Strange brake issues on 308

Did you change your fluid straight from regular DOT3/4 brake fluid to Synthetic or did it always have the sythetic fluid?

Did you bleed it properly? If so it maybe your brake master sylinder.

 

Make sure the check valve in line to the brake booster isn't stuck from sitting.

Sean

 

My vote are the seals in the master cylinder are going bad or are bad. Assuming a rebuild kit is made for the part, rebuilding it should cost under $75, or you can just buy the part from Ferrari, but no doubt it will be considerably more expensive.

 

+1, I had this problem and the check valve was bad on my 328GTS

 

If you cant see any fluid leaking then I bet for sure you will find the fluid has leaked out of your master cylinder into the brake booster which if the diaprham has been bathing in brake fluid for the last six months will have to be reconditioned as well.You can get new aftermarket master cylinders from Superformance for around $US315+shipping.I dont think Ferrari sell them as they sell them complete with the booster.I think Trutlands has one

 

Booster trouble won't cause a soft pedal. The booster helps you push the pedal, and I can't imagine a situation that would cause excessive boost. If the pedal is soft with vacuum supplied, your leg should be strong enough to get it to the floor with the motor off. If fluid is leaking from the master into the booster, the level in the master should be low. It is possible, and likely from your description, that there is an internal leak in you master allowing it to not build up pressure while at the same time not leaking externally.
I am cautious of DIY master rebuilds because the bore surface of the master is of critical importance.
Cheers,
Tom
Would love to make it to the IOM one day for the bike races.

 

Sounds like a problem with the brake booster. But you say you put in "synthetic" fluid. Is it synthetic or silicone? Exactly what fluid did you put in? I know several people who changed over to silicone fluids and did not properly clean the system before putting the silicone fluid in. That can cause all kinds of problems, as silicone (DOT5) is not compatible with standard brake fluids (DOT 3 & 4). Even if it was properly cleaned, silicone fluid can "gel" under severe braking situations, like taking the car on the track. Also, as it does not absorb water, moisture can pool in the system reducing the boiling point significantly. My rule of thumb -- never use silicone brake fluids.

So, assuming you used DOT 3 or 4, and you've bled the system and still have the problem, I'd check the brake booster, and the vacuum line from the engine forward, and clean or replace the one-way valve near the engine to be sure you are holding a good vacuum on the system.

One other thing -- are you missing any brake fluid? If so, check the seals, and look up under the dash and see if you are leaking in their. On some cars, that seal will let go and you don't see the fluid being pumped into the cockpit and running down under the carpets. Just a thought.

 

+1

If the boosters are bad the fluid level would drop as the engine would be sucking it in. The seals in the MC piston are letting fluid bypass them.

Ken

 

I don't recommend synthetic brake fluid and NEVER use silicone!

Castrol GTLMA DOT4 is what I would recommend once you get everything working again.

 

Don't mean to start a fuss, but he says the pedal is firm with the motor off, goes to the floor at idle. How can this be booster trouble? This tells me there is a fluid pressure problem that only becomes evident when vacuum is supplied to the booster. The booster only helps you push the pedal, it does not effect fluid pressure. Maybe if the booster was too large it would suck the pedal down, but you guys haven't explained why the car does not stop.
Cheers,
Tom
I still want to see the IOM one day

 

David,

I did my brakes last winter. Remember, they are Ate brake calipers, the same as late 70's/early 80 Porsches, so rebuild kits are cheap. I ended up sending mine out to a local shop for rebuild because I was short on time and had other things to be working on. Not expensive to have a shop that does brake caliper rebuilds do them. You don't need a "Ferrari" brake shop, any decent brake shop can do them for you.

If you have been running DOT 5 (silicone, not "synthetic", fluid), you need to do more than blow the lines out. You need to flush them to use DOT 3/4 fluid. IIRC, you can flush them with alcohol and then blow them out to clear out all the silicone.

Do you plan on racing your car? If not, don't waste your money on Castrol SRF. It is very expensive and only important if you are doing a lot of heavy track driving. If you are just doing some "track days", use something like Motul 600 or ATE Super Blue (or Amber). I use ATE Super Blue, which is a racing fluid but costs about the same as standard fluid in my Corvette, which I track regularly. If you are just driving the car on the street, not racing, then stick with Castrol LMA. It's all that you need. I use LMA in my Jaguar XKE and my 308. IMHO, short of a real race car, SRF is a waste of money.

 

Caliper rebuilds are simple and straight forward. I would not split the calipers unless it is necessary. Just do a standard rebuild on the fronts and if your rears don't have froozen adjuster screws then you should be OK. I just rebuilt one of my rears and didn't redo the handbrake seals. The caliper seals run about $18 per wheel. I also would not run alcohol through the systen. Just plain brake fluid should do. Use normal method starting with furthest wheel from the drivers seat. Good luck

 

With the engine off, pump up the brake pedal until firm. Now hold strong pedal pressure with your foot for a good 2 minutes. If the pedal starts to sink to the floor, you either have a leak somewhere in the system, or your brake master is leaking internally.

Remove all 4 wheels. With the help of an assistant, have them hold heavy pressure on the brake pedal, and you go around the car and inspect for leaks at the calipers, lines, unions, etc. Look at the master cylinder mounting flange to the brake booster, closely. If you have a trail of wet brake fluid, then your master is leaking from the seals, get it replaced or rebuilt PROFESSIONALLY.

 

Mainly because the bores on the insides get pitted and the require either honing, or resleeving. You need to have the right stuff to do this job correctly. The rebuilders will also have all the correct equipment to pressure check the master to be sure it will hold pressure and maintain the pressure before installing it on the car. If anything goes wrong, you have recourse with the rebuilder.

Please be safe and have a pro do the work, your dealing with brakes here, if they fail its not easy pull over and stop.