Rear drum to disc conversion question, Do I need to do anything with the master cylinder? Options

[GriffGirl]

Someone told me he thought I will need to do something with/replace my master cylinder when I convert my rear drum brakes to disc brakes; something about the proportioning valve.

Here's what he said:

In regard to your brake swap, I could be wrong, but I'm almost positive that you'll need a different proportioning valve...When you do it, though, you should see about swapping the proportioning valve and
master cylinder (if it's different on the GTs)... Drum brake wheel cylinders and disc brake calipers use different amounts of fluid (typically) and if you swap from the former to the latter, your rear discs brakes won't be doing as much work as they should.

This is all greek to me. Help? Is this something I should look further in to?

[njccmd2002]

ok pretty much what he tried to say.

you apply the brakes, that is 100% force.

the master cylinder spreads the force to a 60% to the front and 40 % on the back ( hypothetical )

so by changing the configuration too much or too less % will get to the back.

IDK, thats the way i was explained, i coudl be rong. maybe it does not even matter. you will need to get the braking specs of the drums and calipers.

Maybe it does not matter, hope it helps.

[alltracman78]

That's pretty much how it works.

The P valve only allows a certain bit of pressure to the rears.
Too much pressure and the rear wheels will lock up.
Drum brakes get less pressure than disc brakes, and also get the pressure first [drums have to move further to start working] so ideally you want to replace the P valve when you add the discs.

I'm not sure if the master cylinder is different as well, or the same.
I do know on the 5 th gens the ABS cars have a slightly larger MC, so it's a bit of an upgrade for those that don't have it.

[GriffGirl]

Okay, so just to be perfectly clear. And btw I probably should've mentioned - I don't have ABS.

I should replace the proportioning valve when I do the conversion.
What should I replace it with? Do I try to find a proportioning valve that is intended for the GT? Or is it something that is self-adjusting when replaced, effectively replacing it with the same thing that I have now, but new? Also, is this a part that is easy to find?

I do not need to replace the MC but it wouldn't hurt to do so.
My understanding is correct here, right? So if I were to replace the MC, would it be with a GT part or the ST part? And were I to replace the MC, is the P Valve automatically a part of that? I have NO idea what a proportioning valve is anyway. But I'm about to find out it seems. (Cool!)

[GriffGirl]

Okay, I found the proportioning valve on partsamerica.com. And the MC of course.

Question: do I need them for the ST, or the GT since the rears will be converted? And can I save myself approximately $200 and get them used like from someone off here?

[DEATH]

They [PV and MC] are the same. The only difference is the regular and 4 channel ABS setups. Just going from nonABS ST to nonABS GT there is no difference.
Griffy will be along to confirm this shortly.

This post has been edited by DEATH: May 6, 2008 - 1:45 PM

[GriffGirl]

Yep, here I am. Part numbers for ST and GT P-Valve and MCs are the same. So I guess I've ultimately answered my own question here. But not without the love and support of my fellow 6gcers. Awwwwwwwww..........

[alltracman78]

Good to know.

What I meant by the MC was that there might be an upgrade available, not that it was necessary to change it.

A larger one will give you more braking force, but depending on the setup isn't always the best idea.

[phantom]

i replace my drums for disks and i think it brakes good enough. the e-brake works a thousand times much better than the drums did. but doing that change isnt "really" necesary, right.

[alltracman78]

They [PV and MC] are the same. The only difference is the regular and 4 channel ABS setups. Just going from nonABS ST to nonABS GT there is no difference.
Griffy will be along to confirm this shortly.

So because this didn't make sense to me, I don't trust most aftermarket stuff, I was curious [and work was slow today], I checked this.


There are three different P valves.
1 for all GTs, 1 for the STs without ABS, and 1 for the STs with ABS.
I couldn't check without using VINs, and I'm not as familiar with the 6th gens as I am with the 5th gens, but I'm assuming all GTs have 4 wheel disc, and all STs have rear drum?
If that's the case, they are different depending on rear disc/drum.

