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Old 06-30-2012, 09:39 AM   #21
c4cruiser
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Originally Posted by Ricky 91 vette View Post
Now let me pls put my orignal question again in this form: can i install the 85 to 87 emergency brakes on my 91? i will upgrade the rear brakes since i have the c5 brake sitting at home and it will coast me about $200 only to get the job done, and if i see after that the rear tires are locking before the front does then i will remove the bias spring and that should take care of it, but i dont want to loose my e brake and if i'll be able to install the shoe style e brakes then that would be great
Installing the earlier C4 drum style parking brake on your 91 is going to create more problems. IIRC, you have to use the early rear "knuckle" to be able to use the internal drum brake. The early C4's had a different wheel offset and that was due to the size of the knuckle. Your 91 wheels would then sit further inside the wheel well by 3/4" or 18mm.

The parking brake cable for the early cars connected at the bottom of the knuckle where the 91 parking brake cable connects at the center of the caliper. Effectively this means you have to use the cables from an earlier car.

You said you have "dealer" pads installed. Chances are that means stock C5 front pads and stock C4 rear pads. Maybe that's part of your problem.

I have the C5 conversion on my 87 with the DRM brake bias spring installed. I use C5 Z06 pads in front and Hawk HP+ pads in the rear. With this combination, I see no brake lockup unless I get into the ABS (which does work!!)and the car stops hard and straight. On local road courses, the car can get repeatedly slowed from speeds around 130 to 25 with no problems at all.

Frankly I think you are wasting money in trying to use a C5 rear brake system. The difference in rotor diameter between the C4 and C5 stock rear rotors is not a lot and the C5 rear caliper is a single piston design and not a lot different then the C4 rear caliper. Changing rotor diameters in the rear will also add to the problem.

Try going with different pads that have a bit more aggressive bite and see what happens.
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Old 06-30-2012, 08:41 PM   #22
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I don't understand how the bigger pad doesn't make a diffrence or how the half " extra rotor doesn't make diffrence either!!! Try to put ur car on the jack stand and wear a glove and spin the front tire and try to stop it by using ur fist first and then try to stop it by using the whole palm applying the same pressure, my understanding is when using the same pressure the bigger the pad means more friction therefor easier stopping , and also the bigger the rotor the less pressure needed to have the same stopping power , c5 rear brakes uses 12" or 12.5" rotor ( not sure ) but if I do the upgrade I will use the c6 z51 rotors which are 13" and that's why I'm expecting to have to remove the bias spring if not more like what u said about the valves etc
1st: You're misunderstanding how friction and force work. If you increase pad size (and nothing else) you're PSI of the pad against the rotor goes down, for a given line pressure in the brake system...so total braking torque remains about the same. What does improve from a larger pad, is pad life.

2nd: The C5 upgrade helps because of these reasons: slightly larger rotor diameter, bigger piston area in the calipers (means more force applied to the pad for a given line pressure) and significantly larger components that can absorb and dissipate heat much better.

3rd: If you "upgrade" to C6 Z51 rotors, the cooling fins on the right rotor are backward, and the thing will actually manage heat worse than a plain C5 rotor. Then there is the whole debate about drilled rotors as well, which I won't take a side on.
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Old 06-30-2012, 09:04 PM   #23
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Originally Posted by c4cruiser View Post
Installing the earlier C4 drum style parking brake on your 91 is going to create more problems. IIRC, you have to use the early rear "knuckle" to be able to use the internal drum brake. The early C4's had a different wheel offset and that was due to the size of the knuckle. Your 91 wheels would then sit further inside the wheel well by 3/4" or 18mm.
And you need a custom adapter for the bottom shock mount because the early shocks mount at a different angle
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Old 06-30-2012, 09:20 PM   #24
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Originally Posted by Ricky 91 vette View Post
I don't understand how the bigger pad doesn't make a diffrence or how the half " extra rotor doesn't make diffrence either!!! Try to put ur car on the jack stand and wear a glove and spin the front tire and try to stop it by using ur fist first and then try to stop it by using the whole palm applying the same pressure, my understanding is when using the same pressure the bigger the pad means more friction therefor easier stopping , and also the bigger the rotor the less pressure needed to have the same stopping power , c5 rear brakes uses 12" or 12.5" rotor ( not sure ) but if I do the upgrade I will use the c6 z51 rotors which are 13" and that's why I'm expecting to have to remove the bias spring if not more like what u said about the valves etc
I'll explain, hang on...

Let's look at the rotor first: I said "1/2" won't make a huge change" meaning your proposed 1" larger DIAMETER rotor only nets half that in radial torque. I showed (via the math) that the 1/2" value (and no other changes) does net 4.x % more torque for the given clamping load. That's still simply not 'huge' in a change is all. And could be done with pads although I'd not suggest it due to wear rate. But it is a change to consider as you are correct that the larger rotor will make more torque for the same given pressure.

