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No dealer is going to be able to produce a 5 mm thread chaser. It does not appear that one exists. There are other ways to clean those threads or to insure that those threads are clean. An experienced tech will know that. An inexperienced tech may not, but then, you can probably damage threads with a thread chaser if you do not know what you are doing. If the tech does produce something, will you know if its chaser or a tap? They do, or can, look different, but not always. The main difference is that the chaser is supposed to clean threads and "restore" threads, but not cut new threads. So, its not typically made of hardened steel. Taps cut threads and are made of hardened steel. In this case we are neither restoring theads nor cutting theads, so we do not really need a chaser - just a way to clean or insure that threads are clean. Below are some images of threads and taps. You can see they can look different, or similar. One of them is actually a 5 mm "frame tap" that claims it can be used as a chaser. Is that ok?
Andy I recall my Dad would make a "thread chaser" or actually a way to restore a thread, with a hack saw on an old bolt! His groove was cleaner than this I found as a DIY Thread Chaser:
And we still don't really know if failure to clean the threads was the cause of the (very few) reported instances of the bolts being twisted off. Somehow excessive torque on the bolts had to be involved didn't it? I recall something said, I think by @RKCRLR , that an issue with debris on threads can cause the torque to be distributed differently on the bolt. Something about the difference between a bolt fully seated in its threads vs one that is experiencing resistance due to the "interference" of debris (or thread locker) even though the bolt head is not fully seated. I don't think I can repeat it.
The fact of the matter is all 4 holes are open ended. They are not blind. A competent and knowledgeable mechanic could easliy extract those bolts with the correct size, reverse drill bit. I've removed dozens of broken bolts with a little patience. The 70's weren't kind to me when it came to working on Japanese motorcycles parked near the ocean. The dyno covers on Kawasaki motorcycles always had frozen bolts and I removed dozens of those after customers snapped them off. A shot of penetrating oil from the topside would aid with extraction. Once lubricated, one might even be able to spin them out with a pick. Heat works wonders as well and small propane torch used on the outside of the boss could make things easier. If there's a will, there's a way. I'm liking the stud idea more and more. Re-tap the holes to a 6M, apply some red loctite and mount the studs. Use some quality nylock SS nuts along with a flat washer and be done with broken bolts forever.
this is beyond lame- having to manufacture your own tool to work on a 70/115k car- asked dealer for their explicit instructions from Chevrolet- no dice-
no one manufactures proper thread chaser- filter assembly is pathetically designed - bolts are obviously TOO small and TOO soft- work you pay to have done by dealer is not done according to the Service Manual- took mine in for service- filter got changes at 1250 miles when I told them to wait another year- dealer said not to change filter now instead changed fliud only- then drive car home…..
next time I started it is said SERVICE DOOR LATCH system- I’m not accusing but I’m like Judge Judy and do not believe in coincidence
Yeah, but it says the consequence of not cleaning them is failure to reach the right torque/clamp load - its does not say anything about bolts twisting off. Sound more like the concern is just that the lid may not be secured properly, resulting in a fluid leak. I really suspect that bolts twisting off is due to excessive torque regardless of the presence of residual debris. Instead of the chaser, maybe we should ask the tech to show the inch pound torque wrench used to tighten the bolts, and ask them when it was last calibrated (just kidding here). I wonder how many techs use that.
I think there was a DIY post where the poster twisted off bolts and later discovered a torquing error. I wont be able to find that thread.
And we still don't really know if failure to clean the threads was the cause of the (very few) reported instances of the bolts being twisted off. Somehow excessive torque on the bolts had to be involved didn't it? I recall something said, I think by @RKCRLR , that an issue with debris on threads can cause the torque to be distributed differently on the bolt. Something about the difference between a bolt fully seated in its threads vs one that is experiencing resistance due to the "interference" of debris (or thread locker) even though the bolt head is not fully seated. I don't think I can repeat it.
The comment I made was that about half of your applied torque goes to overcoming friction under the bolt head. So if the threads bind before the bolt seats then all of the applied torque goes through the threaded portion of the bolt. The threaded portion of the bolt may not be able to take the full torque value, especially in small fasteners.
Not saying this is the reason that some people have sheared off the bolt heads,just that it is a possibility. I think it is more likely that the bolts were over torqued. But it is still important to have clean threads to achieve the design preload.
I recently changed the DCT filter and exchanged the fluid. As I was removing the filter cover screws, one of the bolts began turning a little harder. Sometimes, it is common that you would apply more torque. Instead, I stopped, reversed the ratchet and turned the screw back in a couple of turns. After that, reversing the ratchet once again and began removing the screw again, it turned right past that "sticky" spot and came right out without issue. It might be at that sticky point that if more torque were applied, the screw might have broken.
Once I had all the screws out and the filter housing was draining, I ground a slit lengthwise to resemble a tap flute. I then used that screw to thread up into each hole and cleaning out the "flute" after each removal. This effectively removed any remaining thread-locker. The new screws went in just fine to 53 inch/pounds.
