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I've rebuilt the brakes on my '69 350 but two of the bleed screws are leaking, even with new screws. I've tried winding PTFE tape round the threads, blocking off the hole and covering the screw with Hylomar instant gasket and with silicon sealer but no good. The trouble is the brakes have to be bled before any sealer can be added so it's already wet with fluid and the sealer won't adhere. Is the problem that the screws aren't seating properly at the base of the chamber, and if so, how can they be made to shut off? One of the calipers is brand new so buying another wouldn't help.
I would try a different brand of bleeder screw first. But the bottom line is, they are supposed to seal at the bottom tapered seat. return the caliper.
For what its worth, I had to go to three different parts stores to get six bleeder screws. Each store only had one or two of the correct size.
What I did not realize was, that few of those screws were matched. The fitment or lack of fitment was all over the place between perfect and sloppy.
Most were undersized. Keep shopping.
also note you can see how it is seating all the way around or not as it should indent some... maybe not stainless unless perfect seat.. i went thru several and dressing seat
If new bleeder screws don't fix the problem, there is an insert you can install under the bleeder. It will actually form a new seat. They look like inverted washers. Do a search on the forum. I just can't remember exactly what they are called. Jerry
Thanks guys for your advice. I'll try ordering new screws to start with and see if this works. I didn't know the screws could be so different. Thanks also for the link to an earlier thread - very interesting info. About a year ago I noticed two calipers were leaking so I ordered new ones from the States - I live in the UK. I had to wait about four months because of a shortage of new calipers due to the pandemic. I fitted them but noticed the other two were now leaking. Rather than wait for months again I got new lip seals for these old ones. Then I discovered the two brand new calipers were leaking from the pistons. I had to send away for seals and repair them. The other two old ones after having new seals didn't leak so in future I'll always try to repair the old ones first and save several hundred dollars and a huge delay. I haven't heard of Rockauto, so maybe I could ordered parts from there. It would be interesting to see if the inverted washer inserts would fix the problem. Ill let you know how I get on.
I think that the sealing method is AN type (Army-Navy) where the male end is 45 degrees and the female end 44. Or maybe similar. This relies on direct metal-metal contact of the edge of the truncated cone, and usually works best if the male end is a softer metal.
The problem is that so much is made in China and therefore junk.. The angles are off or the edges are rough.
Assuming that the calipers are iron, try sanding the sealing face of the mild steel bleed screws to a smooth face. Put the screw in a drill press and use a sanding block and 220 grit paper. Or better yet, find some US made brass screws.
You'd think it must be possible to insert some sort of small O-ring or nylon washer at the base of the chamber so if the machining isn't perfect the O-ring would allow for any inaccuracy. I might experiment with the idea as long as I can pull it out if it doesn't work. I put in a new screw today and it leaked badly again. It's easy enough to cap the hole but the fluid leaks up through the threads. I hope I can find a solution soon - the first car show of the year is at the end of the month!
You'd think it must be possible to insert some sort of small O-ring or nylon washer at the base of the chamber so if the machining isn't perfect the O-ring would allow for any inaccuracy. I might experiment with the idea as long as I can pull it out if it doesn't work. I put in a new screw today and it leaked badly again. It's easy enough to cap the hole but the fluid leaks up through the threads. I hope I can find a solution soon - the first car show of the year is at the end of the month!
inspect where it seats..shine light up there or phone flash pic.
what does the new screw look like? It should mark where it seals and doesn’t
As I mentioned earlier in this thread, there is an insert you can install on the seat and it will form to any irregularities between the seat and the bleeder screw. Do a search of the forum as they have been mentioned before. Jerry
I just watched a video of someone making their own flair washers using a tubing flair tool. Might be an alternative, if you can’t find the flair washers:
Excellent info regarding the copper washer gaskets and the You Tube video about how to make them fit the caliper bleeder chamber. I'll go down to the hardware store and ask about copper washers and hopefully I can get the right size and flare them myself. If I can't find them here I'll send away to Zoro and ask them to send me a packet. The bleeder screw hole diameter looks like 1/4" with the inlet hole at about 1/8" although I'm not sure if this is definitely right. I think this is the answer and considering how common a problem it is, you'd think a new caliper would come with a packet of these washers, especially when they cost nothing to make, and that you could buy a packet along with the bleeder screws. About the 'broken screws' related thread below - when I took off the calipers and screws I used a blowtorch and a long socket wrench every time before attempting to remove them and every bolt came out with no damage.
It could also be that the sealing seat in the caliper is damaged or has corrosion or 'trash' on the seat so that your bleeder will not seat properly. There is some problem, either with the seat in the caliper or with the bleeder screws (or both) which is causing the leakage.
Leaking caliper bleed screws
