11 replies to this topic

[Jordie]

Hi guys,

 

Just after some opinions and advice, I haven't run this type of brake setup before so not sure if the pedal travel is normal. Seems to be quite a way, doesn't go to the floor.

 

Its a tin master cylinder, single line to T piece on bulkhead, splitting front to back. Front has inline brake light switch on OSF union with brake hose. Pipe to rear goes to a MK1 style brake pressure thing, then splits to either side.

 

I changed the front from 8.4 to 7.5 discs.

 

It passed mot fine, the fronts locked and the backs gave just enough to get it through, although i think the handbrake was ALOT higher reading.

 

I am wondering if the brake valve thing on the rear sub frame is preventing the brakes from working well.

 

The drums are adjusted up with slight drag, evenly balanced according to MOT.

 

Pumping the pedal doesn't seem to have an effect on the travel. If you press the brakes hard and sharply (when not moving) theres a clunk from the rear, which I believe is that valve?

 

Jordie

[mk1leg]

are you running it with a servo..........if not the brakes will be different to that with a servo

[Jordie]

No servo.

 

All the minis ive had in the past without a servo, the pedal has been hard and solid to press. This seems to travel quite a lot.

 

I may have to get a friend to rebleed the brakes with me using the up/down manual method, to see if theres any air in, but the fluid came through clean and bubble free last time.

[GraemeC]

I'd say you have air in after the valve. Once it shuttles shut the pedal goes hard but the rear brakes will be poor.

Bleed again but open the rear nipples BEFORE attaching your easy bleed to the tyre, then lock the nipple off once bled, then remove the easy bleed.

[Jordie]

Will try that. Friend can give me a hand at weekend to manually bleed the old fashioned way.

[GraemeC]

Still need to open nipples first - stops the pressure build up shutting the valve off.

[Jordie]

Will do. Never had one of them valves before. Cheers for that.

[Jordie]

Swapped out that valve for a t piece. Fitted some new brake pipes and pedal is alot better as expected. Need to road test but cant get out of garage due to builders

[Broomer]

I guess the mk1 style brake pressure thing is a shuttle valve? Isn't that quite a important component on a single line system?

[GraemeC]

It is, closes off at a set line pressure.  

Without some form of regulation there is a risk of the rear locking up and turning the car round - I assume Jordie is putting in an adjustable valve?

[dklawson]

Thanks for bringing that up Graeme.  You don't want the rears locking up.  If the rears lock in a stop the rear end can start coming around and put you into a spin.  Proceed with caution using a T piece as it can allow lockup.  Try an adjustable rear valve and "tune" so the rears cannot lock.

 

Your car's brake pedal may appear firmer.  However, the "clunk" and long pedal travel are common with out of adjustment shoes.  Proper shoe adjustment is not a wheel that can freely spin.  You want an elevated rear wheel to spin for no more than 1 revolution then come to a stop.  There should also be just a hint of audible brake drag.  No sound and multiple revolutions before the wheel comes to a stop means the shoes are too loose.

[Jordie]

Rear drums are adjusted as you say allready, the clunk was definately from the valve as witnessed during the mot.

 

My main concern was the long travel and poor brakes. I havent been able to road test it (building work blocking driveway), but the pedal feels much more as expected.

 

I am aware of the issue of the rear brakes and possible locking up, having worked on "shortie" minis. This is a fiberglass kit car, so indeed I will be fitting an adjustable regulator of some sort to the rear brakes to give me fine tuning.

 

Nothing on the car is original, front drums have been swapped to 8,4" discs then to 7.5" disc setup. Rears had new wheel cylinders from local factors in past (no idea on the bore size).

 

So it will be a little trial and error for now to find the best setup/pressure to the rears to suit the kit car.

 

Note: Ive kept the valve as i'm not sure if its a serviceable item, so may have a tinker with it if it is.