I am looking to replace my master cylinder and rubber brake lines on my 92 ZR1. I know I will also need to bleed the ABS module behind the driver seat. Question: What order should I do this in? Replace master, bleed then do brake lines? Do brake lines first, bleed then do master or just do everything then bleed master and lines at the same time? I know I need to bench bleed master first.

Thanks!

 

You can replace those components without having to bleed the ABS. Just keep the car off and perform all the bleeding. Don't cycle it on with a dry line. The ABS is closed unless activated. I replaced all 4 lines with braided and bled it with the car off - no issues.

Bench bleed the master, install it, gravity bleed lines until they are dripping, then bleed with pedal.

If you have a pressure or vacuum bleeder - obviously use that.

 

I assume you're referring to your '96 Collector's Edition here, since you didn't tell us what year car you have and it appears you have multiple Corvettes including multiple C4s based on your post history. In future, it's always good practice to start a thread asking for technical assistance by telling us the year of the Corvette you're having issues with as there were many changes year-by-year to the various systems of the car.

If I am indeed correct and you're talking about the '96, the procedure is to first bench bleed the master cylinder, then bleed the 'normal' brakes (Right Rear, Left Rear, Right Front, Left Front), then attach a diaphragm-style pressure bleeder to the master cylinder and use a Tech 1 with the Bosch ABS cartridge or a Tech 2 to run the automated ABS bleed procedure.

However, I should note that it's only necessary to do this if you notice the pedal not functioning correctly or the ABS not functioning correctly when activated. The Bosch 5 ABS installed in the 95-96 Corvette is completely isolated from the regular brake hydraulic circuit, as opposed to the earlier systems. It only interacts with the brake hydraulics when active. So under normal circumstances, it's not necessary to bleed the ABS when you bleed the brakes or replace the master cylinder.

 

hahah. Sorry. One would think since being a member for 20 years I would have figured that out by now. The car is. 1992 ZR1. I assuming the brake design would be similar to the nonZR1 92? Also, if a Tech 1 is required to bleed the brakes then Houston we have a problem. It is not like I have one of those hanging around the shop or could even get ahold of one even with the promise of giving up my first born. I will repost this in the ZR1 section as well. Thanks for the detailed response. I will save for my 95 and 96 should I ever have to replace my Master.

 

Since you are going to replace the rubber lines you will have to do "some" bleeding of the system.

I hope that your new rubber lines will have a stainless braided jacket on them. The SS braided rubber hoses give a better firmer pedal feel in my opinion. Also be very careful when you buy the new rubber lines as they need to be D.O.T. Approved for use in the United States, they should have a tag on them. If they are not approved and there is an accident it would be problematic. Cheap insurance...

I have a C3 and a C4 and flush them every five years. I use a Phoenix Reverse Bleeder to push the fluid and the air UP the lines and out at the Master cylinder. It can be messy the first time but it gets better. This system gets all the air out in one action. The pump has saved my butt on my Wife's old Chevy pickup with a five speed and hydraulic clutch. It is one of the only tools that makes bleeding less work and helps flush the brakes quickly. I can flush the brakes in less than an hour on either Corvette.

A fellow Corvette Forum member sold me his Snap On MT2500 and it has been great for working on the OBD1 Corvette. I understand that Snap On made a cartridge that is specifically for the Bosch ABS systems used by GM. I have been trying to get my hands on one but they want a lot of money for them. It is supposed to troubleshoot and help bleed the system. Somewhere I read that when the Corvette is first started the ABS will cycle and be ready for action.

 

I would recommend using the ZR-1 discussion for ZR-1 issues, but this is still a question that can be answered here, so it's okay.

No, your '92 ZR-1 uses the Bosch 2U ABS, which does not have an auto bleed procedure, and uses a prime pipe connected to the brake master cylinder. The procedure is completely different from the procedure for the 1995-1996 Corvette.

You still should bench bleed the master cylinder. However, after installing the master cylinder, the very first thing you must do is bleed the prime pipe by using the bleed screw on the ABS unit in the driver's rear storage compartment, the one behind the driver's seat. Expose the bleed screw, attach a clear tube and insert the other end into a container with the end submerged in brake fluid as you would bleeding a caliper. Simply opening this valve should allow fluid to flow without touching the brake pedal. Keep the bleeder open until no more air appears in the fluid. Make sure to keep the master cylinder reservoir full during this process or you'll have to start all over again. Close the bleeder once the fluid is clear. Once the prime pipe is bled, then proceed to bleeding the brakes at each corner (Right Rear, Left Rear, Right Front, Left Front).

For just talking to the car, free software and a $50 cable is all that's actually necessary these days. The Bosch ABS still requires specialized hardware to talk to (Snap-on w/ Bosch ABS cartridge, GM Tech 1A w/ Bosch ABS cartridge, GM Tech 2), but I have a friend with a shop who'll let me borrow his Tech 2 and a logic analyzer, so I'll be reverse-engineering the ABS commands hopefully by the end of this year so that everyone can recalibrate their TPS and bleed the 1995-1996 Corvettes with free software.

 

Thanks for the great info. Good luck with your ABS project. I had the opportunity to buy a TECH 1A about a year ago but just could not justify the price. I am able to get data from the OBD1 interface using OBD1 Bluetooth Scanner/Code reader from 1320 Electronics and the ALDLdroid app. Helped me identify a bad knock sensor circuit in my chip for the 92. Marc H. was able to repair the chip.