GSX caliper questions

[TallestHERETIC]

I just have a few questions for the DSM community because i can't seem to figure this one out. It's a little bit long so please bear with me!

I own a 99 GSX. I have twin pot calipers in the front AND for the rear. I have the stock single pot on the rears right now. The twin rears were starting to hit the bucket so I just switch them out with my old spare singles from my NT. They are all very old, rusty, leaky and nasty looking.

I bought my car with twin pots all around and it had front rotors in the rear. It is now time to change them all. Before I proceed i just want to ask a couple questions......

Does having twin pots calipers all around really aid in braking and handling for a DSM? Should I just stick to the stock twin/single combo? Does it hurt other braking components having twins all around? What could I expect from brand new calipers if I chose either route?

 

[WES_393]

Dual piston really does improve braking force. It gives more clamping load and keeps the load more even. You won't be taking away much from the system as a whole by switching to duals in the rear. It's really just up to what you want to do. Most people rarely, if ever, max out the stock braking system. But it's nice to have that extra bit of braking force just in case.

 

[ed1380]

i've never heard of dual pots in the rear, or do you have the evo calipers?

 

[estoyaqui30]

I have never heard of two pot calipers in rear either. I have a 99 GSX as well and I have two pot fronts and single in the rear. Now, actually I was thinking about EVO 8 rears. I know that they just bolt on and I believe that they are fixed mount, so I'm thinking that they are two pot.

 

[jtmcinder]

I won't quote anybody, but there's a bit of misleading information in the above posts.

The number of pistons (or "pots") is nowhere near as important as the total area of the piston(s). It's area that determines clamping force. Extra pistons are simply a way to (a) get more area and, therefore, more force in a rectangular caliper, (b) stagger the force (which requires multiple pistons that aren't all the same size), and (c) help keep the force square to the rotor.

The ability to stop the car quickly requires that the front/rear balance in braking match the weight distribution of the car when braking. (I'm going to ignore differences in tire-grip due to camber, etc.) The label we use for the distribution of braking force is "bias." If you change the area of the piston(s) or change the effective diameter of the rotors, you change the amount of braking at that end of the car. If you change one end and not the other, you change the bias. If you move the bias away from the weight distribution, you reduce the ability of the car to stop.

DSMs, like almost all cars, especially those by Mitsu, have a bit too much front bias to start with. This is why, when people install a poorly-designed "big front brake kit," they can end up with a car that stops even less well, because they've made the bias worse. This is why you talk to someone like Todd at TCE and don't just grab some Brembos off an Evo.

(Another issue is this: for certain kinds of racing, you might want a bias that doesn't match the weight distribution. I like a lot of rear brake for rallycross, for example, since going to the handbrake doesn't work that well for me.)

Finally, note that there's a proportioning valve that reduces line pressure to the rear by a fixed % starting a certain level of force. The job of the valve is to reduce rear braking as the weight shifts forward. Whether the valve has the right break-point (or "knee") and the right reduction ratio depends on a bunch of things, including whether you have lightened the car and/or switched to larger pistons.

In any event, my point is this. If you're going to mess with your brakes, start by looking up the sizes of the OE pistons in the shop manual. For each of the new possible set-ups, know the pistons areas. If you are considering changing the size of the rotors, know the original effective disc diameter and the new effective disc diameter. Braking force is proportional to the product of piston area and disc diameter, so checking to see if you'd be moving bias forward or back is easy.

 

[PieEyedPiper]

I won't quote anybody, but there's a bit of misleading information in the above posts.

The number of pistons (or "pots") is nowhere near as important as the total area of the piston(s). It's area that determines clamping force. Extra pistons are simply a way to (a) get more area and, therefore, more force in a rectangular caliper, (b) stagger the force (which requires multiple pistons that aren't all the same size), and (c) help keep the force square to the rotor.

The ability to stop the car quickly requires that the front/rear balance in braking match the weight distribution of the car when braking. (I'm going to ignore differences in tire-grip due to camber, etc.) The label we use for the distribution of braking force is "bias." If you change the area of the piston(s) or change the effective diameter of the rotors, you change the amount of braking at that end of the car. If you change one end and not the other, you change the bias. If you move the bias away from the weight distribution, you reduce the ability of the car to stop.

DSMs, like almost all cars, especially those by Mitsu, have a bit too much front bias to start with. This is why, when people install a poorly-designed "big front brake kit," they can end up with a car that stops even less well, because they've made the bias worse. This is why you talk to someone like Todd at TCE and don't just grab some Brembos off an Evo.

(Another issue is this: for certain kinds of racing, you might want a bias that doesn't match the weight distribution. I like a lot of rear brake for rallycross, for example, since going to the handbrake doesn't work that well for me.)

Finally, note that there's a proportioning valve that reduces line pressure to the rear by a fixed % starting a certain level of force. The job of the valve is to reduce rear braking as the weight shifts forward. Whether the valve has the right break-point (or "knee") and the right reduction ratio depends on a bunch of things, including whether you have lightened the car and/or switched to larger pistons.

