404 brake saga

Gilow

Member
Fellow Frogger
Joined
May 21, 2015
Messages
130
Location
Adelaide
Hi all,

I jumped in the lad's 404 the other day to go to the shops. (Think driveway scene from The Castle) and I am very glad I did. The brakes were awful. HUGE amount of pedal travel, and very soft. He, of course, didn't think to mention this.

SO, back to the garage and out with the tools and pull it all apart.

First of all, the car is a late 68 or early 69, with factory disc brakes and standard (non thermo stable) drums on the back. (At least, I assume this is the case, they look very "normal" and simple to me.)

The master cylinder condition was pretty good, it has been rebuilt in the last ten years and still has the hone marks. The seals were all in good condition, but I will replace them as a matter of course.

Then there's the booster. The existing booster looks very much like it was a VH44. I recently bought a remanufactured VH40 from a guy here in South Australia whom I trust, so I figured I would swap the two, which I did. I have mounted it using the brackets that came with it, in the fore-and-aft orientation that I've seen documented here on AussieFrogs.

I assembled everything, bled the whole lot, and took it for a drive.

Not good.

Pedal travel is still very bad, but this time I could pump the brakes up and get a very good pedal feel if I tried. However the extra boost made the brakes super-sensitive and I locked the back up a couple of times without meaning to. Then, on the way back from the very test drive, the brakes started to jamb on somewhere, in a very unpredictable way.

So, what do I do next?

Oh, and also for the record, I have checked the rear drums and the pads are adjusted pretty well.
There is no loss of fluid apparent, and there was no loss apparent prior to the work being done.

Help please!

And as a separate aside, we were both very happy with the level of boost from the VH44. Certainly it was heavy, but no unpleasant, so all else being equal, I'd be happy to buy a new VH44 and fit it, unless there was a reason not to.

Matt
 
Hi all,

I jumped in the lad's 404 the other day to go to the shops. (Think driveway scene from The Castle) and I am very glad I did. The brakes were awful. HUGE amount of pedal travel, and very soft. He, of course, didn't think to mention this.

SO, back to the garage and out with the tools and pull it all apart.

First of all, the car is a late 68 or early 69, with factory disc brakes and standard (non thermo stable) drums on the back. (At least, I assume this is the case, they look very "normal" and simple to me.)

The master cylinder condition was pretty good, it has been rebuilt in the last ten years and still has the hone marks. The seals were all in good condition, but I will replace them as a matter of course.

Then there's the booster. The existing booster looks very much like it was a VH44. I recently bought a remanufactured VH40 from a guy here in South Australia whom I trust, so I figured I would swap the two, which I did. I have mounted it using the brackets that came with it, in the fore-and-aft orientation that I've seen documented here on AussieFrogs.

I assembled everything, bled the whole lot, and took it for a drive.

Not good.

Pedal travel is still very bad, but this time I could pump the brakes up and get a very good pedal feel if I tried. However the extra boost made the brakes super-sensitive and I locked the back up a couple of times without meaning to. Then, on the way back from the very test drive, the brakes started to jamb on somewhere, in a very unpredictable way.

So, what do I do next?

Oh, and also for the record, I have checked the rear drums and the pads are adjusted pretty well.
There is no loss of fluid apparent, and there was no loss apparent prior to the work being done.

Help please!

And as a separate aside, we were both very happy with the level of boost from the VH44. Certainly it was heavy, but no unpleasant, so all else being equal, I'd be happy to buy a new VH44 and fit it, unless there was a reason not to.

Matt

Check the anti lock valve on the diff is working.

Check the flexible hoses for blocked internal bores. There are hoses on each front brake and a single hose on the torque tube.

Always bleed the brakes with the rear wheels on the ground

I'd also suspect master cylinder issues from hard experience and check the brake booster isn't leaking internally , ie check for gungy liquid inside the vacuum diaphragm area. Through the vacuum port.
 
It's not easy -generally all you can do is check the piston moves when pressed. And of course the rear brakes don't lock up prematurely.

I've not seen one leak.

