First I would like to annonce I am the proud owner of a 1990 coupe 6 speed that I saved from "Cash for Clunkers" @96,000mi. My vette needs a brake job soon. I came across a conversion kit to put C5 brakes on a C4. The main question I have is, what is the minimum size of wheel required for adiquate clearence? The only answers I have found is I need GS or Zr-1 or larger wheels. So far all of my reasearch state "Saw blade" wheels don't fit. My vette has the J55 big brake option as well as stock 275/45 zr17 "saw blade" wheels. I think these are the same size as Zr-1 front wheels, right?. Can anyone who has done the conversion or have any information please clearify any confusion with this dilema. I know there are 3 types of "saw blade" wheels 16-17inches. I don't have the funds to do the conversion and wheels/tires all at once.
Thanks.

 

You have to use a 17" Grand Sport style wheel to clear the C5 calipers. The stock 17 sawblade wheels have extra material right where the wheel center meets the rim and that's why the stock wheels won't work.

The C4 caliper is not as wide as the C5 caliper so the J55 brake option does clear the stock wheel.

Try AFS wheels for good prices on the GS/ZR-1 style wheels. I picked up a set last year for $550 on their fleabay store.

 

Your stock '90 wheels may or may not fit over C5 brakes without spacers. I have an 89 with C5 brakes and two sets of stock wheels (more or less the same as a 90 wheel). Two of my 8 wheels cleared the brakes no problem (two wheel vendors were used in 89) but the others just touched the caliper with brand new pads installed. The clearance is just fine once the pads wear a little. I chose to use 1/8" wheel spacers and the brakes clear all my wheels easily.

 

saw blades came on 92 and later...88 option 17'' and 89/90 got 'salad shooters'...91 ?

 

Thank you for the information, this helps out alot. One more thing I forgot to mention was the issue with the parking brake. Some say you lose the parking brake function, and some say it is possible to keep it with modification(s). To my knowlege both C4&C5 have drum-in-rotor parking brake setups. I would imagine both are activated in a similar way. Can anyone explain specifically what modifications are required and or additional parts required to keep the parking brake.
Thanks again.

 

I'm not sure about your 90, but my 92 with the j55 package does NOT have the drum parking brake. The parking brake manually sets the rear calipers.

Look real close at your rears to be sure its the same as a c5.

 

There is no real reason to replace the rear C4 brake setup with C5 stuff. The rotor diameter is very close to the same as is the "swept area" (amount of rotor surface touched by the pad. The pads are very close to the same physical size as C5 pads. And I don't believe anyone makes a good caliper adapter bracket to install C5 rear brakes anyway.

The 84-87 C4 parking brake is a drum-style that is inside the rear rotor hat. From 88 on, the parking brake used the rear caliper. C5's never had a drum-style parking brake.

When doing a C5 front brake conversion, it's a good idea to get the revised brake bias spring from Doug Rippie Motorsports. This spring goes in the master cylinder and changes the amount of brake pressure that is applied to the rear brakes. This spring also takes away any "nose dive" under hard braking.

When I did my C5 upgrade on my 87, any hard braking beyond medium pedal pressure would cause an ABS activation. Installed the bias spring and now I can apply hard braking pressure up to where ABS initiates and the car stays completely level. Great $20 investment.

But with the existing J55 brakes, you should already have excellent braking. J55 has 13" front rotors and nearly as thick as the C5 rotor.. And there are lots of excellent aftermarket pads for C4's that will provide great street performance and lots of pads that can be used for track days or HPDE's.

 

I love opinions - seems everybody has an uninformed one on this forum.

From:
http://www.corvettefever.com/techart...all/index.html

The changeover from C4 to C5 brakes (not compatible with '84 brake systems) increases the braking surface area by 25 percent, a huge improvement. In addition, the VBP rotors are 11 percent lighter than the factory units and offer better cooling through enlarged vents, in both the outer perimeter of the rotor and brake-rotor face vents.



And finally: all C5s have the internal drum style e-brake with its own shoes.

From:http://www.queencitycorvette.com/Tec...Adjustment.htm

From the Corvette Forum:

I posted this fix several years ago, but it was lost in the software upgrade. When My C5 was new, the e-brake barely worked. I took it to the dealer, and was told that brakes are a wear item and that I would have to pay for new shoes. The car had less than 1000 miles on it. The e-brake only engages when the car is stopped so how could they be worn? Anyway, I decided to take a look and see if I could do anything. I was not crazy about the dealer touching my car anyway. OK, here we go…the e-brake works similar to the e-brake on most cars with rear drum brakes. With that in mind, jack up the rear of the car and remove the wheels. Remove the bolts for the calipers, then the calipers and pads. You will see the caliper bracket…it has two bolts that hold this to the brake backing plate, they are very, very tight but they will come off. (They are torqued to 125 ft pounds with loctite). Once the bracket is off you can remove the rotor (make sure the e-brake is not engaged). Next you will see how the system works: it has a set of shoe brakes and the rotor has an internal drum. In the last few years I have found that many, many C5 come from the factory with poorly adjusted e-brakes. Now locate the star adjuster…turn it out to make the shoes grow in diameter (mine were out 33 clicks). I did ten clicks at a time and the slid the rotor back on. I did three sets of ten before I could feel any drag, I then clicked five more and could not get the rotor on. I then backed off two clicks and got the rotor on (it was tight when I started it on the shoes but when I finally seated it, it was perfect). I then did the other side; it was out exactly the same amount, I then put everything back. Now for the test...when I engaged the e-brake, it locked up the brakes at a point about 45 degrees, 90 degrees being straight up. The lock up was so positive, I knew I did it right. Next, to check the release, I took the car to a hill, set the e-brake, put the car in neutral and it stayed there. Then to check on the release, I slowly disengaged the e-brake and found that the shoes where totally retracted after only an inch of lever release.

