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Discussion Starter · #22 ·
I can't use a 7/16 bolt as it will be to big and I don' have the clearance in the mount oval area that allows you to have the bolts in or out more depending on what transmission it goes on. On my turbo 350 where my bolts go in to mount the mount to the housing the 10mm size bolts or can helicoil it to 3/8-16 size if I want, the bolts are towards the most inside of the mount and I have no more clearance and with the way my transmission housing is for spacing on the mount bolts that go to the housing it will not allow a bigger size bolt for the mount as it is hard enough to get the dang thing to screw in and takes a good steady set of hand to get the dang things in and I suffer from neuropathy and my hands shake some when trying to do things at times with my fingers and stuff.

Even with it jacked up to give even more clearance for my hands which makes it a lot easier still makes it a pain. The speedometer cable gear size has nothing to do with it. My housing is just a big gear size one vs the more smaller size ones that I have seen. As you can see in this for example which is what I am going to go to that style of mount but rubber still, I will be able to use a bolt instead of the stud in the mount which will make it easier to change and swap out etc.

If I had another six inch housing I could get a gear if it was the smaller size to replace and I already have a seal kit and stuff. Just need usable threads and since be taking motor out that is the only option I have. I don't have a hundred bucks for a housing from ebay that I don't know if those threads would hold without having to fix them but it would at least be easy to have one already fixed and ready to just swap out and keep the other at the side for the future if it would ever be needed.

I am just really tight on funds at the moment and it has to go towards to finish my 350 build and have it done.

617640
 

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Discussion Starter · #23 ·
I also know my threads and know the course and fine thread stuff and using a drill bit gauge chart which I have a drill bit set for such purposes and I also do have a tap set of all sizes that are most common for metric and standard size. I have drilled and tapped Holley metering blocks and a few other things so I do know my way by feel and stuff. Yeah I could drill it out and tap for bigger bolts but they won't clear the area of the mount that bolts to the housing. I already tried to see if it would work and its right far in to where there is no more area to move bolts inside more. The oval area just by a hair clears where the threads start in the housing where the bolts go in.
 

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Tapping to a bigger size would be the quick shade tree mechanic/poor boy fix, but as you've found, you would have to take a die grinder to the mount slots in order to get those larger bolts to fit through.

Stock mount with just bolt holes you could drill them oversize....but drilling one end of a slot on the aftermarket mount oversize isn't going to happen....you either need a mill for that,or by hand with a die grinder/dremel.

if working underneath the vehicle with a tap/helicoil is a pain, maybe just pull the extension housing off and fix it on the bench, install the mount pad, then put the whole assembled tail housing/mount back on the trans case.
 

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Discussion Starter · #25 ·
The plan is to take the housing off the transmission itself while at the same time my engine is out as I have to tap the front of the transmission for the inspection cover as those holes are striped as well and I can't get to it with a drill because of the exhaust being in the way and its a two person job to get the exhaust off the thing and being a s10 with a v8 and shorty headers its a pain to get in there. Once the engine is out it will be a heck of a lot easier since a lot of things will be out of the road and better access. I have to wait till my Father will have the time to be doing this job and I will have a learning job to drill and tap by hand.

If I had more extra cast to spare I would buy a housing to replace my one and fix it if necessary so all I would have to do is just swap out and be done with it. Can't understand why someone would want a hundred bucks for a housing on ebay on average but yet you can get a th350 used on average for a couple hundred bucks give or take a little if you can find someone who has one. I think this case all the way through has seen better years and of course its about as old as what I am so what can I expect. I have leaks everywhere on the thing and will be changing out my fluid and filter and some seals while I am at it.
 

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Why is everyone talking about taking off the ext housing to repair the mount bolts. The mount bolts are threaded into the main case, or am I not understanding.
 

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Why is everyone talking about taking off the ext housing to repair the mount bolts. The mount bolts are threaded into the main case, or am I not understanding.
Hey, you're right!

Doh!..
Too much Th-400 thinking on my part I guess, I'm not a big fan of the TH-350.
Th-400 mount is on the tailhousing.
 

