I've been working on my brakes and noticed that the 88 brakes (actually the earlier ones too) could be lightened significantly if somebody made aluminum bridges. Is this feasible? I know people show up all the time claiming to have access to CNC machinery wanting to know if there are any product ideas/needs. I think this would be a great thing to have. Thoughts?

Intresting thought. Let me know where you get on this! How the cars coming up there? We'll have to get together sometime!
Matt J

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MRJ
My Black 87GT For Sale

[This message has been edited by MRJ (edited 07-22-2004).]

quote Originally posted by fierogt88: I've been working on my brakes and noticed that the 88 brakes (actually the earlier ones too) could be lightened significantly if somebody made aluminum bridges. Is this feasible? I know people show up all the time claiming to have access to CNC machinery wanting to know if there are any product ideas/needs. I think this would be a great thing to have. Thoughts?

What are you talking about? The calipers are already aluminum, and the term bridge refers to the part of the caliper that goes over the rotor and supports the outboard pad...

Kurt

The bridge is steel. Only the part that actually contains the piston is aluminum. Thus the reasoning behind my suggestion. Aluminum caliper bridges would be a great development.

See https://www.fiero.nl/forum/Forum2/HTML/049325.html

The bridge (at least on the 88's) is not steel. A magnet will not stick to it. (edit) Not true, see below.

[This message has been edited by spark1 (edited 07-25-2004).]

THE BRIDGES ARE STEEL.

My magnet attaches just fine. You need a new magnet.

Got a new magnet and it does stick, to both the piston housing and bridge piece. Looks like the calipers are 100% cast iron. Odd thing is that there is no rust on any of the four bridge pieces but all the piston housings are covered with rust.

Just my 2 cents, but we are talking about a savings of maybe a couple pounds overall. Really not worth it imo. Also, the braking system is not exactly the first place I'd look to start trimming weight.

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The brakes and suspension are the third best places on a car to start trimming weight. Why? They are unsprung weight.

The second best place to start trimming weight is weight that is both unsprung and rotating: wheels, brake rotors and driveline components.

The best place to start trimming weight is engine speed rotating components: flywheel and engine internals.

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'87 Fiero GT: Low, Sleek, Fast, and Loud
'90 Pontiac 6000 SE AWD: None of the Above

Luck, Fate and Destiny are words used by those who lack the courage to define their own future

You guys do know what happends when you bolt aluminum to steel... That they have different expansion rates. Anyone that has to deal with Al heads on an Iron block (Commonly refered to as a bi metal engine) should be familliar with how it actaully causes wear to the head gasket and can work the head bolts loose no matter who perfectly they are torqued durring installation. It is fairly common for bimetal engines to eat head gaskets every few years. Way more often for some. Which is why Federal Mogul (Owners of FelPro) and others have developed products expecially for this application. Like head gaskets that have teflon cladding to allow the head to slip as it grows.

Can it be done? Probably.
Is it a safe thing to do? Not sure. I can tell you that if you don't get this right, you could have major problems.

How fast could a problem show up? No way to predict. Maybe fast maybe never.
Cars that see stop and go heavy traffic or racing may show problems sooner as the system will get more and larger range thermal cycles than a grocery gettter. Any car could show problems.

You could also have corrosion problems where the steel and aluminum meet. Just like many aluminum wheels suffer where they contact iron hub/brake parts. Or Al calipers that commonly weld the steel bleeders into the holes.

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The only thing George Orwell got wrong was the year.

The Ogre's Fiero Cave (It's also at the top of every forum page...)

Excellent points, Ogre, but....

The stock calipers on my 1988 are composed of aluminum piston housings and steel bridges, no ifs-ands-or-buts, absolutely, positively, without a shadow of a doubt, period. Not only would aluminum bridges lighten my calipers significantly (I'm guessing half the weight, approximately), this could alleviate all the problems that you outlined. Apparently all those potential problems were ignored by the factory, or were less of an issue than the cost of aluminum bridges. Regardless, I would still like aluminum bridges to match my aluminum piston housings. Your points just lend even more of a reason for me to see these developed.

So, who does CNC aluminum parts? Archie? WCF? Darrel Morse?

quote Originally posted by fierogt88:

I still have no idea as to where this aluminum would be, but... I don't trust aluminum to high temperature high stress areas. Aluminum gets very weak very quickly when exposed to high temperatures. Remember that the brakes slow down a 2500+lb car, and turn the energy into heat. Here's just an example with yield strength... Aluminum is down to 50% by 500*F. You say "oh, but it's rapid heating, with lots of cool down time"... okay, forget the 1/2 hour exposure, if you heat it 100*F/sec, you'll only gain ~10-20% of your Fty. Moral of the story: aluminum is evil. (except in the right places)

forgot to mention ultimate strength follows roughly the same curve.

[This message has been edited by ryan.hess (edited 07-25-2004).]

I'll be sure to inform Pontiac and Wilwood immediately. Geez WTF was I thinking? I bet all those corvette owners need to know about this too... wouldn't want one of their calipers to blow up on them unexpectedly...

quote Originally posted by fierogt88: I'll be sure to inform Pontiac and Wilwood immediately. Geez WTF was I thinking? I bet all those corvette owners need to know about this too... wouldn't want one of their calipers to blow up on them unexpectedly...

You do that Like I said, I have no idea where you're talking about... And I'm no metallurgist, so FWIW.

