403 brake problems

David Cavanagh

David Cavanagh

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Fellow Frogger
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Romsey, Victoria, Australia
It's not often I need help on the forum but this is doing my head in.

Car is my 1959 403

When I restored it I checked all the brakes, rear were fine but fronts were warn out so I had the shoes rebonded and fitted new wheel cylinders and it's been good for a while.......but.....

A little while ago the pedal went to the floor and I had to pump it up to get home and some horrid noises coming from the rear.

The rear bonding had come away and the metal shoe was rubbing on the drum, the bonding on the right rear had failed so I had both rear brakes rebonded and drums machined and all back together.

I can't get a pedal, pump like mad and it come up but sinks straight back to the floor.

Has to be the old rust in the bore of the master cylinder trick, that's the second time I've fallen for it.

Remove master cyl and sure enough there's rust in there as suspected,
while it was away being fixed I found a new one on ebay so I now have 2.

I fitted the reco one first and bled it and bled it and I'm sure there's no air but still no pedal, still the same, no pedal but after pumping the crap out of my legs I could finally get a pedal but 2 seconds after I stop the pedal has gone again, jest like a faulty master cylinder.

So I tried the brand new one and it's exactly the same.

What am I missing? The adjustment is right from what I remember about adjusting 4 wheel drums that the drum is just spinning and lightly scraping the shoes. All 4 are like that.

I've got it on stands with all 4 wheels off, there's no limit valve on these old things is there? There's something I'm not seeing.

I'm going to have a wine now while I wait for some expert advise.
 
did you strip and rebuild the master cylinder?
I have seen the check valve in the end of the cylinder wrongly fitted or damaged
 
Hi David, sorry to hear of brake woes, very frustrating

school of hard knocks says check the obvious

have you double checked that bleed screws are closed ?

is there air coming out the bleeders ?

the tiny bleed hole in top of master cylinder that allows fluid to fill the master must be clear

old brake hoses can cause odd symptoms , can break down inside am sure you know this anyway

best of luck
 
Check that you have a line pressure valve (disc shaped thing, sits in the end of the spring) in the base of the master cylinder. Cylinders and kits for disc brake cars don't have this. Disc brake 404s have one in the 4 way junction that sits on the cross member, so that the rears have the valve and fronts don't as it causes the pads to stay in contact with the disc.
 
GRAHAM WALLIS said:
Check that you have a line pressure valve (disc shaped thing, sits in the end of the spring) in the base of the master cylinder. Cylinders and kits for disc brake cars don't have this. Disc brake 404s have one in the 4 way junction that sits on the cross member, so that the rears have the valve and fronts don't as it causes the pads to stay in contact with the disc.
Click to expand...

Colin Hague rebuild it and the new one was labeled late 403/early 404 22mm bore so I'm confident there right.
 
Sounds like it's right but you could always ask him in case he wasn't sure what car he was rebuilding the cylinder for.
Many years ago Dave Cochrane and I ran a stock 203 in the Hattah Desert Rally, try as we might we just couldn't get a pedal after rebuilding the master cylinder. In the end we just did the event without brakes, the car was slow and plenty of run off room in that area, combined with really slow pace over the sand dunes though the trees where there wasn't much run off room! Turned out to be no line pressure valve.
 
I've just ordered a pair of brake lines because that's literally the only thing left.

In thinking about it the rear wheels bleed up at full pressure like someone busting for a pee and soak the springs whereas the fronts are just normal, no air but no where near the pressure of the rears so hopefully there's a partial blockage or there collapsing on redraw which is really hard to tell when your on your own.

They'll be here in about a week so old Norman will just have to sit in the shed with his wheels cocked up for a bit longer.
 
Could be front hoses blocked, very common. I couldn't bleed the brakes in a 205 recently and that was the problem
 
Could try isolating the issue, just below the front axle there's the brake pipe divider, separating the front line and the rear line. Remove the rear line and seal that exit with a bolt. Bleed both the front drums and see if problem persist.
 
