Rear brakes inadequate.

[RayD]

My 1992 SE failed the MOT today due to the rear brakes being inadequate. The handbrake passed, ruling out several of the things that might have been at fault. I nevertheless had a look and generally found nothing amiss. The car has the latest proportioning valves fitted.

Any ideas will be more than welcome.

Thank you
Ray

[Specky]

My 1992 SE failed the MOT today due to the rear brakes being inadequate.

How so?

Are they equally bad?

Evenly balanced?

What were your for front and rear readings?

When did you last service the callipers or sliders?

Are they leaking through the centre seal?

When did you last change the fluid?

TTFN

TTFN

[RayD]

Thanks Dave,

They were balanced and equally bad, the fronts were OK, I didn’t get the readings. The rear sliders and pistons were free when I checked today. Because the handbrake works properly it doesn’t seem to leave a lot of options other than the piston seals?

[gmacz]

You need to get the mot tester to check the proper settings for the Elan on the brake tester.It maybe that the tester does not know that the Front Bias on the Elan is high.He needs to check the lowest pass mark and see if you match it.Yours Gmacz

[Specky]

With out readings I'm at a bit of a loss... it would be just supposition..

To coin a phrae.. "The usual suspects"

Sorry...

TTFN

[Candles]

Mine failed 2 years ago in a similar manner. It was possible to achieve the 100kg (IIRC) braking force required for the handbrake by pulling very hard (he let me do it!) but the footbrake could never produce the required braking.

The tester suggested that the pads looked very old and that the compounds tend to 'go hard'. Not sure what the truth of this is, but I put in EBC blackstuff pads, worked the whole mechanism in and out a few times and then gave them the bedding-in of their life and it passed. The odd waft of smoke was still visible from the rear wheels!

Candles.

[RayD]

The readings were N/S 30 and O/S 40. Not as ballanced as I thought. I'll have a look thro the forum for the seal kit and softer pad availability.
Thanks
Ray

[DeeAitch]

The pass criteria is based on a total of all 4 so you need to know the front readings as well to see if it should pass (Unless they are sticking which is also a fail).
Mine passed recently with only 37 & 50 on the rears. Handbrake was fine.

[RayD]

Thanks for that Dave,

On reflection I think I saw 680 as his added up total, does that sound about right, or more to the point - wrong.

It's interesting yours passed with 37 and 50 as mine don't have a long way to go to get there.

[M100 TWO]

Ray take this along it shows the rears do next to nothing after the initial braking.**** does not like uploading a bitmap image will send it in an email

[DeeAitch]

Thanks for that Dave,

On reflection I think I saw 680 as his added up total, does that sound about right, or more to the point - wrong.

It's interesting yours passed with 37 and 50 as mine don't have a long way to go to get there.

IIRC the total needs to add up to 50% of the gross vehicle weight (I forget what that is but it's in your handbook), 16% for the handbrake, with an allowed imbalance for the front steered wheels of 25%.
680 is low for all 4 but you are close to a pass - you will find it hard to improve the rears significantly so maybe you need to look at the fronts.

[RayD]

With that in mind Dave, I stripped the front ones this morning in advance of taking it back this afternoon. Apart from changing the pads over, inner for outer, taking the glaze off, cleaning the pad slides, and giving the sliders a bit of exercise I don't imagine they will have improved much.

The graph M100TWO was refering to is...

[Specky]

I don't know if this helps.... from another thread...

Just got mine thru the MOT a week ago

figures i remember were 76% and 25%, which went thru the centralised server and passed no problems, think it was along the lines of 300/300 front, 100/100 rear and 150/150 parking

Just dun mine ... it's all gone Pete Tong...

The old girl is stock

Rear left 63Kgs
Rear right 73Kgs 20% inbalance inbalance Pass

Hand brake left 140 kgs
Hand brake Right 147 kgs 11% inbalance Pass


Left front 234 Kgs
right front 315kgs inbalance 30% Fail


Guess that's a lazy calliper

I knew the brakes were pulling slightly...

It's a good job I'm waiting for front callipers from SJ's

TTFN

The old girl passed her MOT with her new callipers..

Rear left 70Kgs
Rear right 73Kgs

Hand brake left 145 kgs
Hand brake Right 147 kgs


Left front 310 Kgs
right front 315kgs

TTFN

TTFN

[RayD]

First of all, thank you for your help.

The rear brakes sailed through the retest this afternoon.

For newcomers who have the same problem, here are a few observations. All I did to get them from a failure reading of 30 and 40 to a pass of 70 and 70 was to remove the pads - check the sliders were free – remove the central rubber plug from the piston to check the extent of any internal seal leaks - checked the pistons were free, the offside one turns anticlockwise/inwards (the information in the manual is looking from the back of the car) – clean the edges of the steel backing plates and the corresponding part on the callipers – take the glaze of the pads with sandpaper – and reassemble.

It would of course be a brighter idea to do all this before the MOT test, at which time you could do the same thing at the front but include changing the inner pad to the outside and visa versa. This will even out the wear and put the slider arrangement into a new position.

Ray

[Doug]

good job, Ray. You did exactly the right things to get the rears working too -- it's all about the poor slider design and freeing up the brakes to actually CLAMP down and work. Too bad you'll have to do it all over again (if you really wanted to keep them working) in another year likely!

[muley]

First of all, thank you for your help.

The rear brakes sailed through the retest this afternoon.

For newcomers who have the same problem, here are a few observations. All I did to get them from a failure reading of 30 and 40 to a pass of 70 and 70 was to remove the pads - check the sliders were free – remove the central rubber plug from the piston to check the extent of any internal seal leaks - checked the pistons were free, the offside one turns anticlockwise/inwards (the information in the manual is looking from the back of the car) – clean the edges of the steel backing plates and the corresponding part on the callipers – take the glaze of the pads with sandpaper – and reassemble.

It would of course be a brighter idea to do all this before the MOT test, at which time you could do the same thing at the front but include changing the inner pad to the outside and visa versa. This will even out the wear and put the slider arrangement into a new position.

Ray

Ray (and others)

I found this post very helpful. My rear brakes work a lot better now - I even stalled the car by not taking the handbrake off!!

Just one question; what does it mean when I pull the rubber plug out and fluid comes out - at quite high pressure. I couldn't get the plug back in to begin with but after a short while it stopped dribbling and all seems well?

Cheers

Jim

[RayD]

Just one question; what does it mean when I pull the rubber plug out and fluid comes out - at quite high pressure...?

Jim

Hi Jim,

The air space behind the rubber check valve should be free of oil.

A small amount of oil showing when the plug is removed indicates a small leak, over a long period of time.

Unfortunately a large amount at high pressure signifies the seals in the pistons are leaking quite badly, and the calipers will need an overall.

You could take the plug out again after a few days of use to get an indication of how bad it is, or not.

Ray

United States Patent 4181145

A self-adjusting rear disc brake assembly provided with a parking brake to mechanically actuate the disc brake, as well as having hydraulic service brake actuation, has a confined air space between the outer piston and the inner piston. The two-way check valve embodying the invention operates to maintain the confined air space substantially at ambient air pressure while preventing contamination of the brake actuating mechanism by air borne contaminants normally encountered in the area of a vehicle rear brake mechanism.