Re: The Duchess Project: 1940 Super 8 Convertible Sedan
Posted by HH56 On 2022/4/25 9:47:21
When doing the 47 brakes several years ago I too had the issue of a drop or two leaking each time brakes were applied as apparently have a few others -- but not all -- when using the Napa SL134 switch. Could you check how far your new switch threaded into the bolt. I just looked at mine which is the Napa SL134 replacement and see it threaded in almost to the shoulder of the switch. Out of curiosity I tried an old original but bad switch I have on a spare bolt, making sure the threads were clean on both, and it went about 5 or 6 threads in before starting to get tight. Am almost wondering if the Napa switches actually are 1/8-27 straight thread vs 1/8-27 NPT or if they are using a one size fits all approach with a minimal NPT taper that might be made with a looser spec and doesn't work well with older fittings that were true to US spec..
Am not sure where the brass O_D mentioned is coming from. My output bolt on the 47 master is all steel and so is the spare bolt and the switch thread. I will be the first to agree with O_D any kind of sealant should not be needed and is a practice to be avoided but sometimes need forces bad behavior. I used teflon tape and that seems to have solved the problem for now. If you are going to try some kind of liquid sealant, IMO Permatex #1 (hardening) or #2 (non hardening) or one of the thicker pipe thread sealants impervious to brake fluid might be a better choice than a thin thread sealant. Admittedly my car has just sat in the garage so the teflon tape has been unproven as a permanent fix but it has held up so far and the leak is still not present which was all I wanted at the time.
If you have another SL134 and some calipers maybe you could give a quick check to see if the switch is actually NPT. This old switch has a very very slight taper and difficult to see and more so to photograph but holding up so a light could shine thru from behind I was able to visualize a slight difference in diameter on the original switch. Don't have another SL134 to check and don't want to remove mine from the car but would be curious if you or someone else could check and see a taper.
Attach file:
IMG_2528.jpeg (28.35 KB)
taper.jpg (108.12 KB)
Am not sure where the brass O_D mentioned is coming from. My output bolt on the 47 master is all steel and so is the spare bolt and the switch thread. I will be the first to agree with O_D any kind of sealant should not be needed and is a practice to be avoided but sometimes need forces bad behavior. I used teflon tape and that seems to have solved the problem for now. If you are going to try some kind of liquid sealant, IMO Permatex #1 (hardening) or #2 (non hardening) or one of the thicker pipe thread sealants impervious to brake fluid might be a better choice than a thin thread sealant. Admittedly my car has just sat in the garage so the teflon tape has been unproven as a permanent fix but it has held up so far and the leak is still not present which was all I wanted at the time.
If you have another SL134 and some calipers maybe you could give a quick check to see if the switch is actually NPT. This old switch has a very very slight taper and difficult to see and more so to photograph but holding up so a light could shine thru from behind I was able to visualize a slight difference in diameter on the original switch. Don't have another SL134 to check and don't want to remove mine from the car but would be curious if you or someone else could check and see a taper.
Attach file:
IMG_2528.jpeg (28.35 KB) taper.jpg (108.12 KB)
This Post was from: https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=243085