Clutch hydraulic leaks - some answers and more questions

[JohnK]

I've got a couple of small leaks in my clutch hydraulic line that I'm trying (unsuccessfully, so far) to eliminate. They're both only weeping a drop per hour, but still enough to need addressing. I've already tightened them down as much as I dare, and far more than seems reasonable to get them to seal properly, so I'm wondering if some thread sealant in these two locations is warranted.

The first one I'm pretty sure needs sealant. This was just a brain fart on my part, but I wouldn't mind a sanity check before I do something dumb. This is the NPT to AN adapter where it screws into the Wilwood MC (red arrow is where the leak is at the NPT threads):

https://thefactoryfiveforum.com/attachment.php?attachmentid=153438&d=1631762658

The second leak is at the bleeder coming out of the Tilton hydraulic release bearing. Again, red arrow indicates the location of the leak:

https://thefactoryfiveforum.com/attachment.php?attachmentid=153437&d=1631762658

As a rule I use Permatex high performance thread sealer on all NPT threads, and that's what I would plan to use for the NPT fitting into the MC. The only thing I use on AN fittings is either a little brake fluid (for brake or clutch AN fittings) or some Earls assembly lube (for fuel and PS lines). But I don't know what the guidance is for bleed screws. I see that these bleed screws (https://www.summitracing.com/parts/rnb-12701) at Summit have thread sealant pre-applied to them, so I'm thinking that some sort of thread sealant might be warranted here?

[J R Jones]

John, I use Permatex #2 on ALL threads unless Loctite is required. We did this in marine development to discourage corrosion, salt and galvanic. It also lubricates the threads for assembly.
I always use P#2 on bleeders for that reason and to aid in vacuum bleeding. When I crack the bleeder to pull out the air, I do not want air to pull-in through the threads.
I also use teflon tape on NPT threads, it is less messy. Just wrap the tape CW and at least two layers. NPT threads always need sealant.
jim
BTW look at the bleeder seal seat area to be sure the M & F surfaces match and are not damaged.

[Hoooper]

wilwood recommends using teflon on fittings to the MC, in fact their fittings come with teflon paste already on the threads. I know there is a theory on here that you shouldnt use anything on threads on brake lines but I would be more inclined to listen to the brain trusts at Wilwood and Tilton when it comes to whether to put teflon on the pipe thread fittings to MCs. Just always be careful to only get it on the threads, for obvious reasons anything that is down past the threads needs to be removed.

On the second part, I have the same fitting on mine and I had to tighten the heck out of it to get it to stop leaking. Way tighter than I think it should need to be, but its worth a try to just keep going tighter since the alternative is to replace it anyway. No sealant should go on that fitting. The thread sealant you see on those bleeder screws are not related to sealing when seated, that would just help keep fluid from coming out of the threads when bleeding. The sealing needs to happen on the angled surface at the end so once the bleeder is closed there should be no fluid/pressure at the threads.

[NAZ]

I'll submit to you that there is NO legitimate use for Teflon tape in an automotive system or hydraulic system for that matter. Teflon tape IS NOT a thread sealant (it's a lubricant and a poor one at that) and has caused more issues in hydraulic and pneumatic systems than it has ever solved. And most folks don't know how to use it correctly anyway. So leave the Teflon tape to the plumber and use a REAL thread sealant.

My go-to tapered thread sealant is Loctite PST which comes in a variety of compounds made for a vast array of different uses. All are brake fluid resistant, and some have a light thread locking feature. There are other anaerobic thread sealants out there that also do a great job. I stick with PST as back in the eighties I worked with some Henkel engineers learning about all the Loctite products and was impressed. And these products have never let me down in all those years.

And on hydraulic brake systems, you never use thread sealant on the flared fittings.

https://www.plantengineering.com/articles/guidelines-for-choosing-a-pipe-thread-sealant/

[JohnK]

Thanks for the input everyone. NAZ - I agree with you 100% on teflon tape. I hate the stuff and don't use it anywhere (automotive or otherwise).

I reinstalled the NPT to AN adapter on the MC with Permatex thread sealant, so that should be good to go. The bleeder is another story. Given that it seals at the tapered point, I agree that thread sealant on the threads is not the right way to go. That thing was on there so tightly that it got rounded off a bit when I tried to loosen it (and it was still leaking despite being so tight). So I decided to order a new one (https://www.summitracing.com/parts/til-62-522) from Summit and start over. Unfortunately, the problem appears to be pretty common with this item, as there are two 1-star reviews both complaining that it leaks.

