Making caliper adapters

[ARRX7]

Hi, all. I’m planning on making caliper adapters for my race car. I wanted to know if there were any set procedures for tackling such a project, or is it simply done using the good ole’ trial and error method. Any ideas, formulas, etc, that could get me started would be greatly appreciated.

~M

[Al Weyman]

When I made mine I dummed them up out of a bit of 10mm ply first then when the calipers would mount properly to these cut the real ones out of plate using these as a pattern. Worked out good.

[GORDON STREETER]

Same as AL really but I used windscreen lexan (as I had some laying about ) If the final article isn't quite right you can always washer it one way or the other but make sure the pads are parallel to the discs otherwise the pads will jam up in the calipers.

[ARRX7]

Thanks, guys. I had a feeling I'd had to resort to trial and error. I'm making the bracket out of 6061 aluminum block. I think that should be strong enough. Curious, what type of cars did you do your conversions to? I ask this to gauge the weight (and therefore) added stress the pick-up points will see. I have an 88' Mazda RX7 Turbo and I'm adding 14.5" rotors. Overkill, maybe, alright most likely, but the whole set-up (rotors, calipers) are lighter than what I have now and my track wheel/tire set-up will clear this adaptation.

~M

[Al Weyman]

Nice car! Mine are 2nd gen and 3rd gen Camaros and the 2nd gen has massive Wilwood GN calipers so no worries there with the conversion. I used 1/4 plate steel on the 2nd gen alround and the same on the front of the 3rd gen car with alloy on the rears, I fitted discs all round on both cars with Wilwoods alround on the 3rd gen and Brembos on the back of the 2nd gen.

[ARRX7]

Hopefully it will be nice sooner rather than later. I guess I should have figured out that the two cars in your sig were yours. Sorry, I was having a bit of a Bush moment! Thanks again!
~Mike

[Al Weyman]

No problem.

[johnny yuma]

AARX Are u sure about the Aluminium.The calipers will end up NOT PARALLEL to the rotors if anything goes pear shaped,especially on the front.Is the small weight advantage worth it? Steel also allows a threaded adapter plate on one side at least for maximum accuracy and rigidity.Who needs little things to go wrong ?

[Al Weyman]

The rear aluminium ones made up on my black car I must confess were made by a better fabricator then me who can weld the stuff but on the steel ones I made I did indeed weld spacers on them to get the offset correct. Also another thing I was going to suggest, start the project with some stiff card to get into the ball park as its easier to work with that and a pair of scissors then go over to the ply template and jig saw (or as Gordon said acrillic material which is also a good idea).

Funny enough and long after I fabricated mine I noticed the ones that have been fabricated on the Penske prepared IROC I have in the garage were coincidently almost identical to my steel ones so if its good enough for them......

[SidewaysFeltham]

If the objective is to provide far greater retardation and unsprung weight (within limits) is not a huge consideration and you don't have access to a stress engineer, then I'd opt for the safe route and over-design, because if a caliper twists out of line through heat expansion, whatever, that's going to be pretty dramatic! As it is if stress cracks the mounting points and the plate shears.

Just my gut instinct.

[Tony C]

Originally Posted by ARRX7

Thanks, guys. I had a feeling I'd had to resort to trial and error. I'm making the bracket out of 6061 aluminum block. I think that should be strong enough. Curious, what type of cars did you do your conversions to? I ask this to gauge the weight (and therefore) added stress the pick-up points will see. I have an 88' Mazda RX7 Turbo and I'm adding 14.5" rotors. Overkill, maybe, alright most likely, but the whole set-up (rotors, calipers) are lighter than what I have now and my track wheel/tire set-up will clear this adaptation.

~M

Trial and error is the fastest way if you dont already have drawings for your uprights and calipers, use anything for the template, I have used card and plywood as templates.

The material for the mount will depend on the thickness and position of the fixing points. I have used 6061 T6 25mm thick (1 inch) on cars similar to yours but the uprights were quite large so was only moving the caliper mounts about 1 inch. For small movements I have used steel, anything from 5mm (with lots of siffening) to 10mm solid plate (no stiffening) with out dramas.

Without consulting an engineer it will be trial and error but given that we are talking brakes just make sure it is strong, so as to not break. bending and twisting will cause weird retardation and uneven pad wear, but at least it wont throw you into a wall.

[ARRX7]

Johnny, I was looking to use aluminum because the original adapter was made out of aluminum. Sounds like you're thinking that that is not a good idea?

Sideways, when you discuss over-engineering, what is is you had in mind? I'm assuming you're talking about materials, thickness, etc?

Tony, I think I'm going to use your suggestion and utilize wood and card for my templates as I've got the tools to easily detail the shape of the wood. All measurements will be at least as thick as the original adapters' measurements. That adapter was from a Cadillac Escalade!!!! It was dealing with 6800lbs, or 3,084.43kg for my metric friends, as opposed to 2600lbs, or 1179.34 for my RX7 (by the way, I work in metric-so much easier, LOL).

~M

[johnny yuma]

The adapter I have is 6.5mm thick steel,the hubside mounting holes are threaded,the caliper side holes not.The increase in radius is the critical factor,my adapters mount to the previous drum- brake backing plate holes which are about 80mm inside the caliper holes when mounted so there is may be more twist potential than yours.If you are going from 290mm to 350mm diameter rotors thats 60mm,halve that 30mm roughly less twist only maybe surface toughness issues ??where bolt-up.

[SidewaysFeltham]

Originally Posted by ARRX7

Sideways, when you discuss over-engineering, what is is you had in mind? I'm assuming you're talking about materials, thickness, etc?

