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Discussion Starter · #1 ·
Hello guys I today had my transmission mount changed out and before I took the bolts out I noticed they were not hardly tight at all and did not seem to want to snug much with slowly tightening by hand. The bolts are 3/8x16 and before I did anything I popped the one bolt out to get the correct length for them. I put a board underneath the pan and jacked it up and got my old mount out which was split on the one half of it and the other half was still attached.

I had to wiggle things around some but I got my new mount on and I tried to first tighten the bolts and I was very careful and slow to try and torque them down. I started off with ten ftlbs and it was not going very well. So I went back to my regular ratchet and just wrist turned it and it just seemed like it would not torque down at all but there was some resistance but not much. I tried clear down to 5 ftlbs and it would not click and torque down so I figure the next time trying to tighten them up anymore they are going to strip. I had a tiny amount of never size on the bolt threads since its going into aluminum.

Any ways this is from a 96 chevy s10 and I will have to remove the transmission cross member if I want to be able to get a drill up there and also get a helicoil to repair the threads and restore to original. My question is I looked at the side of the cross member and there are four bolts on each side and my question is first are there nuts welded on the other side of the frame to hold those bolts tight or are they like motor mounts and you have to get access somehow with a wrench to hold the nuts on the other side to loosen up the bolts?

After getting the information on that my next question is will I be able to use a regular hand drill and then drill it to size and then install a helicoil without having to take the whole transmission out? Sorry if this sounds dumb but I am new to this sort of thing. I have a drill bit set and taps and usually the helicoil kit has the tap and stuff I need anyways. Is this easy to do by hand and no worries about having problems keeping things straight or do I need to take it out and all other kinds of things to get it fixed?

Hope you guys can let me know and help me out on what I am looking at.

Thanks guys
Eric
 

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Make sure they aren't metric first....I believe sometime around the late 1977-1980 time frame they went to 10mm x 1.25 threads on the trans tail mount pads. (Prezident Jimmy Carter tried to put the country on the metric system around that time, GM cars ended up sprinkled with metric bolts in various locations).

When converted to english measure, M10 x 1.25 has the same 16 threads per inch as 3/8-16 National Course....but 10mm is .020" bigger than 3/8".(.394" vs .375")
3/8-16 bolt screws right in but will feel sloppy loose and like you guessed, will easily strip it out.

If it does turn out to be bad 3/8" threads, my most common fix is just drill and tap to 7/16" rather than mess with a helicoil.
Your choice though.

I've done it under the car a few times, not hard if you are fairly handy....just try to keep it as square as possible, but it isn't a real critical fastener like a main cap bolt or a head bolt.

I can't help you on the '96 S-10 frame bolts though, no idea....I'm only familiar with the earlier "square nose" S-10.
 

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Discussion Starter · #3 ·
Thanks Ericnova72 I will see about the bolts and buy a few metric ones and see how they fit. The bolts that came out were SAE but that was what my Father put in over ten plus years ago when he put it together for me. I also see where the threads seem to bolt in and I am not going to mess with it anymore and I will try and thank you for your post as that saves me some time to at least check the bolts first.

I can't unfortunately use a 7/16 size bolt as the mount where the elongated holes are just clear the 3/8 size bolts just by a hair and the bolts are clear on the inside towards the center as far as they can go and no room. I had to wiggle the transmission mount back and forth with a screwdriver just to get the bolts to thread in and was a three hour job getting up and down and with a very bad back it was very painful and I had to stop a lot and my back cracked and popped more then a popcorn bag in the microwave and the nerve pain was outrageous. He welded a plate on the factory crossmember to put the transmission on to where the stud goes through.

It had a 700r4 before I put a turbo 350 in it after I bought it. He made a custom driveshaft for it and notched the crossmember to clear the dual exhaust.

I will get bolts and see how it works. Thanks again and appreciate it.
 

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T350 never came with 3/8 mount bolts. They were 7/16 nc or starting around 1978 they went metric. I used to tap the 10 mm hole to 7/16 if they were stripped. You can get a 7/16 bolt that uses a 1/2 inch 12 point wrench for your clearance problem.
 