Question - if this new one also leaks, is attempting to lap it with some lapping compound on the sealing surface to try to improve the seal an option?

[jab351w]

On the second part, I have the same fitting on mine and I had to tighten the heck out of it to get it to stop leaking. Way tighter than I think it should need to be, but its worth a try to just keep going tighter since the alternative is to replace it anyway. No sealant should go on that fitting. The thread sealant you see on those bleeder screws are not related to sealing when seated, that would just help keep fluid from coming out of the threads when bleeding. The sealing needs to happen on the angled surface at the end so once the bleeder is closed there should be no fluid/pressure at the threads.

^^This. I installed the same Tilton TOB on my car last winter and had the same slow leak from the bleeder. Finally ended up tightening it nearly to the point I thought it was either going to break or strip the threads, but no leaks after that. Not looking forward to when I eventually have to open it to flush the fluid though. When installing the new bleeder, try using a deep 6-point socket instead of a wrench. I did that with mine and thankfully avoided rounding over the hex.

[NAZ]

John, if you are looking for another bleeder let me suggest you consider a Speed Bleeder. They go by different names, Russell calls em Speed Bleeders. They all have a check valve that allows you to bleed a system by your lonesome. They come in different threads but here's an example: https://www.summitracing.com/parts/rus-639560

[JohnK]

Thanks NAZ. I suspect I may end up having to go with a different brand of bleeder if this replacement Tilton bleeder also proves to be defective. The issue will be determining whether the defect is in the male or female end of the bleeder tapered surfaces, so I'll probably end up having to go with a complete "set" that's a -4 AN to NPT bleeder. Russell makes this one:

https://www.summitracing.com/parts/rus-641380

From a convenience standpoint, I use a reservoir cap that has a Schrader valve in it, so I can pressurize the reservoir to 10-15 PSI and then I just crack the bleeder and wait for a clear, bubble-free stream. It makes bleeding brakes/clutch foolproof and a one person job.

https://thefactoryfiveforum.com/attachment.php?attachmentid=153470&d=1631834307

[J R Jones]

I'll submit to you that there is NO legitimate use for Teflon tape in an automotive system or hydraulic system for that matter. Teflon tape IS NOT a thread sealant (it's a lubricant and a poor one at that) and has caused more issues in hydraulic and pneumatic systems than it has ever solved. And most folks don't know how to use it correctly anyway. So leave the Teflon tape to the plumber and use a REAL thread sealant.

My go-to tapered thread sealant is Loctite PST which comes in a variety of compounds made for a vast array of different uses. All are brake fluid resistant, and some have a light thread locking feature. There are other anaerobic thread sealants out there that also do a great job. I stick with PST as back in the eighties I worked with some Henkel engineers learning about all the Loctite products and was impressed. And these products have never let me down in all those years.

And on hydraulic brake systems, you never use thread sealant on the flared fittings.

https://www.plantengineering.com/articles/guidelines-for-choosing-a-pipe-thread-sealant/

Yikes, absolutes from the NAZ.
There are two types of pipe threads, straight for ease of manufacturing and tapered. Tapered is a type of interference and the fit tightens radially as well as clamping the threads longitudinally. Sealing is filling the voids, if they exist. Brass fitting threads may seal more easily due to the softer metal deforming to seal.
Three types of thread sealant are popular, teflon tape, solvent based paste and anaerobic compound.
The only application that discourages teflon tape is PVC female threads where the taper male, lubricated with teflon can spread and split the female thread.

