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ZL1 Brakes installed on '88 IROC-Z

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Old 06-11-2018, 12:32 PM   #1  
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ZL1 Brakes installed on '88 IROC-Z



So it took awhile but I finally got my ZL1brakes installed on my IROC. Most of the delays had to do with other upgradesthat weren't exactly right (e.g. wheels, struts, etc). I bought a salvaged ZL1donor car and my plan was to sell the ZL1 brakes and get Baer or Wilwoodbrakes. But after getting no interest when trying sell the ZL1 brakes, Idecided to just install these. It also helped with the "theme" of thecar (i.e. "IROC-ZL1"). Once the decision was made, I contacted Scottat Big Brake Upgrade. He was very helpful and walked me through the wholeprocess.


First order of business was to get all thehardware ordered and find wheels that would fit over these big front brakes. Igot the brackets for the front and rear but decided to hold off on the e-brakehardware due to costs. My car is auto so Iíll save this upgrade for when I getthe LSA/TR6060 swapped in. I ended up ordering some 19Ē wheels just to be onthe safe side. Apparently some 18Ē wheels will clear the ZL1 Brembos and somewonít. Iíve attached some of the specs below.


Next was to get the front calipers machinedto fit the bracket and the rotors bored out to 70.3mm to fit the 3rdgen hubs. Luckily for me, a guy in my local Camaro club owned a machine shopand had done this upgrade on his GTO so he did this for me free of charge.


Once this is done, you can startdisassembling the old stuff. The spindles require some modification for the bracket/calipersto bolt on but otherwise this whole kit from Big Brake Upgrade bolts everythingright into place. The ears of the spindles need the ears cut off, the dustguard wholes tapped to accept the bracket and some material shaved off so everythingwill clear.


The rears just needed the holes on the endsof the axle tubes to be tapped to accept the rear bracket. Might be obvious tosome but keep in mind that the rear axles will need to be pulled to get thebracket bolted in place.


Once all this was done, everything boltedright up without an issue. The longest part of the whole process was bleedingthe system. One thing to keep in mind is that this upgrade will add some offsetto your car (about a ľĒ). My rear wheels are poking out just a bit too far formy taste now but Iíve got some custom wheels on order so this will be remediedsoon.


Now Iíve read on some of the forums aboutthese brakes being too big without ABS as they will cause the wheels to lock upvery easily. This has not been my experience. The car stops significantlybetter than before with the little front discs and the archaic drums. Thewheels have not locked up once even with some intentionally heavy braking. Thebrakes do require quite a bit of effort and the pedal felt mushy at first butthis has improved with a bit of driving. Iíve only put about 50 miles on thecar with these brakes and 40 of that has been highway.


Overall, Iím glad I ended up keeping theZL1 brakes instead of switching to another aftermarket brand. I highly recommendBig Brake Upgrade. Iíve also provided some links below with some of the processwritten out a bit better. Hope this helps with anyone who tries this upgrade ontheir 3rd gen.


https://www.thirdgen.org/ls1reardisc/


http://www.bigbrakeupgrade.com/LS1Spindlemodifications.pdf

http://www.bigbrakeupgrade.com/LS1BracketInstall.pdf




Attached Thumbnails
ZL1 Brakes installed on '88 IROC-Z-brembo-clearance.jpg   ZL1 Brakes installed on '88 IROC-Z-brembo-clearance-2.jpg   ZL1 Brakes installed on '88 IROC-Z-calipers-machined.jpg   ZL1 Brakes installed on '88 IROC-Z-spindles-original-w-bracket.jpg   ZL1 Brakes installed on '88 IROC-Z-spindle-compare-wout-bracket.jpg  

ZL1 Brakes installed on '88 IROC-Z-spindle-compare-bracket.jpg   ZL1 Brakes installed on '88 IROC-Z-front-old-shocks.jpg   ZL1 Brakes installed on '88 IROC-Z-front-dismantled-1.jpg   ZL1 Brakes installed on '88 IROC-Z-rear-bracket-installed.jpg   ZL1 Brakes installed on '88 IROC-Z-rears-installed-1.jpg  

