elusive leak

mbouse · Post by **mbouse** » Tue May 05, 2009 10:17 pm

brake fluid on the floor, but only after the brakes have been bled. once the pressure is gone, there's no leak, even if the reservoir is refilled.

the leak is slow enough not to be seen dripping, but has enough volume to show a noticable volume difference in the reservoir after 24 hours... and quite the puddle.

driver front corner

thoughts on where the leak is before i tear the wheel off and look for the third time?

adrians · Post by **adrians** » Tue May 05, 2009 10:25 pm

Possibility

Split in the rubber hose or the join between hard and rubber lines - my join ( fittings/connector ) blew off a few weeks ago on the 128.

kilrwail · Post by **kilrwail** » Tue May 05, 2009 10:33 pm

Maybe the copper crush washer between the rubber line and the caliper? Was it replaced and tightened well the last time you had the caliper out?

kmead · Post by **kmead** » Tue May 05, 2009 11:07 pm

Is the puddle at the wheel or under the body proper? Gravity is working against you all the way here as a leak at any of the joints around the master cylinder will end up on the floor in the vicinity below the body. A leak at the caliper will tend to leave the wheel, the backer plate or the splash shield wet.

I would start with the reservoirs and work down from there. A drip down the firewall can be difficult to see with all the stuff on there, you will end up with very little paint where its tracing down to the ground after a while.

mbouse · Post by **mbouse** » Wed May 06, 2009 8:22 am

Brand new everything from the transition point of hard to soft lines, Peter. the caliper is painted with the paint i complained about last year, so any leak at the caliper would have been blatantly obvious.

it's the corner we had trouble with last summer, Karl. and, yup, the puddle forms about six inches away from the wheel (toward the center of the car).

i'll giver a look starting at the master cylinder down this evening.

manoa matt · Post by **manoa matt** » Wed May 06, 2009 3:35 pm

Mike,

Jack it up, crawl under and look up where the master cylinder mounts to the booster. See if you have any fluid dripping off there.

rlux4 · Post by **rlux4** » Wed May 06, 2009 8:35 pm

That's where mine was leaking Matt. I finally found it when I saw the paint on the inside of the fender well was coming off.

Ron

lanciahf · Post by **lanciahf** » Wed May 06, 2009 8:42 pm

Mike,
Check the master, I know its new but I bought a new one from a vendor and it leaked from the get go.

Ralph

manoa matt · Post by **manoa matt** » Wed May 06, 2009 9:26 pm

Sorry to hijack, or are we calling it pirating now? Anyway while we are on the subject of master cylinders. Does anybody know the reason for the two screws/caps on the bottom side of some MC's I've seen them on originals, but most of the replacement or aftermarket MC's don't have them. Bench bleeding? Complete fluid flush?

kilrwail · Post by **kilrwail** » Wed May 06, 2009 9:30 pm

Matt - You surprise me - you'd be the guy I would ask that question!

They're called "piston register bolts", which I suspect are there to index the rearmost position of the two pistons.

mbouse · Post by **mbouse** » Thu May 07, 2009 7:44 pm

ding..ding..ding..ding..ding

you are right Matt! leaking like crazy between the master cylinder and the booster.

What now? new master cylinder?

manoa matt · Post by **manoa matt** » Thu May 07, 2009 9:01 pm

Well...chances are, there is some brake fluid in the booster. New master cylinders are relatively cheap ($40) but the boosters are not ($230)

About 1.5 years ago my booster went out. (the one part in the system that was not replaced that soon became the weak link) I didn't have any parts cars at the time so I bought a new booster from IAP, at that time it was slightly cheaper but still around $200. When it came I compared it against the original. The mounting studs were longer and not threaded all the way down, which necessitated some 3/8" thick nylon washers, and an extra foam "doughnut" gasket to properly mount and seal the booster. The booster came with a spec sheet for the pushrod length that differed than the Fiat factory manual spec. Fortunatly there was some overlap in the spec lengths and I adjusted to "in between". The vacuum check valve was plastic instead of metal and felt weaker compared to the original. It could be the original check valve diaphram has hardened over time from the heat.

Needless to say I was less than satisfied with the "new" booster, the high price was icing on the cake. Since installation I have not been able to get a firm pedal. With the car off the pedal if firm. While driving the car will stop when the pedal is depressed half way, but it can continue to the floor. I've pressure bleed, vacuum bleed and old fashioned pedal bleed everything several times and pushed gallons of brake fluid through without firming up the pedal. It's not spongy, with the car running but stationary I can pump the pedal and hear a swooshing noise. To me it seams it's overboosting.

Since then I've aquired two original boosters and I'm tempted to install one of those to see if it makes a difference. Its just a PITA to install one since you have to re-bleed the entire system and lay on your back to undo the mounting bolts at the pedal box. You are welcome to the other booster if interested. I think I'd rather install a used booster than shell out for the new one, even if it goes out in 2 years or so.

rlux4 · Post by **rlux4** » Thu May 07, 2009 9:05 pm

It's not a given that leaking out the rear of the MC will destroy the booster, is it Matt? Mine leaked for a couple of weeks until I finally found it when it drained the reservoir overnight, and the booster wasn't affected in any way I can tell.
Ron

mbouse · Post by **mbouse** » Thu May 07, 2009 9:07 pm

grrr... i was afraid you'd say that. the thought that caustic fluid was entering the booster did not appeal to me, but could not shake the dreaded thought.

i will order a new M/C tomorrow, and then when i tear the system down, inspect as best i can the booster. i'd like to minimize my expenses, but doing things twice does not appeal to me either.

give me dibbs on that spare you have there...it will be a couple of weeks before i get started on this project. Gotta go meet some Fiat Freaks in Toronto next week, and that is always a priority.

manoa matt · Post by **manoa matt** » Thu May 07, 2009 9:23 pm

It might not be THAT bad. I would assume given the proximity of the booster to the master cylinder and that the rear seal on the booster is right there, that the booster would be designed to withstand "some of the effects" of stray brake fluid. The seals in the master cylinder are rubber, the seals in the calipers are rubber, the brake hoses are rubber, and the fluid reservoir is plastic. The seals/diaphragm in the booster are most likely rubber.

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