View Full Version : bias proportioning and caliper upgrad

08-03-2011, 04:23 AM
just tried to do some research but can't find any direct answers to this. First off I swapped my drums to disc, but I knew from the start my proportioning would be jacked up and would like to fix this. What do I need to do to fix this? Will my original master cylinder work on with the disc set up? I saw MC info but just bore size in which they are all the same. And I haven't really looked yet, but where would I locate the proportioning valve? Are there any other valves to worry about? I know how some vehicles use a metering valve to compensate for drums. So what do I do about the proportioning valve? Just remove it or gut it and would an adjustable one be preferred?

Also, I was reading about caliper upgrades but was pretty vague, though I did find it useful to find out ST165 brakes came with dual piston front calipers, so do these bolt up to a 5th gen bracket with no issues? Any down side to swapping these in?

08-05-2011, 01:15 AM
anyone have any info?

08-05-2011, 01:36 AM
when i upgraded my brake system everything bolted up just fine, i was going to use the all trac calipers but sense auto parts store are dumb when it comes to our cars i didnt get very far and went with gt-s calipers but from what i found that the st165 calipers bolt up to the 90-91 gt-s bracket with problems, the brake master cylender is bigger on the 5th gen all trac the other 5th gens but im not sure about the 4th gen all trac. hope that helps a little bit

08-05-2011, 03:16 AM
sure does! I tried to look and look about the twin piston calipers from the ST165 but didn't find a perfectly strait answer. If you don't mind me asking, where did you find your info on it?

08-05-2011, 04:17 PM
I couldn't find the thread on here, but it does a good job of listing out the differences with our rotors. IIRC, ST185s have smaller rotors than the ST184, so upgrading to those calipers would require you to get the rotors as well, plus maybe the torque plate, but there's no guarantee that all of that will just bolt up to the steering knuckle. I'm not sure about the ST165 brake stuff.

As for your proportioning valve, it is located on the firewall just about in the center of it. You'll see several hydraulic lines leading to it. It is described here in the BGB:
From this info, you can see that the proportioning valve is mostly the same whether you have drums or discs, but the ST185 has higher pressures overall and about 30% more pressure to the rear calipers. However, it looks reasonable that you could run dual piston calipers with the stock ST184 proportioning valve.

In conclusion, I think you can rest easy on your proportioning and focus on doing more research on your brakes if you want to. I just completed a brake overhaul on my car and just kept it all stock with DOT4 brake fluid and am very pleased with my car's stopping ability.

Hope this helps.

08-05-2011, 05:35 PM
ST185 didn't have smaller rotors than the ST184 -- particularly the 1990 and 1991 5SFE-equipped vehicles.

The ST184 initially came with 255mm front rotors and, if so optioned, 269 mm rears, moving to 277 mm front rotors with the mid-model revision. The ST185 had 277 mm front rotors throughout the production, though it received the dual-piston calipers. Master cylinders seemed only to vary with ABS (1" diametre) versus not (15/16") rather than braking system. However, couldn't find the diametre for the 4AFE-equipped ST, which used 238 mm front rotors.

08-05-2011, 05:44 PM
What I'm mostly looking at is the ST165 dual piston calipers, as long as they bolt
up then I will use them.

The problem is with my proportiong is it going from
drum to disc, though there are lots of articles on doing the swap I can't seem to
find anyone who has done much about the proportioning, which I can tell you is
now out of whack.

08-05-2011, 08:15 PM
Yeah, I knew there was a difference with the rotors, but I got it a little backwards. Thanks Galcobar for the correction.

Why do you think your proportioning is out of whack? Is it just because you went from drums to discs or are actually experiencing issues with your brakes? I ask because the BGB doesn't distinguish between drums and discs when giving pressure readings for the valve. If the valve itself works, you shouldn't need to adjust it from what I'm seeing in the BGB. But it looks pretty easy to test the valve as long as you have the gauges.

Also, if no one has written about needing to adjust/replace the proportioning, it may be because it doesn't need adjusting/replacing. I'm definitely not as knowledgeable on this topic as a lot of people here, but if it needed to be corrected, it seems like it would have become part of the typical advice when drum to disc converting is brought up. But it could just be an oversight up to this point.

08-05-2011, 08:55 PM
it's an instant difference, my braking performance went down, but its common
when doing this type of swap. Main reason is shoes typically need to travel more
than pads do. Normally on a drum set up the front brakes will be delayed slightly
to compensate. It's odd that theres no further information about this subject,
when doing this on my mustang there is tons of info on performing a disc swap
and how to alter the bias to best performance.

Either way, I can handle altering this, was just looking for a little more info in
case someone knew a little better about it, the only thing I need to know is about
the calipers for sure

08-05-2011, 09:55 PM
sure does! I tried to look and look about the twin piston calipers from the ST165 but didn't find a perfectly strait answer. If you don't mind me asking, where did you find your info on it?

i used this site to look up parts, u will need the mounting brackets as well

08-06-2011, 01:28 AM
hmm I just did a little research and found an interesting thread. Apparently a guy measured the pistons on an ST165 caliper and calculations came up as that the ST184 calipers have a bit more overall force to them. They measured 38mm, anyone have any argument to this?

08-06-2011, 03:27 PM
I don't have allot of experience with Celicas, but it has always been my understanding that the proportioning valve is different between drum and disc brakes. The proportioning valve provides the function that it's name implies - it provides proportional pressure to each wheels caliper or cylinder. Disc brake calipers require far more pressure than drum brake wheel cylinders require, and this is provided for in the proportioning valve which has different size orifices to control the pressure.