The issue here is retrofitting the '88 calipers with aluminum bridges to save unsprung weight. What I see being most important is the design. Sure there are all aluminum calipers out there, like Wilwood and others, but they were designed specifically to work in those applications. That design process took into account testing and thermal modeling, among other processes. A DIY aluminum bridge design won't be validated except through actual use, and what happens if it fails because of some unforseen design issue? I'm sure if there are injuries involved that the lawyers will have brake design engineers looking at those aluminum bridges, and the owner's insurance company will send them a letter saying in effect, "you modified your brakes, we are leaving you to yourself on this one".

To me, the benefits of that miniscule reduction of unsprung weight for a street driven car is just not worth the risk unless I had an independant engineering analysis to validate the design.

JazzMan

... Which is why I'm not contacting a CNC machinist myself. I think it's a great idea for a product, but it does need some engineering and design time. It's just a caliper bridge after all. Some tests with presses combined with heat should knock out the prelims, and then could be driven on a test car or two that sees rigorous use - aka autocross. This sounds like a job for WCF...

quote Originally posted by ryan.hess:Here's just an example with yield strength... Aluminum is down to 50% by 500*F. You say "oh, but it's rapid heating, with lots of cool down time"... okay, forget the 1/2 hour exposure, if you heat it 100*F/sec, you'll only gain ~10-20% of your Fty. Moral of the story: aluminum is evil. (except in the right places)

Ryan... The calipers generally don't run as hot as you think. Brake pads are purposly designed to be fairly lousy at transmitting heat. They want all the heat to go into the rotor, or as much as they can get. The rotor can unload more heat faster even with solid rotors.

If/when you get the caliper to 500F, failing aluminum is most likely the least of your problems. The brake fluid in most cars will have boiled long before that. All but the freshest glycol based fluid, even DOT 5.1, will have a boiling point well below 500F due to water contamination. (See the brake fluid article in my cave.) DOT 3 fluid will boil below 300F with only a few percent water in it.

quote Originally posted by theogre: Ryan... The calipers generally don't run as hot as you think.

Thanks for the information. I did not know that. I just assumed everything down there heated up to 500 on a regular basis. I can't say I've felt the caliper after a good braking run, so I had no first hand experience either. So maybe 200* should be the working temperature to strive for, and make the _(insert whatever you're making here)_ that much stronger...

Just do a Corvette C4 brake conversion. Aluminum is not as strong as the cast iron that is used on the outer half of the 88 caliper. So if you just made a new outer half from aluminum to replace the cast iron piece, there would not be enough serface aria on the mating surfaces to suport an aluminum outer piece. You would need more bolts that spred the load more evenly (there are only two bolts that hold the outer half to the inner half) and a much thicker outer piece to be as strong as the cast iron piece. The aluminum piece is made to mate with the cast iron that is much stronger than aluminum, so the outer dimentions of the cast iron is small compared to an aluminum piece that is the same stenght. In short you would have to reinvent the entire caliper if you want to get rid of the cast iron outer half.
I would just make an adapter kit to put C4 calipers on it. That way you can get rebuilds for them too when something goes wrong with them.

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Rickady88GT QuadCam 3.5 V6

Another thing to consider is the rigidity of the caliper.

The original engineers may have used iron bridges for the stiffness, rather than staying away from aluminum for cost.

The Young's modulus of iron/steel is much higher than that of all but the most exotic (and expen$ive) aluminum alloys. That means that for a given force a strcuture made of steel will deform less than the exact same shape in aluminum. In brake terms, this contributes to firmer pedal feel and better pedal feedback.

Even high end calipers like Wilwoods are still held together with high tensile steel bolts for exactly this reason. Monoblock calipers, unless they are made of very exotic alloys, will provide pedal feel inferior to a two piece caliper held together with an appropriate assortment of steel bolts.

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'87 Fiero GT: Low, Sleek, Fast, and Loud
'90 Pontiac 6000 SE AWD: None of the Above

Luck, Fate and Destiny are words used by those who lack the courage to define their own future

OK, I figured out what this bridge crap is about (I think) I was trying to figure out what part of the caliper you thought was iron, having just looked at 84-87 calipers I thought you were on crack. After recalling that the 88 calipers were like AWD 6000 calipers, I see what you are talking about ( I happen to have an AWD), and IMO, it's not worth it, and it wouldn't be a "great development". It would save not a whole lot of weight, less weight than could be saved, by say, getting a set of aftermarket wheels.
Additionally, everything these guys have been saying about aluminum being weaker and not trusting it is somewhat unfounded. Using an aluminum caliper to stop a 2500+ pound car is not that "scary". For example, take a look at the Ford Freestar van, it has a GVW of near 5000 pounds, and it uses aluminum calipers. In most brake designs, the caliper does not even take the torque generated by the brake assembly, the knuckle does, so they will never break from being "twisted off" The other concern using aluminum is breaking from the hydraulic pressure applied to the caliper, and I can't think of a single caliper made by any manufacturer (including us) aluminum or not that has been tested to burst below 5000-6000 PSI. Also Ogre, having a different expansion rate is really irrelevant in this application, because the body itself would does not contain fluid passages through to a set of opposed pistons like some calipers (such as some AP) do. The tolerances for the slides and such are great enough that using aluminum doesn't really cause a problem.

Kurt