Here's a thought with car on it's wheels do you get any change in brake "feel" if you pull on the handbrake ?

That would indicate the rear brakes are getting fluid to them.

The only other way is to crack a brake fitting and look for fluid squirting.
 
Better check which model it actually is. Does it have chrome tops to the door trims?
 
Could have had discs fitted to a 68, with important bits missing, or even wrong bits on a 1969. If a disc brake master is fitted to a 68 without adding the 1969 4 way junction on the cross member there won't be a line pressure valve for the rears and the pedal feel and level will be bad.Also, locking rears suggests no limiting valve on rear axle, or maybe just seized?
 

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Could have had discs fitted to a 68, with important bits missing, or even wrong bits on a 1969. If a disc brake master is fitted to a 68 without adding the 1969 4 way junction on the cross member there won't be a line pressure valve for the rears and the pedal feel and level will be bad.Also, locking rears suggests no limiting valve on rear axle, or maybe just seized?

Reasonably sure the disks are original, I feel like it would have been mentioned in the car's rather complete history.

It does appear to have the four way junction...
 

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Could have had discs fitted to a 68, with important bits missing, or even wrong bits on a 1969. If a disc brake master is fitted to a 68 without adding the 1969 4 way junction on the cross member there won't be a line pressure valve for the rears and the pedal feel and level will be bad.Also, locking rears suggests no limiting valve on rear axle, or maybe just seized?


The limiting valve is there, sounds like I am going to have to remove it and see what is going on.
 
It's not easy -generally all you can do is check the piston moves when pressed. And of course the rear brakes don't lock up prematurely.

I've not seen one leak.

Here's a thought with car on it's wheels do you get any change in brake "feel" if you pull on the handbrake ?

Yes, prior to this event, I realised i had to adjust the rear brake shoes because the brakes were noticeably better with the handbrake partially applied.

That would indicate the rear brakes are getting fluid to them.

The only other way is to crack a brake fitting and look for fluid squirting.
-----
 
Reasonably sure the disks are original, I feel like it would have been mentioned in the car's rather complete history.

It does appear to have the four way junction...

They both have 4 way junctions but different, this IS the proper disc brake one.
 
I'd be taking a good look at the master and the flexible hoses then.

The hoses can can be economically reproduced by any brake shop with a Brakquip hose making machine.

The 404 hose ends are a standard off the shelf fitting. Just take the original hoses to the shop.

You can even have road legal braided hoses in lieu of standard neoprene. :eek:
 
I'd be taking a good look at the master and the flexible hoses then.

The hoses can can be economically reproduced by any brake shop with a Brakquip hose making machine.

The 404 hose ends are a standard off the shelf fitting. Just take the original hoses to the shop.

You can even have road legal braided hoses in lieu of standard neoprene. :eek:


Will do, but I reckon something else is amiss. The master feels and looks good, and it maintains its position under sustained pressure. The locking problem only appeared after I changed the booster, so I guess it might be the culprit there.

I am looking at some stuff in the manual about residual pressure valves and wondering if the vh40 booster has one of those, because the description fits some of what I am seeing since the booster changeover.
 
One forum (on old holdens) mentions problems with a "minimum pressure valve" in the master cylinder causing problems with the VH40 booster. Could it be there is something like this in the 404 master cylinder?
 
One forum (on old holdens) mentions problems with a "minimum pressure valve" in the master cylinder causing problems with the VH40 booster. Could it be there is something like this in the 404 master cylinder?

This valve will cause problems with disc brakes as it will tend to hold them on. It is only for drums, which is why it is included in the rear output of that 4 way junction mentioned before. It is in the base of the master cylinder for 4 wheel drum braked cars and would be diabolical if fed into a booster, would hold the brakes on slightly.

Maybe the one in the junction isn't working, causing the poor pedal?

Also, there is virtually no chance the rear brake limiter valve is still working after all these years, maybe fit an adjustable aftermarket device? Superstop in Mont Albert, Melbourne could reco the original valve using parts from elsewhere, original bits no longer available, try contacting them?
 
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