Help, Master Cylinder Install/ABS Delete Fail (1 Viewer)

[matthewscruiser]

Hi all,
I'm stumped on this one and have zero brakes now. My ABS pump quit working, and I finally had time to delete it and install a new Advics Master Cylinder at the same time. I decided to keep the OEM LSPV since I replaced mine a year ago. However, the more I bleed the brakes, the worse things get. Here's what I've done so far.

For the ABS delete:
1. Remove ABS pump. Connected "FR" and "FL" outputs on the ABS pump to the "F" line using a brass Tee.
2. Connected the "R" (line to the rear brakes) to the front port on the master cylinder.
3. Hooked up the master cylinder rear port like normal

For master cylinder install:
1. bench bleed new master cylinder with syringe. I don't think I did this well. I used a syringe connected to some scrap brake line to force fluid into each port. I don't think this was a great idea, I should have just bled it on the car with the lines disconnected.
2. Installed on truck and bled brakes with 2-man method. Order was RR, LR, FR, FL, then LSPV. I did this several times, but the fluid was coming out pretty slow. No bubbles
3. Brakes worked. However, with the engine running, the pedal initially felt firm, but then slowly sank to the floor.
4. No leaks noted!

We decided to try again.
1. With master cylinder on the car and absorbent mats below, we used the two lines on the master cylinder ports like bleeder screws. I had steady drips of brake fluid coming out of both of them, so we snugged them back down.
2. We bleed the truck again for 2 hours. We would get slow but clear fluid for 20 minutes, then hit a bubbles/straight air for 10 minutes, and get clear fluid again.
3. We thought we were making progress, but now the pedal very little resistance and easily goes to floor. We kept bleeding, but it just isn't getting better.
4. Still no fluid leaks anywhere on the truck. It doesn't seem like the booster is filling with fluid.

Where did we go wrong? Is my ABS delete with the LSPV the issue? Do I need to bench bleed the Master cylinder better? I'm starting to suspect the master cylinder is faulty and sucking air (even though the reservoir has been kept full).

 

[ZackR]

Although I've never used one I'd try starting over with a pressure bleeder.

 

[matthewscruiser]

Although I've never used one I'd try starting over with a pressure bleeder.

I’ll see if I can get my hands on one. It seems like rock auto will swap the master cylinder, so I may wait until Wednesday and start over.

I’ll probably bench bleed it longer this time too.

 

[JaxFJ]

Hi all,
I'm stumped on this one and have zero brakes now. My ABS pump quit working, and I finally had time to delete it and install a new Advics Master Cylinder at the same time. I decided to keep the OEM LSPV since I replaced mine a year ago. However, the more I bleed the brakes, the worse things get. Here's what I've done so far.

For the ABS delete:
1. Remove ABS pump. Connected "FR" and "FL" outputs on the ABS pump to the "F" line using a brass Tee.
2. Connected the "R" (line to the rear brakes) to the front port on the master cylinder.
3. Hooked up the master cylinder rear port like normal

For master cylinder install:
1. bench bleed new master cylinder with syringe. I don't think I did this well. I used a syringe connected to some scrap brake line to force fluid into each port. I don't think this was a great idea, I should have just bled it on the car with the lines disconnected.
2. Installed on truck and bled brakes with 2-man method. Order was RR, LR, FR, FL, then LSPV. I did this several times, but the fluid was coming out pretty slow. No bubbles
3. Brakes worked. However, with the engine running, the pedal initially felt firm, but then slowly sank to the floor.
4. No leaks noted!

We decided to try again.
1. With master cylinder on the car and absorbent mats below, we used the two lines on the master cylinder ports like bleeder screws. I had steady drips of brake fluid coming out of both of them, so we snugged them back down.
2. We bleed the truck again for 2 hours. We would get slow but clear fluid for 20 minutes, then hit a bubbles/straight air for 10 minutes, and get clear fluid again.
3. We thought we were making progress, but now the pedal very little resistance and easily goes to floor. We kept bleeding, but it just isn't getting better.
4. Still no fluid leaks anywhere on the truck. It doesn't seem like the booster is filling with fluid.

Where did we go wrong? Is my ABS delete with the LSPV the issue? Do I need to bench bleed the Master cylinder better? I'm starting to suspect the master cylinder is faulty and sucking air (even though the reservoir has been kept full).

View attachment 3788268

View attachment 3788269

1. Master Cylinder Bench Bleeding​

• It seems like the bench bleeding wasn't thorough, which is critical for a proper bleed. Any air left in the master cylinder can travel into the brake lines and create persistent issues.
• Solution: Remove the master cylinder and properly bench bleed it. Use plugs to seal the ports and pump until no air bubbles appear in the reservoir. Alternatively, use the on-car bench bleeding method again with clear tubing leading back to the reservoir.

2. Brake Line Connections and Air Traps​

• The addition of the brass T-fitting and modifications to the brake lines may have created air traps or introduced leaks.
• Solution: Double-check all fittings, especially the connections at the T-fitting, master cylinder, and LSPV. Ensure they're tight and free from leaks. Air traps in the lines may require more extensive bleeding or adjustments to the bleeding order.

