RapidC84B

Track Prep Guide says to swap in fluid with dry boiling point of 590 or higher for trackdays then back to DOT4 for street. Personally, I will flush the OEM to SRF and do my normal annual heavy bleed. With the brake by wire, the early high level service tutorials are stressing the importance of disconnecting the battery for any brake work. Apparently, when you open the door the system goes through an initialization process and pressurizes the system. So, if you have pads out or a bleeder open you're going to make a mess. So to my question... can you old school pedal bleed the car with the negative disconnected? Or, will the car have to be pressure bled? I have a Motiv, but unsure if the standard GM cap works on the new car.

Thoughts?

Bill Dearborn

If doing a pedal bleed I would think the process would be to have the brake system fully ready to operate followed by connecting the ground before opening the door. Then once the person gets in the car the door is closed and the door isn't opened again until the bleeding is done or the system is closed again. That would avoid the pressurization cycle that occurs when the door is opened.

Bill

RapidC84B

That would make "one man" bleeding a huge PITA. Will be very interesting to see what the FSM ends up saying. I'm hoping I can disconnect the battery and just pressure bleed with my Motiv.

theblackangus

Im a bit confused about the brake fluid recommendations.
I do a couple of HPDE's a year, do I really need to put in the high performance stuff, or can I just use the stock fluid?
My usual practice is to put in new fluid before each event and then use it until the next event.

MitchAlsup

Many people start with a fresh batch of stock fluid do a track event and survive.
But (BUT) once you encounter a brake fluid boiling event on track, you will understand why a complete change out of the fluid with "the best stuff" before each track event is wise.

Mark@Complete

Before each event is a bit much, most of my club level racers only bleed hydralics a few times a season or during a brake service.


The truth is most DE drivers in entry level groups wont push a car that hard and with a factory upgraded brake system like in the Z51 cars you should be good.....but for the ones that push or start real timed laps or race.. pads/fluid are mandatory.

ChiTownVetteTech

Here is the official GM procedure for brake bleeding. Only list pressure bleeding in service manual. I thought owners manual stated pressure or manual bleed, but no vacuum bleeding. I find it strange that this procedure does not have you disconnect the battery as has been preached already. Possibly error? Wouldn't be the first error in a GM service manual I've ever found.


2020 Chevrolet Corvette | Corvette Service Manual 13097125 | Brakes | Hydraulic Brakes | Repair Instructions | Document ID: 5417357

Hydraulic Brake System Bleeding (J55)
Special Tools

• CH-29532-A Pressure Brake Bleeder
• CH-44894-A Brake Bleeder Adapter

For equivalent regional tools. Special Tools

Warning: Brake Dust Warning

Warning: Brake Fluid Irritant Warning.

Caution: Brake Fluid Effects on Paint and Electrical Components Caution.

Caution: Only use products that comply with GM specifications and check manufacturer information respectively. We recommend the use of GM genuine products. Instructions must be followed at all times. The use of any type of fluid other than the recommended type of brake fluid, may cause contamination which could result in damage to the internal rubber seals and/or rubber linings of hydraulic brake system components.

Note: If the system is opened at the brake master cylinder, a full hydraulic brake system bleed is necessary.
Bleeding a Single Hydraulic Brake Circuit Note: The pressure bleeding equipment must be the diaphragm type. The rubber diaphragm between the air supply and the brake fluid prevents air, moisture, oil, and other contaminants from entering the hydraulic system.

Note: The brake reservoir may have residual pressure after the bleeding operation is complete. Wrap a clean shop towel around the bleeder adapter and all hose connections before disconnecting the pressure bleeding equipment to prevent brake fluid from contacting and damaging vehicle components and painted surfaces

Note: DO NOT allow the vehicle to be driven until it is diagnosed and repaired.