Next is the pad; pad size (in the most basic sense, not taking into account effective radius values) won't make more torque- it only lasts longer. The clamping is by the amount of pressure on the pad via the piston. Let's take a simple view of that: I wear a size 9 shoe and weigh 180lbs. Now suppose I put on a size 12 shoe. My foot print is larger...but I still weigh 180lbs. (shoe weight not withstanding) Brake pads work the same way.


Can't speak to the value of making this whole change you guys speak of but for the complexity to value change in a 1" larger rotor I'm not totally sold on it based upon the net gain. If it's affordable enough perhaps but cost, fit and time could be an issue.

Last edited by Todd TCE; 06-30-2012 at 09:22 PM.
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Old 06-30-2012, 09:45 PM   #25
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Hi Ricky

Front bias is difficult to cure, i recommend removing the bias spring and re-fitting the standard 91 bias spring. This should give the usual problem of locking the rear brakes (when a larger front caliper is fitted) which can easily be cured by installing an adjustable brake bias valve under the vette.

http://www.ebay.com/itm/WILWOOD-DISC...item4d0019013a

Then remove your abs fuse and do some brake testing, adjust so that you prevent the rear brakes locking before the fronts on wet and dry roads.
Then re fit the abs fuse, (see link below for trouble shooting abs problems) most likely a bad sensor or a wire damaged or corrosion in a connector.

http://www.popularmechanics.com/cars...enance/2265091

You should be able to track the abs fault down yourself with that info.
Good luck
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Old 07-01-2012, 04:14 AM   #26
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Originally Posted by c4cruiser View Post
Installing the earlier C4 drum style parking brake on your 91 is going to create more problems. IIRC, you have to use the early rear "knuckle" to be able to use the internal drum brake. The early C4's had a different wheel offset and that was due to the size of the knuckle. Your 91 wheels would then sit further inside the wheel well by 3/4" or 18mm.

The parking brake cable for the early cars connected at the bottom of the knuckle where the 91 parking brake cable connects at the center of the caliper. Effectively this means you have to use the cables from an earlier car.

You said you have "dealer" pads installed. Chances are that means stock C5 front pads and stock C4 rear pads. Maybe that's part of your problem.

I have the C5 conversion on my 87 with the DRM brake bias spring installed. I use C5 Z06 pads in front and Hawk HP+ pads in the rear. With this combination, I see no brake lockup unless I get into the ABS (which does work!!)and the car stops hard and straight. On local road courses, the car can get repeatedly slowed from speeds around 130 to 25 with no problems at all.

Frankly I think you are wasting money in trying to use a C5 rear brake system. The difference in rotor diameter between the C4 and C5 stock rear rotors is not a lot and the C5 rear caliper is a single piston design and not a lot different then the C4 rear caliper. Changing rotor diameters in the rear will also add to the problem.

Try going with different pads that have a bit more aggressive bite and see what happens.
your guess is right, i have stock c5 pads upfront and stock c4 rear, but when i did the upgrade i used hawk ceramic street pads on all 4, but they were too dusty and couple mechanics pointed at my rotors telling me that i'm using wrong pads for street applecation, and when i had to resurface the front rotors i went with dealer pads on all 4, braking feels the same with less dust though,,,,,
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Old 07-01-2012, 04:26 AM   #27
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i'm pretty sure that my car needs more brake in the rear because its not the first time i'm locking the fronts only, i've been driving my vette for 4 years now, almost 3 years with the c5 front brakes, and almost never with abs working, normally i'm very carefull driver, i may speed , accelerate some times, but i always look far and always try to be ready for any road surprise, withen the past 4 years i only had to stop the car like that twice, first time was with the same brake setup about 2 years ago in the freeway from almost 60 to zero, but it was with old and dry tires , and any one could see the freeway scratch mark from the lock up on the front tires only, but as i said the tires were old and dry and alredy had vabration so i didnt care much and after 6 months it almost even out and i couldnt notice the marks anymore, but this time tires are new and fresh 8 months old and less than 6k miles on them and the bold spot was caused on them was un bearable so i went and replaced them the same week with new ones, i know if i had abs this wouldnt happen, but i also know hard braking twice should lock the rear wheels too , but it didnt happen not once but twice which means i need to do something about that
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Old 07-01-2012, 04:33 AM   #28
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for the others who have done the front upgrade but havent notice a problem with their rear brakes it should be because they have a working ABS , which i think when the front wheel is about locking the abs release some brake from there and maybe apply it on the rear to even the braking according to the desired persentage between the rear and front brakes, and i'm sure if they try and pull the abs fuse and try a hard braking they would be surprised from the result!!!
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Old 07-01-2012, 04:42 AM   #29
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i think i have nothing to lose but a lot to gain if i'm right, i will say good bye for the e brake and order the adapters tomorrow, and i'll take some pics during the instalation and i'll post the results here with my opinion about the upgrade and if i see that it was a weast of money and time i'll be the first one saying that to everyone else.....

