tslsa28

Hello, I have a base 2013 C6 that I use for track days. I have J55 (I think this was the also on the Z51 package) larger brake rotors on it and have been using the base calipers. I need to replace the calipers and am quite sure the front calipers are the same as the base but think the rears are slightly different. Does anyone have the part numbers for front and rear calipers in either the grey or black finish? I have searched the forum but can't find them. Thanks.

Arthur

jaredtxrx

https://www.cultragfactoryparts.com/...ar-brakes-scat

19208039 Caliper
Caliper, RIGHT
BASE, W/ HVY DUTY BRAKES

19208040 Caliper
Caliper, LEFT
BASE, W/ HVY DUTY BRAKES

tslsa28

19208039 Caliper
Caliper, RIGHT
BASE, W/ HVY DUTY BRAKES

19208040 Caliper
Caliper, LEFT
BASE, W/ HVY DUTY BRAKES[/QUOTE]

Thanks for the part numbers. I searched the gmparts websites and also found these. I also then searched the later C6 years and completely different numbers came up and for 2013 only one option was listed and it still called the heavy duty option with part numbers 22799273/4. I wonder if anything changed or if the part numbers just changed? I also wonder if all the rear calipers on the 2013s were heavy duty since no other option is listed?

jaredtxrx

Looks like in 2012 the part number changed. I have no idea why that is through.

Right Rear
22799274

Left Rear
22799273

https://www.cultragfactoryparts.com/...rake%20caliper
That is the complete list of brake calipers for the 2013. They have rears listed for both w/out and w/heavy duty brakes.

tslsa28

Thanks again. Before I order the old or new part numbers I think I'll remove my calipers which are original and see if maybe all the 2013s had the heavy duty rear calipers. I can check by measuring the diameter of the pistons. I use it on race tracks and the ABS comes on sometimes and it feels like the rear. If I don't already have the heavy duty rear calipers with smaller pistons, going with them might take some bias out of the rear brakes.

HOXXOH

Checking the 2013 production numbers, shows both JL9 and J55 brakes on base cars. 75% JL9's and 25% J55. Since J55 was part of the F55 package, a pretty good chunk went on the F55 cars.

Don't trust the online sites for accuracy, since GM didn't create most of them. It's possible that the late part number changes were to identify the optional caliper paint colors and had no relation to JL9 or J55.

I'd be very inclined to believe GM never used J55 rear calipers on JL9 rotors. That's a combo I use, specifically to have less capable rear brakes to allow easier burnouts for drag racing.

tslsa28

HOXXOH, thanks and makes sense. I don't have the F55 suspension and the car was built with JL9 rotors. Would you happen to know what part number you used for your rear calipers and what color? I am using J55 sized rotors in front and base sized rotors in the rear so with the smaller pistons in rear calipers, should be able to get the brake bias I think I need on the race track.

HOXXOH

Since you now provided more information about your car and the brake parts you are using, I think we need to start from scratch to make sure you understand which parts work together properly for most driving.

Front brakes
Both JL9 and J55 have identical calipers with 2 40.5mm dia pistons
JL9 has 12.8" dia rotors weighing 19.5#
J55 has 13.4" dia rotors weighing 22.5#

Rear brakes
Both JL9 and J55 caliper are identical with the following significant exception.
JL9 calipers have a 45mm dia piston
J55 calipers have a 42mm dia piston
JL9 has 12.0" dia rotors weighing 14.2#
J55 has 13.0" dia rotors weighing 20.2#

Rotor size, piston size, pad size, number of pistons, master cyl piston size, tire size, brake pedal mechanical ratio, and front to rear vehicle weight are all factors to create a brake system that provides the correct amount of braking force needed to stop the car in the shortest distance. Too much force on either the front or rear will cause skidding aka loss of traction to where the ABS will kick in.

Assuming you don't change the F/R weight bias or tire sizes, The rotor/caliper selection you are attempting to use, will shift the bias toward the front by quite a bit. If you want the front brakes to do a much bigger percentage of the job, then you're heading the right direction, however you need to understand the ABS will activate quite often.

The F/R bias in my application (JL9 rotors with J55 rear calipers) only slightly shifted the bias forward enough to allow a little less grip on the rear to allow easier burnouts at the drags.

BTW, I have a F55 car, so I only needed to change rotor sizes.

tslsa28

HOXXOH, I have been using my C6 for NASA Time Trials since I bought it in 2013. For 15 years before that I used a 1991 Camaro that I built into a dedicated track car. On the Camaro I didn't have ABS and used a brake bias valve to put as much bias as possible to the front and could brake at the threshold with no lock ups. On the C6 I also use R compound tires and have 275/35/18s on the front and 305/35/18s on the rear. I use Raybestos 47 race pads (their most aggressive) and 43 on the rear (their least aggressive). I use either DBA two piece or GM rotors in J55 size in front and JL9 size in rear. I still have original calipers which are JL9. I do get into ABS in very heavy high speed braking and it feels like the rear. Also the wear on the rotors look like the rears are doing too much work. For all that I want to try the smaller piston J55 calipers in the rear to put more bias on the front. The original calipers have spread a bit and it's time to replace them so that's why I am looking for part numbers.

