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 Post subject: Rear Brakes upgrade
PostPosted: Thu Jun 06, 2013 1:00 pm 
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Group N

Joined: Wed Dec 10, 2008 5:23 pm
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Location: London
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Looking to upgrade my front system but I was thinking.
What have people done with the rears? Has anyone tried fitting the front 4 pots inc disk in the rear?


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 Post subject: Re: Rear Brakes upgrade
PostPosted: Thu Jun 06, 2013 1:18 pm 
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If you want more braking force at the back of the car, replace the brake bias / max pressure reducer limiter .

I think for the 185 and 205 it tops out at 60 to 80 bar in the rear brake lines.

On another much lighter car on the rear axle. I upgraded from 45 bar to 85 bar. Only on very steep down hill would the back end lock before the front in wet conditions. But in snow or ice then it would be a different story. As the gt4 has about a 60/40 split front to rear, you can up the back end braking force to some extent.

Ideally you could put an adjustable bias valve in the rear lines.

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 Post subject: Re: Rear Brakes upgrade
PostPosted: Thu Jun 06, 2013 2:25 pm 
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Group N

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any pictures on how you replaced the bias?


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 Post subject: Re: Rear Brakes upgrade
PostPosted: Thu Jun 06, 2013 6:56 pm 
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Joined: Wed Jul 13, 2005 12:06 am
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Location: Perth, Western Australia
Car Model: ST205
I am running OEM rear calipers on my track toy with bespoke Carbotech pads and adjustable front/rear brake bias.

Interesting info regarding the line pressures Darryl. I am intending to monitor the bias and am currently looking for suitable sensors.

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1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
1994 Toyota Celica GT-Four Special GT 590bhp @ 1.8bar
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 Post subject: Re: Rear Brakes upgrade
PostPosted: Thu Jun 06, 2013 7:08 pm 
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Group N
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yellowchinaman wrote:
any pictures on how you replaced the bias?


I replaced them on a vw scirocco when it was two screwing in direct to the brake master cylinder.

On the gt4 its a single unit doing both brakes lines to the rear together. On abs cars, ( well 185 ) its mounted alongside the abs unit. I would expect 205 to be the same. If no abs, then its mounted on the firewall between engine bay and foot well. Just above the steering rack.

I have a 205 complete rear end on my 185 , so still use the Toyota bias valve. Chris ( nibbles ) had said he ran a short while without valve, then I think as part of a hydraulic handbrake intended to fit a adjustable bias valve. Not sure if he has yet.

The bgb lists the brake pressures in one of them, its easier to find one from another car with a higher limit if you want to do it easily.

I will go take a photo of the valve in question. And upload in another post.
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 Post subject: Re: Rear Brakes upgrade
PostPosted: Thu Jun 06, 2013 7:10 pm 
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 Post subject: Re: Rear Brakes upgrade
PostPosted: Thu Jun 06, 2013 7:23 pm 
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the toyota bias / limitter valve has 5 lines on it..... its used as a joiner to the front left wheel as well, but this outlet is not pressure limited.

so two lines in, two lines out to rear axle. and one extra for the front wheel. this same valve is the one fitted by the ABS unit on 185's and I'm fairly sure i've seen them on 205's in the same front location by the ABS unit.

it might be a case of some brake pipe plumbing, to get the front no longer using the standard bias valve. but if you do it, then you will unleash the full power that can be obtained from the stock rear disk setup.

on my old VW, i was able ( with no limit valve fitted in testing ) to lock the rear end first even at 70+mph speeds.... so go careful, if you remove it fully.... unless you can handle a rear end going sidewards very very quickly, dont test on location someone else might be around.
I did my first testing in a field.... then to a empty industrial estate, then finally on the road.
due to the power, i had to fit a bias valve.... I think mine came from a vauxhaul van in the end.

i've not looked any further into this valve on my 185, as I have larger ( 205 ) setup on the rear, and although I have a TT front disk setup on my car. i've got a similar front to rear disk size as stock.

stock 185, has 278mm front and 285 rear IIRC. now i'm 312mm front and 315mm rear. this gives braking that is front biased. when I first had a 205 rear end and stock ( smaller disks ) on the front, I noticed a better rear end braking.... and a quick spin in a field confirmed on downhill slopes I could lock the rear end by the footbrake alone.

