Drums to disc- residual valve question

[ameisner]

Hi All,

I am wanting to change from rear drums to discs on my '96 Caldina. Have read all the excellent post on this topic but don't see anything about removing the residual valve from the master cylinder (or even where it is and if it's removable?). Does staying with the 'drum' master cylinder (assuming that's where the valve is) lead to dragging rear brakes?

Hope to sort this out before I do the swap.

Thanks,

Andrew

[oldcorollas]

is it a 19x or a 21x? i have a 21x manual i could look at....

[Tom86]

Hi All,

I am wanting to change from rear drums to discs on my '96 Caldina. Have read all the excellent post on this topic but don't see anything about removing the residual valve from the master cylinder (or even where it is and if it's removable?). Does staying with the 'drum' master cylinder (assuming that's where the valve is) lead to dragging rear brakes?

I rememebered asking this question before but I didn't get any reply(in my case it was for AE86).I've read that the drum brake system use a 10PSI valves and disc use 2PSI and if not remove when swapping drum to disc this can cause dragging rear brakes.

[ameisner]

Is a CT190G - 2WD diesel. My manual doesn't show anything of use ... it tells me all ABS models have rear discs although mine has ABS but has rear drums!

Thanks,

Andrew

[oldcorollas]

from what i can see in the 21x manual, there is no residual pressure valve in the master cylinder or the lines...
there is a spring inside the drum brake slave cylinder, but i'm not sure if it pushes the pistons out, or just stops them going in too far... perhaps that is enough to keep the pistons out, and residual pressure is not actually needed?

although my KE10/5's were meant to have a residual pressure valves (some are all drum) i never saw one installed in the master where it was meant to be.. and never had any issus with pistons retraction either....

i reckon just swap it.. if they drag... search further

or better yet... connect master directly to the drum brake slave and see if it retracts... then try to compress the piston manually and see if it springs back...
if it springs back.. there is no need for residual pressure?

[clubagreenie]

Spring inside wheel cylinder pushes piston out. There shouldn't really be any residual pressure in the system should there? Any will cause pressure on the brakes unless the friction of the pistons is a constant and calculated and the presure maintaining valve calibrated to this.

[ameisner]

As I understand it, in a drum system, the resudual pressure is matched by the springs in the drum brakes pulling the shoes away from the drum. In a disc application, these springs aren't there so less residual pressure is required. May just use a master cylinder off a disc/disc version of my car.

[wilbo666]

I've also not heard of residual pressure values fitted in brake systems....

What I would be concerned about is the brake bias however!

I'd be making sure to use the bias valve from the 4 wheel disk brake model, other wise it will be like having a foot hand brake when you stand on the brakes (It will lock the rear well before the front with the stock drum bias valve).... -> not good!

Cheers
Wilbo

[oldcorollas]

As I understand it, in a drum system, the resudual pressure is matched by the springs in the drum brakes pulling the shoes away from the drum. In a disc application, these springs aren't there so less residual pressure is required. May just use a master cylinder off a disc/disc version of my car.

yah, btu there are springs in the slave cylinders themselves, possibly to do away witht he need to have a residual pressure valve...

Wilbo, the KE1X are MEANT to have them in the master cylinder (at the end), but in all of mine they have not been installed....

[wagonist]

I probably should reply to this, seeing as I have a FWD CT190G with the rear drums changed to discs....

When I did my conversion (I'm guessing you read about it in the Tech FAQ), I used the original discs from the wreckers.
I didn't get them machined to get rid of the slight surface rust.
I've since had to replace one side, including the disc with another set from the wrecker.

That was about 18months ago. It still has some marks on it from the surface rust, so I'm very much guessing that the discs will drag.
The pads are supposed to be in contact with the disc at all times, its just that they don't have any pressure on them.

So.... GO FOR IT.
It looks so much better with them on, especially when you've got fairly open rims like I do.
PS, if you can, make sure you use ST20x parts, the conversion will be much simpler.

You probably find (like I did), that the "owner's manual" you got with the car is a translation of the 92-95 book.
Mine doesn't even list that the diesel is a turbo (96-)
A guy in the UK had one of our models & made a full website about the history, etc.
But after it got written off, he neglected the site & its since been lost If I've known, I would've copied everything & redone it somewhere.
If you want to know any more info, just PM me.

[wagonist]

And to respond to other questions, bias hasn't been a problem.
Mind you, I'm also not running the stock front brakes either, so maybe those upgrades have negated the rear one.

I wouldn't have a clue where the bias valve is.
All the Caldina wagons (not the van versions which still look like the pre 95 wagon) have ABS (because the wiring is suited to run the speedo off the front ABS sensors) so the bias valve is probably built into the ABS motor unit on the firewall.

aha
a topic in Tech & Conversions I finally know something about