New C3 Caliper Bleeder Screws Leaking

[Jim T.]

Re: New C3 Caliper Bleeder Screws Leaking

Something else you could try with the stainless bleeders is coating the threads with anti-sieze lubricant. This lubricant may allow the stainless steel to thighten more and seal without damaging anything.

[Joe L.]

Re: New C3 Caliper Bleeder Screws Leaking

Even if the bleeder is properly sealing against the caliper vacuum could still pull air from around the threads through the hole in the bleeder screw, right?
Jack

Jack------


Yes, I think that's correct. However, what I don't understand, then, is why you have no leakage with the original bleeder valves but do have such with the replacements.

Another question for you: are the calipers original to the car and what are the first 3 digits of the casting number?

[Jack O.]

Re: New C3 Caliper Bleeder Screws Leaking

Joe,

Using the tape on the threads seems to do the trick. My best guess on why the original bleeder held is that its threads were not as clean and perhaps somewhat better "fitted" to the caliper threads.

I doubt my calipers are original but I've never checked the numbers or dates. I was told by the previous owner that it had SS sleeved calipers so my guess is the originals are gone. Casting #'s on rear are 5473807 and front is 5473796.

Jack

[Joe L.]

Re: New C3 Caliper Bleeder Screws Leaking

Joe,

Using the tape on the threads seems to do the trick. My best guess on why the original bleeder held is that its threads were not as clean and perhaps somewhat better "fitted" to the caliper threads.

I doubt my calipers are original but I've never checked the numbers or dates. I was told by the previous owner that it had SS sleeved calipers so my guess is the originals are gone. Casting #'s on rear are 5473807 and front is 5473796.

Jack

Jack------


Assuming the car is a 1969, these are definitely NOT the original calipers. These calipers are from a 1973-82 Corvette but they will SERVICE any 65-72.

One interesting tid-bit: GM says that late 1980-81 Corvettes used METRIC bleeder valves. If your castings were originally from a late 1980-81, they would be metric threads. I don't know, off hand, how close the metric thread size might be to the SAE size used on all other Corvettes.

[Richard M.]

Re: New C3 Caliper Bleeder Screws Leaking

Jack------


Assuming the car is a 1969, these are definitely NOT the original calipers. These calipers are from a 1973-82 Corvette but they will SERVICE any 65-72.

One interesting tid-bit: GM says that late 1980-81 Corvettes used METRIC bleeder valves. If your castings were originally from a late 1980-81, they would be metric threads. I don't know, off hand, how close the metric thread size might be to the SAE size used on all other Corvettes.

Jack,

I'd be very uncomfortable with Teflon tape sealing your bleeders for "normal" driving. Something isn't right.

Joe,

Good Catch ! I for one never knew that. I did a little research to find the thread sizes. I may have made a error in my calculations as I'm only on one coffee at this time.

It certainly appears that Jack's replacement bleeders are mismatched if the original bleeders seal and the NAPA replacements do not. I went to the Napa site. It shows the same bleeder used for 1965 to 1982. Maybe NAPA is wrong, but they say up to 1982. ??? Click on the "BUYERS GUIDE" in the links below at the bottom for more applications.

1965 to 1982
Thread size SAE 5/16"-24 (fine thread)
UP20089



However, for 1984 to 1996 it shows the Metric version.
M10 - 1.0" (fine thread)
UP 22069




Jack, since your calipers were rebuilt at one time, and the fact that they cannot be C4+ calipers as they likely wouldn't fit, then maybe a prior rebuilder inadvertently used the incorrect Tap to clean the threads of those calipers, thus his "original"(present) bleeders may in fact be Metric, replaced by someone in the past after a rebuild anomaly.(i.e. screw-up)

5/16' = 7.9375mm. A Metric M10-1 is equivalent to apx 3/8" diameter. Which means IF your old bleeders in there seal well, and IF they're Metric, then those SAE 5/16" bleeders you got at Napa will be loose, thus the reason that Teflon tape is sealing them.

