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

[AnaXyd]

Great information in addition to Culp's thread. Is the ST brakes the same as the GT brakes?

[Fastbird]

Great information in addition to Culp's thread. Is the ST brakes the same as the GT brakes?

Same knuckle as the GT, different caliper and rotor size, but once everything's off the same stuff I'm getting geared up will go right on the ST.

[Batman722]

here's an option also
so to add this up

GT4 calipers $325
rebuild $120
new pads $80
shim/carrier kit $50
SS braided lines (GT lines too short) $80
5-10mm spacers $100
rotors...$100 ? (hopefully)

EEK ! all together is $855...if you can get the rotors that cheap but maybe your wheels have a great offset and won't need spacers...
but tough for many to swallow.

I would love to have GT-Four brakes on my car but for that much $ I would rather get a Willwood BBK for $750 or just go ahead and get the TRD Scion BBK for about 1K (which also fits on 7th gens no prob).

I'm glad you and Stevenson are doing this, it's great info for everyone.

[Fastbird]

here's an option also
so to add this up

GT4 calipers $325
rebuild $120
new pads $80
shim/carrier kit $50
SS braided lines (GT lines too short) $80
5-10mm spacers $100
rotors...$100 ? (hopefully)

EEK ! all together is $855...if you can get the rotors that cheap but maybe your wheels have a great offset and won't need spacers...
but tough for many to swallow.

I would love to have GT-Four brakes on my car but for that much $ I would rather get a Willwood BBK for $750 or just go ahead and get the TRD Scion BBK for about 1K (which also fits on 7th gens no prob).

I'm glad you and Stevenson are doing this, it's great info for everyone.

The caliper rebuild is only $100 if you need pistons. A simple seal kit is about $10 for both sides, and everything else (shim kit, clips, bars, ect) is only about $40 or so. Lines are going to run a tad obviously. It's not going to be cheap, but it's still half the cost of all but the cheapest of legit brake kits out there.

[AnaXyd]

Why do we need spacers after this rebuild? Im sorry if its explained already. Thank you for answering by the way.. This swap is exactly what I need to do to get my car legal with the 3S-GTE.

The knuckles/hus will hold the power, btw? Have anyone checked this?

[vincent_doggy]

Why do we need spacers after this rebuild? Im sorry if its explained already. Thank you for answering by the way.. This swap is exactly what I need to do to get my car legal with the 3S-GTE.

The knuckles/hus will hold the power, btw? Have anyone checked this?

If your rims have 35 offset or lower, say 32 or even 30, u can clear the thick thick caliper, other than those offsets sure u need spacer, that make you have more clearance.

This post has been edited by vincent_doggy: Jun 20, 2009 - 2:35 PM

[azian_advanced]

you may need the spacers (depending on you wheel width and offset) so that the rims clear the calipers.
i would be more concerned with the caliper mounts breaking before the knuckles. but i'm sure the metal won't break as the brakes are only as good as the tires. so one would lose traction before damaging the caliper or the knuckle.

[AnaXyd]

Ah, thanks! I got this now. So, I cant run these calipers and rotors with my 14's winterwheels anymore! I got some big 18's at summer, so I think they got enough offset to clear the calipers.

Just to be sure: Bigger offset = more clearance?

I really dont like the thought of the hub breaking, or the caliper mount at the hub.. A loose caliper is not what I want when I need to to a emergency break!

[azian_advanced]

bigger offset = less clearance

[Fastbird]

Quick update: Heading to the junkyard tomorrow to grab a kunckle/hub/stock brake setup off of a 6gc that's there. Word is they just got a fresh one in and I should be able to get to it. Hopefully I'll come home with something and be able to get rolling.

GT4 calipers should be here by weeks end also.

[Rusty]

hey azian_advanced nice helpful pic you have there

so any wheel bigger than 16" GT4 6-spoke rim will fit << with the correct offset


so with the front's pretty much set for going in with a few minor adjustments... what about the rear brakes? drum brake sizes for the handbrake and cable length etc?? I'm kind of worried about how well they will fit in?

