted. Is there any manual adjustment possible on the rest position of the rear brake shoes?

Mark.

[peterux]

Originally Posted by mashtun

It would be interesting to know if that's the same as others see. Might indicate a faulty servo unit if not?

Maybe you need a pressure reducing valve for the rear brakes? Mind you, I don't think those do anything when the pedal's not pressed...

Is it possible to have too much vacuum? What would the effects be if so? I've seen minimum but not maximum vacuum levels quoted. Is there any manual adjustment possible on the rest position of the rear brake shoes?

Mark.

Hi Mark,
thanks for your input.....

Faulty servo? - well I guess it's possible but it passes all the tests suggested in the MBM troubleshooting guide. Others may be exactly the same but not obvious because they have disk brakes at the back.
Pressure reducing valve to rear brakes - yup, got one of those fitted. It is the BMW one that's always been fitted. Brake testing yesterday proves the fronts break traction first so I think this is working OK
Too much vacuum? - don't know?
Manual adjustment of brake shoes - I can back them off but they have self adjusting mechanism so they will just reset themselves.

If you search for 'bake pedal return spring' in eBay you do get lots of items so it does seem like most car makers (inc. BMW) fit pedal return springs to pull the pedal back. As these servos come from the US I expect US cars have big heavy pedals and strong return springs.
Maybe the servo just needs a little help?

[Mike]

Originally Posted by peterux

Hi Mark,
thanks for your input.....

Faulty servo? - well I guess it's possible but it passes all the tests suggested in the MBM troubleshooting guide. Others may be exactly the same but not obvious because they have disk brakes at the back.
Pressure reducing valve to rear brakes - yup, got one of those fitted. It is the BMW one that's always been fitted. Brake testing yesterday proves the fronts break traction first so I think this is working OK
Too much vacuum? - don't know?
Manual adjustment of brake shoes - I can back them off but they have self adjusting mechanism so they will just reset themselves.

If you search for 'bake pedal return spring' in eBay you do get lots of items so it does seem like most car makers (inc. BMW) fit pedal return springs to pull the pedal back. As these servos come from the US I expect US cars have big heavy pedals and strong return springs.
Maybe the servo just needs a little help?

Peter

I am sure you should not need a return spring, and really would not recommend exploring that route. There appears to be a fundamental problem and as it is your brakes, should be 100% resolved, not masked over.

From your description it sounds as though you have eliminated the pedal, and the pedal clasp connection. Since the problem is resolved by pulling the pedal back, this suggests it is not the brake M/C - it would still stick if that was the issue. Therefore you appear to have reduced the issue to being servo related.
Stupid question - but get the easy ones out the way first - have you fitted the anti return vacuum pipe valve, and is it the corect way around? I guess it must be, but.......its an easy one to look for, and could cause the same symptoms?

Next would be to try using a dome head 6mm stud without your tube as Dennis has suggested, since that is different to everyone else. I guess if it is a snug fit it may not allow the servo to re-seat the vacuum arrangement and it is an easy one to test.

If the problem persists you have reduced it to only the servo.
I currently have John's servo, so could post it to you (I'm sure John will not mind - he's up for helping a good cause!). You could then test it in your set up.

If you would like to try it, PM me your address (I have deleted all my Servo PMs now), and I'll gladly forward it on today. And if this solves the problem, you can keep it, and I'll order an extra one as a replacement later this month in the second batch.

Mike

[peterux]

Originally Posted by Mike

Peter

I am sure you should not need a return spring, and really would not recommend exploring that route. There appears to be a fundamental problem and as it is your brakes, should be 100% resolved, not masked over.

From your description it sounds as though you have eliminated the pedal, and the pedal clasp connection. Since the problem is resolved by pulling the pedal back, this suggests it is not the brake M/C - it would still stick if that was the issue. Therefore you appear to have reduced the issue to being servo related.
Stupid question - but get the easy ones out the way first - have you fitted the anti return vacuum pipe valve, and is it the corect way around? I guess it must be, but.......its an easy one to look for, and could cause the same symptoms?

Next would be to try using a dome head 6mm stud without your tube as Dennis has suggested, since that is different to everyone else. I guess if it is a snug fit it may not allow the servo to re-seat the vacuum arrangement and it is an easy one to test.

If the problem persists you have reduced it to only the servo.
I currently have John's servo, so could post it to you (I'm sure John will not mind - he's up for helping a good cause!). You could then test it in your set up.

If you would like to try it, PM me your address (I have deleted all my Servo PMs now), and I'll gladly forward it on today. And if this solves the problem, you can keep it, and I'll order an extra one as a replacement later this month in the second batch.

Mike

Hi Mike,
I think that is a great plan and many thanks for the offer of a servo swap.

Easy one first, my vacuum non-return valve is 'as per the original' and it holds the vacuum for 3 or 4 pumps after the engine is off so I'm pretty sure it's not that.

Next, I'll try removing the 6mm sleeve and see if that makes any difference. It means i'll have to drain the m/c and re-bleed again.
I''ll PM you my details but it can wait until after Stoneliegh as I know you want to take a servo to the show to drum up more orders.

thanks again for your help,

...peter

[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

[Grey V8 Pete]

Anybody else got any ideas?[/QUOTE]

Is your master cylinder new or used? I am thinking that there is still residual hydraulic pressure in the lines? Is the return port blocked? Is the hydraulic fluid free to bleed back into the resevoir when you release the brake pedal? Try the brakes with the reservoir cap temporarily loosened. Just a thought. Peter.

[peterux]

Originally Posted by 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

Many thanks John!

[peterux]

Originally Posted by Grey V8 Pete

Is your master cylinder new or used? I am thinking that there is still residual hydraulic pressure in the lines? Is the return port blocked? Is the hydraulic fluid free to bleed back into the resevoir when you release the brake pedal? Try the brakes with the reservoir cap temporarily loosened. Just a thought. Peter.

Peter,
thanks for the ideas...
I have a brand new m/c.
Is the return port blocked? The rear brakes are releasing fully when I pull the brake pedal back to it's stop position so I think the m/c is OK.
But I'll will try your idea of loosening the reservoir cap to see if it makes any difference.

Mike,
I'm thinking of operating the brake pedal and servo (with the engine running) but with the master cylinder removed. Do you think this will damage the servo?
I want to see if the servo returns under it's own spring without the help of the m/c. It will also eliminate any issue with my m/c pushrod.

thanks

Peter