how can I fix a leaking nipple...

jwasbury · 08-12-2010, 08:01 PM

...on my rear brake caliper

My car is up on stands for a suspension rebuild and I noticed that one of the bleeder screws has been leaking. Just a little wetness around the nipple, but I've never noticed any fluid on the ground in the garage.

So I ordered up a new bleeder from our host, installed it tonight and now its much worse...drips pretty well with pressure on the pedal and leaves a little puddle on the ground. Reinstalled the old one and its now leaking like a sieve too. The leak is from the nipple, not the threads.

pete3799 · pete3799's Garage

Does the inside of the caliper (mating surface) look alright?

Ofishbein · Ofishbein's Garage

Wow - I thought this post was about something else entirely. Never mind.

KTL · 08-13-2010, 05:58 AM

Sounds like someone may have overtightened the bleeder screw and deformed the seat surface in the caliper casting. If that's the case, i'd not diddle around with some sort of fix attempt. Simply get a replacement caliper because the rear calipers for your car are VERY plentiful on the used market.

Point of reference: Friend with a '96 993 had a rear caliper that showed a bleeder screw that appeared a little bit loose when bleeding the brakes at a track day event. We didn't think much of it and snugged it down. Next day while on the track his brakes went soft at perfectly the wrong corner of the track- Blackhawk Farms T4 which has little runoff room and a concrete wall. Pedal went to the floor and there wasn't enough time for him to get the car slowed with some pedal pumps, so he ended up nosing the car into the wall. Turns out that bleeder screw hole was stripped and the bleeder backed out again.

jwasbury · 08-13-2010, 06:03 AM

Quote:

Originally Posted by pete3799

Does the inside of the caliper (mating surface) look alright?

I suspect the problem is with the seat inside the caliper. I noted the old bleed screw had some rust/corrosion on the bottom where it beds against the seat. The caliper is aluminum I think, so I don't think it can rust. Not sure how the nipple rusts either...the only thing I can think of is that the system had a lot of moisture in it at some point.

My question now is is there any way to clean up the seat to get a good seal again or will I need to source a new (good used) caliper? The hole is deep and I'm trying to think of something I can get down in there with to refresh the surface. I'm thinking mini brass bristle wire brush attachment on a dremel, but I don't think they make such a thing that will fit in this small hole.

Oh, and the thread title was meant to attract some attention and get some ideas from the brain trust. Someone has dealt with this before and I really hope I can save the caliper.

KTL · 06:18 AM

Oops. I take that back that your calipers are plentiful on the used market. I mistakenly read someone else's signature, thinking that your car is a '79 SC. '79 930 calipers demand a premium and are not all that plentiful. That being said, I still say the caliper should be replaced.

You could have a machinist re-drill the hole for the next size bleeder screw. The reason I say it should be drilled oversize is that I believe the threads in the hole will get damaged if the hole is drilled for the same size/shape seat, but just a little deeper?

Maybe contact someone like this, who specializes in restoring vintage calipers

http://www.whitepost.com/brake.html

jwasbury · 08-13-2010, 06:35 AM

Dremel 537 is a small brass brush...anyone think this may work or am I smoking crack? Never seen one at the Home Creepshow, but they are available online.

My friend also suggested a kit where you drill and tap the hole, and an insert screws in that has an integrated new seat. This may be an option

If I have to source another caliper, so be it. Just seems like a waste to toss this part with such a stupid (yet deadly) problem.

dad911 · 08-13-2010, 06:44 AM

Look in the bleeder hole. Compare it to the other one. Need more info.........

Might be stripped, might just be dirty.

If it needs repair, talk to Bob Denzer at:
Verden Tool & Manufacturing Company 121 E Blackwell Street Dover NJ (973) 366-7510

jwasbury · 08-13-2010, 06:55 AM

Threads are not stripped...the leak is from the bleed nipple, not from the threads.

Verden did the machine work for my recent DIY engine rebuild. Know them and trust that they can do something, but I'm hoping for a DIY fix if possible.

hoyabear · hoyabear's Garage

Jdub · 08-13-2010, 08:06 AM

The best advice is outright replacement. You may have to purchase a pair for the rear end so that the action of both calipers is identical and the history the same (assume rebuilt).

That said, what happens when you put a Q-tip into the caliper hole - what shows up on the cotton? You might get lucky and find only rust that is preventing the ~45degree mating surfaces from mating. If no luck removing rust particulate, I have know folks to use a drill bit, undersized so it does not touch the threads, angled at the same degree as the caliper seating area (measure the nipple bevel to determine - drill bits are re-angled on a fine stone grinder making sure that the biting surface is the highest "point" of the drill bit). Here you are unseating stubborn rust, etc. CAUTION: You could ruin the caliper this way, so be careful - slight easy turning BY HAND with copious amounts of compressed air. Bleed after to purge anything that might be in there. Then reseat the nipple and see how it goes.

Dodgy advice for certain, esp. around brakes which are the most important part of your car, period. Please be careful with any fix other than outright replacement. The core $$ for your 930s should be pretty solid on tradein I would guess.

Best of luck - John

cfries · cfries's Garage

Great pic Hoyabear, it was only a matter of time...