HELP: From Drum to Disc Conversion Plan

[Dongskie]

Good day fellow toymodders,

I'm planning to convert my rear drums into discs, but I do not know from what more known Toyota vehicle my diff came from, hence I cannot acertain which conversion parts I should get.

I have a 1994 Toyota Asian Utility Vehicle named Tamaraw released only in the Philiipines, in Indonesia as Kijang, in China, Taiwan and South Africa as Zace.

I know some may not be familiar with it so here it is:


Here is my drum's back view:


For reference here is the front disc brake:




The Spindle:


Your comments and suggestions will lead me to the correct direction and are greatly appreciated.

[Mjh]

Have a look at the build plate and see what the diff code is then we can work out the best plan from there.
Why do you want to go rear discs anyway?

[Dongskie]

Have a look at the build plate and see what the diff code is then we can work out the best plan from there.
Why do you want to go rear discs anyway?

Thanks for the reply Mjh, Im not sure about the ID Plate but it houses an A03A differential codes.

I'm planning to change to discs because I find them more convenient to work on, stronger
and looks good too

I know it will take a lot of conversions, and thats the part I like most.

[Ken_T]

What are you planning to replace the drums with? Any pre-requisites for disc sizes? Do you have access to a machinist? (you will need one.)

On the other hand, what's at the local junkyards, readily available and cheap in terms of replacement parts?

It's a lot of effort. I made the thing below. It took a prototype to get things all lined up but I'm better at measuring and drawing stuff now so I could probably get something workable in one go. Could even get it 3D printed these days.

[Dongskie]

What are you planning to replace the drums with? Any pre-requisites for disc sizes? Do you have access to a machinist? (you will need one.)

On the other hand, what's at the local junkyards, readily available and cheap in terms of replacement parts?

It's a lot of effort. I made the thing below. It took a prototype to get things all lined up but I'm better at measuring and drawing stuff now so I could probably get something workable in one go. Could even get it 3D printed these days.

Hi Ken,

As for the junkyards, I can get a pair of spindles with the caliper and disc (exactly same as my fronts) as a whole set for about $40AU

I was thinking of working on the caliper mounts from that spindle set and start from there...

I remember back in 1993 my late dad converted our 1983 Isuzu Gemini rear drums into calipers by using the same front sets, but he made a custom mount.

I have seen some setup with the disc in the sense is floating, I dunno the exact term of it but when the wheels are removed the disc is also loose and floats in the wheel bolts and centers itself via the wheel center hub when the wheels are replaced and tightened.

If I do the above mentioned, I can see that I will be forced to replace my wheel bolts with longer ones, and gain wheel offset, which I wanted to as well.

I'm still on my rough drawing board

[Ken_T]

I wouldn't use the front brakes on the rear without upgrading the front as well. The brake bias will end up at ~50/50 and you'll be locking the rears before the fronts, which is not a good thing. I would first look at rear brakes from a similar sized car than use the fronts on the rear.

See how your front has the hub bolted to the disc, if you remove it and go to a floating disc set-up, you'll end up with the caliper protruding past the disc face. That might be a problem if your wheel doesn't have enough clearance there. Grab a picture of the caliper and the caliper mount. Best thing to do for now is to start measuring up heights, disc mounting face to disc centreline, caliper mounting face to disc centreline and axle flange to disc mounting face.

[Dongskie]

I wouldn't use the front brakes on the rear without upgrading the front as well. The brake bias will end up at ~50/50 and you'll be locking the rears before the fronts, which is not a good thing. I would first look at rear brakes from a similar sized car than use the fronts on the rear.

I do remember my dad's work locked up the rears all the time during hard braking

On my vehicle there is a Load Sensing Proportioning Valve installed in the rear brake lines, does it help preventing the lock-up?

See how your front has the hub bolted to the disc, if you remove it and go to a floating disc set-up, you'll end up with the caliper protruding past the disc face. That might be a problem if your wheel doesn't have enough clearance there. Grab a picture of the caliper and the caliper mount. Best thing to do for now is to start measuring up heights, disc mounting face to disc centreline, caliper mounting face to disc centreline and axle flange to disc mounting face.

Oh yeah, I can already picture that in my mind...

I will then need to bolt my disc into the rear axle hub just like the fronts then.. that case the disc face is closer to the caliper mounting points.

Pictures to follow.

Thanks Ken_T.

[Ken_T]

That prop valve probably helps it give more bias to the rear when the rear is loaded up. Those things change brake bias based on ride height, yeah? (I don't know much about them things, never had to deal with them.) It probably won't help preventing lock-up when there's too much braking power. You need a prop valve from wilwood, of the like.

Where/how are you going to bolt it? The axle doesn't have a hub thing that you can bolt a disc to. The back of the studs protrude on the back face so you'll have to machine holes for them and the axle end is only like 8mm thick so not much material to put (threaded) studs going back towards the diff. It's starting to look real messy. If you did manage to get the disc mounted to the back face, you'll only move the disc back by ~16mm. The front hub is thicker than that.

Thinking outside the box (and it's pretty ridiculous): 20mm bolt on spacer on the back face of the axle with the spacer's studs going through the original axle stud holes and wheel. Original, cut down, wheel studs used to bolt disc to spacer.
Using discs from another car would be way easier. : )

[Dongskie]

That prop valve probably helps it give more bias to the rear when the rear is loaded up. Those things change brake bias based on ride height, yeah? (I don't know much about them things, never had to deal with them.) It probably won't help preventing lock-up when there's too much braking power. You need a prop valve from wilwood, of the like.

Hi Ken_t, I used to have a 1979 RT130 Wagon with no LSPV and I could lock-up the rears at my discretion (LOL) . Currently on my "van" i couldn't. unless I use the parking brake

Where/how are you going to bolt it? The axle doesn't have a hub thing that you can bolt a disc to. The back of the studs protrude on the back face so you'll have to machine holes for them and the axle end is only like 8mm thick so not much material to put (threaded) studs going back towards the diff. It's starting to look real messy. If you did manage to get the disc mounted to the back face, you'll only move the disc back by ~16mm. The front hub is thicker than that.

My dad bolted the same disc on the Gemini here on the round plate (#3) where the wheel bolts are too, made 4 additional holes and bolted and used a self locking nut plus loctite. I was thinking of the same idea.

Thinking outside the box (and it's pretty ridiculous): 20mm bolt on spacer on the back face of the axle with the spacer's studs going through the original axle stud holes and wheel. Original, cut down, wheel studs used to bolt disc to spacer.
Using discs from another car would be way easier. : )

I think I like that

I'm off to the measurements again..

Thanks Ken_t,

[Ken_T]

I hope the disk wasn't placed over the back of the studs. and having nut and bolt would mean that he had wheels with a second set of holes. Do your wheels have that?

I wouldn't be doing that bolt on spacer idea. It's probably way illegal (maybe not in the Philippines?) not that I know the much about mods you can do with brakes.

[Dongskie]

I hope the disk wasn't placed over the back of the studs. and having nut and bolt would mean that he had wheels with a second set of holes. Do your wheels have that?

In fact he did

I wouldn't be doing that bolt on spacer idea. It's probably way illegal (maybe not in the Philippines?) not that I know the much about mods you can do with brakes.

Illegal in the Philippines? You can do just about anything you like with your car and the authorities wouldn't even notice it lol.

I'm taking your suggestion of getting a different disc and caliper set, smaller than the fronts.