After this fix I could stop the car using only the e-brake with the car doing ten miles an hour. The e-brake also has an auto adjust feature, but it will only work if your e-brake lever is between 45 and 55 degrees; if your e-brake is out further than that, the e-brake will not auto adjust (AUTO ADJUST feature: roll the car backwards on a hill or in reverse @ 5 mph, pull up on the e-brake lever--this will slam your car to an abrupt stop. The engagement of the shoes to the drum while the car is moving backwards will cause the shoe assembly to flex…it is the flex that causes the blade to click the adjusting star one click). Do this three or four times and it will expand your shoes. You cannot over tighten these shoes...if it needs two clicks to get to max and you do four clicks, it will only adjust the star two clicks. Also remember to use loctite on the brackets and caliper bolts. If you have any questions on this repair, feel free to e-mail me or instant message me.

Good Luck! Many people have e-mailed me with their positive results from this fix.

Bill (Evil-Twin)
from GM :

Park Brake Shoe Adjustment

Tools required:

J 21177-A Drum-to-Brake Shoe Clearance Gauge (or brake shoe caliper from your local auto parts store)

Important:

Adjustments are not normally necessary after replacing the park brake lever or cables. The park brake is adjusted automatically by cycling the part brake lever three or four times.

Never operate the park brake lever while the rotor is removed.

1. Remove the brake rotor. Procedure:

Raise the vehicle and support.

Remove the tire and wheel assembly.

Caution: Do not place your fingers in front of the piston in order to catch or protect the piston while applying compressed air. This could result in serious injury.

Depress the piston into the brake caliper housing to provide clearance between the brake pads and the brake rotor. When depressing the piston some fluid should be removed from the master cylinder.

Caution: These fasteners MUST be replaced with new fasteners anytime they become loose or are removed. Failure to replace these fasteners after they become loose or are removed may cause loss of vehicle control and personal injury

Remove the brake caliper mounting bracket bolts and discard.

Remove the brake caliper mounting bracket and the caliper as a unit and support it to the vehicle so there is no weight on the brake hose.

Disconnect the park brake cable from the apply lever.

Important:

Never operate the parking brake with the rotor removed.

Do not force the rotor off. If the rotor is difficult to remove, ease it off by gently rotating it as you pull outward.

Remove the brake rotor.

2. Check if the brake drum inner diameter is within specifications.

Important: If the gap between the adjuster nut and screw exceeds 5mm (0.25 in) during the adjustment procedure, the brake shoe assembly must be replaced.

3. Adjust the parking brake shoe-to-drum clearance to 0.38 mm (0.015 in) using the drum-to-brake clearance gauge mentioned at top.

4. Center the brake shoe.

5. Measure the brake shoe lining diameter across the horizontal centerline using

the clearance gauge. The diameter should measure 189.6mm (7.464 in) to 189.8 mm (7472 in).

6. Install the brake rotor.

7. Install two wheel nuts to retain the rotor.

Tighten: Tighten the wheel nuts finger tight. Do not overtighten.

8. Cycle the part brake lever three times.

9. Rotate the rotor and check for drag.

If drag is present check and adjust the shoe-to-drum clearance.

10. Install the rotor.

Procedure:

1. Adjust the parking brake shoe-to-drum clearance.

Notice: Whenever the brake rotor has been separated from the wheel bearing flange, clean any rust or foreign material from the mating surface of the rotor and flange with a hub cleaning kit. Failure to do this may result in increased lateral runout of the rotor and brake pulsation.

Clean the metal surfaces between the brake rotor and the hub bearing flange.

Install the brake rotor.

Install the disc brake caliper mounting bracket and the brake caliper as a unit.

Install NEW brake caliper mounting bracket bolts.

Tighten: Tighten the brake caliper mounting bracket bolts to 175 N-m (129 lb ft).

Install the tire and wheel assembly.

Tighten: Tighten the wheel nuts in sequence to 140 N-m (100 lb ft).

Lower the vehicle

Check the fluid level.

Caution: Do not move the vehicle until a firm brake pedal is obtained. Air in the brake system can cause the loss of brakes with possible personal injury.

With the engine running, pump the brake pedal slowly and firmly to seat the brake pads.

Burnish the brakes as necessary.

 

The OP said he has the 13" J55 front brakes on his car. Isn't that the same diameter or very close to the C5 front rotors?? The C5 pad is slightly larger but I don't think it's 25% to gain that amount of swept area. Going from the 11.5" diameter early C4 rotors to C5 rotors would certainly provide a substantial increase in surface area.

Cam Bentley may have been pushing the VBP upgrade package in his magazine article (as writers will do) but if you use OEM style rotors, they are still cast iron and not slotted or drilled for weight savings. The OP never mentioned what style of rotor he was considering. Some C5 rotors may have vanes that are angled to improve airflow through the rotor for cooling but some don't. Depends on what rotors you buy. I have less than $600 total in my 87 brake upgrade with using C5 Z06 front pads.

And you can install C5 front brakes on an 84. The adapter will be slightly different that the one needed for 84-87 cars and the 88 and later adapters are different than the earlier ones. A former forum member made adapter brackets for the early C4's (including 84's) and sold a number of them to members. The only real problem in the 84 upgrade is the lack of sufficient material around the bolt holes on the 84 knuckle to provide for the strength needed for extreme braking activity..

OK, so I screwed up on this. My bad.