Brake upgrade

General discussion about our beloved Tercel 4WD cars
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3A-C Power
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Post by 3A-C Power »

I got the GT-S front and rear calipers and discs last weekend and took some measurements. The rear ones will be able to be adapted to the Tercel axle using the adapter I'm working on. The Tercel axle flange also needs to be cut down about 1/4" for the disc to fit on. The front calipers actually bolt right onto the Tercel hub putting them in the right position for the larger brake disc. The disc however is the wrong offset so it will not work. I need to find a disc that's the same size but a shallower offset. What's interesting is the GT-S calipers appear to be exactly the same dimensionally, such as the distance between pins and the diameter of the piston. The disc is only about 1/2" bigger which would give you a 5% increase in braking but the real advantage is that it's a vented disc. The Tercel front disc looks like the exact same thing as the GT-S rear disc. I should be able to find a front disc that matches given that there are basically 3 variables of concern - diameter, offset and the bolt pattern (4x100mm, 54mm center) and any disc from any car will likely fit if those 3 things are right. The rear calipers will be pretty much bolt-on with the adapter plate and some modification to the steel brake line (might get away with just pliers and no tube bender) and the fronts will require a GT-S brake line because the fitting that goes into the caliper is different. The flexible lines front and rear should be changed to stainless steel braided ones at the same time anyways, because that makes such a big improvement from what I hear. Rear lines made for the AE86 Corolla GT-S should fit (haven't verified this). I assume they have used the same size of tubing and flare nut on the Tercel and Corolla brake systems. I can probably get the adapter plates made where I work, if nobody minds me going in after hours and using the shop. If that doesn't work, I will have to come up with something else that will cost money. If I can make the plates myself, it would only be about $10 for the steel. Here are the parts I bought so far

Front calipers + brackets
Front discs (bad, for r&d purposes only)
Rear calipers + brackets
Rear discs (bad, for r&d purposes only)
Proportioning valve
Rear handbrake cables

Total cost from the junkyard - about $80, and this isn't from a cheap junkyard.

The parts I foresee having to buy to finish the job:

New front discs $50
New rear discs $50
1/2" steel plate $10
Steel braided lines $40
Caliper rebuild kits $30
New pads $40

Total $230

So it adds up to about $300 Canadian funds, and that's mostly because of the new parts I'd buy to make sure that it works well right away. If anyone else would like to do this, I can provide technical support and the rear adapter.
warbstrd
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Post by warbstrd »

what about brake bias?
how does one go about doing that?
improper brake balance can make a complete mess out of even the best components.
3A-C Power
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Post by 3A-C Power »

That is why I'm using the proportioning valve out of the same car as the front and rear brakes. If it doesn't end up being right, there's always the option of adding an adjustable brake bias valve.
GTSSportCoupe
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Post by GTSSportCoupe »

I look forward to hearing how it goes. Keep us posted.

BTW, 3AC-Power, your email seems to be full. I've tried sending you a couple emails and have had them bounce back. Or maybe you just put my email addy in your spam blocker :lol: :lol: .
Current:
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Guest
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Post by Guest »

It was full but I erased the junk folder so it should be okay now. I had someone at the parts store who I'm on good terms with show me a few brake rotors and try to help me find one that fits but it doesn't seem likely. The Corolla and MR2 rotors are all the same size and offset. Another idea I have is to use the front GT-S rotors on the rear and then use some even bigger ones on the front, and that way the caliper would be mounted further out so I could make an adapter bracket that goes out and to the side. And the brakes would be better.

I found out at the parts store that the newer Tercel discs are the same diameter as the old ones except they are vented instead of solid. So these discs would make an easy upgrade for an old Tercel.
looking-to-buy
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Post by looking-to-buy »

All this talk about bigger/better brakes, and I'm not seeing anything about a bigger/better vacuum booster and M/C. The only reason I even popped in was, I found a very nice 85 4dr, for $400, and have thought about several upgrades for it, brakes included. I've been wondering if Supra or Cressida brakes would fit
warbstrd
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Post by warbstrd »

went to club4ag in the tech ref section and ( my home away from this home) and the one thing they said that a lot of people are missing is stainless steel braided lines. are you going to use them. one guy said he put ss braided lines on his clutch cable (hydrolic clutch) and it was a difference between night and day...after the 4age is in ill do a complete brake overhaul and use ss braided lines. not going after the bigger brakes.
T Pie
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Post by T Pie »