With the Lockheed MCs for early Renaults there were at least two different pistons, needing different length pushrods from the pedal and one associated issue was the piston not necessarily coming back far enough to clear that little fluid entry hole. The one time I had something like you described it was my fault, with too large a cup on the piston and it wasn't returning properly.

Re rust, silicone fluid is good if you are replacing rubber components.

I've had internal trouble with rubber hoses too, and now go new and ss braided. Much better pedal. Made down the road for about $50 each.

I can understand the wine.....

Good luck with it!
 
peugeotnut said:
Could try isolating the issue, just below the front axle there's the brake pipe divider, separating the front line and the rear line. Remove the rear line and seal that exit with a bolt. Bleed both the front drums and see if problem persist.
Click to expand...

That's a good idea. I'll leave it now until the new hoses arrive. No point bleeding it twice.
 
JohnW said:
With the Lockheed MCs for early Renaults there were at least two different pistons, needing different length pushrods from the pedal and one associated issue was the piston not necessarily coming back far enough to clear that little fluid entry hole. The one time I had something like you described it was my fault, with too large a cup on the piston and it wasn't returning properly.

Re rust, silicone fluid is good if you are replacing rubber components.

I've had internal trouble with rubber hoses too, and now go new and ss braided. Much better pedal. Made down the road for about $50 each.

I can understand the wine.....

Good luck with it!
Click to expand...

I've tried 2 master cylinders now, the reco one and the new one and the same problem.

Silicone fluid is a good idea in a car that's lucky to 1000kms a year, I should do that.
 
Front adjusters turn in direction of wheel rotation, leading shoe at rear in direction of rotation, trailing opposite to rotation.
 
Yeah that's the way I was told 100 years ago. Joe at Sims motors also confirmed it last week. Fronts in the direction of rotation and back ones both go down.
 
ianrobbo said:
did you strip and rebuild the master cylinder?
I have seen the check valve in the end of the cylinder wrongly fitted or damaged
Click to expand...
Hello Dave, As Ian said, the residual line pressure check valve is a possibility. An item that is sometimes overlooked is the rubber seal, which is the FIRST thing that goes into the master cylinder. The residual line pressure check valve sits against this to give a proper seal, so it can do it's job, then followed by the spring which holds it snugly against that rubber seal (4616.02). If you are sure there's no air in the system, and there's no loss of brake fluid anywhere, there's only a few other possibilities. If the master has been re sleeved had the inside been de burred prior to the components going in? As the cup (4619.03) moves back and forth over that point it will be 'scratched' leading to a slow loss of pedal if a continuous pressure is applied. Is the check valve in there? No crud around the check valve diaphram? Is the rubber seal in there? Is it a healthy rubber seal? The only other possible culprits are internal collapse of flexible hoses. How old are they?
 

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lo203404 said:
Hello Dave, As Ian said, the residual line pressure check valve is a possibility. An item that is sometimes overlooked is the rubber seal, which is the FIRST thing that goes into the master cylinder. The residual line pressure check valve sits against this to give a proper seal, so it can do it's job, then followed by the spring which holds it snugly against that rubber seal (4616.02). If you are sure there's no air in the system, and there's no loss of brake fluid anywhere, there's only a few other possibilities. If the master has been re sleeved had the inside been de burred prior to the components going in? As the cup (4619.03) moves back and forth over that point it will be 'scratched' leading to a slow loss of pedal if a continuous pressure is applied. Is the check valve in there? No crud around the check valve diaphram? Is the rubber seal in there? Is it a healthy rubber seal? The only other possible culprits are internal collapse of flexible hoses. How old are they?
Click to expand...

Thanks for that it's all very helpful.
The thing is though I now have 2 master cylinders, the reco one and a brand new one and there both doing the same thing. I've ordered new brake hose because internal collapsing is the only thing that makes sense. They'll be here in a week so I'll have another go then.
 
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