My introduction to teflon tape was working in the fire protection industry where it was required for plumbing and pressurized vessels. Two issues with solvent based and anaerobic sealant was that it could contaminate dry powders, accumulate powder in plumbing and could be dissolved by liquid agent, like halon.
The medical industry also prefers teflon tape to avoid fumes and contamination.
I cannot remember a personal teflon tape failure in decades. It could happen, that is why we evaluate what we do.
Another issue with anaerobic compounds is allergies, and health risk. Primer is a particularly dangerous lung hazard. Anaerobic compounds can cause a skin allergy. I designed marine products when the allergy issue came up and threated a production walk-out. We had to re-engineer all our anaerobic applications to fastener thread pre-apply which because it is dry, it is not a skin hazard.
Henkel may not handle teflon tape but they do offer pre-apply.
jim

[JohnK]

The new bleeder arrived today (Tilton P/N 62-522 from Summit Racing). I compared the new one to the one I took off the car. New one on the left, and "old" one on the right (old being a few days old).

https://thefactoryfiveforum.com/attachment.php?attachmentid=153475&d=1631911549

There is what appears to be material that broke off the threads in the bottom of the fitting. I wonder if this is some sort of vicious cycle, where a small leak causes the fitting to be tightened further to try to stop the leak, thereby further damaging the the threads.

In any case, I re-installed the AN to NPT adapter at the MC outlet with some thread sealer on the NPT threads and replaced the bleeder with the new one, and re-bled the system. So far, everything appears leak-tight. But I have a puzzling situation that I don't understand. Yesterday, I was working to install a clutch pedal stop to prevent over travel, as the Tilton instructions require. Even though the system was leaking, the leak was minor enough that it didn't prevent me from finding the clutch friction point and setting up the clutch stop (details of that in my build thread here (https://thefactoryfiveforum.com/showthread.php?31167-Greek-Guys-Garage-Roadster-Build-9509-(clutch-pedal-stop-first-start-video!)&p=468968&viewfull=1#post468968)). Today, after bleeding the system I went to confirm that the friction point is unchanged, and the pedal stop is still properly set and found that the pedal had to be depressed much further. I re-bled the system, and no air bubbles came out the second time (ran probably 8 oz. of fluid through the system with no bubbles), and yet the friction point is still much further down than it was yesterday. I did not bench bleed the MC again when I re-sealed the NPT to AN fitting at the outlet of the MC (I did bench bleed it the other day), but regardless I would have thought that any residual air would have come out through the normal bleeding process. Is it possible that there's air in the MC that will only come out with a bench bleed, and that I can be flowing bubble-free fluid out the bleeder even though there's air in the MC?

I REALLY hate the thought of taking things apart to bench bleed and then re-bleed now that everything appears to be leak-free (especially with how finicky the bleeder appears to be) but if that's what I gotta do...

[jab351w]

In any case, I re-installed the AN to NPT adapter at the MC outlet with some thread sealer on the NPT threads and replaced the bleeder with the new one, and re-bled the system. So far, everything appears leak-tight. But I have a puzzling situation that I don't understand. Yesterday, I was working to install a clutch pedal stop to prevent over travel, as the Tilton instructions require. Even though the system was leaking, the leak was minor enough that it didn't prevent me from finding the clutch friction point and setting up the clutch stop (details of that in my build thread here (https://thefactoryfiveforum.com/showthread.php?31167-Greek-Guys-Garage-Roadster-Build-9509-(clutch-pedal-stop-first-start-video!)&p=468968&viewfull=1#post468968)). Today, after bleeding the system I went to confirm that the friction point is unchanged, and the pedal stop is still properly set and found that the pedal had to be depressed much further. I re-bled the system, and no air bubbles came out the second time (ran probably 8 oz. of fluid through the system with no bubbles), and yet the friction point is still much further down than it was yesterday. I did not bench bleed the MC again when I re-sealed the NPT to AN fitting at the outlet of the MC (I did bench bleed it the other day), but regardless I would have thought that any residual air would have come out through the normal bleeding process. Is it possible that there's air in the MC that will only come out with a bench bleed, and that I can be flowing bubble-free fluid out the bleeder even though there's air in the MC?

Keep bleeding it, as there's likely more air trapped in the system. When I went through this (Tilton TOB and new master cylinder) I wound up pressure bleeding more than a gallon of fluid through it to get all of the air out. It helps to use a clean container and recycle the fluid. Might also try bleeding for a while, closing the bleeder and giving the pedal a few pumps, then bleeding some more (don't pump the pedal while you've got pressure applied to the reservoir, as supposedly that can damage the seals in the MC). Eventually you'll get all the air out, but it'll take longer and way more fluid than you would think such a small closed system should. Oh, and I didn't bench-bleed my MC beforehand, either.

[JohnK]

Thanks - got it. It took 3-4 more cycles bleeding it but I now have a good firm pedal and no leaks.