Yeah, but it says the consequence of not cleaning them is failure to reach the right torque/clamp load - its does not say anything about bolts twisting off. Sound more like the concern is just that the lid may not be secured properly, resulting in a fluid leak. I really suspect that bolts twisting off is due to excessive torque regardless of the presence of residual debris. Instead of the chaser, maybe we should ask the tech to show the inch pound torque wrench used to tighten the bolts, and ask them when it was last calibrated (just kidding here). I wonder how many techs use that.
I think there was a DIY post where the poster twisted off bolts and later discovered a torquing error. I wont be able to find that thread.
Yes. Well its my reasoning that in order to seal, the O-ring must be properly compressed between the lid and housing. And that happens when the heads of the bolts are pressed (clamped) against the lid (clamp load its called in the cautionary statement) and properly torqued. If the bolt torque is high due to debris in the threads, then the heads may not be properly tightened against the lid - the seal not properly compressed - and under pressure (and I think its pretty high) the fluid leaks. That's why I think the the caution says if there is debris in the threads the proper clamp load may not be achieved resulting in transmission damage. Because the max torque may be measured due to the resistance on the bolt threads before the bolt heads are fully clamped on the lid.
When it is an oring in a counterbore there is no clamping force and the seal is at its maximum when the two components are assembled.
Unless the oring is being clamped against a shoulder. This is not as common because the accuracy of the mating parts becomes critical because it determines the compression of the oring.
It's around the barrel of the cap not the base of the cap. As long as the cap is in the barrel there's a seal.
Thanks. So where is it on this image of the lid then? To me it looked like it will get compressed as the lid is tightened. Is there a groove in the housing then where the seal fits, so that the "barrel" of the lid slideds past the ring as pictured in example 2 in the attached illustration. If so, then I agree, it might remained sealed and it would not necessarily depend on the clamping force on the housing cover.
It is not any of those scenarios that you have depicted. The oring groove is in the cover and it slides into the bore of the housing. This is a very standard method and is good for a fairly high pressure. As the pressure increases it loads the oring which increases its normal force against the housing. The screws are there for retention of the cover which may have 300-500lbs of force acting on it.
By the way, per my post just above, if its like example 2, I can see where the seal works without the clamping force, but the clamping force on the lid also pushes the filter up against a seal at the top of the filter doesn't it? So if the lid it not tight, perhaps there is leak at the top of the filter? The context of my original comment was that the caution seems to be about clamping force on the lid if there is debris in the threads, and not so much an issue of twisting the bolts off.
It is not any of those scenarios that you have depicted. The oring groove is in the cover and it slides into the bore of the housing. This is a very standard method and is good for a fairly high pressure. As the pressure increases it loads the oring which increases its normal force against the housing. The screws are there for retention of the cover which may have 300-500lbs of force acting on it.
Got it thanks. But the clamping force on the lid is also what keeps the filter sealed at the top of the filter isn't it? That is, the lid pushes up on the filter. so the top it tight against its flange inside of the housing? As I noted, the context of my original comment is that the caution about debris seemed to be about clamping force on the lid and not about breaking off the bolts.
It is not any of those scenarios that you have depicted. The oring groove is in the cover and it slides into the bore of the housing. This is a very standard method and is good for a fairly high pressure. As the pressure increases it loads the oring which increases its normal force against the housing. The screws are there for retention of the cover which may have 300-500lbs of force acting on it.
Got it thanks. But the clamping force on the lid is also what keeps the filter sealed at the top of the filter isn't it? That is, the lid pushes up on the filter. so the top it tight against its flange inside of the housing? How does that seal work? As I noted, the context of my original comment is that the caution about debris seemed to be about clamping force on the lid and not about breaking off the bolts. I'm picking at that the purpose of that caution.
The cover has a circumferential groove that the oring sits in, see pict below. If there is clearance where the lid can move in and out (dynamic loading) it might just blow the cover off after X number of cycles. Maybe you did not understand my estimate about how much force is on the cover. If the line pressure is 100-150psi and the cover has 3-4 sq-in's of area the force on the cover could be quite high. If the fasteners are over torqued, yielded, hurt, but not completely fractured the operating force might be enough to finish them off.
The filter theory might depend on the length of engagement of the interface between the filter and housing. It might be greater than the length of the fasteners. The fasteners might actually have to fall out for the lid to leak and the filter to bypass.
Here is my updated rendition, with a filter added. I assume the filter sits on those raised bumps in the lid. Looks like it has a ring in a groove at the top, so I assume it also fits in a barrel and does not rely on lid pressure to be tight. So, that just leaves the pressure on the filter and lid as an issue if the bolts are loose, I suppose. As someone above noted.
Last edited by Andybump; Oct 16, 2024 at 07:03 PM.