Take a close measurement of your old/new bleeders and with a caliper to see if different diameters. You may want to go back to Napa and get the UP 22069 Metric bleeders and give those a try. .....edit- just be careful you don't munge up the threads in your calipers. I hope that hasn't already happened if Metric/SAE thread sizes intermingled.

Rich

[Joe L.]

Re: New C3 Caliper Bleeder Screws Leaking

Jack,

I'd be very uncomfortable with Teflon tape sealing your bleeders for "normal" driving. Something isn't right.

Joe,

Good Catch ! I for one never knew that. I did a little research to find the thread sizes. I may have made a error in my calculations as I'm only on one coffee at this time.

It certainly appears that Jack's replacement bleeders are mismatched if the original bleeders seal and the NAPA replacements do not. I went to the Napa site. It shows the same bleeder used for 1965 to 1982. Maybe NAPA is wrong, but they say up to 1982. ??? Click on the "BUYERS GUIDE" in the links below at the bottom for more applications.

1965 to 1982
Thread size SAE 5/16"-24 (fine thread)
UP20089



However, for 1984 to 1996 it shows the Metric version.
M10 - 1.0" (fine thread)
UP 22069




Jack, since your calipers were rebuilt at one time, and the fact that they cannot be C4+ calipers as they likely wouldn't fit, then maybe a prior rebuilder inadvertently used the incorrect Tap to clean the threads of those calipers, thus his "original"(present) bleeders may in fact be Metric, replaced by someone in the past after a rebuild anomaly.(i.e. screw-up)

5/16' = 7.9375mm. A Metric M10-1 is equivalent to apx 3/8" diameter. Which means IF your old bleeders in there seal well, and IF they're Metric, then those SAE 5/16" bleeders you got at Napa will be loose, thus the reason that Teflon tape is sealing them.

Take a close measurement of your old/new bleeders and with a caliper to see if different diameters. You may want to go back to Napa and get the UP 22069 Metric bleeders and give those a try. .....edit- just be careful you don't munge up the threads in your calipers. I hope that hasn't already happened if Metric/SAE thread sizes intermingled.

Rich

Rich-----

I never knew it, either. It seems very strange to me that GM would switch to metric thread bleeders for late 1980 through 1981 and then back to SAE for 1982. But, that's what GM says happened. Could it be an error? Yes, it could but this kind of an error seems unlikely to me. GM says that the original part number for the metric bleeders was GM #18003151 which later changed to GM #18060081 and is currently GM #19244561. The thread size is supposed to be 8 mm X 1.25.

C4 Corvettes use a different bleeder valve of GM #14071826. These are 10 mm X 1.0.

[Richard M.]

Re: New C3 Caliper Bleeder Screws Leaking

Rich-----

I never knew it, either. It seems very strange to me that GM would switch to metric thread bleeders for late 1980 through 1981 and then back to SAE for 1982. But, that's what GM says happened. Could it be an error? Yes, it could but this kind of an error seems unlikely to me. GM says that the original part number for the metric bleeders was GM #18003151 which later changed to GM #18060081 and is currently GM #19244561. The thread size is supposed to be 8 mm X 1.25.

C4 Corvettes use a different bleeder valve of GM #14071826. These are 10 mm X 1.0.

I'd bet Napa data is wrong. I've seen it before many times.

Strange discovery however. I hope Jack gets the right bleeders in there. Leaking brake fluid is not a good thing.

I have to stop at my Napa store later and will ask them to investigate.

Hmmmm, just did a conversion......

8mm = 0.3149"

5/16" - 0.3125"


Rich

[Joe L.]

Re: New C3 Caliper Bleeder Screws Leaking

I'd bet Napa data is wrong. I've seen it before many times.

Strange discovery however. I hope Jack gets the right bleeders in there. Leaking brake fluid is not a good thing.

I have to stop at my Napa store later and will ask them to investigate.

Hmmmm, just did a conversion......