Won't you have to use the master cylinder out of the GT-S? It seems to me that a disc/drum m/c won't have enough volume to the rear half to operate the calipers. The volume question isn't answered by the proportioning valve. I agree that the GT-S valve should have the correct bias, since you are using the matching calipers and same diameter rotor.
3A-C Power
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Post by 3A-C Power »

I don't know what you're saying about the volume. With disc brakes the pads are always in contact with the disc, they don't retract, so the only fluid that actually goes into the caliper when the brakes are applied is only accounted for by the deflection in the brake parts. Unless for some reason the rear calipers do retract. The Tercel's brake system is a diagonal one, meaning that each piston in the master cylinder operates one front and one rear brake, on opposite sides of the car. This necessitates both piston and bore diameters to be the same. I don't know if the Corolla GT-S system is the same, if it isn't there may be different bore diameters for the front and rear brakes, further complicating matters. The master cylinders are way different where they mount to the brake booster, but if it is really for the better I can get the GT-S one mounted somehow.
3A-C Power
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Post by 3A-C Power »

I found an extensive database of rotor dimensions at Brembo's website, and that there are some BMW and Volkswagen rotors with acceptable dimensions to be used on the Tercel with a Corolla GT-S caliper and bracket. The only thing wrong is the wheel centre is too big, but centering rings can easily be made such as those that you use to centre aftermarket rims with a bigger hole. It would not even be necessary if the lugs centre it well enough. The trick was finding one with a shallow offset, but with the whole world of brake rotors at my fingertips, a couple did turn up. So there will be no more fussing with the front caliper mounting, I only have to grab some rotors and brake lines and put it together. I have the rear assembly drawn up in Autocad and have arrived at a tentative adapter plate design, but there may be some changes. In the interest of eliminating bending forces in the axle flange, which it was not designed for being a drum brake axle, I may choose a rear rotor with a deeper offset which moves the braking surface directly around the axle flange, thus eliminating bending on the flange. This would also add considerable weight and make the bracket more complex. I want to determine how significant the bending force would be and decide based on that. My gut feeling is that it will not be significant, so I will stick to my current design. In order to only use one piece of plate steel, this design involves cutting part of the mounting boss off of the caliper which is okay because that part was only there to add offset for the original application, which I need to remove. I should be able to use the machine shop at work fairly soon, especially since I'm about to get promoted from a temp labourer to a mechanical engineer.
GTSSportCoupe
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Post by GTSSportCoupe »

Awesome work! And congrats on your promotion!
Current:
91 LJ78 Landcruiser EX5
95 A32 Maxima SE
Former:
87 AW11 MR2 Smallport 4AGZE
93 Taurus SHO ATX
86 AL25 SR5 6spd 4wd
90 AE92 GTS
82 KP61 SR5
85 MX73
87 AE86 GTS 4AGZE
85 AE86 GTS
83 AL21
Fingers
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Post by Fingers »

I would think the force at the rear discs would not be sufficient enough to warrant the weight and complexity of a different bracket. The majority of your braking power will always come from the front. Unless you are going full out with motor swap and all that is.

I have know a few people who had put discs on the back of std tercels without swapping out prop. valves with no problems. They have seen improved braking and less fade with just the conversion to discs. I wouldn't recommend this, but I thought I would just put it out there as a bit of reference.
86 Tercel Wagon 4WD, 4AC, 3sp Auto. (2) 89 Corolla GT-S, 4AGE. 87 Corolla GT-S, 4AGE, SOLD! 68 Mustang Fastback, 351c.i.=>429c.i., 3 Speed Manual, 10 Year Plan. 66 Mustang GT350, 289c.i., 4 Speed Manual, SOLD!

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3A-C Power
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Post by 3A-C Power »

Thanks for the tip. I may try just the calipers and discs and see how the balance is with that. You don't really need more braking power with more engine power because there is still the same peak adhesion value of the tire and most brakes can already lock the wheel if you step on them hard enough. I think it's more about control and how well the brakes put up with heavy use.
Fingers
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Post by Fingers »

I was just commenting on bending forces in relation to speed, speed man. If I had the money to do the engine swap, damn, I'd have to throw down some speed, just to see all the muffler-boys out there freak!
86 Tercel Wagon 4WD, 4AC, 3sp Auto. (2) 89 Corolla GT-S, 4AGE. 87 Corolla GT-S, 4AGE, SOLD! 68 Mustang Fastback, 351c.i.=>429c.i., 3 Speed Manual, 10 Year Plan. 66 Mustang GT350, 289c.i., 4 Speed Manual, SOLD!

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tercel4wdrules
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Post by tercel4wdrules »

:D :lol: :) B)


Gentlemen start your engines! Vroom, Vroom! Ha now for some real speed.
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