thanks to all the members who joined this thread i, your tips are always helpfull
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Old 07-01-2012, 11:42 AM   #30
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Originally Posted by gerardvg View Post
Hi Ricky

Front bias is difficult to cure, i recommend removing the bias spring and re-fitting the standard 91 bias spring. This should give the usual problem of locking the rear brakes (when a larger front caliper is fitted) which can easily be cured by installing an adjustable brake bias valve under the vette.

http://www.ebay.com/itm/WILWOOD-DISC...item4d0019013a

Then remove your abs fuse and do some brake testing, adjust so that you prevent the rear brakes locking before the fronts on wet and dry roads.
Then re fit the abs fuse, (see link below for trouble shooting abs problems) most likely a bad sensor or a wire damaged or corrosion in a connector.

http://www.popularmechanics.com/cars...enance/2265091

You should be able to track the abs fault down yourself with that info.
Good luck
oh hi gerard, how u doing buddy? thanks for the tip mate, the problem with my abs is i'm not even able to pull codes of it, i'll give it another try though
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Old 07-04-2012, 12:52 PM   #31
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Don't drive so fast..Next..
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Old 07-05-2012, 06:00 AM   #32
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Don't drive so fast..Next..
I can't promise u that lol, it's a vette for the god Sake !! but I can promise to fix my brakes right !!
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Old 07-05-2012, 08:01 PM   #33
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I can't promise u that lol, it's a vette for the god Sake !! but I can promise to fix my brakes right !!
If you do a little sprited drivening need good brakes .I think the brakes on MOST C-4 BAD BAD new or not.The brakes on my RPO-Z07 good after in rebuild them with all new stuff and went to Hawk HP+ pads staness lines...The 96 LT-4 Hot Rod vett for sure C-5 on front slotted roters all new in rear staness lines Hawk HP+ pads stops very good for a do it at home thing got about $1000 in the brake did it in my shop way better the old brakes put me in a ditch tryed to slow down from about 70mph to make a 90% turn in the ditch had about half block ..Went home orderd parts it will stop now...Money and time to get it right i have J55s on the 95 Ok not as good as the 96 with C-5 brakes ..Good luck..The brakes can be seen at radar502 take a look...
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Old 07-05-2012, 09:17 PM   #34
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Hi everyone, as many other c4 owners I did the c5 brake upgrade for the front brakes including stanless steel brake lines and slotted and drilled front and rear rotors and bias spring, my brakes improved a lot since then and that was 2 years ago, last week I had to hit the brakes hard to stop the car after coming out of a curve doing 50 miles per hour and getting surprised with unusual long line of cars at the 1/2 mile away traffic light, by the way my abs is not working and the dealer couldn't figure out how to connect his tech1 with its computer and told me to live without it!! as a result from that hard breaking with no abs I was able with a help of an ingle to stop the car without killing anyone but I got a flat spot on my 6 months 6k miles tires and that was causing a lot of vabration and because of that and I had to replace the tires again, the damage was on the front tires only, which tells me that the rear brakes didn't do much in that stop, it got me thinking of using the rear c5 calipers that I bought as a set with the front ones and they been setting in the garage since then, I did some research and found somebody who his name is dale who will sell his adapters for a reasonable price, using c6 13" rotors, but I will loose my e brake, he make adapters for early c4 too with the shoe style e brakes inside the rotors and those early c4 get to keep their e brakes even when installing the c5 rear brakes calipers, sorry for my poor English and long story BUT my question is : can I install the early c4 e brakes in my 91? So I can have all c5 calipers and all 13" rotors and e brake the same time ????
Hey Ricky,I have some c5 brakes that I'm about to install,I'm putting on all 4 just because I have them and I like that they match.
About the E-brake situation I was thinking of using a line lock brake.
It's just a toggle switch,you apply the brake and flip the switch and your brakes are locked.
I havent heard of anyone doing it though,maybe jeep guys.
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Old 07-07-2012, 09:49 PM   #35
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I have an 86, and installed the C5 front brakes. Big change.
Since my front brake hoses were 23 years old, and the C5 hoses were 4 years old, I used the C5 front hoses as well.
I tried some heavy braking, and could not get the ABS to engage.
I changed the rear pads to some that were new and with moderate bite, and now my rear ABS will engage if I slam the pedal down.
My car was 23 years old, and had the original pads.
Tells you how effective the GM pads were. But then, they were half worn, and 23 years old.
I believe your rear calipers are just out of adjustment on the automatic adjuster. readjust your rear calipers to have the pads just touch your rear rotors, and I think you will be fine.
I have read things time and time again about using the hand brake to adjust the 88 and newer calipers, but I don't want another argument.
Read up on how to adjust your rear calipers.

