GT4 Brakes on a 6th Gen Options

[Fastbird]

After consideration I've decided to start my own thread on adapting GT4 Calipers to the 6th Gen Celica. This is a working thread, if you want to know something you don't see mentioned please ask, I have no problem giving up the info that I know or have found.

FIRST AND FOREMOST, I want to offer thanks to Stevenson a.k.a. Culpable04 for the work he's done. Between him and Preludekid on NewCelica, we'd still most likely be stranded with nothing. That said........

I'm not going to rehash how to get the caliper to fit. Culp's thread covered that quite nicely. This thread is going to be about getting it all to work, finding out what does and doesn't, ect.

First up, with some searching we know that the 7th Gen uses an amazingly similar brake design to our own. A lot of teh information I've gathered came from there. What I know right now:

You can use a max diameter rotor of 300mm without having to use a custom caliper bracket. I was originally going to make a caliper bracket and use a larger rotor, but I though, hey, let's just use what Toyota gave us. So 300mm rotors is what I"m looking for.

Sourcing the calipers is hard. I am in the process of paying approx $325 (200 pounds) for a set delivered from England. I'd suggest hitting GT4OC as there's usually a couple of part out's going on. If the caliper needs a rebuild, don't worry. I have verified that the 93-98 Supra does indeed use the same hardware, pistons, seals, and pads as the ST205, and parts are readily available. Current pricing for a basic piston rebuild will run you about $120ish so factor that in if you go to buy a set of bare calipers (was a factor in my purchase, I could have gotten bare housings for 140 pounds shipped, and $100 less, but it wasn't worth it in the end).

So.........knowing we can use 7th Gen front brakes on our cars, I used that as a starting point. The 7th gen guys are using a Mercedes rotor, though the FEBI part number won't cross reference on the site. Not a big deal though. As soon as I have calipers in hand I'm going to start snagging rotors that look like they're going to work. How am I figuring this out?

Math and measurements. Right now the information I've got says that the stock Celica GT rotor is 275 (274.9) mm diameter, with a 55mm center bore and 14.4mm bolt holes. Thickness is 28 with a height of 49.1 giving a hat size or offset of 21.1mm.

Once I get the ST205 caliper in hand I can mount and take some comparing measurements as to the new offset of the rotor pad surface centerline location between the stock rotor/caliper setup and the new one. This is going to easily be accomplished by measuring the stock rotor centerline, then mounting the ST205 caliper and finding the new centerline. Then it's going to be a matter of finding a rotor with an offset that gets close enough to either center up or work with a spacer. I know it's going to change so I'm stuck at this point right now. *EDIT 1* The outer edge to centerline for the ST205 caliper is 54mm. Found a good depiction in an OLD thread on here. I'm going to measure the knuckle edge to centerline of the stock rotor tomorrow so that should give a good basis. I'm ALSO going to measure the knuckle thickness because I'm also open to backside mounting the caliper which would open up rotor options too.

*NOTE* The ST205 rotor is 32mm thick. Most of these aftermarket rotors I'm putting on my test list are 28mm thick. I can't find extrusion specs for the caliper pistons, so rather than take a chance I'm planning on using a 2mm pad spacer on each side to prevent possible over extrusion of the caliper pistons.

Right now based on my research, there are three veyr likely candidates for this:

CLK320 2003ish model year
CL55 AMG 00-03 model year
SL500 Mid-90's (97 is what I used) model year.

All are 300mm and have varying offsets.

Then there's the bolt pattern issue. The Benz's are a 5x4.5 (114.3mm) bolt pattern and are not dual pattern. How do we correct this?? I was doing some searching yesterday morning and came across the following website, and just though it was an ingenious way to accomplish the task. You essentially make a three hole jig. Two holes with the 114.3 spacing, the third offset in the proper location for a pilot hole for the 100 spacing. I'm going to grab some junkyard rotors to play with this one, probably next week I'll start working on my jig. Here's the link for those interested: clicky

That's all I've got right now. More to come!!!

This post has been edited by Fastbird: Jun 19, 2009 - 9:43 PM

[Fastbird]

what about using the GT4 ST185 calipers and rotors Front and rear to make the conversion into an ST, I heard that the rear rotor drum will fit into our regular drums, just need to clarify this

Couldn't tell you there, haven't messed with any of the ST185 stuff.

right my brakes should be arriving in the next day or so... but I cant really do much at the moment, I might also get some knuckles just incase I screw up. then I need to get some flexi lines, 297mm front rotors (now with the front rotor sbeing smaller would it look really funny/odd with the back rotors bigger??)...oh and bigger rims so they'll actually fit, but I STILL cant decide lol

My calipers have been shipped (reportedly) and I'm getting one set of my test rotors this weekend (buddy has car with rotors I want to use and is conveniently doing a brake job on Friday).

Still stuck waiting for calipers though.