14 replies to this topic

[Stevie W]

Good evening All,

 

I am still having issues with what seems poor brake performance on my '72 Mini. I've fitted Cooper "S" front disc and calipers (7.5") and bled the brakes using a Gunsons Eeezi-bleed. I can get a good hard pedal, but the brakes seem inefficient. They're good enough to pass the MOT brake dynamometer test but just seem really weak out on the road.

 

I've also tried the Minispares single line brake servo, which was new a few years ago but this doesn't seem to have much effect..almost like it's not boosting at all. On their website it states the air-valve should be at the bottom when the servo is mounted or at between 30-45 degrees up from the bottom, mine was mounted at the top...would this be the reason for it appearing to not be working? I'm also thinking of purchasing the rebuild kit for it just in case storing it has caused some of the seals to perish.

 

I would welcome any advice on this issue as it's spoiling what is otherwise and enjoyable drive!

 

Cheers, Steve.     

[Batmini]

The servo does not increase the amount of braking force. It just makes the pedal lighter. If your braking is no good, i would suggest you take another look at your pads/shoes/discs/drums. I had no servo and could easily get all 4 wheels to lock-up during braking.

[nicklouse]

Don't quite understand what you are saying about the servo. Pictures?

As above re the applied force.

[Swift_General]

If you put your foot on the brake pedal (after pumping the pedal to remove any residual vacuum in the servo) with the engine off and the start the engine does the pedal drop?

[Spider]

On their website it states the air-valve should be at the bottom when the servo is mounted or at between 30-45 degrees up from the bottom, mine was mounted at the top...would this be the reason for it appearing to not be working?

 

With Hydraulic Servos, it is important to have the Outlet higher than the Inlet Hydraulic fittings.

 

This is so when you bleed it, you can be sure of getting all the Air out of the Servo.

[Stevie W]

Good afternoon Guys, thanks for the answers.

 

Nicklouse:

 

Sorry, I have no pics  but regard the servo, Minispares say the air valve should be positioned at the bottom (6 o'clock) with the servo mounted horizontally and I had it mounted with the air valve at the top, I'm assuming the air valve is the white circular housing on the side of the servo.  

 

Swift_general:

 

No, the pedal doesn't sink at all which makes me suspect the servo is faulty, tried this several times but got the same result.

 

Moke Spider:

 

I had the outlet of the servo positioned higher than the inlet, so I'm confident I got all the air out of the system when bleeding with the servo connected into the system.

 

Thanks again, Steve

[Ethel]

You can check the servo as the hydraulic pressure lifts the air valve. The valve itself can trap some air on the hydraulic side if it's upright.

[Swift_General]

From memory the air value is actuated by a small piston sitting in a cylinder off the main bore, hence the reason I suspect that it's recommended to have the valve on the underside so any air will make its way out. That said the volume of air would be very minimal, and it sounds like a you had a decent pedal, able to develop enough pressure for the servo to operate. I would therefore suspect the servo itself.

[floormanager]

As Swift_General says, if you pump the brakes with the engine off, the pedal goes hard.  It should then sink when you start the car.  This is the positioning of a servo in a MK1 and 2

 

 brake pipe routing 3.jpg   109.03K   25 downloads

[Stevie W]

Many thanks for the info all,

 

I think with the above in mind I shall:

 

1). Strip & rebuild the servo with a rebuild kit from Minispares, that way I can check the servo thoroughly and be sure it's ok.

2). Mount the servo as in "floormanagers" photo and see what I get.

 

One last question: will having a take-off on the inlet manifold for the Smiths vacuum gauge affect the servos efficiency?

 

Thanks again, Steve  

[Swift_General]

No a vacuum gauge will not affect servo efficiency. The gauge does not 'use' air as such (assuming no leaks anywhere!) only measures air pressure, and so the air pressure in the manifold with be the same with a gauge fitted or not.

[Swift_General]

Just a thought. Is the one way valve okay? Not fitted the wrong way otherwise the servo with never be subject to any vacuum!

[Stevie W]

Thanks for the info!

 

Did think of the one way valve, but alas that was fitted the correct way round and it seems to work ok.

 

Cheers, Steve.

[KernowCooper]

The Cooper S 7.5 disc setup was designed to run with a servo, i added one to mine and the difference in on road braking was transformed, sounds like yours is not working.

[Stevie W]

Thanks Kernow,

 

Hopefully a strip and rebuild of the servo, plus correct mounting will solve the problem!

 

Cheers, Steve.