JoelP
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 posted on 4/2/04 at 08:44 PM |
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Has anyone used a brake servo?
As the title says really. Just wondering cos everyone says the brakes are too sensitive with one, but then everyone also says the brakes need
squeezing very hard without. So why not use a servo and a 3 to 1 pedal ratio? Its a technical question really cos theres no way im gonna fit one in
mine...!
Anyone?
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zetec
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| posted on 4/2/04 at 09:04 PM |
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I have thought the same, might have a look to see if one would fit, always take it off if no good.
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JoelP
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| posted on 4/2/04 at 09:07 PM |
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i get the feeling it is maybe blind faith, cos ron said it in his bible...
not all that glitters is gold, and not all who wander are lost...
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theconrodkid
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| posted on 4/2/04 at 09:09 PM |
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in my experiance the brakes without a servo or 4 pot calipers are crap,with a servo they are brilliant,trub is space for the servo is minimal or non
exsistant
who cares who wins
pass the pork pies
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Julian B
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| posted on 4/2/04 at 11:09 PM |
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I used a sierra servo in my old Robin Hood. I also used the break compensation valve on the rear wheels, which was set up by a process of hit and
miss. The brakes however were very good (disk at front drum at rear) the big caveat is that the hood weighed a lot and with a heavy pinto block some
serious stopping power was required. I, however have no intention of using a servo in the new build but I am interested to see if any one else has
used multi pot callipers on normal master cylinders!
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stephen_gusterson
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| posted on 4/2/04 at 11:32 PM |
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isnt there a test in SVA to test brakes with servo failure...... a 3 to 1 ratio might make it hard to stop in that state.
I managed to get a massive abs valve block and master cylinder to fit my car. I did it by fitting the master ACROSS the car in front of pasenger side.
I then ran a control rod across the car (12mm steel) to a crank that transmitted the force thro 90 degrees with two 8mm rose joints.
 
Rescued attachment crank.jpg
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britishtrident
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| posted on 13/3/04 at 02:07 PM |
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Depends on the master cylinder size car models without a servo always use a smaller master cylinder bore.
Your existing cylinder will be at guess a 7/8" bore (that is 0.875 inch = 22.25 mm) a 3/4" bore (0.75 inch = 19mm) would be more
appropriate. As no servo ford cylinders are rare try a non servo VW Polo cylinder (19mm bore) cylinder which are available very cheaply from Euro
parts and the like. Mine cost about 19 pounds but came without a resevoir.
Ideally also you want a pedal ratio of a bit more than 4 to 1.
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JoelP
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| posted on 13/3/04 at 04:47 PM |
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i ended up with around 5 or 6 to 1 ratio, using a sierra mc with the servo hacked off. time will tell how good it is i guess! i was quite concerned
because when my normal car lost the servo assist the braking was appauling!
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theconrodkid
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| posted on 13/3/04 at 04:53 PM |
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a bit of hill walking will improve your brake leg,5/6 to 1 should work ok
who cares who wins
pass the pork pies
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JoelP
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| posted on 13/3/04 at 05:09 PM |
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hills? walking?
whats all that about then?
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theconrodkid
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| posted on 13/3/04 at 05:35 PM |
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improve your muscles
who cares who wins
pass the pork pies
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JoelP
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| posted on 13/3/04 at 06:03 PM |
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i think a more fun way would be the vroom vroom in the part built banger! pumping the clutch, 20 reps on each foot!
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Mark Allanson
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| posted on 13/3/04 at 07:08 PM |
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I have intentially left enough room in my engine bay for a servo. I have bad knees, and the condition is getting worse, to the point that it hurts to
press the brakes on an unservoed car after a while. I would have put a servo in to begin with, but I think it is a SVA no no.
I wonder if they would accept a medical certificate?
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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britishtrident
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| posted on 15/3/04 at 04:15 PM |
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------- I have intentially left enough room in my engine bay for a servo. I have bad knees, and the condition is getting worse, to the point that it
hurts to press the brakes on an unservoed car after a while. I would have put a servo in to begin with, but I think it is a SVA no no. ------
No problem with SVA and servo but it must be working , the SVA regs (and now MOT regs) are framed to stop people trying to pass with no-working
servos by simply disconnection the vac tube.
However I would still be tempted to try it without a servo first, the Locost is 1/3 the weight of a fully laden Cortina so should stop with 1/3
the pressure in the hydraulic system. With Sierra brakes the front calipers are a bit less effective.'
For a book car if you can get a leverage ratio of 5 to 1, and use a 19mm master cylinder, even with a duff knee you should have no problems.
Servos provide about 40% of the braking effort on a production car (perhaps a bit more on recent models which tend to be over-servoed), although this
feels like more if you get a servo failure. This why non servo models use smaller bore master cylinders normal between 18 or 19 mm instead of
22.3 mm used on servo models.
Many servo models also used a harder grade of pad than the non servo sibbling, however just try getting hold of a a set of Cortina Mk3 1300 (an non
servo model) pads and the guy behind the counter will just laugh.------- BUT "Green Stuff" pads as well as being fade ressistant have
a 10% higher coefficient of friction than standard pads ie 10% less pedal pressure. for the same braking..
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