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Having the trans out definitely makes it easier. Drilling to the next larger size can be characterized as a "shade tree" option, but its common practice not only on cars/trucks, but in actual real machine shops. The problem with heli-coils is they sometimes unwind when removing bolts and you have to buy another heli-coil and install it. You need the correct drill size and an installation tool to put them in. There is nothing wrong with drilling to a larger size and using a larger bolt. I've done it more times than I can count, and I have a Journeyman machinist background in a government facility. We didn't drill holes oversize on govt specs, but tooling and one off jobs were often modified rather than scrapped. I also installed heli-coils in parts. I've got a bunch of heli-coils and installation tools in a drawer in my shop. Don't remember the last time I used one. They are handy when you absolutely can't change the size of a holes threads, such as a head bolt or something. Given the option of using a larger thread size or a heli-coil, I always go with the larger bolt.

As for your problem with the bolt size not fitting the slot.............simply take an air grinder and gently widen the slot. Been there and done that before too. Just take your time and try to be neat, but even if you get it a little odd, it won't hurt anything. Now don't take this as condoning sloppy work, but when you are building things at home on a limited budget, sometimes you don't get perfection but it still works just fine. If every car builder only accepted perfection, no cars would ever get built. Strive for perfection but also know that often you will have a good usable part even though it isn't perfect.

Going back to the bolt size, once you have the slot opened up, will the head of the bolt fit ok? Most likely it will, but you can also replace them with small headed bolts or even allen bolts if necessary.

Don't overthink what you are trying to do. Its really a simple process. Personally I would not go to all the trouble to pull the transmission. I would get some good jackstands or some extra wheels and jack the truck up far enough that you can work under it comfortably. Being comfortable and having ease of movement goes a long way towards doing things right. I would simply drill and tap the mount holes and do the same thing for the inspection cover. The inspection cover will need to have its holes enlarged for the larger bolts. Again, don't make this a big deal as worrying about it makes it 10 times harder. Remember how nerve racking it was anticipating your drivers test? Now you drive and its easy. Same thing here, drilling and tapping is easy, and modifying parts to make them fit your needs is a big part of working on cars..........
 

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Discussion Starter · #29 ·
Not pulling the whole transmission out, just taking the tail housing off and then fixing it and then putting it back on. Now the easier thing I could do is take the transmission crossmeber off which is a total of six bolts I think and then I could hand drill the holes with the correct helicoil kit but I don't have steady hands thanks to my cancer treatments I had many years back and I don't know if I would be able to get real straight on doing that part or I would give it a shot.

The housing in case some don't remember comes off the tranny itself in case anyone does not read the whole post. I am going to maybe try that but I want to keep this thing as simple as possible and would like to just fix it and keep the 10mm or 3/8 bolt size deal. I am going to want to use a standard 3/8-16 repair because I like working with SAE bolts vs Metric.

I have the tools but would hate to mess this thing up as I only have one try in each one. I would hate to ruin it and then end up having to get another housing. I will have to get with my Father and see how he wants to tackle this but from talking with him, taking the housing off is his idea so in do time we will see. Hopefully in the next two weeks once he gets caught up with stuff I can get my truck in and pull out the engine and get my new build in and then get the rest of the few other things done that is needed.
 

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Rod...from a Chrysler?
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It was mentioned earlier that a TH350 doesn't have the mount holes on the extension housing, but the case itself. See below.
perhaps you have a 400?

617666
 
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Rod...from a Chrysler?
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Hard to see, right behind the pan.

617667
 

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Discussion Starter · #32 ·
Well heck I can't believe I missed that part, but yes it is on the case and not the housing part and I know for sure its a th350 as the length of it and the pan shape. I apologize that I did not know that part and learned something new today. I was going by looking at it from the bottom with the transmission crossmember covering so much of it and everything else I thought it was part of the housing and I did not pay attention to detail. I feel dumb but just a slight mistake.