In fact, if I go to ToyotaDIY, choose a car that had both rear disc and drum options (in this case a 192 Celica GT), I find the following entry for the proportioning valve:

47150‑16040 ST184..CP, LB 1 $238.65
47150‑20130 ST184..GT 1 $238.65
47150‑32060 ST184..CP, LB, W(*66) 1 $275.73

Note the CP, LB (coupe, liftback) is for disc brake and the W(*66) is for ABS (which also has a different master cylinder), and the "plain" ST184 is for drums.

So - the part numbers for the proportioning valve are different for disc and drum brakes.

08-07-2011, 10:12 PM
usually thats normal, maybe I'll just cut out the valve and install an adjustable, seems like it'd prove to be the best route, theres no way I'm paying those prices lol

08-07-2011, 10:39 PM
Those are toyota dealer list prices - Lithia Toyota would be less.

You could get one a a junkyard for next to nothing - any 91-93 GT or GTS with rear disks would do.

If you use the proportioning valve from a drum brake car you would have little braking from your rear disc brakes. It is like - in the past - many cars did not have a power booster on the brake master cylinder - to use disc brakes on such a system you would literally need to stand on the brake pedal to stop the thing.

I believe the proportioning valve also compensates for the different lengths of the brake lines.

Best bet is to just get the right part from a junkyard - I would think it would be cheapest alternative in the long run. It will bolt right on with the same brake lines.

08-08-2011, 08:05 PM
What Klapa said. You need to use the p-valve from a rear-disced Celica. The proportioning valve is different disc vs drum. Brakes are your safety equipment get it done.


08-09-2011, 01:48 AM
I know its different lol but I just never see anyone mention how to do it, all other articles just say hey slap the rears on! My big question is is this the only valve the celicas have in their drum system?

08-09-2011, 09:02 AM
Well, you certainly don't need to do any cutting to the proportioning valve off. The brake hoses just screw into it. Without ABS, it is located on the firewall, but with ABS it looks like it could be located somewhere else, perhaps on the ABS actuator itself.

This may seem stubborn on my part, but I don't see any proof that you need to change the proportioning valve when you swap from drums to disc pads. I know you've said that other cars have a different set up, but that doesn't seem to be the case with a 5th gen Celica. I can see that there are different proportioning valves that Toyota offers for sale, but when I look at what the pressures are supposed to be at the valve according to the BGB, there is no differentiation between disc and drum brakes for the 5S. Also, the only platform that has substantially higher pressures at the rear brakes is the ST185.

I'm not trying to be difficult, and please don't think I'm just trying to prove a point or something, I just want to understand our brakes systems and our cars in general. I only bring this point up again because the information that I have that is for a 5th gen Toyota Celica, the BGB, tells me different than what you're saying. So if there's something I'm missing, I want to be corrected so that I understand this better. Or, if you want to tell me to go to hell and you're replacing the valve anyways, that's fine too :) Thanks for your patience.

08-09-2011, 05:37 PM
This may seem stubborn on my part, but I don't see any proof that you need to change the proportioning valve when you swap from drums to disc pads.

Well - suit yourself - I'ds be interested to know how it goes - a drim brake proportioning valve with disc brakes.

I would certainly think that at least a little "proof" lies in the fact that the two valves have different part numbers.

And - like Terracar said - this is your brakes! - why risk anything for a bolt-on replacement that would probably cost $5 at a junkyard?

08-09-2011, 08:33 PM
I agree that there are different proportioning valves for the different platforms and that they function a little different from platform to platform, but from the information that we have, it appears that whether you have ABS or not and drum brakes or disc brakes, only the ST185 has a substantially different proportioning valve than the other cars. Again, I'm going from what the BGB says when you are checking the proportioning valve.

However, I'm not going to argue with you if you do go to a junk yard and grab the proportioning valve off a car and stick it on yours. My argument is that you'll just be replacing the part that's already on your car with a part that does the same thing with the same results. But if it gives you peace of mind to go through that, then by all means do so.

08-09-2011, 10:24 PM
You're just going to be down on rear braking power with the drum valve - better than having too much rear brake power and potentially swapping ends!

Modern vehicles with ABS have the proportioning control built into the ABS unit, plus the rears can't just lock up first and spin you out.

Best way to balance the brakes (on a non ABS car) is to use an adjustable proportioning valve (wilwood makes a nice dial type one) installed in the rear line, and do hard braking until the rears don't lock up first (you can tell as the car really wants to swap ends when they lock up before the fronts). You should do this on a dry road/hot day, as with less traction there is less overall braking, less weight transfer and thus even less chance the rears will lock up first.

08-10-2011, 12:56 AM
The thing is as I said shoes typically require a little more distance to move than pads do per system. They may use the same pressure, but they still use different compensation. Has anyone looked into difference in master cylinders? I'll have to take a look at that. My mustang was so easy on this subject because Ford basically made the braking system to be converted to disc so there are a TON of write ups.

I already swapped to disc, and yes you can drive it this way. However if an emergency situation comes up you don't want to then find out your brakes don't have enough performance. I actually did have this happen when a jackass tried brake checking me, luckily I stopped, but it was close. Long story short I knew right away it was an insurance fraud attempt and had my brakes been up to par it wouldn't have been close

08-10-2011, 04:15 PM
Master cylinders seemed only to vary with ABS (1" diametre) versus not (15/16") rather than braking system. However, couldn't find the diametre for the 4AFE-equipped ST, which used 238 mm front rotors.

08-10-2011, 05:35 PM
thanks grifter, I overlooked it