jps
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| posted on 19/2/24 at 03:31 PM |
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Is brake mc pushrod retaining clip necessary?
I’m using a non-servo mk1 Fiesta master brake cylinder. It has no pushrod built into the cylinder, I’m using a cut down M6 dome headed bolt.
It has a wire spring/clip at the opening where the pushrod goes in, which I assume is to retain the pushrod, I.e. stop the domed end “falling out” in
any event, although the return spring and the stop for the pedal travel do make this unlikely (I stop short of saying ‘impossible!’)
My M6 dome headed bolt, is too small to be retained by the clip and I’m realising it will be a fair bit of work to makeup an appropriate replacement
pushrod end that will work smoothly with the retaining clip.
Is that retaining clip type solution normally used, or is it usual to rely on the m/c return spring and the pedal travel stop?
[Edited on 19/2/24 by jps]
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nick205
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| posted on 19/2/24 at 04:10 PM |
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If I'm understanding your question correctly, my setup (MK Indy, Sierra brake master cylinder (non servo)) didn't have a retaining clip.
Just the pedal stop to prevent the pushrod dropping out. No problem for SVA test and no problem for driving.
[img]
 
Brake pedal & adjustable p/rod
[/img]
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jps
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| posted on 19/2/24 at 06:45 PM |
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Yes, there’s a grove inside the opening to the master cylinder that the wire clip seats in.
It looks like it would retain something like this:
https://rimmerbros.com/Item--i-17H7985--SelectedCurrency-1?src=UK0124W&gad_source=1&gclid=CjwKCAiAlcyuBhBnEiwAOGZ2S_Qz4WHBOWBuEnSIRvSRK26PUT3C
zbCVe82JkW-_Bt-mKB_IFacfVhoCWN0QAvD_BwE
A bit of Googling suggests vintage Ford Mustangs have something similar, but I am not sure if I’m being too “belt AND braces”here…
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gremlin1234
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| posted on 19/2/24 at 08:03 PM |
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it may be there to prevent it 'falling apart' in transit. ie before fitment
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nick205
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| posted on 20/2/24 at 08:24 AM |
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I should add:
Sierra brake master cylinder came from my Sierra donor car
Brake pedal and chassis fitting were MK designed & supplied
Pushrod (threaded adjustable) I sourced from a web supplier
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jps
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| posted on 14/4/24 at 08:13 AM |
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To add an update incase anyone else comes across this.
With careful measurement I made up a pushrod to work with a washer behind the retaining clip.
Despite making a new brake pedal, with a better aligned mounting hole for the pushrod, the pushrod still does stay entirely horizontal through the
whole travel. As a result the pushrod binds on the washer that is used to retain it and, over time, can work its way out from behind the retaining
clip, making the whole setup redundant.
I’m going to stick with the ‘standard’ floor mounted pedal stop, albeit with a piece of angled steel bolted to the floor rather than a bolt, as it
works better with the angle of the pedal at rest.
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FOSSIE
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| posted on 19/4/24 at 02:00 PM |
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quote:
Originally posted by nick205
If I'm understanding your question correctly, my setup (MK Indy, Sierra brake master cylinder (non servo)) didn't have a retaining clip.
Just the pedal stop to prevent the pushrod dropping out. No problem for SVA test and no problem for driving.
[img]
Brake pedal & adjustable p/rod
[/img]
I'm busy rebuilding the pedal box / braking system in general on my Avon at the moment and I have a similar set up to this, albeit with the
original Sierra pedal box rather than floor mount job. What concerns me about it is, although unlikely, if the pedal were to return quicker than the
m/cyl piston, the push-rod could drop out of the counterbore in the cylinder piston, or have I misunderstood?
I suspect the Sierra master cylinder was designed to be used with a servo where the 2 things are located better. For a non-servo system I think a
push-rod with a retaining clip would be safer, but not sure such a thing exists (i.e. same bore, tandem outlet, same mounting patter etc)
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jps
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| posted on 19/4/24 at 10:35 PM |
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quote:
Originally posted by FOSSIE
, if the pedal were to return quicker than the m/cyl piston, the push-rod could drop out of the counterbore in the cylinder piston, or have I
misunderstood?
No, I’d say you’re correct. If the pushrod is retained in the master cylinder then the pedal is directly mechanically linked to the master cylinder
piston. Relying on a stop for the pedal means the pedal can move independently of the master cylinder and potentially the problem you describe can
happen.
In practice it appears plenty of people are relying on the setup without the pushrod being retained directly in the m/c, so I think we can be
confident that it’s a sufficient solution
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