Brake pedal adjustment

[leyther8008]

Ok I,ve now rebuilt the full brake system, and apart from getting the return springs wrong on the front, its gone swimmingly, however I noticed that the brake lights are on all the time, so digging about I found there is no noticable play in the brake pedal, I cant really use the before as a comparison as the pedal went halfway down before anything happened.
I presume I,ve now got to adjust the pushrod to give the required 3/4 inch free movement.
My question is would replacing the master cylinder have such an effect on the brakes physical set up ie where has the clearance gone? is a new cylinder likely to be a different actual size to an old one? anybody any views or experience of this.
Or point me in the right direction, this would be the first time I,ve ever had to adjust this rod on any of the minors I,ve ever worked on.
Should also say that I put a remote reservoir on at the same time and apart from a leak from the thread of the new blank filler plug solved by PTFE tape all went well, cant see how that could affect anything apart from having a bit more 'head' leading to slightly higher residual pressure in the system.

[Willie]

If you have no free play on the pedal then you should first check that the brakes DO free off when you release it. There is a fault condition whereby the piston assembly in the Master cylinder cannot return fully to its proper rest position which means that the fluid cannot return to the reservoir so pressure builds up. If you have rebuilt everything then it is possible that you do not have the required free play any more. You have to remove the small plate over the pedal and you will see that the rod which enters the Master is adjustable. You need to adjust this so that there is at least a 32nd of an inch free play. WARNING adjust it with the brake pedal in the position where it will be with the floor plate screwed down otherwise you will have to readjust. In other words the free play must be there when everything is firmly back in place.

[kennatt]

can you push the car easily.If not then the system is holding pressure,if you can then the problem is within the brake light switch,which is pressure activated.I would have thought that it would take more than adjustment to provide enough pressure to activate the switch.

[MoggyTech]

Did you remember to refit the brake pedal return spring?
The master cylinder pushrod should never really need adjusting.
Given that you have replaced everything? it will be a case of back tracking and checking the new components.

There is a valve inside the master cylinder than retains 8PSI of brake line pressure for DRUM brakes, and has to be removed for DISC brakes.

If the car won't roll easily, open a bleed nipple slightly and then see if it will roll. If that cures it, something is holding more pressure than required.

There are two different sizes of master cylinder 7/8ths and 13/16ths, the size is cast into the master cylinder casing on the side.

Adjusting the freeplay on the pedal should be the last resort, once you are happy everyting else is AOK.

[leyther8008]

Thanks people, looks like another weekend of drums off on on again!

[bmcecosse]

But you must have some free-play there - when the floors back in place. So - adjust that rod until there is some play.

[Willie]

Moggy tech, of course the pedal rod should never need adjusting but it is quite possible that the previous owner adjusted it in an effort to compensate for wear in the pedal bushes etc. It is an obvious thing to check.

[MoggyTech]

Moggy tech, of course the pedal rod should never need adjusting but it is quite possible that the previous owner adjusted it in an effort to compensate for wear in the pedal bushes etc. It is an obvious thing to check.

Yes roger that. The one fitted to my traveller was actually bent!

[leyther8008]

Ok fully checked over now and adjusted to give 3/4 inch free travel and for the first time since I,ve had the van I got four stripes on the rugby club car park (or as I refer to it my brake balance testing surface) apart from first press of the day which must pump up the system to 8psi I,ve now got brakes I am reasonable confident in and I dont have my hand hovering over the handbrake when coming up to roundabouts and junctions.
The remote reservoir is such a great idea, my congrats go to whoever dreamt it up! I have been lokking at some american underfloor master cylinders that give dual circuit brakes they use them on hot rods a lot to give a clean bulkhead or firewall as they call it.
Has any body ever used one?

[MoggyTech]

I like the idea of dual circuit brakes, but you will find that aftermarket master cylinders for Hotrods produce way to much line pressure, and you would end up blowing wheel cylinders at a great rate of knots. No doubt there could be brake pressure limiters, but it would probably be a tricky mod to get right. Single circuit brakes are scarey, so I really look after my brakes.