single piston vs. 4 piston calipers

stihl-066 · Feb 14, 2006

What do you guys think of the two and which are better. Cant make up my mind on one or the either. Could you give me some pros and cons on both. I did a search and nothing came up.

rbohm · Feb 14, 2006

4 piston caliper pro's;

more pressure on pads
pressure on both pads at the same time

con's;

pistons stick inconsistantly as calipers age creating abnormal pad wear.

single piston caliper pro's;

easier to replace
consistant pad wear
lighter pedal pressure

con's;

less pressure on pads
main pressure on one pad only
caliper can stick on its locating pins

overall i prefer the four piston calipers, but they do require more maintenance, and more inspection. for the street though, either works fine.

65notch · Feb 14, 2006

4 piston

RFMustangGT · Feb 15, 2006

not that it's more pressure with 4 piston but it's a more even pressure for better stopping. and the big difference is price.

Rusty67 · Feb 15, 2006

RFMustangGT said:
not that it's more pressure with 4 piston but it's a more even pressure for better stopping. and the big difference is price.

Actually, you do get more pressure with the 4 piston calipers. I can't remember where I found the formula (and I don't have it anymore) but I calculated out the pressure going through my hydrolic lines with the pistion area you get for 4 piston and single pistion calipers. There is significantly greater amount of pressure from the 4 piston calipers.

degins · Feb 15, 2006

Rusty67 said:
Actually, you do get more pressure with the 4 piston calipers. I can't remember where I found the formula (and I don't have it anymore) but I calculated out the pressure going through my hydrolic lines with the pistion area you get for 4 piston and single pistion calipers. There is significantly greater amount of pressure from the 4 piston calipers.

Given all other factors are equal, the pressure applied by the piston or pistons is a function of their cross sectional surface area, not their number. I suspect that the area is about the same for a typical OEM system regardless of the number of pistons. The typical single piston has a diameter of about 2.6". A 4 piston system has pistons about 1.3" in diameter. Do the math, they both have cross sectional surface areas of about 7 square inches.

The main advantage of a multi-piston system is it tends to spreads the applied pressure over the pad surface. On the otherhand, pads have the stout metal plate behind the friction material for a reason. This rigid plate is there to spread the applied force over the entire surface of the pad. Also, more pistons mean more moving parts, more maintanence, more chance of failure.

Rusty67 · Feb 15, 2006

There are almost as many moving parts in a single piston caliper as there are in the 4 piston calipers. Don't forget about the slide pins. A fixed caliper is superior in performance to a single piston floating caliper in every way.

Rebuilding the 4 piston caliper is fairly easy and only costs about 15 dollars in parts. Since it only needs to be done something like every 40,000 miles then whats the big deal ? Plus if you are using the stainless steel pistons they work better and have a longer service interval as it is.

I say the mild inconvience of servicing the calipers every now and again is far outwieghed by their much superior stoping power.

And if I remember correctly the 68 and up are a 10 inch rotor as opposed to the K-H brakes which use an 11 inch rotor.

THX 138 · Feb 16, 2006

haha whoops.

Force = Pressure x Area

and Pressure = Force/Area

So if you want more braking force, the extra area is linearly related.

Jester67 · Feb 16, 2006

Another vote for 4 !

Edbert · Feb 16, 2006

I aksed a similar question when I swapped my brand new 4-piston Kelsey-Hayes out for some 2-piston PBRs.

I know the performance is skewed by the size of the rotors but speaking just of calipers the old school design looks better to me, and although they were cast iron the weight is roughly equal between the two.

It seems intuitive that 4 pistons squeezing the two pads (which are very close in size between the two calipers) would give more grab AND more even pressure than having two pistons. Of course in engineering what seems intuitive is not always right. The benefit of the PBR is the floating nature, so the two pistons lose no "evenness" over the 4 since the outside pad is getting pulled in also, and not even "just as" evenly...MORE evenly. So in reality even though there are only two pistons I get the pressure applies as if there were four without the increased pedal pressure.

So, in the one piston full-floater design it actually behaves more like two pistons opposed to one another, but I'd still take 4 over two. I put a set of four-piston Wilwoods with 12.2 inch rotors on the back.

iskwezm · Feb 16, 2006

Edbert said:
I aksed a similar question when I swapped my brand new 4-piston Kelsey-Hayes out for some 2-piston PBRs.

what kit are you using to adapt the Cobra set up and how much. Also do you know where where to find the parts to rebuild the 4 piston calipers, mine are sitcking AGAIN

Rusty67 · Feb 16, 2006

To "rebuild" the calipers, the only thing you need is a new set of seals/dustboots. They come in a set for each caliper. I don't requent the local chain autoparts stores, but the autoparts stores I go to can get them in about 4 hours or less from the supply wearhouse.

