It is currently Mon Sep 27, 2021 5:40 pm




Post new topic Reply to topic  [ 7 posts ] 
Libra brake issue. 
Author Message
GTM delivered

Joined: Mon Apr 17, 2017 10:05 pm
Posts: 34
Location: Bristol
GTM: Libra
Post Libra brake issue.
Despite it having big AP calipers & discs, I've not been happy with the brakes on the Libra since I got it, so latest project has been trying to sort it out. Doing some research I came across a few posts on here re. similar issues, so my findings may be of interest.

My problem was an inconsistent brake pedal with an occasional hard/dead feel - not very often but it caused a few sweaty-palm moments, :shock: so had to be fixed.

Tried all the usual stuff (bleeding, etc.) to no avail, so I was beginning to blame the "Yellow Stuff" pads for being too hard for road use - not a very convincing theory as the brakes were acceptable most of the time but I was running out of ideas.

Then I recalled a similar pedal feel from decades ago when I had a servo develop a small leak, so I focussed on the Libra servo.
I thought perhaps there was a leak in the long vacuum pipe down the tunnel but when I hooked up a vacuum pump and gauge to the engine end of the pipe, it held vacuum. So I crossed that off the list of possible causes and started looking for a replacement servo in case that was failing under braking.

Then I gave it a bit more thought and decided to remove and check the non-return valve in the vacuum pipe - Bingo! It was no longer doing its non-return duties, so I swapped it for a spare and the brakes are now terrific.

I presume that when the engine was generating high vacuum the failure of the valve was of no consequence but when there was little vacuum available the servo-effect was reduced or absent all together - just depended what the engine was doing when I was braking.

So it's worth checking the little black and grey valve in the vacuum pipe if you have similar issues.


Wed May 19, 2021 9:33 pm
Profile E-mail
Part built GTM

Joined: Sat Oct 22, 2016 12:41 am
Posts: 119
Location: Brisbane Australia
GTM: Spyder
Post Re: Libra brake issue.
Great info - thanks for posting.
I have wondered about the check valve location - mine seems to be near the booster - surely it should be as close to the engine as possible. The long run of line would then be additional volume under vacuum, waiting for the brakes to be applied.


Thu May 20, 2021 3:30 am
Profile E-mail
On the Road

Joined: Wed Aug 11, 2010 9:27 am
Posts: 574
Location: Sheffield
GTM: Libra
Post Re: Libra brake issue.
Yeah my valve is only a few inches from the engine outlet.

_________________
2000 GTM Libra 1.8VVC 145BHP


Thu May 20, 2021 10:50 am
Profile E-mail
GTM delivered

Joined: Mon Apr 17, 2017 10:05 pm
Posts: 34
Location: Bristol
GTM: Libra
Post Re: Libra brake issue.
Biggest issue is getting the valve out of the pipe - had to cut the pipe to get mine out but luckily happened to have a spare bit of pipe from an old K-series I could use to make up the lost length, then use a surprising amount of heat to soften the pipe so I could get the new valve back into the pipe.

I agree about the best valve location being as far from the servo as possible, so would expect to find it at the engine end but it's always interesting to hear about other cars; it would be an easy thing to overlook or get wrong during a build, especially as the pipe connector onto the servo looks a bit like a valve.

If it helps, here is a pic of an old Metro servo vacuum pipe:


The banjo connects to the manifold, next comes the all-important non-return valve, then the right-angled connector into the servo - bit shorter than the Libra!


Attachments:
Vacuum pipe.jpg
Vacuum pipe.jpg [ 357.75 KiB | Viewed 144 times ]
Thu May 20, 2021 3:40 pm
Profile E-mail
On the Road

Joined: Wed Aug 11, 2010 9:27 am
Posts: 574
Location: Sheffield
GTM: Libra
Post Re: Libra brake issue.
Yup, that black plastic pipe is a nightmare to get fittings on/off of.

_________________
2000 GTM Libra 1.8VVC 145BHP


Thu May 20, 2021 3:43 pm
Profile E-mail
GTM delivered

Joined: Mon Apr 17, 2017 10:05 pm
Posts: 34
Location: Bristol
GTM: Libra
Post Re: Libra brake issue.
Help - I need to sort out the picture thing!

I've worked out how to change the physical size of a JPG before I insert it but how do I control the size at which it displays on-screen?


Thu May 20, 2021 3:46 pm
Profile E-mail
On the Road

Joined: Wed Aug 11, 2010 9:27 am
Posts: 574
Location: Sheffield
GTM: Libra
Post Re: Libra brake issue.
Dunno but I always resize to limit to about 1000pixel width.

_________________
2000 GTM Libra 1.8VVC 145BHP


Thu May 20, 2021 4:06 pm
Profile E-mail
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 


Who is online

Users browsing this forum: No registered users and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © phpBB Group.
Designed by Vjacheslav Trushkin for Free Forums/DivisionCore.

phpBB SEO