C8 brake bleed discussion
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? |
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 |
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.
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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. |
Originally Posted by theblackangus
(Post 1601037984)
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. 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. |
Originally Posted by MitchAlsup
(Post 1601041859)
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. 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. |
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
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.
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.
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@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!:
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. |
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.
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Originally Posted by Mark@Complete
(Post 1601042498)
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.
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Originally Posted by Tool Hoarder
(Post 1601050931)
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.
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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.
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Originally Posted by ChiTownVetteTech
(Post 1601051513)
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.
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. |
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. |
Originally Posted by ChiTownVetteTech
(Post 1601051632)
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.
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? |
https://cimg2.ibsrv.net/gimg/www.cor...9f162f0ac.jpeg
https://cimg3.ibsrv.net/gimg/www.cor...64f04923c.jpeg 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. |
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.
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Originally Posted by Tool Hoarder
(Post 1601052111)
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.
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Originally Posted by ChiTownVetteTech
(Post 1601052130)
you’re going to find a better fluid than the ACDelco one. Higher boiling point the better. Who make your normal Dot 4?
Castrol SRF Brake Fluid – Ultimate Racing (Dry Boil Point 590°F – Wet Boil Point 518°F) The wet boiling point is what makes it amazing... you can just bleed once a year, even with a race car. |
Originally Posted by theblackangus
(Post 1601037984)
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. Bill |
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