1. Disconnect brake fluid level sensor
2. Use Global Diagnostic System (GDS) to deactivate brake boost system.
3. Place a clean shop cloth beneath the brake master cylinder to prevent brake fluid spills.
4. Clean the outside of the reservoir on and around the reservoir cap prior to removing the cap and diaphragm.
5. Fill the brake master cylinder reservoir with GM approved brake fluid from a clean, sealed brake fluid container. Ensure that the brake master cylinder reservoir remains at least half-full during this bleeding procedure. Add fluid as needed to maintain the proper level. Brake Master Cylinder Reservoir Filling
6. Check the brake fluid level in the CH-29532-A Pressure Brake Bleeder. Add GM approved brake fluid from a clean, sealed brake fluid container as necessary to bring the level to approximately the half-full point. Adhesives, Fluids, Lubricants, and Sealers
7. Install the CH-44894-A Brake Bleeder Adapter to the brake master cylinder reservoir.
8. Connect the CH-29532-A Pressure Brake Bleeder, to the CH-44894-A Brake Bleeder Adapter.
9. Charge the CH-29532-A Pressure Brake Bleeder, air tank to 207 - 310 kPa (30 - 45 psi).
10. Open the CH-29532-A Pressure Brake Bleeder, fluid tank valve to allow pressurized brake fluid to enter the brake system.
11. Wait approximately 30 seconds, then inspect the entire hydraulic brake system in order to ensure that there are no existing external brake fluid leaks. Any brake fluid leaks identified require repair prior to completing this procedure. Brake System External Leak Inspection
12. Install a proper box-end wrench onto the wheel hydraulic circuit bleeder valve which has been serviced.
13. Install a transparent hose over the end of the bleeder valve.
14. Submerge the open end of the transparent hose into a transparent container partially filled with GM approved brake fluid from a clean, sealed brake fluid container. Adhesives, Fluids, Lubricants, and Sealers
15. Loosen the bleeder valve to purge air from the wheel hydraulic circuit.
16. Allow fluid to flow until air bubbles stop flowing from the bleeder.
17. Cycle the park brake ON and OFF after opening the bleeder valve on the rear calipers.
18. After all air has been purged from the hydraulic circuit, tighten the bleeder valve to the necessary torque specification and install the dust cap.
    • Front Brake Caliper Bleeder Valve Replacement
    • Rear Brake Bleeder Valve Replacement
19. Close the CH-29532-A Pressure Brake Bleeder, fluid tank valve, then disconnect the CH-29532-A Pressure Brake Bleeder, from the CH-44894-A Brake Bleeder Adapter.
20. Remove the CH-44894-A Brake Bleeder Adapter from the brake master cylinder reservoir.
21. Fill the brake master cylinder reservoir to the maximum-fill level with GM approved brake fluid from a clean, sealed brake fluid container. Adhesives, Fluids, Lubricants, and Sealers
22. Inspect the brake system for external leaks. Brake System External Leak Inspection
23. Run the GDS - Brake Hydraulic Test, if it fails, perform the Bleeding the Complete Brake Hydraulic System procedure.
24. Connect the brake fluid level sensor
25. Turn the ignition ON, with the engine OFF. Check to see if the brake system warning lamp remains illuminated.
26. Inspect the brake system for external leaks. Brake System External Leak Inspection
27. If the brake system warning lamp remains illuminated, go to Diagnostic Starting Point - Vehicle.

Bleeding Complete Brake Hydraulic SystemNote: The pressure bleeding equipment must be the diaphragm type. The rubber diaphragm between the air supply and the brake fluid prevents air, moisture, oil, and other contaminants from entering the hydraulic system.

Note: Squeeze rapidly, faster pad/piston retraction guarantees high fluid flow to release air.

Note: DO NOT allow the vehicle to be driven until it is diagnosed and repaired.

