Printable Version | Subscribe | Add to Favourites
New Topic New Poll New Reply
Author: Subject: Is brake mc pushrod retaining clip necessary?
jps

posted on 19/2/24 at 03:31 PM Reply With Quote
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]






View User's Profile Visit User's Homepage View All Posts By User U2U Member
nick205

posted on 19/2/24 at 04:10 PM Reply With Quote
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
Brake pedal & adjustable p/rod
[/img]

View User's Profile View All Posts By User U2U Member
jps

posted on 19/2/24 at 06:45 PM Reply With Quote
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…






View User's Profile Visit User's Homepage View All Posts By User U2U Member
gremlin1234

posted on 19/2/24 at 08:03 PM Reply With Quote
it may be there to prevent it 'falling apart' in transit. ie before fitment
View User's Profile View All Posts By User U2U Member
nick205

posted on 20/2/24 at 08:24 AM Reply With Quote
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

View User's Profile View All Posts By User U2U Member
jps

posted on 14/4/24 at 08:13 AM Reply With Quote
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.

View User's Profile Visit User's Homepage View All Posts By User U2U Member
FOSSIE

posted on 19/4/24 at 02:00 PM Reply With Quote
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
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)

View User's Profile View All Posts By User U2U Member
jps

posted on 19/4/24 at 10:35 PM Reply With Quote
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

View User's Profile Visit User's Homepage View All Posts By User U2U Member

New Topic New Poll New Reply


go to top






Website design and SEO by Studio Montage

All content © 2001-16 LocostBuilders. Reproduction prohibited
Opinions expressed in public posts are those of the author and do not necessarily represent
the views of other users or any member of the LocostBuilders team.
Running XMB 1.8 Partagium [© 2002 XMB Group] on Apache under CentOS Linux
Founded, built and operated by ChrisW.