By the way, the C5 has the same "shoe" emergency brake as the 86, but they are designed just a little different.

Last edited by coupeguy2001; 07-07-2012 at 09:53 PM.
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Old 07-08-2012, 04:33 AM   #36
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Hey Ricky,I have some c5 brakes that I'm about to install,I'm putting on all 4 just because I have them and I like that they match.
About the E-brake situation I was thinking of using a line lock brake.
It's just a toggle switch,you apply the brake and flip the switch and your brakes are locked.
I havent heard of anyone doing it though,maybe jeep guys.
that sounds really intresting, i would prefer an emergency sulotion though, u know in case of brake failure like a blown brake line, bad master cylender.....but thats really hard to happen specially when u have new bake system and u can always shut down the engine and shift down to third gear and then second till u stop the car and the e brake in these cars would never stop the car faster than that so its not a big deal, but let me know how u will do it, and also what adapters will u be using in the front and rear and what rotors?
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Old 07-08-2012, 04:42 AM   #37
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I have an 86, and installed the C5 front brakes. Big change.
Since my front brake hoses were 23 years old, and the C5 hoses were 4 years old, I used the C5 front hoses as well.
I tried some heavy braking, and could not get the ABS to engage.
I changed the rear pads to some that were new and with moderate bite, and now my rear ABS will engage if I slam the pedal down.
My car was 23 years old, and had the original pads.
Tells you how effective the GM pads were. But then, they were half worn, and 23 years old.
I believe your rear calipers are just out of adjustment on the automatic adjuster. readjust your rear calipers to have the pads just touch your rear rotors, and I think you will be fine.
I have read things time and time again about using the hand brake to adjust the 88 and newer calipers, but I don't want another argument.
Read up on how to adjust your rear calipers.

By the way, the C5 has the same "shoe" emergency brake as the 86, but they are designed just a little different.
i dont think they need to be adjusted, and when my abs is working ( it does it between time to time like today out of 7 engine cycles it worked normaly twice and in the rest the abs service light was on) i can ingaged it easy and i feel it in the front and thats another reason makes me think that i need to strenth the rear brakes more, about pads, i tried hawks and the dealer pads, the dealer pads are better for the rotors while the hawk once eats it
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Old 07-11-2012, 06:52 PM   #38
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Why not just get an adjustable front to rear proporting valve & adjust the front to rear braking yourself without having to buy other parts that may not make a difference?I do agree that you need to get the ABS(anti-lock) brake issue fixed
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Old 07-11-2012, 08:03 PM   #39
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Why not just get an adjustable front to rear proporting valve & adjust the front to rear braking yourself without having to buy other parts that may not make a difference?
Proportioning valves don't work that way. They (it) goes in line to the rear brakes and limits rear pressure.

You can't fit a valve that increases or really 'balances' the brake system. These are used to reduce rear pressure and lessen them proportionally to the amount of total input only. They allow higher line pressure to the rear at a lower input, then you adjust the 'knee point' or cut to lessen the rear pressure as you increase the total pressure. Under light duty they allow for more rear brake, under high pressure less- thus keeping the rears from locking up. You simply adjust when the reduction begins and most valves then reduce that output by up to 50% or so.

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Old 07-14-2012, 04:32 PM   #40
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Proportioning valves don't work that way. They (it) goes in line to the rear brakes and limits rear pressure.

You can't fit a valve that increases or really 'balances' the brake system. These are used to reduce rear pressure and lessen them proportionally to the amount of total input only. They allow higher line pressure to the rear at a lower input, then you adjust the 'knee point' or cut to lessen the rear pressure as you increase the total pressure. Under light duty they allow for more rear brake, under high pressure less- thus keeping the rears from locking up. You simply adjust when the reduction begins and most valves then reduce that output by up to 50% or so.
Thanks.I did not know that.How bout a different master cylinder or more aggressive pads on the back?I don't think changing the rear calipers will make a difference I think your will have to have a new or custom built proportioning valve or a custom master cylinder that provides more brake fluid to rear brakes.Also make sure the rear calipers are adjusted properly like previously stated.There is a screw in the caliper that moves the pads closer to the brake rotor-I looked it up & found this info on Alldata
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