On the Subject of Brakes...

[karmavore]

1) Now that I’ve swapped the TMC calipers and rotors on my S4 to the Hi Spec set provided by PNM Engineering there is a delay in my braking of about two seconds when I hit the pedal. When they grab, they grab, but it takes a moment and it is very disconcerting. I imagine that the switch from 1 piston to 4 four requires more pressure in the system, and if this is true how can I account for it and eliminate the wait?

2) What does it mean when the ABS light flashes? Mine does this occasionally and only goes away when the car is recycled?

3) How often is that pump in the front of the car supposed to activate? I had heard that it was every fourth hit of the brakes, but after a day of twisties in the north Georgia mountains mine was turning on every time I hit the brakes. What does this pump do and is this normal”

Thanks for any help!!

Luke.

[mikelr]

Luke,

You may have one or more problems with your system,

- your ABS accumulator (brake bomb) may have gone south.

- you may just need to thoughly bleed the brake system as per the factory manual (including the bleed screws on the master cylinder itself).

On a side note,
The HiSpec 4-pot caliper actually displaces less fluid than the stock TMC single pot, the increased rotor diameter makes up for the decrease in brake torque applied by the smaller caliper.
Overall the HiSpec kit offers a 1% increase in brake torque over the stock setup. Although they are lighter and may offer better heat management.

If I were you I would bleed the system agian (by the book) and afterwards if the ABS pump is still cycling after only one press of the pedal replace the accumulator.

Good Luck!

Mike

[karmavore]

Thanks Mike.

<search> first, ask questions later. I see lots of posts on this topic.

Luke.

[fflyingdog]

Before you replace the accumulator check your accumulator pressure switch is working correctly as this will cause the pump to run,ie: pressure drops switch senses it and puts the pump on,bad switch will mean pump runs when it doesnt need to,cheaper to replace switch first ! Lotus have replaced the switch with a different part number which has changed operating parameters( the old switch is black the new one is grey)
Hope this helps
Nick S4s

[karmavore]

I replaced the accumulator (via (www.GMPartsDriect.com) per Karl's instructions:

(www.pistonheads.com/gassing/topic.asp?t=128888&f=17&h=1&hw=25528382)

..and things are back to normal. Easy fix, though I recommend to anyone doing it to wrap a rag around the end of the unit as they're twisting it off because it will squirt some very high pressure brake fluid – I skipped this part. I depressurized the system as best as I could (50ish hard pumps) and it still squirted a little.

Anyway, it's hard to believe that something so solid can go bad. Mine did have some corrosion around it, but still..

Thanks guys,

Luke.