If that is true, I would suggest changing the proportioning valve along with the rear brake components.
If you don't it's not the end of the world; I'm currrently using a FWD P valve on my Alltrac, and it brakes just fine. Also, I'm sure others that have done the swap are using the valve with no problems.
But, it will most likely improve your braking quality a bit if you do, and make your rear wheels less likely to lock up.

I didn't check master cylinders. Maybe one of these days I'll dig through it.

[GriffGirl]

I'm researching this part - on 1stToyotaParts.com, there is what they call a Pressure Metering Valve. Is this the same thing? The options for this part for a GT are for GTs w/ABS. There is no w/o ABS option. Am I to assume all GTs came w/ABS? If so, how if at all does this affect me? (No ABS)

[alltracman78]

For something like this you can't use the online stuff for 1sttoyotaparts, it's not even close to complete.

Part #s for the proportioning valve.
47150-20370 ST W/ABS
47150-20280 ST W/out ABS
47150-20240 GT

Originally there were 5 different proportioning valves, but Toyota superseded several part #s.

The master cylinder is also different, but only for ABS or non ABS.
I assume the ABS cylinder is larger, like it is on the 5th gens.

47201-2B090 W/out ABS
47201-2B050 W/ABS

These are for a 94 Celica specifically. Dunno for other years.

[GriffGirl]

Bowchikawowow, my stuff came today!!!


Too bad it'll probably be another two weeks or so until I get the conversion done.

[D-Man]

YAY! for rear disks!!

[GriffGirl]

Question:

Is this the proportioning valve?

[alltracman78]

Nope.
That's just a side to side [front IIRC] splitter.

[playr158]

proportioning vavle



how it ties into the system + the Front splitter "T"



This post has been edited by playr158: Jun 9, 2008 - 10:56 AM

[alltracman78]

You don't have ABS.

IIRC her "splitter" is for an ABS equipped car.

Griff, that's one thing you need to pay attention to when you try to pick one up.
If you don't have ABS you can't use an ABS prop valve.

[Batman722]

I've done the drum to disk swap on 2 cars and neither needed a different valve.
The GT and ST master cylinder are the same.
All of your ST stuff will work fine except you need (GT) the backing plate w/e brake assembly, rear disks/pads/calipers, the rubber lines, and the cables to the e brake handle (all GT stuff).

[GriffGirl]

^I have all of that stuff you listed. It was the proportioning valve that came into question; it's my understanding that it is not something that is required for the conversion, but if swapped, will increase braking efficiency. I just wanna make sure I'm thorough and cover the details. I'm kinda OCD like that.

What may happen is if I don't find a p-valve by the time I do the swap, I'll do the swap w/out it, and swap out the p-valve at another time when I do find it. If it goes that way, it'll be interesting to see if there is any difference in braking efficiency.

[alltracman78]

I've done the drum to disk swap on 2 cars and neither needed a different valve.
The GT and ST master cylinder are the same.
All of your ST stuff will work fine except you need (GT) the backing plate w/e brake assembly, rear disks/pads/calipers, the rubber lines, and the cables to the e brake handle (all GT stuff).

The GT and ST master cylinders are NOT necessarily the same.
With ABS is the same, and without ABS is the same.
If you have a GT w/out ABS and an ST w ABS the master cylinders are different.
Most likely the difference is the size of the piston, just like in the 5th gens.

Also, rear drum and disc brakes DO require different pressures to work correctly.
This is why there are different part #s for the different P valves.
It doesn't mean your brakes aren't going to work if you don't use the correct valve, but most likely they will work better if you do. Toyota didn't design them different just to spend extra money....

^I have all of that stuff you listed. It was the proportioning valve that came into question; it's my understanding that it is not something that is required for the conversion, but if swapped, will increase braking efficiency.

Exactly

[hurley97]

I believe the only difference in the master cylinders is the amount of lines that come out of it. There still could be internal differences though.

Either way, the master cylinder and proportioning valves for the ST work just fine with GT brakes. I did not change either, which could possibly be why I really didn't feel a huge difference in braking power from the ST front/drums to the GT front/rear disc setup.

The complete GT setup does look much better though, especially with bigger wheels. With the ST fronts and GT rear discs I felt like the rotors appeared to be the same size between front and rear which looked very strange to me.

