Brake pedal is firm on starting, soft after moving - dealer says it's OK! Anyone else?

[bikerlady]

I have a 2018 Spyder RT SM6 that has a issue with the brakes. My pedal is firm upon starting and after I have moved about 50 ft the pedal is soft and it slows slowly. If I touch the brake again I have a full hard pedal.
I have replaced the pads on all 3 wheels and bled the system including the VCM several times. No fix. I replaced the master cylinder seeing a small amount of moisture on the boot. Still nothing. Took to the dealer and they did the BUDS system. Said it was ok. Everything was within spec. Not fixed. Returned and they replaced the VCM. Still not fixed. I am going back to see if they can finally find the problem but I would like to know if anyone else has had this issue.

 

[JayBros]

IMO you have a dealership that doesn't know what they're doing. How did you bed in the new brake pads?Did you do a succession of high speed panic slowings? When they bled the brake system, did they bleed the ABS module? Politely tell them to call and open a case with BRP and find out what's going wrong.

 

[mecsw500]

How old is the brake fluid? Did you bleed some out and measure the moisture content? Perhaps it needs a complete fluid flush from master cylinder to front and rear calipers? I had a Jaguar XF that did the same. The fluid looked OK in the master cylinder, but the fluid deep in the lines was too high a moisture level having been pumped down from the master cylinder over time. All the seals were good at the calipers and the master cylinder, it was just aging fluid. Once it was all flushed out to new fluid it was all just fine. I bought the car from a humid southern state and I didn't expect it to be an issue as it's really desert dry here and I'm used to brake fluid seeming to last much longer. The fluid was four years old but it measured like it was double that. I changed the fluid as a last resort after trying all kinds of things relating to ABS pumps and what do you know, it fixed it.

 

[UtahPete]

How old is the brake fluid? Did you bleed some out and measure the moisture content? Perhaps it needs a complete fluid flush from master cylinder to front and rear calipers? I had a Jaguar XF that did the same. The fluid looked OK in the master cylinder, but the fluid deep in the lines was too high a moisture level having been pumped down from the master cylinder over time. All the seals were good at the calipers and the master cylinder, it was just aging fluid. Once it was all flushed out to new fluid it was all just fine. I bought the car from a humid southern state and I didn't expect it to be an issue as it's really desert dry here and I'm used to brake fluid seeming to last much longer. The fluid was four years old but it measured like it was double that. I changed the fluid as a last resort after trying all kinds of things relating to ABS pumps and what do you know, it fixed it.

Per OP "I have replaced the pads on all 3 wheels and bled the system including the VCM several times".

 

[mecsw500]

Bled, but was it a full flush through to clear? That was the mistake I made with the Jag. I bled the air at the calipers and exercised the ABS pump but it still had tired fluid in the lines. It didn't take much to feel weird like the OP described.

 

[UtahPete]

Bled, but was it a full flush through to clear? That was the mistake I made with the Jag. I bled the air at the calipers and exercised the ABS pump but it still had tired fluid in the lines. It didn't take much to feel weird like the OP described.

Good point.

 

[mecsw500]

Good point.

Thinking of it, if they replaced the VCM I'm sure they must have put new fluid into it.

Perhaps the only thing left is the ABS hydraulic modulator unit itself which is what actually controls the brake pressure in the lines, under control from the VCM?

The BUDS testing should have exercised that unit when they replaced the VCM, but if the problem is intermittent?