ABS Issues post manual install

SVXMAN2001 · #1 02-19-2023, 04:28 PM

Good news is i installed a MY17 sti 6 speed w/ dccd.

However now I have an ABS Sensor (Left Rear) trouble code post install. An issue which did not exist prior the install.

My current symptoms are ABS warning light, ABS trouble code indicating LR ABS wheel speed sensor and most importantly braking distance has significantly increased. The car is currently unsafe to drive. The vehicle does stop but if an emergency arose, the brakes would not react in such a way to prevent an accident.

What I've done thus far is:

- Modified brake booster. Shortened the push rod. Pedal travel is significantly less.
- Bled brakes and hydraulic pump multiple times (according to FSM). No air in system
- Checked brake booster and master cylinder. No leaks from master cylinder or vacuum leaks from booster;
- Installed MAPDCCD Advanced Wheel Speed Sensor. Required slicing into ABS Electronic Control Module and VSS wire/pin in ECU
- unplugged all connections to ABS ECM and ABS light still illuminated and displayed LR ABS WSS error code

I've since ordered a LR WSS and awaiting delivery, but would one speed sensor significantly decrease brake performance? If so, it should be a relatively straightforward fixed.

I am most concerned that the wire splicing may have harmed the ABS ECM somehow or that the internals of the brake booster were harmed during the modificdation process.

Any help appreciated.

Blacky · #2 02-20-2023, 05:28 AM

A wheel speed sensor should have no influence on braking distance unless ABS intervention is needed. Under normal heavy braking with no lock-up detected the car should brake normally.
I would say modifying the brake booster is likely the cause of the poor braking performance. Just out of curiosity why would you do that and complicate things?

SVXMAN2001 · #3 02-20-2023, 07:18 AM

It was needed to fit the new clutch assembly. The stock svx booster push rod far extended past the brake pedal bumpstop/sensor.

Other's have done it w/out issue. It's quite possible that I harmed the internals in the modification process. The FSM seems to go to great lengths of treating the removal and install of the booster with care.

Blacky · #4 02-20-2023, 03:07 PM

Thanks for the clarification. I didn't know that was part of the manual conversion.

Tireiron · #5 02-22-2023, 12:40 AM

Normally when swapping the pedal assembly, you also swap the brake booster to match the pedal assembly.

TomsSVX · #6 02-22-2023, 01:09 PM

You say you tapped into the ABS wiring for the DCCD controller. I would start by removing this wire tap and see if your ABS worries are gone. I think you may have gotten some wiring wrong here. Sounds like the ABS is running when you are trying to brake and possibly keeping you from braking correctly and thus the longer stopping distance? My 0.02

Tom

SVXMAN2001 · #7 02-22-2023, 01:59 PM

Tomssvx, it's quite possible. I tapped into the ABS ECM for the MAPDCCD's (company name) Advanced Wheel Speed Sensor module (necessary since i no longer have a Vehicle Speed Sensor). It appears to be working correctly based on the manufacturer's instructions and that the speedometer is registering speed.

The MAPDCCD - DCCD controller does not splice into the ABS system, aside from the brake light switch.

With that said, i disconnected all wires spliced into the ABS ECM and still received the same ABS trouble code indicating a faulty left rear ABS sensor.

TomsSVX · #8 02-22-2023, 05:22 PM

Quote:

Originally Posted by SVXMAN2001

Tomssvx, it's quite possible. I tapped into the ABS ECM for the MAPDCCD's (company name) Advanced Wheel Speed Sensor module (necessary since i no longer have a Vehicle Speed Sensor). It appears to be working correctly based on the manufacturer's instructions and that the speedometer is registering speed.

The MAPDCCD - DCCD controller does not splice into the ABS system, aside from the brake light switch.

With that said, i disconnected all wires spliced into the ABS ECM and still received the same ABS trouble code indicating a faulty left rear ABS sensor.

It's possible it's just a sensor, just a little coincidental. Keep us posted

Tom

SVXMAN2001 · #9 03-04-2023, 08:43 PM

Installed new ABS sensor (left rear), no longer getting ABS light or code...which is good.

However, now speedo doesn't work. I am thinking it has to do with my connection to the Vehicle Speed Sensor wire into the ECU.

Sadley, the soft ineffective brakes still exist.

My buddy helping out with this project seems to think it's electrical and related either the ABS or hydraulic pump.

However, I think the issue may due to a faulty brake booster and the angle of the pedal assembly MY2017 sti pedal assembly.

The pedal assembly angles were all wrong but we made it work through extensive modifications, while still using the stock gas pedal. As other's have mentioned, I now know why they don't use the newer model assembly's. The brake pedal rests at least an inch down (closer to the firewall) than the gas pedal. The alignment is very unnatural, and dangerous frankly.

My thoughts are that given the angle we may have modified (shorten) the brake booster push rod more than what others have. Due to the angle and shorten push rod, perhaps there isn't enough travel to actuate the booster throughout it's normal span of operation?

There may still be hope in salvaging the current pedal assembly, but just in case will a MY2002 WRX pedal assembly be a better fit for our cars? What brake booster would be best to match it up with? The MY2002 WRX's brake booster vacuum line point up, whereas our (SVX) booster projects out.

Tireiron · #10 03-04-2023, 09:47 PM

A GD Impreza pedal assembly and booster work great. Get the booster vacuum line from the Impreza also, it has a hard 90⁰ to face in the correct direction.

TomsSVX · #11 03-07-2023, 07:14 AM

Might want to check and make sure the brake booster hose is connected correctly. It has a check valve inside and will render the booster ineffective if backwards

Tom

SVXMAN2001 · #12 03-07-2023, 09:45 PM

Tom, the booster hose is form fit. I just now tried switching it around but it was definitely in a forced position. I didn't realize there was a check valve in there. Looks to have one on both ends

SVXMAN2001 · #13 04-02-2023, 10:14 PM

Problem solved. All had to do with the travel of the brake boosters push rod. Modified the brake pedal to allow for more travel. Also had to create a new mount for the brake switch to accommodate the brake pedals new position. But all is well now. Still some fine kinks to resolve but she's running very well.