ZL1 Brakes installed on '88 IROC-Z-rears-installed-4.jpg   ZL1 Brakes installed on '88 IROC-Z-rears-installed-wheels.jpg   ZL1 Brakes installed on '88 IROC-Z-spindles-installed.jpg   ZL1 Brakes installed on '88 IROC-Z-calipers-brackets.jpg   ZL1 Brakes installed on '88 IROC-Z-fronts-installed.jpg  

ZL1 Brakes installed on '88 IROC-Z-fronts-installed-wheels-turned.jpg   ZL1 Brakes installed on '88 IROC-Z-rears-installed-2.jpg   ZL1 Brakes installed on '88 IROC-Z-fronts-installed-wheel.jpg   ZL1 Brakes installed on '88 IROC-Z-bleeding.jpg   ZL1 Brakes installed on '88 IROC-Z-whole-car.jpg  

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Old 06-11-2018, 12:42 PM   #2  
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Re: ZL1 Brakes installed on '88 IROC-Z

Impressive upgrade.

Quote:
Originally Posted by Jeff TX View Post
The brakes do require quite a bit of effort and the pedal felt mushy at first but this has improved with a bit of driving.
You may want to consider a master cylinder as part of the swap. If the volume needed for the calipers is substantially different from what the OEM MC was engineered to provide, you may notice issues such as what you're describing.



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Old 06-11-2018, 12:58 PM   #3  
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Re: ZL1 Brakes installed on '88 IROC-Z

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Originally Posted by skinny z View Post
Impressive upgrade.



You may want to consider a master cylinder as part of the swap. If the volume needed for the calipers is substantially different from what the OEM MC was engineered to provide, you may notice issues such as what you're describing.



Yeah, that is one of the first things I thought but Scott at BBU said it shouldn't be necessary. I'll keep driving some more miles and see how things feel. It has improved as I've used the brakes more. If I can get by for the time being then I'll save that for when I do the LSA/TR6060 swap as well.
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Old 06-11-2018, 04:04 PM   #4  
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Re: ZL1 Brakes installed on '88 IROC-Z

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Now Iíve read on some of the forums aboutthese brakes being too big without ABS as they will cause the wheels to lock upvery easily. This has not been my experience. The car stops significantlybetter than before with the little front discs and the archaic drums. Thewheels have not locked up once even with some intentionally heavy braking. Thebrakes do require quite a bit of effort and the pedal felt mushy at first butthis has improved with a bit of driving. Iíve only put about 50 miles on thecar with these brakes and 40 of that has been highway.
Well, a couple of thoughts. The one that really pops out is that you added those huge brakes and you couldn't get them to lock up? If so then you have a problem. I have the C4 HD rotors with 4 piston Wilwood FSL calipers and mine will definitely lock up if I lay into it. Could be you have something as little as the new pads and rotors never being broken in properly and now they are glazed over. Could be that the master cylinder is the wrong size now. Could be there is still air in the line or calipers. Could be that the master cylinder needs bench bled. At any rate your brakes are made to stop a 4100-4300 pound car. That's 1000 pounds heavier than our cars!
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Old 06-11-2018, 05:08 PM   #5  
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Re: ZL1 Brakes installed on '88 IROC-Z

235 is a really skinny tire up front.
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Old 06-11-2018, 06:42 PM   #6  
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Re: ZL1 Brakes installed on '88 IROC-Z

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Originally Posted by Tibo View Post
Well, a couple of thoughts. The one that really pops out is that you added those huge brakes and you couldn't get them to lock up? If so then you have a problem. I have the C4 HD rotors with 4 piston Wilwood FSL calipers and mine will definitely lock up if I lay into it. Could be you have something as little as the new pads and rotors never being broken in properly and now they are glazed over. Could be that the master cylinder is the wrong size now. Could be there is still air in the line or calipers. Could be that the master cylinder needs bench bled. At any rate your brakes are made to stop a 4100-4300 pound car. That's 1000 pounds heavier than our cars!
99.9% sure there is no air in the lines but Iíll keep testing and maybe swap the master cylinder. It seems to stop really well right now but there is always room for improvement. Thanks

Last edited by Jeff TX; 06-11-2018 at 09:11 PM.
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Old 06-13-2018, 07:26 AM   #7  
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Re: ZL1 Brakes installed on '88 IROC-Z

Looks great and thanks for taking the time to document. I agree that you should be able to lock up with no issues, at least the rears. This is why I would think you need an adj. prop. valve. Not sure if you already have one. They are cheap and easy to install.

