Spongy Brake Pedal after VT Brake Upgrade

[DJ Ice]

Just finished fitting one of these kits, COMMODORE VR VS TO VT BIG BRAKE UPGRADE SLOTTED DISCS - eBay Standard Parts, Holden, Car Parts, Cars, Bikes, Boats. (end time 30-Nov-07 11:06:06 AEDST). VT Calipers discs and braided brake lines and now have a really spongy brake pedal. Have bled all 4 brakes as per Gregorys and PBR guide and still have a really spongy pedal....like bleeding the brakes made no change.

What am I missing ????

 

[Not_An_Abba_Fan]

You will probably find that you will need to upgrade to the VT master cylinder and fit the spacer to the pushrod. VT brakes require more fluid volume and the VS m/cyl isn't quite up to the task.

 

[DJ Ice]

You will probably find that you will need to upgrade to the VT master cylinder and fit the spacer to the pushrod. VT brakes require more fluid volume and the VS m/cyl isn't quite up to the task.

Thanks for your input but I think something else might be off (But you could be so right). I've gone from a really firm high pedal to a very spongy low pedal which improves with a few pumps.

 

[hako]

You may need to drive the car for a few miles to wear the brakes in before the pedal becomes firm. If you have ABS you may need to bleed the ABS unit with a scanning tool.

 

[Not_An_Abba_Fan]

The low pedal would be the amount of fluid required to push the twin pistons of the calipers out, pumping it just pushes the volume through the lines until you have enough there to push the pistons out. Unless you have removed the ABS module or let the reservior run dry, it shouldn't be necessary to bleed the ABS module.

When you bleed the brakes, the best way to do it is to have two people, one to push the pedal, one to open the bleed nipple on the caliper.

Attach a clear hose to the bleed nipple with the other end in a bottle.
Open the nipple and have your assistant push the pedal down half way.
Close the nipple and release the pedal.
Repeat until you have a steady stream of fluid through the clear hose, with no bubbles.
It is important not to push the pedal all the way to the floor, as this will make the internal cups of the M/cyl push past their normal operating area and it may damage them. This may cause the piston in the M/cyl to bypass and the pedal will slowly go to the floor when applied.
Make sure the reservior is kept topped up.

If this doesn't improve the brake feel, then I would fit a VT M/cyl.

 

[hako]

Adding to the good advice from NAAF, bleeding may cause the brake fail light to be activated when you start the engine. This warning light should extinguish when you get a firm pedal and can apply firm pressure to the pedal - this should reset the light.

 

[DJ Ice]

Thanks guys I hope it doesn't come to having to change to VT booster and master cylinder...it will blow out the cost and I don't feel like getting custom brackets made etc.

Here is a thought....I've looked on PBR's website and see there is no 1" Master cylinder for VR with ABS, could you use the Non-ABS 1" Master cylinder and blank off the extra outlet ?? like on the VT.

 

[Boonz]

pretty sure you cna do that

 

[DJ Ice]

pretty sure you cna do that

cna ? Not sure what or who you mean.

Doh...just worked out what you meant....typo can't do that

 

[muttley383]

I would have thought that once the piston and pad assembly is initially bled and with the pad in contact with the rotor then bugger all fluid capacity would be required as there is no gap to fill, just pressure needed for pad to rotor contact.

I have the AP four spot set up on front and rear of a VR and I did not change the master cylinder and the pedal height feels ok to me.