Rock auto has the kit for a 66. I think the 65/66 were different then the 67. I believe the 67 had slightly larger pistons but I could be wrong. Not SURE on that tho.
https://www.rockauto.com/applet3.html

Edbert · Feb 16, 2006

iskwezm said:
what kit are you using to adapt the Cobra set up and how much. Also do you know where where to find the parts to rebuild the 4 piston calipers, mine are sitcking AGAIN

The kit I used is from "Mustang Steve", google and ebay know all about him

When you rebuild your calipers and only replace the seals and dustboots you are not really rebuilding much. The pistons and the bores are the source of almost all sticking. Of course worn out boots and sheilds are usually what CAUSES the pistons to go bad, that and water in the fluid. But once the pistons or the bores are pitted they'll need replacing and/or re-honing. If the pits are bad enough the calipers will need replacing altogether.

iskwezm · Feb 16, 2006

Rusty67 said:
To "rebuild" the calipers, the only thing you need is a new set of seals/dustboots. They come in a set for each caliper. I don't requent the local chain autoparts stores, but the autoparts stores I go to can get them in about 4 hours or less from the supply wearhouse.

Rock auto has the kit for a 66. I think the 65/66 were different then the 67. I believe the 67 had slightly larger pistons but I could be wrong. Not SURE on that tho.
https://www.rockauto.com/applet3.html

dont i need to replace the pistons too????one is rusted in the caliper, and they were supposed to be stainless last time i had them done

Rusty67 · Feb 16, 2006

If the pistons are pited or rusting then of course they need to be replaced. Rock auto sells the pistons too.

As for needing to replace the caliper you don't really have to if you know a good machine shop. You can have the caliper bore sleeved. I have heard people sleeve these with copper or some other metal but I don't really know why.

iskwezm · Feb 16, 2006

probably just gonna sell these or ?????????? Parts are gonna run about 160 bucks and still have mediocre stopping

Jester67 · Feb 16, 2006

Copper does not pit when it oxidizes

Hack · Feb 17, 2006

I would look for the calipers that have the largest area, since they provide more stopping force. It's likely that you will need to upgrade your master cylinder to one that can supply enough fluid for the larger calipers.

There is a huge difference in the caliper piston area between different OEM brake calipers. Modern cars have larger pistons. Also, believe it or not, the design of braking components has been improved in the past 30-40 years. The newer brakes work better and last longer. Newer braking designs are also easier to assemble and disassemble.

Edbert · Feb 17, 2006

The surface area of the pads has more to do with "stopping force" than piston area does, not that piston size doesn't also affect stopping force of course. Larger pistons require less pedal effort to do the same "work" but as Hack said they require more fluid to do the same work. I put a MC on mine that holds 25 cubic inches of fluid!

reenmachine · Feb 17, 2006

Number of pistons has nothing to do with pressure, "stopping power", etc. It all has to do with surface area. Not just piston surface area, but also master cylinder piston surface area (bore size). You can get single-piston calipers that apply more force to the rotors than 4-piston calipers, and vice-versa.

Good 1- or 2-piston calipers with the pistons on one side only do not apply pressure unevenly or apply more pressure to one side. For every action there is an equal and opposite reaction, and the slider mechanism efficiently allows this reaction force to be applied to the other side of the rotor.

There is one major factor that hasn't been brought up yet, and that is temperature. I'll make the disclaimer first that this really isn't a concern when choosing brakes for the street, only for the track (road course) where high temperatures are the norm. Temperature is the enemy of brake performance (in general), especially when the brake fluid gets overheated, which gives you a spongy pedal and brake fade. Think of how the heat gets to the fluid -- it is generated at the pad/rotor interface, travels through the pads, through the backing plates, through the pistons, and into the fluid. Along the way, the caliper body absorbs some of this heat and dissipates it.

Comparing two calipers, a single-piston and a four-piston, with equal total piston area, the four-piston caliper can typically dissipate heat better due to the increased piston mass and caliper housing size. The caliper is a heat sink, so bigger is better in simple terms.

Compare Willwood Superlite 4-piston calipers to Wilwood Superlite 6-piston calipers. The total piston area is about the same, giving the same braking force, all other things being equal. However, the 6-piston calipers are what you would prefer for road racing, as they can dissipate heat much better.

The things that have been said about distributing the force along the pad better are true as well, but modern calipers compensate for this well.

The stock early-model Kelsey-Hayes 4-piston caliper is actually a pretty good unit, and is comparable to the Wilwood 4-piston. The Wilwood will deal with temperature better though.

single piston vs. 4 piston calipers

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