I am searching for a good looking caliper setup for my show(ish) car and these look nice.
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Old 06-13-2018, 09:36 AM   #8  
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Re: ZL1 Brakes installed on '88 IROC-Z

The last thing you want to happen is having the rear brakes lock up. That's how people spin out of control.
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Old 06-13-2018, 09:54 AM   #9  
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Re: ZL1 Brakes installed on '88 IROC-Z

Any suggested master cylinder/brake booster upgrades if I decide to go that route?
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Old 06-13-2018, 12:02 PM   #10  
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Re: ZL1 Brakes installed on '88 IROC-Z

I was not suggesting that you want to be able to lock up the rears once the car is dialed in.

I can see how this could have been misunderstood.

Let me rephrase... While building the car and dialing in the final tune of the brakes, you should be at a starting point of being able to lock up the rears (at a minimum). From there, you pull pressure out of the rear bias via an adj. prop valve. Do this 1/4 turn at a time and keep slamming on the brakes from 60 to 0 to see if your rears lock up. If they keep locking, keep pulling pressure out of the rear. Once they no longer lock, you are set with the right pressure. You want the most braking possible in the rear, with no lock up.

Hope this clears things up.

When modifying a car you have to keep in mind a lot of stuff, more than just master cylinder size. Although that is an important one. Have you modified the weight? Overall tire diameter, contact patch, tire compound (hopefully stickier), etc...

Try and consider all factors and take them into account. The more you modify the more you should have to "tune" a particular system to function at its peak.

The "slap it on and now it is better" approach leaves a lot on the table or can even make expensive mods go in the wrong direction in terms of increasing performance.
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Old 06-13-2018, 12:41 PM   #11  
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Re: ZL1 Brakes installed on '88 IROC-Z

Quote:
Originally Posted by dennisbernal91z View Post
I was not suggesting that you want to be able to lock up the rears once the car is dialed in.

I can see how this could have been misunderstood.

Let me rephrase... While building the car and dialing in the final tune of the brakes, you should be at a starting point of being able to lock up the rears (at a minimum). From there, you pull pressure out of the rear bias via an adj. prop valve. Do this 1/4 turn at a time and keep slamming on the brakes from 60 to 0 to see if your rears lock up. If they keep locking, keep pulling pressure out of the rear. Once they no longer lock, you are set with the right pressure. You want the most braking possible in the rear, with no lock up.

Hope this clears things up.

When modifying a car you have to keep in mind a lot of stuff, more than just master cylinder size. Although that is an important one. Have you modified the weight? Overall tire diameter, contact patch, tire compound (hopefully stickier), etc...

Try and consider all factors and take them into account. The more you modify the more you should have to "tune" a particular system to function at its peak.

The "slap it on and now it is better" approach leaves a lot on the table or can even make expensive mods go in the wrong direction in terms of increasing performance.

I've increased tire diameter by about an inch. Aluminum wheels on order should reduce some weight. Currently running Michelin Pilot 4S tires which are definitely stickier than what was on before. Have some weight savings with some of the suspension parts (e.g. a-arms) but nothing significant. But also added weight with these brakes. The motor currently has a 305 with a Paxton supercharger which is not light. LSA will be going in later this year which should provide some weight savings.


It's probably worth noting that I'll never "race" this car but it's more of a weekend cruiser. That said, I'd like to get the brakes dialed in as much as possible without obsessing about squeezing every last drop of performance out of them. I need to do some more driving and experiment a bit more with different speeds/pedal pressure then go from there based on how the brakes react. As I mentioned, I've only driven the car about 50 miles since the brakes went on and most of that was highway. I'll do some more testing this weekend and post about how it goes.
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