Changing trans case half--- Need to shim diff?

[93rev2sev]

Yes, check the diff shim. Yes, that repair should work, but it looks one step away from "correct". Just have that chunk of aluminum welded in place and the hole filled, drilled and tapped.

Finding an accomplished aluminum welder will be the toughest part.

 

[jonheese]

Finding an accomplished aluminum welder will be the toughest part.

Yeah, that's what I was thinking too...

I was thinking about the "tapped or untapped" concept for the hole in the spacer last night, and I'm definitely agreeing that it needs to be tapped, even if I don't get it welded.

On one hand, the threads in the spacer won't be doing anything to keep the bolt (and hence the mount) connected to the transmission case (because it's not welded to the transmission), but the threads in the spacer will allow the torque applied to the bolt to be spread out over (roughly) the original amount of threads. That is, there will be roughly the same about of clamping force per thread (or per inch of threads, whatever) as originally designed. If it's just a clean hole through the spacer, there will be a lot more clamping force per thread, since the first 10-15 threads will be gone, but the bolt torque value will not have changed. That could be bad for the remaining threads (i.e. strippage under load).

If I tap the spacer, I'll just have to be careful about making sure that there is no gap between the spacer and the trans case, but also that it's not too tight so the threads don't bind up. Here's how I imagine I'll do that:

Poke the bolt through the trans mount, spin spacer on to the bolt a little, start threading the bolt into the remaining transmission boss, then spin the spacer back towards the transmission until it's tight up against it. At this point, the threads should be roughly lined up, and if I hold the spacer from turning, the bolt should thread in roughly normally and torque down properly.

Now, if I spin the spacer down too tight against the remaining boss, it could possibly bind up the threads between the bolt and the two threaded holes (like binding two nuts up on a stud to use as a makeshift head). That would be bad, because it would affect the torque vs. clamping force relationship for that bolt.

Any other opinions of this "not quite correct" repair idea?

 

[93rev2sev]

Don't tap the spacer unless it's welded in place.

The only way to make the threads in the spacer do anything is to tighten the spacer onto the trans (like with a stud) and THEN tighen something to the spacer...this effectively DOUBLES the stress on the threads that are left in the trans, but does nothing to increase the amount of force holding the trans mount to the trans case.

 

[jonheese]

Maybe I misspoke. I wasn't suggesting that I tighten the spacer against the trans, just spin it up snug. The idea I was going for was to sort of have the threads match up between them. No gap, but no stress on the trans threads caused by the spacer being there.

Does that make sense?

 

[kumba]

I wouldn't bother with threading the spacer. That just has potential for causing problems without fixing or really helping anything. Given your situation, I can really only think of two things to do:

1) Thread Repair - Either drill and tap to next size, and use a larger bolt, or install a thread repair kit like a Heli-Coil or TimeSert. The TimeSert is what I'd go with over a heli-coil. You will still need to grind the boss down flush and create a spacer with either option in my opinion.

2) Replace the case half.

The last option, the most involved option, is to cut the boss off and machine a new aluminum stub piece to be welded on. I wouldn't really not recommend this unless you just want to do it as welding cast alum is a PITA. You will need to find a TIG welder who can use free-hand fill sticks (not wire feed) and who has an oven that he can preheat the casing in. The new stub will also need to be machined at an angle at the welding end so that he can get thorough *********** between the old and new alum and then fill in the valley with filler. Then after all that there is no guarantee that you won't warp the case enough requiring you to re-shim it anyways. The good new is that the boss will end up as strong, if not stronger, then the original. You could even grab 1/8" alum sheet and make reinforcement webbing for it if you wanted to. Still a lot of damn work and unnecessary for your situation IMHO.

Have you tried calling a trans shop and ask them how much to have them swap the case end and re-shim? It might be cheaper then you think, and they will be able to give it the evil eye and tell you right away if anything is majorly wrong with it.

 

[93rev2sev]

Still when you tighten the bolt, you will be tightening the spacer against the case unless you put sides on it and hold it in position while you turn the bolt...this will make it nearly impossible for you to determine how tight the bolt really is and it still won't get you anything, structurally.

Just use some aluminum tube...According to machinists handbooks, you need a thread depth 1.5 times the width of the bolt in order to be safe. So with an M12 bolt, you need 18mm of thread engagement. If you have that...then your aluminum spacer will suffice. If not, it's a temp repair until you get the case half replaced.


Another option is the use of "aluma-weld" or HTS2000...whatever it's called. I've used this stuff and it takes a little practice to get it right. But once it's done...it's repaired forever.
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[gmorrell]

Jon,

don't tap the spacer if it's going to float between the mount plate and the boss on the trans case, it will make it difficult, if not impossible, for the bolt to take a torque and come into tension.

If you do a spacer, you will want to Heli-coil what's left of the hole in the boss.

Whatever that trans came out of took a decent front end hit.

Gary M.

