ST to GT brake conversion Options

[bryanf]

I finally got my brake conversion done and wanted to share some details. Brakes must be one of the Celica ST's weakest points. Or one of its best opportunities for improvement.

I got Celica GT rear backing plates with parking brake cables, a proportioning valve, plus four rear caliper bolts from ebay seller rude-day. The transaction went well and I would definitely buy from him again. The prop valve isn't essential but it's a good idea.

After receiving these parts I disassembled, cleaned, lubricated, and reassembled the parking brake assemblies.



You can use new or used calipers and rotors. I decided to buy all new ones.

I got four new Brembo rotors. Here they are masked off and ready to paint:



The GT front rotor will bolt right up to the ST suspension. The disc just barely touches the rear brake shield and it's easy to bend it back slightly by hand.



Painted discs:



GT front brake rotors are much bigger than ST rotors. I've gone to significant expense and effort to do similar brake conversions on Datsun 510s and 240Zs over the years, so it always surprises me when someone says this conversion is not worthwhile. To me, since it's an easy bolt-on, it's irresistable.



First step in the rear brake installation is to disconnect the parking brake cables. The connection is inside the tunnel above the exhaust system. Make sure to release the hand brake. Remove the heat shield which is held in with four bolts, then disconnect the front ends of the cables. Working space was a little bit tight but I did not need to move the exhaust system.



If your brake drums don't come off easily, find a couple of 8mm bolts which will thread into the holes in the drums. Run them down evenly until the drum comes off. With the drum removed, you can see the bolts that hold the spindle and backing plate onto the hub.



Spindle removed:



There are thin O-rings beneath the spindle. Be sure to keep track of them and reinstall them during reassembly. Replace them if they are brittle or damaged.

Drum brake backing plate removed:



Disc backing plate installed and held temporarily by one bolt while I checked the fit of the hand brake cables:



Spindle, rotor and caliper installed:



You'll need the proper brake hoses for the rear discs; the drum brake hoses won't work.

Front brakes installed. These brake hoses are interchangeable.



Car on scales. I recently installed Megan coilovers and wanted to check corner weights.



Weights with full tank of fuel and no occupants. With no adjustment of coilovers at all. Not bad.



This post has been edited by bryanf: Mar 29, 2022 - 9:53 PM

[jesse09]

Great write up. Looks clean.

Recently did mine as well. Didn't use a brake prop valve though. Can you shed some light on the results of using one?

[CelicaDICE]

Excellent write up! Now you can swap to the Avalon front twin piston calipers.

[bryanf]

Great write up. Looks clean.

Recently did mine as well. Didn't use a brake prop valve though. Can you shed some light on the results of using one?

Sorry I don't have any specifics. Just know that the ST vs. GT prop valve is different and so to have the front-to-rear balance that Toyota intended with the GT brakes, one should use the GT valve. But how much different they are and how important it is, I don't know.

[BonzaiCelica]

Only the GT4 has a different part # for that valve. All other chassis are the same I'm 95% sure.

He should of done it from get go.

Toyota museum says 94 GT lift back with ABS is 2,560 lbs. I'm amazed that the side to side weight distribution is so identical

[jesse09]

Great write up. Looks clean.

Recently did mine as well. Didn't use a brake prop valve though. Can you shed some light on the results of using one?

Sorry I don't have any specifics. Just know that the ST vs. GT prop valve is different and so to have the front-to-rear balance that Toyota intended with the GT brakes, one should use the GT valve. But how much different they are and how important it is, I don't know.

Ah ok. It's probably not that different but I'm sure it can't hurt. Thanks

[BonzaiCelica]

trying to install a proportion valve isn't hard but the testing is what takes time and will eat away at your tires. as stated by tigawood. its been discussed before

This post has been edited by BonzaiCelica: Feb 13, 2016 - 12:04 AM

[bryanf]

Got this from a testing spec in a Celica manual. It seems to indicate that the difference between the various proportioning valves is pretty significant.



At low pressures, balance is 50-50, but at higher pressures, rear proportion is reduced by varying amounts. So in everyday driving performance will be the same but with hard braking the difference matters. Somewhat...

1 kg/sq. cm. == 14.2 lb/sq.in. (psi)

This post has been edited by bryanf: Mar 29, 2022 - 9:59 PM

[HectortheRican]

Could you find it in your heart to do a quick write up on how to disassemble/reassemble the shoe mechanism in the backing plates? I'm about to do this swap myself!

[bryanf]

Could you find it in your heart to do a quick write up on how to disassemble/reassemble the shoe mechanism in the backing plates? I'm about to do this swap myself!

http://bgbonline.celicatech.com/94_6gmanua...ke%20system.pdf

Hope that helps. It's easy to do.

[msk59]

Many thanks Bryanf for this post. I almost have everything except the rear calipers as they are seized and need new rotors, which caused me to stop the swap. Now I need to find GT proportioning valve. Do you by any chance know the part number for the rear rotors? My car is 96 ST hatchback

This post has been edited by msk59: Feb 18, 2016 - 4:31 PM

[bryanf]

Brembo rotor part numbers:

Front: W0133-1818688 (25425)
Rear: W0133-1833479 (25162)

Toyota part numbers:

Front : 43512-20630
Rear: 42431-20330

[HectortheRican]

Could you find it in your heart to do a quick write up on how to disassemble/reassemble the shoe mechanism in the backing plates? I'm about to do this swap myself!

http://bgbonline.celicatech.com/94_6gmanua...ke%20system.pdf

Hope that helps. It's easy to do.

It even has all the torque values! Thanks so much, this'll be a big help. Great write up, too!

[msk59]

Thank You for the part numbers. Much appreciated.

[bryanf]

The prop valves have different markings on the back:



This post has been edited by bryanf: Mar 29, 2022 - 10:00 PM

[Tigawoods]

it would make sense that the GT and ST had different proportioning values. Do they have different part numbers?

[bryanf]

I should have mentioned these are non-ABS parts.

[HectortheRican]

it would make sense that the GT and ST had different proportioning values. Do they have different part numbers?

I'll check when I get home - I have a GT prop valve sitting in a box for when I change my brakes out.

[richee3]

Different part numbers. GT is 47150-20240 and ST is 47150-20280.

[Bitter]

The difference is because disc and drum rear brakes need different pressures but honestly you'd probably be OK reusing your ST valve. It's not a huge difference, I think drum rear apply a little less pressure out back so the rear disc brakes would apply a little less hard.