79 Spider Brake Issue

[phillyfiat]

Hey all -- having an interesting issue with my 79 Spider under braking. Most of the time I have pretty even pedal pressure when I go to brake, but recently there have been moments when I go to push the pedal and it goes to the floor. If I pump it quickly, I get pressure back and the car stops normally, but that first moment is a bit exciting.

I had some work done on the brakes about a year ago (rubber lines replaced and the system was bled). I checked my fluid level and it was a little low so I topped it up, but still having the intermittent issue.

How should I proceed from here?

[TX82FIAT]

Could be a slight leak in line or caliper the rebuilds pressure when you pump the brakes. Check around your master cylinder to make sure no leak. Brake Fade is a likely suspect as the brakes get hot during heavy braking on hills and corners, has scared the heck out of me before, to remedy this I replaced all the brake fluid. Moisture or air in the brake lines could be a culprit as well. Feel your wheels after a drive to make sure you do not have brakes rubbing, once brake fluid boils it will never brake properly. If no heat on wheel or sign of leak I would blead the entire braking system. A small leak can let air in and not change the level of fluid dramatically. You may need an assistant to pump the brakes as you inspect the braking system. While it is messy, I have also used baby powder in the area of a suspected brake, coolant, oil leak to see where the leak is originating from. Good luck.

[phillyfiat]

Thanks TX -- That makes sense now that I think of it, the last time I had it out before the brakes gave me trouble I went up and over a few smaller mountain passes. I'll bleed the system and see if that does the trick.

[18Fiatsandcounting]

A soft pedal can be air in the brake lines or in one (or more) of the wheel calipers, but a pedal that goes to the floor and then "recovers" is often air in the master cylinder. These can be notoriously hard to bleed, but numerous brake bleeds is usually the fix.

I start with the rear calipers, bleed those, then move to the front and bleed those. Then repeat. It's not usual to go through at least a pint of brake fluid, and sometimes it takes almost a quart. Make sure the reservoir never goes dry when bleeding as you then have to start over.

When bleeding the rears, lift the rear axle up by the differential (not the car body), as that insures that the rear brake regulator isn't limiting fluid to the rear calipers as you try to bleed them.

If the fluid level drops in the fluid reservoir over time, then yes, you likely have a leak somewhere.

-Bryan

[davidbruce]

How old is your master cylinder? I have seen cases where the piston cups in the m/c have started to fail. Slow steady pressure lead to the pedal going to the floor but stomping on the pedal caused the cups to flare out resulting in a hard pedal. When you pumped the brakes were they relatively fast hard applications? Try a slow steady application and then a sudden hard application. Is there a difference in pedal firmness?

[phillyfiat]

Dave -- in a word -- old. I have a feeling the best course of action is to replace the master, booster, and flush. I know all four calipers have been replaced not long before I purchased a few years back, and I had most of the brake lines replaced as well so this seems like the best course of action.

I have it parked for the winter, but I'm going to do a flush, see what happens and look at updating the rest of the system.

[davidbruce]

That is probably the best course of action. If you haven't replaced all 5 rubber brake hoses, now is a good time. The hose from the body to the centre of the diff on my '73 looked fine externally. It was swollen inside and caused the rear brakes to lock on. Spoiled my (and my wife's) day! This one is often overlooked.