*&%^&%&^... :blast: :blast: Tonight I wanted to replace the seal ring on my vacuum modulator (TH400) and the *^*(^*^&* bolt broke. There is no thread sticking out, so I'm left to drill and get a new thread... But how deep can I drill???
No wait a minute. You did not break the bolt, you stripped the case where the bolt threads into, right?
No, it IS the bolt....( never could imagine THAT bolt could snap.... it must be Murphey) There must have been some "repair" in the past (lock tide??) looking at the damages in the direct area of the bolt and "push-in bracket thingy" and on the tranny housing. I probably can not take out the old thread without damaging the (aluminium) thread of the housing So, in fact looking for the thread length of the original bolt
The bolt may have been cross threaded, or the bolt was corroded. I would say the bolt is no more than 3/4" long. It has a 1/2" head. Try to drill the bolt out and use a heli coil repair kit.
What about putting a nut over the hole with the broken bolt, weld the nut from the inside to that bolt, let it cool down for a few hours and try to turn the nut with a spanner ? When drilling the bolt out, try to fabricate some sort of a guide plate to put solid over the hole. Otherwise you will end up drilling in the transmission housing in no time.
That's why you have to weld it from the inside of the nut, sort of filling it up with liquid metal. I had the same thing with a broken exhaust manifold bolt in a cylinder head, it worked well after a few attempts :TU:
If you use a nut that's exactly the same size as the broken bolt, you easily break the spots where it's attached to the transmission housing. I understand what you mean, but after a few attempts it worked for me with that (aluminium) cylinderhead.
If it's flush, it's even easier to position a smaller size nut over the broken bolt :TU: ! Edit: I would also say give it a try, and Rob is working on his car in a well-equipped garage at the air base :TU:
I have a feeling someone cross threaded the bolt in the first place and that is why the head snapped. We will see.
the thread of the bolt broke half way, so there is no way to weld a nut without damaging the thread in the housing (welding a nut was the way I took a broken bolt out of the exhaust manifold.... had to take exhaust away because it was blocking working space near the broken modulator bolt...ou: ) Left handed thread will be a first solution, but I don't know how deep I can go. Second will be a new thread or heli coil, with same problem/question: how deep can I drill?. Thanks for all your input so far :TU:
You have this spare TH-400 in your garage, so use that one for references :TU: Tomorrow I'm going over to Gert's garage, the other week he had this Chebby TH-400 with a cracked bellhousing laying around. I can take out the bolt on that one and use a drill to check how deep I can go.
Problem solved... After first estimating the length of the thread (3/4":TU: ) I started with a left handed drill bit, which I used with very low RPM. The bit took the last part of the broken bolt out while drilling. Haven't even damaged the thread in the housing and so the modulator is locked in again. Thanks for all info :beers2: :TU:
