C5 Brakes on 88, worth it?

[draven]

Ok, while waiting on the C4 ZR1 steering rack inner tie rod extensions to be machined, and also scored a set of 'well made' Ryan/Held tubular front control arms that solve my longer shock length requirement, I turned my attention to the C5 brakes to wrap up the front so I can move onto the XTS engine swap.

I also scored a set of wilwood FDL calipers, 88 adapters (very easy to copy), and 13" rotors for the front in the same deal as the control arms.. but I'm not thrilled about the 'race-only' status of these calipers, i.e. no dust seals, rattling, squealing for a part time daily driver.

Before I look at copying the adapters and purchasing nicer wilwood calipers I want to exhaust looking at adapting the C5 brake setup. I have a full set on hand and I've got a working demo of the rear C5 parking brake working on the 88 rear hub with a plexiglass bracket... however, I'm still looking at the oem C5 caliper brackets and how to adapt them to the 88 hub/knuckle. The 88 caliper holes are 3" on center and the C5 brackets are roughly 5.09" on center, however the damn C5 bracket has a cross bar between the mounting holes that prevent a standard offset caliper adapter from being made.

OEM C5 Caliper brackets



The only way I can see getting these to work with an 88 knuckle is to cut the cross bar between the mounting holes, offset/clock the bracket to straddle the 88 mounting holes like most other adapter setups, and then tying it all together with a custom bracket. So effectively, the C5 mounting holes would be tied together just not in OEM form.

Safe? Stupid? Not worth the risk?

Thoughts?

[The Dark Side of Will]

The Fiero likes a "square" brake setup with the same rotors and calipers at all four corners. The Corvette rear brakes are TINY compared to the fronts and thus don't make a good swap onto a Fiero. I looked at C6 Z51 rear rotors, as they're the same diameter as C5 fronts, but they don't have enough annulus (radial dimension of the friction surface) to work with the C5 (or 4th gen F-body) front calipers.

I'm putting together a fabbed knuckle that will use either BMW E30 or Chrysler drum-in-hat P-brakes. These drums are small enough that they can fit inside reasonably sized rotors in order to use the same hardware at all four corners. I'm expecting to use 2 piece rotors, if that wasn't clear from the foregoing.

[draven]

I agree the rear C5 brake is paltry while the front is quite stout...and would 'require' a proportioning solution to reduce the front braking forces even more so than the 88 does already.

I should have included that I was planning on running a set of front calipers on the rear with rear ebrake capable rotors. But from what you said about swept area that's not possible... If not, I'll pull my C5 ebrake solution, go with a front caliper in the rear with front rotor and then run an Ipsco rear parking brake caliper in tandem.

Any thoughts on cutting the caliper brackets?

Any data on the fabbed rear knuckles would be welcome..

[The Dark Side of Will]

The '88 benefits from an adjustable prop valve on the *REAR* circuit.

[draven]

The '88 benefits from an adjustable prop valve on the *REAR* circuit.

Yes, however, the only fiero I've driven with a 'Balanced' C5 setup was an 86GT that had the rear circuit proportioning valve spring removed and a wilwood prop valve on the front circuit because the C5 brakes are so overly biased toward the front given their disparity between the front and rear OEM setup, not ideal for a mid-engine obviously.

The solution I'm gunning for would be to run front C5 calipers all the way around, with a 1 1/8" master cylinder for the larger ~19.25 sq inches of such a piston area (if my math is correct) and a screw in proportioning valve for the stock distribution block.

[ericjon262]

I have C5 fronts on all four corners of my 85. It does have an 88 rear cradle. I imagine it will stop very fast, but I haven't had a chance to prove them yet.

[draven]

I have C5 fronts on all four corners of my 85. It does have an 88 rear cradle. I imagine it will stop very fast, but I haven't had a chance to prove them yet.

What did you use for rear rotors, c5 front rotors? If so, what was your ebrake solution?

Mind sharing your caliper to knuckle attachment solution for the C5 calipers on the 88 rear knuckle.

Thanks in advance

[ericjon262]

Currently using a brick for parking brake... Lol. I am planning on trying to adapt a drum in hat setup, or maybe a spot caliper. I'll have to find my bracket dimensions, it was a pretty simple design.

[ericjon262]

int he attached ZIP file are several different cad formats of the bracket I used. mine were also powdercoated before install. I'll try and dig up come installed pictures sometime today.

also, yes, they are currently C5 front rotors and calipers. I have other more long term plans I may execute to allow for an actual parking brake, but I'm not quite there yet. I can also email you my cad files if they don't work on here. they were drawn using Onshape.

brake dimensions.jpg (56.09 KiB) Viewed 2324 times

C5 front to 88 fiero rear.png (84.6 KiB) Viewed 2324 times

[draven]

Currently using a brick for parking brake... Lol. I am planning on trying to adapt a drum in hat setup, or maybe a spot caliper. I'll have to find my bracket dimensions, it was a pretty simple design.

Please do, although I made a functional plexiglass bracket for C5 the internal drum ebrake... I can't see how to mount the C5/C6 caliper brackets without cutting the back of the bracket or cutting the stock ears off the 88 upright and going with a mounting plate attached to the upright through the unit bearing holes, then that increases offset, which is already at the max on my 18x9 rears etc..etc..blah blah...

IPSCO makes the only 'decent' spot caliper that I've found than can mount to 1"+ thick rotors..

UPDATE:
Thanks for the design/cad drawings. Please send me an installed pic on how you got the calipers mounted close enough upright without having to trim the outboard sides of the 88 mounting ears or trim the inboard portions of the C5 caliper mounting brackets..

[ericjon262]

Currently using a brick for parking brake... Lol. I am planning on trying to adapt a drum in hat setup, or maybe a spot caliper. I'll have to find my bracket dimensions, it was a pretty simple design.

Please do, although I made a functional plexiglass bracket for C5 the internal drum ebrake... I can't see how to mount the C5/C6 caliper brackets without cutting the back of the bracket or cutting the stock ears off the 88 upright and going with a mounting plate attached to the upright through the unit bearing holes, then that increases offset, which is already at the max on my 18x9 rears etc..etc..blah blah...

IPSCO makes the only 'decent' spot caliper that I've found than can mount to 1"+ thick rotors..

UPDATE:
Thanks for the design/cad drawings. Please send me an installed pic on how you got the calipers mounted close enough upright without having to trim the outboard sides of the 88 mounting ears or trim the inboard portions of the C5 caliper mounting brackets..

I forgot that slight clearancing was required to the caliper slider, and the upright, if done to just one side, it might be a little much, but divided between the two, it's an easy day. also, if you didn't already anticipate it, custom brake lines will be required. The red in the slider drawing shows the area requiring clearance, not the amount of clearance. I don't have any pictures of it apart, so I can't show the required clearance.

also, important fact to note, while the 4th gen F body calipers are SIMILAR to C5 Calipers, they are NOT the same, they use different caliper sliders, different pad hardware, different pads, the list goes on and on, it's most likely way cheaper to get C5 calipers andrun them as it than to get 4th gen F body parts and run them as C5 brackets. I mention this because it has been said on here and other places that they are the same, and they aren't. I learned that the hard way.

brake4.jpg (80.36 KiB) Viewed 2319 times

brake2.jpg (93.56 KiB) Viewed 2319 times

bracket.png (34.73 KiB) Viewed 2319 times

[The Dark Side of Will]

What do you think of OnShape? For better or worse I've gotten pretty good with it, but it wasn't easy.

[The Dark Side of Will]

they were drawn using Onshape.

What do you think of OnShape? For better or worse I've gotten pretty good with it, but it wasn't easy.

I mention this because it has been said on here and other places that they are the same, and they aren't. I learned that the hard way.

Heh... oops, my bad. I've probably propagated that myth. The actual calipers are supposed to be dimensionally the same, except that C5 calipers are pressure cast while F-body calipers are gravity cast. However, that doesn't actually say anything about the brackets. I hadn't previously looked, but the LS1 F-body calipers take AP749 pads while the C5 (and several other apps) take AP731's.

https://www.porterfield-brakes.com/prod ... uctID=3331
https://www.porterfield-brakes.com/prod ... uctID=3357

[ericjon262]

they were drawn using Onshape.

What do you think of OnShape? For better or worse I've gotten pretty good with it, but it wasn't easy.

I mention this because it has been said on here and other places that they are the same, and they aren't. I learned that the hard way.

Heh... oops, my bad. I've probably propagated that myth. The actual calipers are supposed to be dimensionally the same, except that C5 calipers are pressure cast while F-body calipers are gravity cast. However, that doesn't actually say anything about the brackets. I hadn't previously looked, but the LS1 F-body calipers take AP749 pads while the C5 (and several other apps) take AP731's.

https://www.porterfield-brakes.com/prod ... uctID=3331
https://www.porterfield-brakes.com/prod ... uctID=3357

I liked onshape, I haven't used it in ages though, and was never "good" at it, just enough to make simple parts.

most of the dimensions are the same or close, but some of the sheet metal hardware is very different. I wouldn't recommend trying to use them in place of C5 calipers at all. the main difference in the pads, it the outer curvature, the F body pads have a shorter radius than the C5

[draven]

Did you cnc/mill your brackets or did you have a shop do it for you?

Can you make any more for $$ or hand me off to the shop that made them for you? The only machine shop I have around here for making one off is really really good, but super super busy and I have to wait many weeks to get an opening in his queue.

[ericjon262]

I had a shop make them, it was about $180 bucks I think, shipped to my door, black powdercoated. I'll PM you his info.

[draven]

Many thanks!

[The Dark Side of Will]

I liked onshape, I haven't used it in ages though, and was never "good" at it, just enough to make simple parts.

Ahh, ok.
It's just "millenial CAD"... it's good for collaboration, distributed teams, version control... but it's not actually very good CAD. AutoCAD R14 did some things better 20 years ago.

[draven]

FYI, I ordered up 4 C5 caliper to 88 upright brackets. This should work all the way around as the 88 rotors and calipers are interchangeable from front to rear, sans parking brake of course...

[ericjon262]

I liked onshape, I haven't used it in ages though, and was never "good" at it, just enough to make simple parts.

Ahh, ok.
It's just "millenial CAD"... it's good for collaboration, distributed teams, version control... but it's not actually very good CAD. AutoCAD R14 did some things better 20 years ago.

what I meant by that, was that *I* was never very good with the program, not that it is a sub par program, to be honest, I have minimal experience with CAD programs, so I'm not a very educated opinion on them.

some of the things that have been drawn up in it look pretty good, from a modeling standpoint, it appears to perform very well. as far as an engineering program, FEA type stuff, I have no idea where it stands. models can be exported to almost all of the popular formats, and my understanding, is that it was developed by the some of the people who created Solidworks.

FYI, I ordered up 4 C5 caliper to 88 upright brackets. This should work all the way around as the 88 rotors and calipers are interchangeable from front to rear, sans parking brake of course...

Good luck, I hope it works for the front, feel free to modify the design as needed, if anyone else wants to build these, feel free, all I ask is that I get credited with the design, and that anyone using the design understand that while I don't anticipate the design to fail, I will not be held liable for any failures, the design is definitely a use at own risk product.