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Discussion Starter · #5 ·
Well the bolts that came out were 3/8 bolts and took a 9/16 socket and were from my bolt case that I have rows with bolts in them by size. I took the old ones out and matched them up with the bolts from my case, then went shorter since the ones in the tranny was to long. The one bolt fits slightly tight but won't go super tight. The other side is a lot looser and screws in easier but neither one will torque even at five ftlbs. The housing is not original to the transmission as when I bought it the guy gave me a tail housing that is a 6 inch housing from another transmission and don't know what one.

I am no expert on what parts can swap from one transmission to another. All I know is the housing takes the larger size speedometer gear that hooks up to the speedometer cable and the original one that he took off the transmission when I got it was one that has the smaller transmission speedometer housing on it. Also I can't go larger on the bolt if it is stripping out because the 3/8 bolt barely clears the elongated hole because the head clears fine but its the shank part of the bolt that hardly clears things and is tough enough to get threaded in and I have to move the mount around a little bit to get them in.
 

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FYI: A 3/8 NC bolt will thread into a 10mm hole by hand but feel as if it's stripped. Prolly what's going on here. Hopefully you'll have enough room to clean up the threads with a 10mm tap.

Russ
 

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Discussion Starter · #7 ·
Yeah I got room to clean up the threads if need be. From all the information it should be a size 7/16 bolt or a 12MM bolt but it was a 3/8 bolt that came out from the housing. I don't know if other transmission housings from another unit will fit a 350 turbo with the 6 inch tail or not but the housing came off of something else when I got it so I don't know what its origin is to have a different size bolt then the norm from what I have read. I am going to get some bolts in the metric size and see how it goes.
 

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Discussion Starter · #8 ·
Well guys some good news so far. My threads might not be bad after all. I took my bolt out and went to the hardware store and sure enough thanks to ericnova72, the threads have to be metric. I took the 3/8 course thread bolt and it would screw into a 10mm-1.5 thread pitch nut but was loose but would screw into it. I have not messed them today as my back is out and nerves are pinched from bending and getting up and down and in a lot of pain and can't move to much but will go to put them in tomorrow and hope they will torque down and not strip. The transmission is as old as me most likely or close and after so many years of heat cycles it a wonder they can last as long as they do.

I will post how it goes. With this bolt not being that big I am wondering with some antiseize on the bolt threads since its going into aluminum how much should I torque it too? I am thinking maybe 25 ftlbs like you would an intake manifold bolt for that size of a fastener. I don't want to strip those threads out and don't want to have to drill and tap as I have not done that yet before except one time on a carb main body and that was a nightmare and a long story on that one.
 

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Trans mount to trans case/tail housing bolts were 3/8' or 10 mm.

Trans crossmember to trans mount rubber portion would be 7/16" or 12mm.

That may be where the size coonfusion from a couple of posts is coming from.

25-30 ft.lbs. should be good into aluminum...bu that is one of those places I've never used a torque wrench on, just good old boy tight, one hand tight with a 1/2" drive ratchet or lean into a 3/8" drive ratchet a little harder.
 

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Discussion Starter · #10 ·
Yeah I agree as the stud that comes out of the mount is bigger and seems to be the 7/16 size or a 12mm size deal. I always use a regular ratchet first before using a torque wrench to get a good feel with things before using a torque wrench as there has been times that I was waiting for the click and not paying attention to the feel and I did not have the torque wrench handled right and I was already past the torque point and over tightened the bolt and lucky for me I did not strip anything but was past the needed fastener torque spec.

I am very careful when it comes to those sort of things especially the more critical the fastener. Thanks again to everyone above and especially to you ericnova72 for giving me that knowledge and you might have saved me a lot of time and work for nothing but a minor mistake of the wrong bolt being used. Now the other thing to figure out is the crossmember I found from trans dapt that I could use to replace the factory modified one and have a lot more room and a better look for my truck, but don't know if it would be an easy install or not as I have never messed with anything like that before.
 