This post has been edited by hurley97: Jun 16, 2008 - 8:34 PM

[GriffGirl]

Saturday's the day! (bagging the P-valve for now, just wanna get it done)

Any last minute tips/advice from anyone?

[GriffGirl]

DONE!

[BloodyStupidDave...]

DONE!

Prove it. No pictures, no step-by-step how to = didn't happen

[GriffGirl]

I'd love to, but currently my car is with the self-professed Window Tint King of Portland, having its windows tinted!

Pix likely tomorrow, Wednesday at the outside. I could take pix of the nasty bruises on my forearms that prove I've spent a quality weekend with my car, wrestling with the bumper (high beam replacement) and installing said brakes, rebuilding seized calipers (mmm, good times)... I need more iron in my diet, I think, these are some nasty bruises!

[DEATH]

You've risen another rung on the tuner ladder Griffy - congradulations. Now about that tiny motor...

[GriffGirl]

Yeah, that's what she said.

[DEATH]

I believe "pathetic" was the term used

[CelicaST_CALI]

so deaths hows that 20 mpg going

[GriffGirl]

[xs94st]

good job with the conversion griff

can't wait to see pix, as this is the summer of celica lovin

my rear drums are shot to hell, so i've been savin up that $$ n orderin stuff slowly but surely.

also, i don't mean to hijack the thread, but seein as there are a few people online, in reference to the conversion from drum to disc with abs, is it any harder than without? also, my ABS isn't functional at the moment..

[GriffGirl]

I don't actually have ABS, although I don't think it would be any harder than without ABS. I imagine you would use the sensors that are on your car already. They actually detect wheel speed, so it stands to reason that they control the application of the brake regardless of being drum or disc. However, I don't know this for a fact. It could also be that ABS on an ST only has wheel speed sensors on the front wheels, since that's where the majority of your braking load is anyway. Do GTs have wheel speed sensors on all 4 wheels? It seems like I read on here they do. . . IDK.

[Batman722]

glad you did the conversion

GTs with ABS have sensors at all 4 corners.

[GriffGirl]

DONE!

Prove it. No pictures, no step-by-step how to = didn't happen

[BloodyStupidDave...]

Awesome work, Michelle. And I know you are still in pain about that electric windows conversion but it is great to see new things being tried and such mods do put you in a different league.

I guess a little pain is the price of innovation. Hopefully with time you'll enjoy the mod and decide it was worth the effort and hopefully others will follow where you lead and find it easier with guidance than you did working blind.

Still looking for that how-to .

[alltracman78]

Awesome, glad to see you got it sorted out.

also, i don't mean to hijack the thread, but seein as there are a few people online, in reference to the conversion from drum to disc with abs, is it any harder than without? also, my ABS isn't functional at the moment..

Lines in the rear are the same either way, the difference is in the stuff up front.
The only potential problem I can see is if you need different knuckles, you'll need to make sure they're for ABS so they will hold the sensors. I'm assuming you can use your old wheel bearing assy, if not you will need ABS ones for those too.

I don't actually have ABS, although I don't think it would be any harder than without ABS. I imagine you would use the sensors that are on your car already. They actually detect wheel speed, so it stands to reason that they control the application of the brake regardless of being drum or disc. However, I don't know this for a fact. It could also be that ABS on an ST only has wheel speed sensors on the front wheels, since that's where the majority of your braking load is anyway. Do GTs have wheel speed sensors on all 4 wheels? It seems like I read on here they do. . . IDK.

All Toyota cars have 4 wheel ABS, only some early 90s trucks have 2 wheel ABS.

This post has been edited by alltracman78: Jul 13, 2008 - 5:29 PM

[GriffGirl]

Awesome, glad to see you got it sorted out.

All Toyota cars have 4 wheel ABS, only some early 90s trucks have 2 wheel ABS.

Thanks, me too! I'm totally happy with my new brakes. They did AWESOME on my road trip down to Vegas and up through California. We drove up Hwy 101 home (the coastal highway - LOTS of steep curves, mountains, etc!) and the brakes just did great. They felt totally solid. Gotta love that kind of security!

As for the ABS - makes total sense. My last car was a '92 4Runner, which is what I was basing my ABS question on originally.