And lastly should any work be done the the GT4 brakes when you get them?

[Batman722]

what about the rear brakes? drum brake sizes for the handbrake and cable length etc?? I'm kind of worried about how well they will fit in?

the rears bolt right up with the rear 205 rotors. You do need a 5.5mm spacer between the caliper and hub and the ebrake lines work fine.

Lubu did the 205 front and rears a while back here.

[Fastbird]

what about the rear brakes? drum brake sizes for the handbrake and cable length etc?? I'm kind of worried about how well they will fit in?

the rears bolt right up with the rear 205 rotors. You do need a 5.5mm spacer between the caliper and hub and the ebrake lines work fine.

Lubu did the 205 front and rears a while back here.

No sh*t??????? The rears just bolt up? Dang.......... I wasn't expecting that one.

This is going to take a slightly different turn. I've taken some initial measurements and my goal now is to make a caliper bracket and space the caliper out in order to fit in a 12.7" or 13" rotor (323mm or 330mm). More to come on this. I'm going to post some sketches about the offsets and spacing up later once I get them done.

I DID get a hub/knuckle today though. Junkyard had two new 96's in there, a GT and an ST. Sadly the Yota's were in the back of the yard and that knuckle loaded up is HEAVY when carrying it a half mile.

LOTS more to follow.

[Fastbird]

Ok, so my chicken scratch isn't really worth posting here. Here's the measurements I've got:

Knuckle thickness = 10mm
Frontside of knuckle to stock caliper centerline = 30mm
Backside of knuckle to stock caliper centerline = 40mm

GT4 Caliper mounting backside to centerline = 54mm

Knuckle thickness is important as the caliper can be mounted front or backside.

I plan to work up proper specs for a 300mm rotor AND a 323 or 330mm rotor with a custom cut spacer.

For the 300mm rotors, I need to see how thick the bolt flange on the caliper is first, but if it's what I'm anticipating it to be I may have found an array of rotors that would nearly be a direct bolt on once redrilled. More to come here, I'm kind of stuck without having the GT4 calipers in hand.

For the larger calipers with the bracket, I absolutely have to know the bolt flange thickness, so I'm REALLY stuck there.

More to come.

[Culpable04]

here is a hint

4runner has the same calipers, and they come in 2 versions.

standard = ~ 319 mm rotors ( with 16" wheels )
Sport ~ 338 mm rotors ( with 17" wheels )

I assume the calipers used with the 319mm rotors, have a bracket the same length as ST205s, the Sport ones are 9 mm taller ( on the bracket ) to so that means those bolted on a celica would accommodate a 320 mm rotor.

4runner 2003-2006 sport package (17 wheels with this brake set-up )

also when planning on bigger rotors for the front, don't forget about the back, the brake force has to remain at the same ratio ( or close enough ) to OEM or your tail may come and say hi in a event of hard breaking, so bigger rear brakes and maybe an adjustable proportioning valve may be needed. if using ST205 size rotors front and rear just swap to a ST205 brake proportioning valve if easy to find, but as far as I've found so far, the number ( ratio of braking force front : back ) seems to be the same even with our non performance brake systems.

[AnaXyd]

So what you are saying, is that the brake ratio is not perfect when we swap the both front and rear calipers to a ST/GT?

[Fastbird]

So what you are saying, is that the brake ratio is not perfect when we swap the both front and rear calipers to a ST/GT?

Both would most likely be fine. Just the fronts you may or may not be where you need to be.

Nothing new going on. Waiting on calipers to show up before I can get cracking. Using some numbers I've found in various places has given me enough to work off of but I want to get a caliper in hand and double check the measurements before really digging into it and modding rotors.

[Rusty]

when are your GT4 brakes arriving, mine should be with me early next week, and just slowly start gathering the parts.

[RavenAegis45]

Awesome Post my Friend