A was for Austin, but now B is for Bedford

Hi,

if the brake light switch is not an inline hydraulic switch but a mechanical one actuated off the pedal then I have seen 'brake drag' caused by the switch being poorly adjusted and holding the pedal slightly lower than it should be along the lines of thought in the previous post.

Terry

jon_d : Yes and yes. I have 1/4" clearance at rest in the push rod as stipulated in the manual. The thought that crossed my mind while transferring comments was to disconnect at the pedal by dropping the pin out after applying pressure, then drawing the push rod out of the cylinder to ensure this wasn't causing the issue. I'll do that sometime this morning before calling John.D (the other one). 

Gryphon: Obviously we were writing at the same time so I had to come back in here to reply to you also. Yes I fitted one actuated by the pedal when wiring as I had no joy with the original hydraulic pressure operated one at that time. Of course looking back it seems a reasonably logical conclusion why it wasn't working. The pressure switch is mounted in the brake line to the front brakes and it is now apparent there was no pressure available in that line until the master cylinder was sorted (?).  

I will check where my switch has been mounted being the cause while doing the pin removal mentioned in my last post, but I am confident that it will be okay (we shall see???).

Damn, I was hoping Gryphon's idea was going to be the answer as that would have been a straight forward fix. Even with the piston coming all the way forward and hitting the circlip the drums were still locked up until I released the pressure at the bleed nipple. 

Phoned John.D and interestingly he suggested the pushrod also, before I had a chance to mention what I've tried so far. He had put some cups in the check valves (that is what they are referred to in the D Type Manual) but in hindsight was uncertain if they were the right ones. 

Job for Friday: Remove master cylinder and servo combination to relay back to John.D. Hopefully my wife will do this for me on Sunday, although she is already going to pick up a wall oven and grille!? She has grown to dislike my pick-ups or drop-offs at the best of times   and I was surprised when she had volunteered to pick up the wall oven. I would say my chances of her doing both is somewhere between remote and unlikely, so I may need to make the trip down and do both myself.   

Late news: No drama, she is going to do it!  

What a wonderful, wonderful wife I have, I love her and really don't deserve her.    

Are you sure the brakes are assembled correctly
If not then maybe the springs on the shoes are not enough pressure to push the pistons back on their own

Paul

Yes they were all in the right positions and were moving okay when I looked in there about that long ago that I can't remember when Paul.

If it isn't the two valves in the master cylinder the only thing left is the servo . . . ? 

Two of them going down to Adelaide with the master cylinder.    

Master cylinder and servo off, less than twenty minutes this time, and not a drop of brake fluid on me miraculously!

It's not really that hard once you've done it a couple of times, just the thought of struggling to get to that awkward brake fitting on the chassis side that is a hang-up. Mind you it's harder getting that aligned and back on again . . . 

Anyway it's off now and I will be taking it down to Adelaide tomorrow, plus picking up the oven.   

Not sure if this will help, but.....

this is from the SB Parts catalogue  (about 1965 onwards).

If shows a vacuum brake master with only one outlet (i think) but does quite clearly show the shape of the valve in question.

 

Although I dropped the master cylinder off to John last week he couldn't start until he had an 1" & 5/16" impact socket to undo the large nut on the back of the cylinder. I offered to attempt getting one on the way home, and knowing he only had 1/2" drive handles I said I would either buy one to suit or send down a large ratchet handle, plus the larger impact socket, with my wife on Sunday. Needless to say all they had in stock were 3/4" drive sockets, ($33 for the larger size, $17 for the smaller one), but what the hey I can add it to my stock later and wife dropped it off Sunday afternoon. 

I was just leaving this morning to go to the Men's Shed when John.D phoned to let me know he had gone over the master and servo particularly carefully and had spent much care with the check valves and internal porting. He had put new rubbers in the check valves previously but found them to be reluctant to lift off enough so, rather than drop them out completely, shortened the light return spring slightly (re-coiling the end appropriately) and tested them with a small pressure fitting he has made for the job. Apparently the back brake check valve was the most reluctant to lift and he discovered that it worked okay sometimes - but not every time   and was the most likely reason for the confusing behaviour that I had been experiencing. He also noticed the piston seal did not open the small return hole completely which he improved by shortening the piston length slightly. (This could have been a contributing factor too.) 

Having solved the master cylinder he had a look at the servo, applying vacuum to it, and found it to be working in the large cylinder where the leather seal is, but not in the small valve arrangement that directs the servo. This is not a major concern as the assistance given is not great and I wasn't fussed whether it worked or not anyway, as long as it wasn't detrimental to brake operation. The annoying part is I had taken a spare servo down with me originally but ended up not leaving it there as the master cylinder was the main issue . . . a pity really as there was another servo control valve on it that may well have been okay? 

Best part about it all was his enthusiasm in describing what he had been doing, 25 minutes approximately.   Even better, when I asked him what I owed him for his extra input he said, "Nothing, I wanted it to work properly too." I followed that by asking him how he had felt about the problems experienced and his reply was, "Like you." (Confused and basically frustrated!?)  Now I can only hope it will prove okay once back on the truck.

Bottom line I can only recommend him, and his work, highly to anyone in South Australia needing brake work done - even though he's not keen to work on trucks! 

Roll on another week for wife to pick it up (after her next 'long weekend' with grandson). Meanwhile I've been busy fitting the new (old) oven into the kitchen and tomorrow will need to gather up all the old renmants and tidy my shed again!  

BDU (Big Down Ubder)
gudday m8
For th@ odd size socket 
some times a truck wheel brace can fit
or buy a socket to do the job and weld an extension on the socket to git er dun
we use Reo Bar ...... the cheapest high tensile steel
https://www.ausconbs.com.au/assets/full/n12at6m.jpg?20240418012232

cya
Best O Luck O