 

[jonheese]

Still when you tighten the bolt, you will be tightening the spacer against the case unless you put sides on it and hold it in position while you turn the bolt...this will make it nearly impossible for you to determine how tight the bolt really is and it still won't get you anything, structurally.

Yeah, I was thinking about grinding some flats onto the spacer, but you make a good point...

Just use some aluminum tube...

Okay, that's pretty much what I was thinking originally. Makes sense to me.

I wouldn't bother with threading the spacer. That just has potential for causing problems without fixing or really helping anything.

Okay, I'm with you on that now.

Given your situation, I can really only think of two things to do:

1) Thread Repair - Either drill and tap to next size, and use a larger bolt, or install a thread repair kit like a Heli-Coil or TimeSert. The TimeSert is what I'd go with over a heli-coil. You will still need to grind the boss down flush and create a spacer with either option in my opinion.

Well now, the threads in the remaining portion of the trans boss are still good (not 100% perfect, but I believe that if I run a tap through them, they'll be most of the way there). So I don't see the need for any thread repair, just a spacer. Am I missing something there?

2) Replace the case half.

Yeah, I've got my finger poised over the "ORDER" button on the SHONut site for a diff shim kit... It just depends on how confident I am about the spacer idea.

The last option, the most involved option, is to cut the boss off and machine a new aluminum stub piece to be welded on. I wouldn't really not recommend this unless you just want to do it as welding cast alum is a PITA. You will need to find a TIG welder who can use free-hand fill sticks (not wire feed) and who has an oven that he can preheat the casing in. The new stub will also need to be machined at an angle at the welding end so that he can get thorough *********** between the old and new alum and then fill in the valley with filler. Then after all that there is no guarantee that you won't warp the case enough requiring you to re-shim it anyways. The good new is that the boss will end up as strong, if not stronger, then the original. You could even grab 1/8" alum sheet and make reinforcement webbing for it if you wanted to. Still a lot of damn work and unnecessary for your situation IMHO.

Yeah, that sounds like Overkill City. This is really a budget build, and I'm out in the middle of nowhere with no connections and no helpers or technical buddies.

Have you tried calling a trans shop and ask them how much to have them swap the case end and re-shim? It might be cheaper then you think, and they will be able to give it the evil eye and tell you right away if anything is majorly wrong with it.

No, I haven't tried that, and forgive me for saying so, but I don't want anyone but myself to work on any part of this car. It isn't that I'm a know-it-all (okay, maybe I am, but that's not why) or that the car is something special (it's not), it's just a matter of principle. I took on this project by myself, and I will complete it by myself or fail trying. This car is part of my hobby, not my transportation, so if I can't fix it, then that just means that I've just got more to learn before I try again. I can't learn anything by farming the work out to "professionals", so I'd rather just save my gas and hermit-like ways and do it myself.

I would imagine that the closest reputable transmission shop is probably in Denver (an hour or two away from me), and I wouldn't have the first clue which one of the many is reputable. I've had way too many run-ins with idiot transmission techs in my day to just trust anyone with an "AAMCO" shirt on.

I guess that's one thing I ought to be clear on: My first goal in this project is to learn as much as I can, in a hands-on fashion. My second goal is to get the car put together with the upgrades and working well. My third goal is to get good performance out of it. So, if I put this transmission in, and there's something wrong with it, or it breaks again because the mount is insufficient, then I'll pull it back out, assess the issue and attempt to fix it myself. Of course, I'll attempt to make good decisions the first time, but I won't have anyone else work on anything, because then I've given up the point of having this as a hobby.

Thanks again for all of your input. Please understand that I'm stubborn about working on it myself, but I do recognize that I wouldn't be anywhere without the input from others here, so I do welcome your comments.

 

[jonheese]

don't tap the spacer if it's going to float between the mount plate and the boss on the trans case, it will make it difficult, if not impossible, for the bolt to take a torque and come into tension.

Right, I'm with you guys on that now. You came in right before my response on that one. Thanks.

If you do a spacer, you will want to Heli-coil what's left of the hole in the boss.

Whatever that trans came out of took a decent front end hit.

Hm, okay, that's the second recommendation to re-thread the original hole. Does anyone know off-hand the diameter and thread pitch of the stock bolt in that location?

 

[kumba]

Well, the first thing you need to buy is the factory repair manual. Along with the R&R procedures, it will also have all the spec's in it that you have been asking about. The reason I suggested you try a trans shop is usually the Tech's wont mind showing you what they are doing. That way you can get an idea for what is involved and learn without necessarily going through the school of hard knocks first.

