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Old 5th January 2022, 18:10   #1
COLVERT
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Default HELP. One of a handful of requests in 13.1/2 thousand posts.

Baffled. The car failed its MOT today for the first time in 13 plus years.

Rear brakes well out of balance. One being OK the other showing only 64% braking effort.

The underside of the car is virtually rust free.--Nothing on or around the caliper.

Stripped the caliper down and no corrosion under the piston seal.
It's possible to slide the piston in and out about 3/8 " without too much effort.

I expected to find a partially seized piston.
No such luck.--

Now the question for those DIY experts on here. Is it possible to have air in that single line to the LH rear caliper to give that result on the MOT ??

Could the anti-lock braking system be involved here somewhere ??

The reservoir has lost no fluid. No sign of a leak anywhere. If air is getting in then maybe a small stain from leaking fluid should be apparent.--


I have pics of all the bits on my smart phone but have no idea how to post them on the forum.

Year after year life is getting more and more complicated when all I want to do is sink gently into old age and oblivion.

However I seem to have ended up with this red hot needle where I don't want it.
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Old 5th January 2022, 18:52   #2
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could be a disc or pad issue.

If you have not had the brakes apart and no leak, I would not have thought there was air on one side.

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Old 5th January 2022, 19:14   #3
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sometimes the flexi hoses , if not renewed when aged can give restricted pressure . they can swell and constrict internally. old fluid is another issue . moisture absorbed over time. a good strong bleedout after a change of fluid may release any trapped air at the tops of the piston cylinder if any in there. sometimes the bleed nipples are lower than the top of the casting . plenty for you to check out , in that lovely heated garage of yours mr colvert ....
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Old 5th January 2022, 19:24   #4
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i have had the rear pads picking up on the surfaces of the pad carriers. on first appearance they looked ok, but notchy in places. im sure alot of these problems are caused by aftermarket product copies. even rimmers dont supply the "original" pads anymore. i think the whole set up now is using non original parts as the quality parts are no longer made. give them a good clean up and replace if nessessary , as i did ....
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Old 5th January 2022, 19:46   #5
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How old is your brake fluid , when did you last change it ? Are the flex hoses original ? Get an assistant to stand on the brakes while you inspect the flex hose for any signs of breaking down, eg ballooning
As said by xsport really , strip , clean , lubricate pad edges to carrier , work calliper piston in and out , and put some New brake fluid through your system to flush out any old fluid in that calliper , something I usually do annually before I take the car for MOT
If still down on efficiency after that try replacing your flex hose before delving deeper into your braking system
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Old 5th January 2022, 19:47   #6
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Pad sticking on the carrier?
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Old 5th January 2022, 19:49   #7
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Have you checked the rear of the discs? Sometimes the rear of the disks do not operate properly because of lack of use....rusty.
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Old 5th January 2022, 19:55   #8
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are the discs scoured ? have you cleand and lubed the pins , they can go black and pick up on the rubbers. glazed pads another issue. as said above give them a good going over after a fluid change and hoses renewed. the hoses can bellow outwards when in use.not much but all these things will add up to weak braking. its time to put down the readers digest and slippers and get stuck in...
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Old 5th January 2022, 20:49   #9
COLVERT
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Thank you all for your replies.

1st---I fitted two new discs about 3 months ago.

If I apply the hand brake at 3 mph the rear wheels lock.

2nd---The pad carriers are clean with no trace of rust.

3rd.---All the bits that need to be smooth and shiny really ARE smooth and shiny. They could not be much more shiny if I had just fitted them new.

4th---Original brake fluid. Never changed.---

5th---The flexi looks fine with no trace of stretching. There is dust and a film of dirt on it but no sign of movement.

6th---Normally if the hoses swell internally they will let fluid pass under pressure but tend not to let it return under only spring pressure. The brakes stick on and can get very hot when driving.

7th---I'm going to get the brake fluid replaced and also fit new pads.



8th--- If that doesn't cure it, it might just get a Viking funeral.----
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Old 5th January 2022, 20:58   #10
COLVERT
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Quote:
Originally Posted by xsport View Post
Are the discs scoured ? Have you cleaned and lubed the pins , they can go black and pick up on the rubbers. Glazed pads another issue. As said above give them a good going over after a fluid change and hoses renewed. The hoses can bellow outwards when in use, not much but all these things will add up to weak braking. It's time to put down the readers digest and slippers and get stuck in...
You must be using a crystal ball.---I did go down to the MOT place in my slippers.---( My excuse is I'm VERY old.---Lol. )

It's really odd to see three wheels showing up perfect on the brake test with the fourth one so far behind.----
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