I guess what will be happening is most likely take the crossmember off and then have access to the holes and get them drilled and tapped for helicoils. Kind of a bummer but still a slight easy fix with careful time. I will have him do that as I have never been good drilling straight holes and having unsteady hands to boot I don't want to mess it up.
 

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Rod...from a Chrysler?
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Just don't drill too deep or you'll be right into the case or worse, out the side.
 

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Discussion Starter · #34 ·
I always measure the depth to which I can drill when going into a blind hole. I usually put tape around the drill bit to where I can't go any further to make sure as to not go to deep. I have done that with a drill press when doing stuff with my carbs and some other things over the last few years. I am hoping to get it done soon and such but I don't know if I would be able to be that good at being able to hold the drill nice and straight by look.

I definitely don't have the cash for a rebuilt transmission that is for sure. I will see in the next week. I don't have enough of experience of using a hand drill when trying to keep it straight to have that feel of it and by eyeing it when doing critical jobs like that. I have drilled holes by hand when trying to keep it straight as possible and eyeing it but I have not been good at it yet, and with something this critical I don't know if its safe for me to try or not.

Like stated in previous post I have not done my own helicoil repair before by straight hand drilling and the tapping part is a piece of cake but its getting a straight hole that is what is holding me up.
 

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Drilling a hole to a larger size is no great problem. The drill will follow the old hole. As long as both cutting surfaces of the drill are even drilling will be easy. But if 1 cutting edge is larger the hole will end up wonky.
 

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Discussion Starter · #36 ·
The drill bits I have are not the best quality and are harbor freight cheap ones but they have not been used to often though, so I don't know if they would be good up to the job or not and I will look at the auto store today while I am out and look at what kits they have and see if they have one with a drill bit so I have something brand new to use with. Below is the drill bit set I have from harbor freight.

 

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I don't understand why you think enlarging a hole 1/16" (.0625) is going to be such a major issue. The drill bit will follow the hole and it will be easy.........especially in aluminum. I can guarantee you that drilling and putting a helicoil in place will be more difficult than just drilling and tapping. If you screw it up, then use a 7/16 helicoil ........but you won't screw it up. The only thing you need to do is use light to medium pressure on the drill. Get a piece of aluminum and drill a small hole in it, then drill it to 3/8 and tap it to 7/16. I know you are hesitant because of the nuero problems, but try it on a piece of scrap aluminum. If you plan to work on old cars, you WILL be doing this again..............and again..............................and again. Just give it a try and quit worrying. :)
 

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Discussion Starter · #38 ·
Well I don't have any scrap aluminum just laying around but thinking of that and you mentioning it I will see if my local hardware store has a chunk of aluminum I can get and use it as a practice for drilling and then tapping and see how good I can get before I try to tackle this thing on my own. Yeah I know don't worry about things, well easier said then done when you are good at it and I have yet to do my first time and if it was something not as critical as a mount then I would have gone at it alerady lol but the way things are going I need to get this done soon.

I don't like having an engine making a lot of power and not having a fuctional transmission mount in the rear. I am going out to check on helicoil kits at the auto store here shortly and then maybe later on in the week take my crossmember off and then have all the access I need.
 

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Discussion Starter · #39 ·
I forgot one thing and I am needing a refresher on it is what am I looking for when buying a coil repair kit that tells what amount of thread engagement it will allow? I at least would like a 1.5 thread engagement if I can get that much but when the coil in not inside I don't know what the length would be like in compressed form. From fastener stuff that I do know is they say you want at least minimum of 1 inch of engagement but 1 and a half times is the best.
 

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The drill bits I have are not the best quality and are harbor freight cheap ones but they have not been used to often though, so I don't know if they would be good up to the job or not and I will look at the auto store today while I am out and look at what kits they have and see if they have one with a drill bit so I have something brand new to use with. Below is the drill bit set I have from harbor freight.

Don’t need fancy bits. Drill SLOWLY. Don’t squeeze the trigger full tilt. Small short blasts are better. Practice on a threaded hole on your bench.
 
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