Yep! Stress engineers (Like Colin Chapman), tend to engineer down to the smallest, lightest part that will take out the loads put through it.

Which was why Chapman's cars often broke!

In your case, I would beef-up the parts in order to create robust rigidity, and freedom from twisting, bending and cracking around the mount holes.

A little more weight: plus a whole lot more safety margin seems a fair compromise, to me!

[boyracer]

Just to stir up the hornets nest. Look at the loads imposed on a caliper bracket. Are they really that severe ? They make aluminum disc bells, so heat and warping aren't really that big an issue. Stripping loads between aluminum and steel are not that much different if the correct thickness is used and you're really only looking for a structural friction grip connection between the caliper and the bracket, so as long as the aluminum will take the bolt tension, with appropriate factors for fatigue of course, it's really not that bad. Do the calcs on pulling the bolt sideways thru an appropriate thickness aluminum bracket and you'll find you need a bulldozer, to pull it out of there.
Bending, twisting in the bracket is going to be minimal, by the time the disc gets enough run-out to cause issues you're going to be well and truly fed up with it as a driver.

If you're starting from scratch and welding straight to a hub, the added fatigue strength from mild steel is pretty much unbeatable (note though the allowables for a welded steel structure are far lower than a bolted connection), but if you're adapting something on I certainly wouldn't be against aluminium brackets, given the right thinking goes into it's design.

As for working out it's location, CAD has always worked for me.

[SidewaysFeltham]

so as long as the aluminum will take the bolt tension

Ummm, remembering that ally rims will pull out if the stud nuts or set bolts are tightened past the recommmended torque (which is never much above 40 foot lbs) since the compression action of the high tensile steel bolt/stud crystalises the contact area and that this is high spec alloy which has been heat treated and that since circa 90% of the car's whole weight is loaded through the front brakes when they are vigorously applied (Load Transfer), the caliper mounting has to resist the kinetic energy applied through the rotor as it turns, which would be quite significant to me.

The type of ally, thickness and mounting bolt spacing are all fairly critical.

Of course, one could take a Brunnel type approach and estimate a safety factor of ten!

[Al Weyman]

I would guess that most of the loads are on the bolts holding the brackets and calipers in place and they would be subject more to a shear load than a pull force which can take way more punishment. I'm no engineer but used to survey and design curtain walling installations and any component or bracket in shear was rated far stonger than one in pull.

[GORDON STREETER]

If you are not talking about a massive weight saving then I would always go for steel over alloy on something important. I had some lightweight front hubs on my racer and I was checking it out before taking a women round Brands Hatch for her 50th birthday. I saw a "funny" mark on the n/s hub and tapped it with a hammer. The front flange fell off with the wheel studs ! OK it had had a hard life of rumble strips etc, but seeing that put me off certain lightweight parts, and two up round Paddock bend doesn't bear thinking about !

[GordonG]

Mr streeter

That did bear repeating. Better safe than sorry...

G

[GORDON STREETER]

Come on you mods get rid of it

[johnny yuma]

The forces are not huge,as they say it's not the brakes that stop the car it's the tyres.If you can hit the brakes hard at 240 klix and slow for a 60 k hairpin in say 4 seconds the work is spread over time of decelerating say a 1000 kg mass.However the fatigue building up over many thousands of hard brake applications with evil shock loadings when you lock a brake makes me shy of aluminium..you know..that stuff they make beer cans and dodgy garden chairs from.

[Chris Y]

Removed your duplicate, Gordon

[SidewaysFeltham]

In similar vein to Gordon, same place too, I was roped in to marshall at Brands, quite some years ago, working the post half way up towards what we used to call Druid's bend (The hairpin ooop the hill from Paddock).

A Formula 750 (Austin 7/ Reliant) was rushing oooop the hill, when suddenly there was a loud and very expensive sounding BANG!

And an ally conrod exited stage left from the block and lay steaming on the Reslo, together with bits of cast iron block, oil and other stuff.

Ally's great if you have heat treatment facilities plus the engineering skills to pretty accurately calc the stress take out in the first place: and the time and wallet to replace stuff very regularly and pretty often.

So, as I said much earlier on, unless unsprung weight is critical, go the safe way!

I can't actually see where you are going, Johnny Y?? The tyres are connected to the wheels: and the wheels fit on the hubs; and the given rotational load is taken out in the case of retardation via the calipers acting on the rotor. Tyres don't reduce the given load!

If the car weighs -e.g.- one tonne: and weight transfer on braking means the front brakes are stopping 90% of One Tonne, then if the suspension is well set up that's 90% X 1K Kils :2 = 450 Kilos of actual load/wheel/brake rotor.

Yes, the effectiveness of good brakes and good tyre footprint to surface contact, means that the actual braking time is less; but the loading is a constant.

[ARRX7]

Wow! I didn't think I'd start a thread with so much staying power. Thanks for the advice and keep it coming.

[SidewaysFeltham]

BTW:

I wanted to edit my last post, but by the time I returned, the "Edit" facility had evaporated!

Since engineering dynamics are constant, if, due to superior tyres, suspension etc, the speed reduction time is reduced and since energy is never ever lost (The Law of Entropy), work done, ergs e.g., is transmuted into heat.

Therefore, the quicker the timescale to reduce the speed by the same given amount, then the greater the heat generated: which has to be dissapated.

Thus bigger disks/calipers which promote greater retardation for a given load will create more heat. Which can lead to work-hardening and distortion over time of all braking components. Not the least being the mounting plates.