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MG Midget and Sprite Technical - KAD Calipers still no joy

Further to my previous post, Having gone through bleeding again all 4 nipples it hasn't made the slightest difference, the brakes feel soft (in fact I cant lock up) but no air in the system!!

What other M/C will give me greater pressure, at the moment it has a 1500 dual line fitted, or will I have to get a triple cylinder pedal box?
K Harris

Sorry if I state the obvious but have you got the calipers on the right side wheels. Are the bleed nipples at the top?
Bob (robert) Midget Turbo

4 bleed nipples!! There is no air in the system, my concern is there isn't enough push to work 8 36mm pistons from a standard M/C
K Harris

Yes I know you said 4 but just asking if you had 2 of them at the top? Metro calipers have 4 nipples and if fitted to the wrong side will not have 2 nipples at the top and would therefore not bleed correctly. Forgive me for stating the obvious
Bob (robert) Midget Turbo

If that is not clear then they will have 2 at the bottom and 2 in the centre. Don't know how better to describe it?
Bob (robert) Midget Turbo

KAD has a nipple at the top and the bottom, so I put speed bleeders on the top's, the fluid is clear from all nipples (must have pumped 500ml with a easy bleed)

I'm at wits end so to speak..
K Harris

OK I have not seen the KAD items but if the nipples are at the highest point then bleeding ought to be straight forward. Therefore the next thing should be total requirement of fluid. This means is the rear brakes adjusted up well and not scavaging all the fluid pressure. When confronted with this kind of issue we generally place a clamp on the rear axle hose effectively blocking off the rear brakes to see if this improves the pedal drastically thus confirming a problem at the rear. Could try that next.
Meant to say also that the master cylinder should be easily capable of driving your brakes so must be a problem somewhere.
Bob (robert) Midget Turbo

Hi K, I would at this point try to disconnect as many brake pipes as possible (blocked off with bleen nipples) and prove one caliper and one bit of pipe. Usint the tandam master cyclinder it is important that the front brakes go into the right port on the master. I am sure I had a similar problem on my race car when i plumbed the front brakes into the rear port and vice a versa. I hope this helps. Spinner
spinner

Sorry to be a pain, the rear is fine and came up well on the MoT the M/C is a dual line so all clear on the rear, the fronts only just passed.

I know a friend of mine fitted Princes calipers on the race midget and the M/C couldnt cope until they went twin cylinders

K Harris

Just to confirm KH how the master works. The rear brakes are operated from pressure in the front brake part of the master so a problem with the rear will affect the fronts to a lesser degree. With the MOT test the rear brake efficiency is very low compared to the fronts and will show a good pass even if the total efficiency is generally poor. However you are probably correct it probably aint the rears at fault.
Bob (robert) Midget Turbo

I proved the rears by just filling the front part of the M/C, and I had a firm pedal only when I did the fronts problems appeared.

I will now test one caliper at a time!!
K Harris

thats a real possability....not sure how to write this.....

the front calipers are 4 pot instead of 2pot, so it takes more fluid and more umpf (pressure??) to do twice as much work as before....meaning you may need a bigger master cly.


example...A huge truck MC on a small car brake system would lock up the brakes at a touch

A Small car MC on a huge truck brake system ...the pads would never reach the rotor disk....

see where Im going with this???


prop
Prop

By the sound of it you don't have a big enough surface area in the master cylinder when the piston moves, just as Prop explained.
You may be able to source a new master cylinder for a split system from a larger car. Failing that try AP Racing.
I know when i fitted my 6 pots i had to go to a larger diameter 0.875" IIRC just to get the pedal pressure, albeit on a single line system.
brian

Ah ...thanks brian,

surface area!!!, Thats what I was going for..thanks

prop
Prop

Brian did you have to fit reducer valves on the back to stop over braking? like a MGB rear..
K Harris

No, i didn't fit a reducer valve, but then i did fit a rear disc set up from Frontline. So that in effect increased the volume of fluid to the rears and so balanced out the rest of the system. I have tested them on a private stretch of road and found no imbalance between front and rear and try as i might could not get the rear to out brake the front, which was a relief otherwise i would have to have an inline proportioning valve fitted.
Brian

Noticed a fault with the M/C today, on the advice of KAD I took out the pads on one caliper, pushed the pedal gently expecting to see the piston move only the carside pistons moved, the pedal then had no feel at all.

Then replaced the pads and tried a quick bleed, only one pump and again loss of pedal, so the M/C only has push no suck if that makes any sense.

This is the second faulty M/C in a row..
K Harris

Keith,

I don't see what the pad removal test will tell you except that one set of piston is stiffer than another. I wouldn't expect all to move just the ones that are most free to move. Also much of the fluid is pushed back to the master cylinder by the piston seals pulling the pistons back in.

David Billington

That sounds more like it KH now you are starting to get somewhere, well diagnosed. So what is causing that? Must say had you bled the brakes in the traditional "Abingdon" method then perhaps you would have seen this as it would probably not pumped fluid.
Struggling to understand what could cause this I must admit.
Bob (robert) Midget Turbo

Strange why I should have 2 duff M/C both from the same supplier who is sending yet another unit, I've asked if they could check the unit first before dispatch!!

Maybe theres a batch of duff M/C

As for bleeding brakes, its not called that for nothing:-)
K Harris

Referring to David’s comment. I would usually test the caliper to see if the pistons move then put a G clamp over the one/s that do and try again to see if the non moving pistons move...

Wouldn’t expect new calipers + pistons to be ceased though, unless the assembly guy was having a very negligent day.
R T Jakeman

We have brakes that work, turns out I did have 2 duff M/C's. Brakes still feel strange and not a sudden bite but a smoother pull up if that makes sense, would still like a firmer pedal..
K Harris

The pedal on our midge is a bit soft with the KAD calipers-but used in anger it really does stop - as proved on the Hughes rally last week.
PROP - any chance of some more details of your tilton set up - part numbers etc?
David Brenchley

This thread was discussed between 02/06/2008 and 06/06/2008

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