Dual piston Big Brake upgrade?

[DSM1.8T]

Has any one done the factory brake upgrade? I want to do it but is it cheaper to buy all the parts seperate, like at autozone, or just order the kit? If anyone has it let me know how much you spent. Thanks

 

[Kinetic Boost]

Well I'm in the middle of doing my factory big brake upgrade and What I did was just find the best deals I could. For example, I found my calipers for 100 on the trader and then I bought my rotors through RRe which are like 190 for both. I'm still going to get stainless steal brake lines and also a good performance orieanted brake pad.

 

[BOMEX DSM]

Mind as well get the BAER kit for 815 u get everything and 13inch drilled slotted rotors not stockers.

AWD calipers: 150
Metal Master Pads: 100
Brake Lines: 150
Rotors: 200

U already at 600 mind as well get the baer kit highly recommend.

 

[Bullitt]

I'm in the process of completing purchase of a big brake upgrade (1g 1 piston to 2g 2 piston factory upgrade), and the best prices i found were private sales. I did not however price out buying each part individually. Generally parts sold in sets are discounted over what the normal combined price is, so i dont think it'd be worth buying each individual part.

 

[Omega]

BOMEX DSM has a good point but he forgot to mention that you need at least 17" wheels for the BAER kit.

 

[steve]

Last time I bought dual piston calipers w/brackets at the junk yard they were $30 each. The rebuild kits were like $20 each in case you find a torn boot or seal.
Keep in mind that most autopart stores will gladly sell you calipers but they don't stock the brackets you need to make them work.

Steve

 

[Todd TCE]

I'll ask the 'stupid' question on this;

What's the big deal on this 'upgrade' over what you have now?

I have looked at the specs on the caliper and rotor. The caliper is a twin piston set up with a slightly larger rotor I believe. The piston area is nearly identical to what you have now. The rotor is how much larger?

Benefits; a bit more mass for thermal capacity and better pressure distribution on the pad.

What am I missing?

 

[my97mitsGSX]

more pistons means that the force is spread out more on the caliper i believe..

bigger rotors and pads means that you have more surface area to brake with.. bigger rotors also means heat can disipate better

stainless steel lines are good because rubber lines expand when hot.. so you get a solid feel with SS lines

 

[Todd TCE]

I asked this somewhat tongue-in-cheek knowing much the answers I'd get.

But for the information minded I'll work up some data for you that shows the increase is not as much as you may think it is.

Now calm down all of you who have done this; I'm not saying its a poor choice. I simply think it gets more hype than fact.

I had to dig for some numbers on the calipers and have them. What I don't have is the rotor diameters exact for the 'stock' and 'big' set ups. I think they are 10.25 and 10.75 so if someone can confirm I'll work up some informative numbers for you.


What really makes this work is not the 'bigger' or 'two piston' set up, it's the fact that the pad is has its load more evenly placed on the rotor. i.e. its not a banana under pressure of a single piston caliper.

The factory spec sheet only list 'effective' diameter and without going into what that is, I'd rather work from the actualy diameter of each.

Anyone wish to share those numbers?

 

[steve]

From the '91 and '93 service manuals

Single piston rotor 256mm
Dual piston AWD rotor 276mm
Single piston NA and FWD bore 53.9mm
Single piston AWD bore 60.3mm
Dual piston AWD bore 41.3mm x2
I don't have data on the pad size differences. I can't find my old calipers and pads in the garage.

NA non-abs master cyl bore 22.2mm
NA abs master cyl bore 23.8mm
Turbo master cyl 25.4mm

All AWD's have larger rear pistons too. 30.1 vs 34.9mm

It will be interesting to see what numbers you come up with but there was a sigificant improvement in braking since switching. Perhaps that has more to do with how poorly the single piston caliper performed than how great the dual piston setup is.

Steve

 

[Todd TCE]

Intersting numbers. I was looking at the 2G parts on my list at the shop. Not the same.


Single piston rotor 10.06
Dual piston AWD rotor 10.85

Single piston NA and FWD bore 2.118
Single piston AWD bore 2.37
Dual piston AWD bore 1.623

NA non-abs master cyl bore 7/8
NA abs master cyl bore 15/16
Turbo master cyl 1.0


I can see where you can really do some good and really do some bad here. Example; a larger rotor and the twin piston on a 7/8 bore set up will really over bias the front. Or, putting a 1" mc on a FWD wil take you and your best bud to stop the car!

What do you want to compare?

 

[steve]

Originally posted by Todd TCE
Intersting numbers. I was looking at the 2G parts on my list at the shop. Not the same.

According to my 2G manuals:
Non-ABS FWD's get 23.8 (15/16") MC and 25.4 (1") on the ABS and AWD.
All the FWD cars get the same 60.3 (2 3/8" caliper bore as the 1G AWD and I believe a 256mm rotor.
The 2G AWD has the same caliper and rotor as the 93 & 94 1G AWD.
All 2G's with rear disks have a 34.9mm (1 3/8) rear caliper piston.

Steve

 

[Todd TCE]

Sounds about right.
But you left out the twin pot 'premium' model with the 2 x 1 11/16 set up.

 

[Todd TCE]

Ok, because it's a healthy discussion;

Assuming some basic controls; leg input pressure, front pad Cf, rear rotor dia, rear piston area and rear pad Cf, as well as all being calculated in 'static' form here's what you get.

The controls:
Leg 70lbs
Cf .40
Rear Rotor 9.0
Rear piston 1.5
Rear Cf .40


The single piston on a 10.06 rotor nets 82.0%
The twin piston on the 10.85 rotor nets 82.3%

Yes, I think the total % is too high but the difference between the two is the issue. It changes the same if we go to a 10" rear rotor for example.

Now, if you change the MC you retain the same %. Only you ALSO chang the feel and leg requirements as well as the operating pressures.



So,what's all the fuss on the 'big brakes' over the single? Sorry guys, the total brake torque is the same. But man I know it's different! I agree. I also understand that if you do the 'big change' you are also doing new pads and likely SS hoses as well. And maybe the bigger MC.

Let's suppose this is what you do; the hoses firm up the feel, the pads appy more bite and the MC requires more leg. As a general rule a 10% increase in piston area in the MC will require a 10% increase in leg required. This is the 'better feel' you get.

But I know it stops better! Perhaps, but it's more due to pad choice as well as the ability to modulate the pedal better with the lines and bigger MC.

What's the difference in the part and why do it? The larger caliper has twin pistons. This in turn places a better load on the pad. The pad in turn bites the rotor better. And if you check the pads (I could not) and find the pad is taller and narrower this also adds to the 'pad radial height' and nets a bit more 'effective diameter' as the book calls it. All good things.

Now lastly, if you do the pads, the hoses and the MC you get better feel, firmer pedal and more bite. And a bit more RADIUS to work from. And perhaps a bit more mass, but not a lot.

Still all in all it's not a bod deal. However it does not create more stopping power all things being the same.