1. Disconnect brake fluid level sensor
2. Use Global Diagnostic System (GDS) to deactivate brake boost system.
3. Place a clean shop cloth beneath the brake master cylinder to prevent brake fluid spills.
4. Clean the outside of the reservoir on and around the reservoir cap prior to removing the cap and diaphragm.
5. Fill the brake master cylinder reservoir with GM approved brake fluid from a clean, sealed brake fluid container. Ensure that the brake master cylinder reservoir remains at least half-full during this bleeding procedure. Add fluid as needed to maintain the proper level. Brake Master Cylinder Reservoir Filling
6. Check the brake fluid level in the CH-29532-A Pressure Brake Bleeder. Add GM approved brake fluid from a clean, sealed brake fluid container as necessary to bring the level to approximately the half-full point. Adhesives, Fluids, Lubricants, and Sealers
7. Install the CH-44894-A Brake Bleeder Adapter to the brake master cylinder reservoir.
8. Connect the CH-29532-A Pressure Brake Bleeder, to the CH-44894-A Brake Bleeder Adapter.
9. Charge the CH-29532-A Pressure Brake Bleeder, air tank to 207 - 310 kPa (30 - 45 psi).
10. Open the CH-29532-A Pressure Brake Bleeder, fluid tank valve to allow pressurized brake fluid to enter the brake system.
11. Wait approximately 30 seconds, then inspect the entire hydraulic brake system in order to ensure that there are no existing external brake fluid leaks. Any brake fluid leaks identified require repair prior to completing this procedure. Brake System External Leak Inspection
12. Install a proper box-end wrench onto the RIGHT FRONT wheel hydraulic circuit bleeder valve.
13. Install a transparent hose over the end of the bleeder valve.
14. Submerge the open end of the transparent hose into a transparent, graduated container partially filled with GM approved brake fluid from a clean, sealed brake fluid container. Note amount of fluid in the container. Adhesives, Fluids, Lubricants, and Sealers
15. Open bleeder, allow fluid to flow for 10 seconds, close bleeder and repeat the step two more times before moving on.
16. Reopen bleeder, use channel locks to quickly squeeze pad to caliper in locations by each piston beginning with Sequence A, then repeating with Sequence B:
    1. Sequence A: Beginning with the pad section furthest from the bleeder and ending with the pad section nearest to the bleeder:
       1. Outboard leading piston
       2. Inboard leading piston
       3. Outboard trailing piston
       4. Inboard trailing piston
    2. Sequence B: Beginning with the pad section nearest to the bleeder and ending with the pad section furthest from the bleeder:
       1. Inboard trailing piston
       2. Inboard leading piston
       3. Outboard trailing piston
       4. Outboard leading piston
17. Use a mallet to tap 3 times behind each piston and 3 times tangentially on the top and bottom of caliper.
18. Close bleeder and wait 5 seconds to allow pressure to rebuild and pistons/pads to spread back out to rotor.
19. Repeat steps 3-5 four more times.
20. Close RF bleeder and repeat entire process for LF caliper.
21. Install an appropriate box-end wrench onto the LEFT REAR wheel hydraulic circuit bleeder valve.
22. Loosen the bleeder valve to purge air from the wheel hydraulic circuit.
23. Allow fluid to flow until air bubbles stop flowing from the bleeder.
24. After all air has been purged from the hydraulic circuit, close the bleeder valve.
25. Install a proper box-end wrench onto the RIGHT REAR wheel hydraulic circuit bleeder valve, then repeat steps 23-25.
26. After all air has been purged from the hydraulic circuit, tighten the bleeder valve to the necessary torque specification and install the dust cap.
    • Front Brake Caliper Bleeder Valve Replacement
    • Rear Brake Bleeder Valve Replacement
27. Close the CH-29532-A Pressure Brake Bleeder, fluid tank valve, then disconnect the CH-29532-A Pressure Brake Bleeder, from the CH-44894-A Brake Bleeder Adapter.
28. Remove the CH-44894-A Brake Bleeder Adapter from the brake master cylinder reservoir.
29. Fill the brake master cylinder reservoir to the maximum-fill level with GM approved brake fluid from a clean, sealed brake fluid container. Adhesives, Fluids, Lubricants, and Sealers
30. Inspect the brake system for external leaks. Brake System External Leak Inspection
31. Run the GDS — Brake Hydraulic Test, if it fails.  Antilock Brake System Automated Bleed
32. Connect the brake fluid level sensor
33. Turn the ignition ON, with the engine OFF. Check to see if the brake system warning lamp remains illuminated.
34. If the brake system warning lamp remains illuminated, go to Diagnostic Starting Point - Vehicle.

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RapidC84B

@ChiTownVetteTech what it the heck kind of process is that? It's unlike anything from the C5/6/7 FSMs I've owned. I've done of brake work over my 20 years tracking these cars.

1. I think "Use Global Diagnostic System (GDS) to deactivate brake boost system" is why you don't have to disconnect the battery?

2. Why does the first section say to cycle the parking brake when bleeding the rear calipers? The parking brake is a separate caliper unrelated to the rear main calipers.

3. This process seems pretty nuts for bleeding 1 corner. Especially if GM thinks you're going to swap fluid back and forth every track weekend. This would create a bunch of unneeded torque cycles on the bleeder screw. Aluminum calipers can only take so many cycles before they start to wear out. Most people are bleeding the brakes once in a car's life, but if you follow GM and do 5 track weekends a year that's 10 bleeds a year!:
So tech's are supposed to take channel locks to nice new painted brembos and squeeze on them?

What's the part about repeating steps 3-5 4X on one caliper? The J55 front calipers have bottom and top bleeders only so the parts MFG can make one SKU for each side of the car. Should be as simple as bleeding the top caliper on each side while tapping with a rubber mallet.

What's your input? What am I missing? Why is the process for bleeding one circuit pretty normal (other than the oddity about the parking brake) vs. the process for doing the whole thing?

Another oddity is the rear calipers have two vertical bleeder screws, yet it says nothing about bleeding the inboard and outboard like the C7 FSM. The fronts have two horizontal inboard bleeders but you only use the top one each side.

