I know I have posted 3 post already about my abs lights. But anyway, I changed the wheel cylinders from 27MM(stock) to 30MM(for a like 83 chevy 3500) to stop my truck a little better. I was wondering if you guys think that the bigger wheel cylinders aren't getting enough pressure and that is setting off the ABS light. Once again my code says-- Code 78,Partial Brake Failure. I am thinking of changing back to the stock 27MM ones because the light never came on until like 2 days after I changed the cylinders out. Well maybe you guys have some words of advice. Thanks

 

Changing to larger wheel cylinders won't cause the light to come on. You may need to bleed the brakes better though and make sure they are adjusted correctly.

 

If you ran the master cylinder too low while bleeding it could set off the light. It will stay lit for 50 or so key on/off cycles or may go off if you disconnect the batteries for awhile.