3. Brake Bleeding Order​

• While your bleeding order is generally correct, including the LSPV adds complexity since it's another point where air could be trapped.
• Solution: Try bleeding the LSPV first before moving to the rear wheels. Ensure the LSPV is fully operational and adjusted correctly.

4. Sinking Pedal with Engine Running​

• This is typically a symptom of a faulty master cylinder or an air leak in the system. Since you mentioned that no leaks are visible, it’s possible the master cylinder is faulty.
• Solution: Check if the master cylinder is defective by capping the ports and pressing the brake pedal. If it still sinks, the master cylinder is the issue.

5. Slow Fluid Movement During Bleeding​

• This could indicate a blockage or restriction in the lines, air in the system, or insufficient pressure from the booster.
• Solution: Use a pressure or vacuum bleeder to ensure faster fluid flow and eliminate air pockets. This can often solve persistent air-related issues more effectively than the 2-man method.

6. LSPV Retention​

• While keeping the LSPV is fine, it may require manual adjustment or could have air trapped in its lines.
• Solution: Bleed and adjust the LSPV thoroughly. Confirm it’s working correctly and not introducing complications.

Next Steps:​

1. Re-bench bleed the master cylinder to eliminate any air.
2. Reconnect the master cylinder and bleed the system with a vacuum or pressure bleeder.
3. Start with the LSPV, then follow the correct bleeding order (RR, LR, FR, FL).
4. If the pedal still sinks, suspect a faulty master cylinder and consider replacing it.

Additional Notes:​

If the issue persists after these steps, it may be worth re-evaluating the ABS delete setup. While the brass T-fitting seems logical, it might be introducing inefficiencies.

 

[matthewscruiser]

1. Master Cylinder Bench Bleeding​

• It seems like the bench bleeding wasn't thorough, which is critical for a proper bleed. Any air left in the master cylinder can travel into the brake lines and create persistent issues.
• Solution: Remove the master cylinder and properly bench bleed it. Use plugs to seal the ports and pump until no air bubbles appear in the reservoir. Alternatively, use the on-car bench bleeding method again with clear tubing leading back to the reservoir.

2. Brake Line Connections and Air Traps​

• The addition of the brass T-fitting and modifications to the brake lines may have created air traps or introduced leaks.
• Solution: Double-check all fittings, especially the connections at the T-fitting, master cylinder, and LSPV. Ensure they're tight and free from leaks. Air traps in the lines may require more extensive bleeding or adjustments to the bleeding order.

3. Brake Bleeding Order​

• While your bleeding order is generally correct, including the LSPV adds complexity since it's another point where air could be trapped.
• Solution: Try bleeding the LSPV first before moving to the rear wheels. Ensure the LSPV is fully operational and adjusted correctly.

4. Sinking Pedal with Engine Running​

• This is typically a symptom of a faulty master cylinder or an air leak in the system. Since you mentioned that no leaks are visible, it’s possible the master cylinder is faulty.
• Solution: Check if the master cylinder is defective by capping the ports and pressing the brake pedal. If it still sinks, the master cylinder is the issue.

5. Slow Fluid Movement During Bleeding​

• This could indicate a blockage or restriction in the lines, air in the system, or insufficient pressure from the booster.
• Solution: Use a pressure or vacuum bleeder to ensure faster fluid flow and eliminate air pockets. This can often solve persistent air-related issues more effectively than the 2-man method.

6. LSPV Retention​

• While keeping the LSPV is fine, it may require manual adjustment or could have air trapped in its lines.
• Solution: Bleed and adjust the LSPV thoroughly. Confirm it’s working correctly and not introducing complications.

Next Steps:​

1. Re-bench bleed the master cylinder to eliminate any air.
2. Reconnect the master cylinder and bleed the system with a vacuum or pressure bleeder.
3. Start with the LSPV, then follow the correct bleeding order (RR, LR, FR, FL).
4. If the pedal still sinks, suspect a faulty master cylinder and consider replacing it.

Additional Notes:​

If the issue persists after these steps, it may be worth re-evaluating the ABS delete setup. While the brass T-fitting seems logical, it might be introducing inefficiencies. Consider checking forums or contacting a specialist for advice on similar ABS delete setups.

Thanks for the thorough reply!

 

[Surfdc]

​

4. Sinking Pedal with Engine Running​

• This is typically a symptom of a faulty master cylinder or an air leak in the system. Since you mentioned that no leaks are visible, it’s possible the master cylinder is faulty.
• Solution: Check if the master cylinder is defective by capping the ports and pressing the brake pedal. If it still sinks, the master cylinder is the issue.

Cap the mc and press brake pedal with engine running?

 

[matthewscruiser]

Update: I repeated the process with a new master cylinder and it works perfect.

 

[Surfdc]

So the new Advics mc you put in was faulty? I just installed one too and my pedal is more squishy now.

 

[Surfdc]

Also if I delete the ABS on my 97, do I need to swap in a non-abs master cylinder?
Thanks

 

[77mustard40]

Also if I delete the ABS on my 97, do I need to swap in a non-abs master cylinder?
Thanks

I've deleted the ABS and LSPV and kept the ABS MC, no issues at all.

 

[matthewscruiser]

I’m thinking the first master cylinder may have been faulty or I just had some air trapped in it. Yes, use the same MC even if you delete ABS.