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HOXXOH

And with the additional info about how you use the car, I see you aren't like the other guy a couple of days ago who was trying to do similar things with his daily driver.
I hope the little bit of brake info helps you. We both race, but on totally different types of tracks. Not very much works the same.

tslsa28

Yes, your info was very helpful and thanks. Now I just need to make sure I'm getting the correct rear calipers and will probably measure the pistons to be 100% sure before I install them.
And racing is racing, whether it's going straight, turning left and right, or just turning left. I would race a lawn mower if I didn't have a car.

tslsa28

To follow up on this, I just measured my rear caliper pistons and they are 42 mm. So it looks like possibly every 2013 base Corvette came with the HD J55 rear calipers. I bought it new and it does not have any options other than the dual mode exhaust. Some of the online GM parts lists also only show the HD rear calipers for a 2013 which matches my car.

HOXXOH

Wow, that's a surprise. You have JL9 rotors and J55 calipers. What's the RPO code on the glovebox?
I wonder how the factory claimed the number of cars produced with each brake package. Hmm!

tslsa28

The codes show JL9 with no J55 listed anywhere. I bought it new and window sticker shows no options other than NPP exhaust. Rear pistons are definitely 42 mm and if you go to gmpartsdirect.com or gmpartshouse.com they only show HD calipers for the rear. Maybe that's all they had in 2013.

HOXXOH

I did a little research today on the corvetteactioncenter.com sister site. While I didn't find any J55 numbers for the '10 MY, I found at least 71,473 cars that according to the production stats left the factory with J55 brakes. As expected, the Z51 option accounted for the majority (about 76%) and the F55 option came in next (about 20%) and stand-alone options last (4%).

It's not a surprise that the stand-alone numbers were high in '05 and '06, since those years didn't include J55 on F55 cars, so F55 buyers could get their J55 brakes as a separate option. In '07, '08, and '09 combined, only 36 stand-alone J55 options were sold. Lacking numbers for '10 J55 numbers, but having 757 F55 cars sold, does mean those all had J55 brakes. I just don't know how many stand-alone cars there might have been.
The '10, '11, '12, and '13 MY numbers are below.

Year J55 F55 Assumed stand-alone
'10 757+ 757 ? (~300 my guess)
'11 815 495 320
'12 981 650 331
'13 804 294 510

Because the Z51 option cars no longer existed, you might expect some of the base buyers (non-F55) to want the J55 brakes to appear to the casual observer that they had a Z51 optioned car or just really wanted the bigger brakes.

The '12 cars had a painted caliper option. Red, Silver, Yellow, and Dark Gray Metallic could be had with either the F55 option or J55 option. Black was only available with the J55 option. There were a total of 161 base cars with painted calipers. Colors were not available on JL9 brakes.

The '13 cars also had the same color option. Since the '13's also had a Black wheel option (replaced the Competition Gray), there were 819 base cars with painted calipers. There were 565 cars with black calipers and that includes GS cars.

So now I'm going to walk back my earlier remark about Bowling Green not putting J55 rear calipers on JL9 cars, since with all the different options for colors in '12 and '13 and closing in on the end of production, I wouldn't doubt someone could pull an individual or pair of rear calipers out of the wrong bin or the only full bin, just to fill an order.

That said, If you have a 42 mm piston on one caliper, it might not be a bad idea to check the other side. With only 2597 base coupes produced in '13, yours might have been near the very end. Check the VIN.

tslsa28

I checked both sides and both are 42 mm. Mine was one of the last C6s built at the end on the 2013 model year production. I guess they did just put them on my car and you're probably right about that's the caliper they had at the time. My car seems to be a bit of a ringer on power too. It's completely stock and has never made less than 390 corrected rear wheel HP on multiple dynos at shops and at the race track (my car was impounded by NASA and dyno'd at an event). Maybe the engineers put a tune or something on the last LS3s to make us miss them even more.

jaredtxrx

This is some really weird and interesting information. Thanks HOXXOH and tslsa for checking into these things.

tslsa28

I learned something thru all this. But I'm back to my original problem of less rear brake bias on the race track. The answer will be to keep using less and less aggressive rear brake pads to get bias towards front since I already have the J55 calipers.

jaredtxrx

It sounds like you have too much front bias.

So list the brakes on your car again? Through all the post I may have gotten confused.

Front Rotor - J55 or JL9?
Front Caliper - Base

Rear Rotor - J55 or JL9?
Rear Caliper - J55 or JL9?

tslsa28

I bought it new and it came with JL9 front rotors/base calipers and JL9 rear rotors/J55 calipers.
I bought J55 front sized DBA rotors and bought the J55 caliper bracket and used original calipers on the front.
I kept the JL9 sized rotors and original caliper bracket/calipers on the rear.
I think I have too much rear bias on the racetrack as the ABS comes on in very heavy, very high speed braking (120 mph plus) and it just feels like the rear to me.