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 Post subject: Re: Rear Brakes upgrade
PostPosted: Fri Jun 07, 2013 11:14 am 
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Group N

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This is very interesting. :)


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 Post subject: Re: Rear Brakes upgrade
PostPosted: Fri Jun 07, 2013 12:22 pm 
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Joined: Thu Jul 14, 2005 12:44 pm
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The pressure regulator/joining block is on the firewall on a 205 below the inlet manifold passenger side


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 Post subject: Re: Rear Brakes upgrade
PostPosted: Fri Jun 07, 2013 7:17 pm 
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If you have ABS, I believe the pressure limiting is done up at the ABS pump end and the fitting on the bulkhead is just a joiner, although it looks near identical.

On my 185 I removed the pressure limiter altogether which left it with a bit much rear bias as I have 205 rear setup and standard 185 fronts. It made for great rally style late braking into corners, but has since glazed the rear pads as the standard ones couldn't cope with the extra work.

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 Post subject: Re: Rear Brakes upgrade
PostPosted: Fri Jun 21, 2013 2:00 am 
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Joined: Fri Jan 11, 2008 11:59 pm
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Why not use the bias valve from a 2 litre Toyota Estate with rear drum brakes like Carina E. This will give you more rear braking effort.

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98 Celica GT4 ST205
Full forged rebuild with Wiesco pistons, Crower rods, mildly ported head, 264/272 HKS cams, FMIC, PFC Pro, GT35 BB turbo, turbo back 3" system.
Currently running 1.6bar/520+bhp


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 Post subject: Re: Rear Brakes upgrade
PostPosted: Fri Jun 21, 2013 4:38 pm 
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Very interesting stuff chaps. Nice info and reduces my concerns about the impact of fitting ST205 rear brake setup I have whilst I figure out a fianl front setup on the NON-ABS RC.

In practice the braking setup will not cause any issues of course as the car hasn't moved further than 5 feet in 5 years ;-)

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 Post subject: Re: Rear Brakes upgrade
PostPosted: Sat Jun 22, 2013 12:16 pm 
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Diceman wrote:
Very interesting stuff chaps. Nice info and reduces my concerns about the impact of fitting ST205 rear brake setup I have whilst I figure out a fianl front setup on the NON-ABS RC.

In practice the braking setup will not cause any issues of course as the car hasn't moved further than 5 feet in 5 years ;-)



I ran my cs with a 205 brake setup on larger UK disks ( which the rc also has )
at the front and its a good balance, but as I wanted more all round braking force I made my own brackets to use TT discs. All going fine, just recently put a new set of discs on. So done many miles with no issues.

Sent from my HTC One X using Tapatalk 2

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 Post subject: Re: Rear Brakes upgrade
PostPosted: Sat Jun 22, 2013 9:24 pm 
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jeffrosie6 wrote:
Why not use the bias valve from a 2 litre Toyota Estate with rear drum brakes like Carina E. This will give you more rear braking effort.



Reason I say this is because I converted a CarinaE GLi to G6 Celica brakes including the rears which were drums. You can deffinately feel the extra braking effort at the rear without it being excessive. Can feel the rears scrubbing more than they used to before the conversion.

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98 Celica GT4 ST205
Full forged rebuild with Wiesco pistons, Crower rods, mildly ported head, 264/272 HKS cams, FMIC, PFC Pro, GT35 BB turbo, turbo back 3" system.
Currently running 1.6bar/520+bhp


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 Post subject: Re: Rear Brakes upgrade
PostPosted: Wed Nov 02, 2016 5:10 pm 
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Joined: Tue May 23, 2006 8:06 pm
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Location: Knoxville, TN USA
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Does anyone know the flow rate of the stock intercooler pump? From my research going with a larger heat exchanger and faster flowing pump improves efficiency.

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