In any event, my point is this. If you're going to mess with your brakes, start by looking up the sizes of the OE pistons in the shop manual. For each of the new possible set-ups, know the pistons areas. If you are considering changing the size of the rotors, know the original effective disc diameter and the new effective disc diameter. Braking force is proportional to the product of piston area and disc diameter, so checking to see if you'd be moving bias forward or back is easy.

Since you and I had been discussing this topic recently, I figured I'd share a thread that I happened across. No real resolutions but I found it to be very interesting discussion.
2g Brake Bias and the Proportioning Valve - Club DSM Canada

Kinda wish that guy really did upload that spreadsheet.

 

[jtmcinder]

Someone with time should go through the shop manuals (which are all on-line if look hard enough) and get all the piston areas, effective disc radii, and prop-valve specs for all DSMs. Since people seem to like the Brembos from Evos, you can do that, too, but I, personally, am not at all impressed by these.

Actually, I have the brake data for Evo Xs in front of me:

front: pistons: 1.58 + 1.81 = 4.51 eff disc diam: 11.6
rear: piston 1.58 = 1.96 eff disc diam: 10.9

 

[TallestHERETIC]

i've never heard of dual pots in the rear, or do you have the evo calipers?

Nope. They are the GSX double pots. Basically the setup is GSX front calipers but also equipped in the rear. Everything is exactly the same.

Dual piston really does improve braking force. It gives more clamping load and keeps the load more even. You won't be taking away much from the system as a whole by switching to duals in the rear. It's really just up to what you want to do. Most people rarely, if ever, max out the stock braking system. But it's nice to have that extra bit of braking force just in case.

Good answer! I think you might be right on the money with the clamping and even load distribution. The owner before me went through quite a bit of trouble, too. Changed the hoses, rotors, wheel hubs, even the dust shield! Everything in the front is exactly like the back.

The E-brake is still fully intact and functional and fits nicely in the rotor "hat". Just needs new shoes!

Still makes me wonder why someone would go through all that work when they could have simply just bought a big brake kit all around instead?

 

[jtmcinder]

Nope. They are the GSX double pots. Basically the setup is GSX front calipers but also equipped in the rear. Everything is exactly the same.

That has to be the stupidest set-up for a front-heavy road-going car that I've ever heard of.

 

[turbosax2]

Someone with time should go through the shop manuals (which are all on-line if look hard enough) and get all the piston areas, effective disc radii, and prop-valve specs for all DSMs. Since people seem to like the Brembos from Evos, you can do that, too, but I, personally, am not at all impressed by these.

Actually, I have the brake data for Evo Xs in front of me:

front: pistons: 1.58 + 1.81 = 4.51 eff disc diam: 11.6
rear: piston 1.58 = 1.96 eff disc diam: 10.9

I'm bored so I'm working on a list of relevant specs now. Do you have access to an Evo X FSM?

 

[jtmcinder]

Evo X FSM: Evo X Service Manuals

 

[pauleyman]

According to CAPS no GSX ever came with dual piston calipers in the rear. Whatever you have I don't think it's stock.

 

[PieEyedPiper]

Nope. They are the GSX double pots. Basically the setup is GSX front calipers but also equipped in the rear. Everything is exactly the same.



Good answer! I think you might be right on the money with the clamping and even load distribution. The owner before me went through quite a bit of trouble, too. Changed the hoses, rotors, wheel hubs, even the dust shield! Everything in the front is exactly like the back.

The E-brake is still fully intact and functional and fits nicely in the rotor "hat". Just needs new shoes!

Still makes me wonder why someone would go through all that work when they could have simply just bought a big brake kit all around instead?

We've got to see pictures of these front awd calipers fitted to the rear.

 

[jtmcinder]

Have you tried googling "totaled DSM" in image mode?

 

[TallestHERETIC]

I am probrably going to get rid of all of them and just keep it stock. If i can find a nice big brake kit, I might get that. They are all in very old and crappy condition, so no use putting them back on. Sorry, I dont have pictures.

It was interesting though having twin pots all around. I originally purchased the car with them on. The previous owner did it. It MIGHT be from a Evo but there are no logos, names or anything on them. Thats why i said they are from a GSX because it is the same size and shape as the front.

Have you tried googling "totaled DSM" in image mode?

Are you usually this rude & sarcastic to other members? All your comments seem mean spirited and domineering.

 

[ed1380]

This is what evo rear brakes look like. I'm interested in seeing what and how yours are bolted on.

You must be logged in to view this image or video.

 

[pauleyman]

If i can find a nice big brake kit, I might get that.

The only question I have is why? Are you experiencing brake fade now? Are the existing brakes inadequate? have you put on different pads and or brake fluid? You can upgrade anything you like, it's your car. This is only in response to the many people I see who want to upgrade something when it was never said why they want to do so. How can we help anybody when we dont' know what problem you're trying to solve or what you're trying to do with the car?

 

[jtmcinder]

Are you usually this rude & sarcastic to other members?

When they won't take a hint, yes.

All your comments seem mean spirited and domineering.

No, mean-spirited would be saying "having the braking torque be equal at all four corners will make your front-heavy car stop faster" and domineering is something I only do on 18+ websites.