@RichieRichZ06 check this process out... seems like it's full of errors.

RapidC84B

EDIT - A racing acquaintance who's a GM tech says the whole process about squeezing calipers and tapping and multiple bleeds at each corner would make sense if pressure bleeding is the only option and if you can't pedal bleed. They want to make absolutely sure no air is stuck in the system. He has seen instances where pressure bleeding didn't quite get everything out. Personally I've never had that happen... always use my Motiv as a pressure source only, no fluid.

vndkshn

I find entry level drivers tend to cook their pads/fluid more than anyone else, and often it is not due to the pads or fluid, but how they use the brakes. They think they are braking as hard as they should, but they aren't and that means more heat (due to longer stops). And they often slow more than they need to/should. Had my son-in-law as a student and he was complaining about fade, I tried to tell him it was his braking, he didn't believe me, I went out and ran a full session in his car (street tires, HP+ pads, DOT4 fluid) with little to no issues. Next session out with him driving, brake "problems" solved!

vndkshn

Weirdly, I have seen that, but not on any of the track cars I've bled before for some reason. My 3/4 ton truck? Jeez, it's bad.

ChiTownVetteTech

Any of our vehicles with the e-boost brake by wire system, ex. Hybrids, has the same convoluted procedure. Personally I have successfully pedal bled those. I think if you’re just flushing a higher boiling point fluid through you can use a pressure bleeder with no problem as there wasn’t any air introduced into the system. I do believe I saw that the front calipers have a downward facing bleeder also. Just don’t use a vacuum bleeder. The parking brake activation while bleeding I don’t understand. Obviously whoever wrote that procedure was oblivious with the channel locks step. Biggest thing is if the pedal feel isn’t right will proceed a scan tool. Pedal feel is artificial in these systems.

RapidC84B

Yeah the Z51 caliper has a top and bottom bleeder, but if it's like Wilwoods, it's only done so the MFG can make one SKU and use it on both sides of the car. You only ever use the top bleeder. The rear Z51 calipers are like the C7 with two vertical bleeders (inboard and outboard).

Curious if you get clarification on the need to disconnect the battery. Will I be able to flush my own SRF fluid in? Hopefully I can disconnect the battery and flush with my Motiv pressure bleeder.

ChiTownVetteTech

You should be able to pressure bleed new fluid right in. I’m thinking we’re not disconnecting the battery because the brake system is put together. That’s really if you remove a caliper or pads, so the module do wake up and blow a piston out. I’ll post the description and operation later so you can get an understanding of how the brake/abs system operate.
I’m more curious how these copper free pads hold up and if the aftermarket ones will work with the fade warning. GM only validates with original equipment.

RapidC84B

That makes sense regarding only needing to disconnect battery for taking pads out or swapping components, but why does it tell you:

1. Disconnect brake fluid level sensor
2. Use Global Diagnostic System (GDS) to deactivate brake boost system.

Clearly the home mechanic like me won't have a GDS to do any of that.

My intent is to track the car with nothing more than a slightly more aggerssive street alignment. (BTDT with track cars and full race cars). I will be testing the OEM pads at VIR, hopefully by Hyperfest in May. I don't want to be a beta-tester for track pads playing nice with the car's fade warning systems.

I was hoping the OEM DOT4 fluid would hold up for the OEM pad compound. Can you look up the dry boiling point for the OEM DOT4?

ChiTownVetteTech

This is the service Dot 4 fluid. May or may not be identical to what the factory uses. Only has wet boiling point listed.
I did find a dry boiling point on acdelco website. Shows 446 I’m assuming in Fahrenheit. Crappy pop up that’s partially cut off.

RapidC84B

That's annoying.... GM says if you're going to track the car the fluid needs to have dry boiling point over 590 I believe. However, if that fluid is in the 550 range it'll be perfectly find for aggressive HPDE driving.

ChiTownVetteTech

you’re going to find a better fluid than the ACDelco one. Higher boiling point the better. Who make your normal Dot 4?

RapidC84B

I run Castrol SRF in my tracked cars. My goal was to be able to track the car shortly after I get it. Was hoping to break it on on the way back from the museum, add the 2 quarts to the DCT and get it to VIR in May, then worry about the brakes as my next track weekend won't be until October.



The wet boiling point is what makes it amazing... you can just bleed once a year, even with a race car.

Bill Dearborn

The C8 recommendation is almost the same track prep recommendation in the C7 OMs. On the C7 they said brake fluid with a dry boiling point of 534 deg F Vs 590 on the C8.

Bill