8mm = 0.3149"

5/16" - 0.3125"


Rich

Rich------


I'm going to try to call a friend of mine in the brake caliper rebuilding business. He's been doing this for more than 25 years and thousands of calipers have gone through his operation.

[Jack O.]

Re: New C3 Caliper Bleeder Screws Leaking

Rich,
Totally agree - only using the thread tape to seal the threads for purposes of using the mityvac.

I double checked my old and new bleeders and they're all definitely SAE. Isn't it very unusual for GM to make such a major change to a component and not change the casting number? Seems like a recipe for disaster.

Now my next issue may be the brake lines. I replaced all the lines/hoses from the distribution block to the rear and I'm getting seeping from the line at the distribution block even though I've tightened it beyond what the assembly manual specifies. My big fear is I'm going to get leaking at one of the many joints in the rear and get brake fluid on my freshly rebuilt trailing arms.

Jack

[Gene M.]

Re: New C3 Caliper Bleeder Screws Leaking

Rich,
......................... My big fear is I'm going to get leaking at one of the many joints in the rear and get brake fluid on my freshly rebuilt trailing arms.

Jack

Use dot 5 fluid it will not remove the paint. Also most catalyzed urethanes resist brake fluid.

[Joe L.]

Re: New C3 Caliper Bleeder Screws Leaking

Rich,
Totally agree - only using the thread tape to seal the threads for purposes of using the mityvac.

I double checked my old and new bleeders and they're all definitely SAE. Isn't it very unusual for GM to make such a major change to a component and not change the casting number? Seems like a recipe for disaster.

Now my next issue may be the brake lines. I replaced all the lines/hoses from the distribution block to the rear and I'm getting seeping from the line at the distribution block even though I've tightened it beyond what the assembly manual specifies. My big fear is I'm going to get leaking at one of the many joints in the rear and get brake fluid on my freshly rebuilt trailing arms.

Jack

Jack------


There would have been no need to change the casting or casting number. The metric bleeder valves involved a machining operation. They would have affected the finished part number but not the casting number.

[Joe L.]

Re: New C3 Caliper Bleeder Screws Leaking

The plot thickens: the part numbers for the 1980 Corvette caliper assemblies, front and rear, were different than those used for 1979 or 1981 (although the 1980 calipers may have carried over into the 1981 model year). In addition, the 1980 part numbers are consistent with a part number series usually used for metric parts during that period.

[Richard M.]

Re: New C3 Caliper Bleeder Screws Leaking

Rich,
Totally agree - only using the thread tape to seal the threads for purposes of using the mityvac.

Okay I understand now. I still think your new bleeders may be wrong for those calipers. But I always Teflon tape the bleeder threads when Mity-vac'ing. A must do.

The plot thickens: the part numbers for the 1980 Corvette caliper assemblies, front and rear, were different than those used for 1979 or 1981 (although the 1980 calipers may have carried over into the 1981 model year). In addition, the 1980 part numbers are consistent with a part number series usually used for metric parts during that period.

Wow !!! Great research Joe. Thank you for your digging in to that.

I see here.....(in my online 1953 to 1982 P&A book research)

http://www.gmpartswiki.com/getpage?pageid=39667

that it shows the bleeder part#'s as ist and 2nd Designs. Wow is that confusing, especially where those thread sizes ar soooooo close.

I did a little research too. I stopped in at my NAPA store yesterday morning and had a little session with my friend the store manager who is always a great help. I told him about your data regarding the 1980-1981 Metric machined calipers. The "Buyers Guide" did not differentiate and he agreed there is a error in the Napa listing. He did however take out the "book" and he found....

Napa Part# 22430 This is size M8 X 1.25 Thread
Napa22430.jpg
The above part is used for many GM marques, but the 1980-1981? Corvette is not listed, which is where we now believe the Napa error exists. The "Buyers Guide" listing does show many 1980 vehicle applications

Jack, this may be the part you need if you verify thread sizes.

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