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I found that going on Ebay and doing a search for Flanged Metric Nuts (or bolts) will yield sites like the one below. I have bought from this particular vendor and had good results. There are a bunch of other good vendors too. Best to look for a larger quanity and get better buys. You can't hardly find this stuff locally and easily and when you do.......its $5 for one or two. I just avoid the problem and order a 100 or so and use them on all my projects. They look much more professional and often have serrated bottoms. Its also nice to get the smaller sizes in American Standard threads too. Lot better than losing a day trying to find one locally.

Note: The price is for 1 pack not one nut.

 

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Get a new tail housing, one option. Remove crossmember after jackin up trans slightly to give room to work, take current tailshaft off and put on bench and work on it...several ways to go here
 

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Discussion Starter · #13 ·
I am going to have the tailshaft taken off and fixed and done on the bench. Getting a replacement tailshaft is over a hundred bucks used from ebay on average and I don't have the funds for that and most likely the housing might be no better off and need a thread repair anyways. Going to have it redone for the same size bolt and will be fixing the front threads on the tranny for the inspection cover. Engine going to be pulled soon so will have a lot more ease of moving things around.
 

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The red neck farmer repair on expensive machinery on stripped bolts is to poke a bare copper wire into the hole an sometimes grind the bolt to a point and turn the bolt with a box end wrench and tap with a hammer at the same time an it makes its own "helicoi;"
 

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What housing length are you looking for? I'm sure I have a short one and it's certainly not worth a $100 to me.
 

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Well, i just noticed they want $25 to ship!! So not that good a deal. WTH, shipping is outta control...
 

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I'd just drill and tap the thing and be done with it. When you start removing the housing you have to deal with a lot more things.......... Drilling and tapping it should be easy. Just lube the tap with some WD-40 and try to stay straight. Its a really simple fix.
 

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Discussion Starter · #19 ·
I can have it just drilled and tapped if need be. I won't ever have something done ******* on my truck especially with something as critical like a mount lol. I know some folks use straps for there bumpers and things but some kind of fix by poking a wire up and doing a poor mans job of a helicoil fix is horrible to even think of. My housing is a 6 inch length.

For about$30 bucks I can get a helicoil kit at my local auto store. From last when I searched ebay they wanted in excess of about a hundred bucks on average including shipping which I paid only 125 for my whole transmission when I got it from somebody back in 2007.
 

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You don't need a heli-coil or anything like that. The drill chart shows that for a 7/16-14-UNC thread that you need a "U" diameter drill bit that is .368 in diameter. My suggestion is to use a 3/8 (.375) diameter bit as it will make tapping easier and won't hurt anything. Buy a 7/16-14 tap. Drill a hole in a practice piece of aluminum and run the tap into it. Use WD-40 to lube as you go. Turn the tap a few times and then back it up a little to clear the thread chip. Turn a little more and "feel" what the tap is doing. Is it threading easily or fighting you. If its fighting, then back it up and break the chip. You may need to back it all the way out and blow some air in it. Just go slowly and don't force it. If it fights, then take small 1/2 turns cuts and back it up. You may have to go forward and back several times to break a chip, but you will develop a feel for what the tap wants you to do. With aluminum, most likely it will cut fairly easily and not give you a problem. After you have done a couple of test holes, do your housing. Its not rocket science, and its really not hard to do. And everyone needs to be able to drill and tap holes when you work on mechanical things.

The 7/16 (.4375) is the external diameter of the thread.
The -14 is the pitch of the thread, which simply means there will be 14 threads in an inch.....or if you tighten the bolt 14 turns, it will have traveled 1 inch
All the common standard American threads come in two basic forms. Fine and Coarse It simply means that you can tap the hole to have either 14 threads per inch or 20 threads per inch depending on which drill bit and which tap you choose. Look at the chart I provided. If you look at the other thread sizes, they will have different pitches. (1/2-13 or 1/2-20)

Don't overthink this thing, its really pretty simple if you just give it a try. It really doesn't take much talent to tap a hole..........and sooner or later everyone who taps a hole will break a tap. So don't worry about it, just try it.
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