If the threads past the broken-off part look decent, then buy a thread-forming tap (as opposed to thread cutting) and use it to chase the threads. The reason you specifically want a thread-forming tap is that it will push the metal back into place and essentially fix slightly damaged threads. There should be almost no removal of material if the threads aren't damaged too bad. If you get a lot of material coming off on the tap then this means the threads were warped, out of round, or rolled over (cross-thread, stripped, etc). If this happens, thread the bolt in to where it would be as installed, but without the bracket and spacer, and wiggle the bolt. If you get a lot of movement (say more then 1/8" or so side to side) then those threads will probably not hold much or just pull out when you torque it. If that's the case then I would look to insert it or go with a bigger bolt. I am guessing that is a 12mm bolt. If it is, you can easily go to 1/2" without having to modify the bracket hole. That will give you an extra 30-thou of fresh material to tap. Just go slow with plenty of **** when drilling out the boss for tapping.

As far as the thread of the bolt I am guessing it is either M12x1.75 or M14x2. The second thing you should look to invest in is a set of digital std/met calipers. Always useful and can be had cheaply

 

[93rev2sev]

It's m12 course.
(I'm pretty sure that makes it m12x1.5)

 

[kumba]

M12x1.75 would be coarse. M12x1.5 would be fine. Problem is they are close enough to look alike without measuring. Sounds like a good time to take the old bolt to a hardware store and match up the thread/pitch to me.

 

[jonheese]

Well, the first thing you need to buy is the factory repair manual.

Which one? I have the '90 Helm manual and the EVTM supplement as well as the CD-ROM based ones for the later years. I don't know if you're referring to a specific manual for the MTX-IV transmission, but I've never heard of such an animal before.

FYI, this isn't my first rodeo. I'm no SHO expert, but I've been wrenching on them for the past 12 years, and I've been on the SHOTimes, TechSHO, then V6SHO e-mail lists as well as SHOForum for at least half of that time. In that time, I've picked up a lot of information about the cars, engines and transmissions general operation, but this is a little outside of the scope of general information...

Not trying to be snippy, I just want to make sure you realize that I'm not just walking in off the street trying to be a SHO mechanic.

If the threads past the broken-off part look decent, then buy a thread-forming tap (as opposed to thread cutting) and use it to chase the threads. The reason you specifically want a thread-forming tap is that it will push the metal back into place and essentially fix slightly damaged threads. There should be almost no removal of material if the threads aren't damaged too bad. If you get a lot of material coming off on the tap then this means the threads were warped, out of round, or rolled over (cross-thread, stripped, etc). If this happens, thread the bolt in to where it would be as installed, but without the bracket and spacer, and wiggle the bolt. If you get a lot of movement (say more then 1/8" or so side to side) then those threads will probably not hold much or just pull out when you torque it. If that's the case then I would look to insert it or go with a bigger bolt. I am guessing that is a 12mm bolt. If it is, you can easily go to 1/2" without having to modify the bracket hole. That will give you an extra 30-thou of fresh material to tap. Just go slow with plenty of **** when drilling out the boss for tapping.

Yup, I know the drill (pardon the pun) when it comes to thread tapping. Done it plenty of times (already twice this past weekend to bolt the MTX coil mount to the 3.2L head).

As far as the thread of the bolt I am guessing it is either M12x1.75 or M14x2. The second thing you should look to invest in is a set of digital std/met calipers. Always useful and can be had cheaply

Yup, I've got two cheap (Harbor Freight?) digital calipers and a digital micrometer I got a few months ago to measure the rod journals. I just don't have either of them in my office, and I wanted to spec out some thread inserts now.

 

[jonheese]

M12x1.75 would be coarse. M12x1.5 would be fine. Problem is they are close enough to look alike without measuring. Sounds like a good time to take the old bolt to a hardware store and match up the thread/pitch to me.

Thanks, M12 is all I really needed I guess. I just want to make sure the thread insert I get is the next biggest size that will work in the old hole.

I have thread gauges in my tap/die set at home; for curiosity's sake, I'll check the bolt this afternoon and tell you for sure what the thread pitch is.

 

[kumba]

What I meant by factory repair manual is the Ford one. These will have the full procedure for rebuilding the transmission, shimming, inspection, etc.

 

[jonheese]

Yes, that's what I meant too. The Ford shop manual.

My shop manual is at home, but I've got the EVTM version here at the office. Here's a couple shots of it:

The Ford shop manuals are all published by Helm Incorporated, and they're referred to as the "Helm manuals".

I don't need any assistance with the procedure for rebuilding, shimming, or inspecting the transmission; I've got all that covered. I'm only looking for specific guidance on my "outside the box" repair ideas and confirmation of what factors will influence the diff shim gap. And I've gotten all of that from you guys, so thanks for that.

 

[jonheese]

Okay, so now on to the thread repair...

According to ISO 68-1, which defines the ISO metric thread standards, the minimum diameter of a M14x2.0 bolt (i.e. the diameter across the thread troughs) is ~11.835mm, but the outer diameter of a M12x1.75 threaded hole is (obviously) 12mm. So if I drilled out the original hole and re-tapped it to M14x2.0, the hole would (in theory) be slightly too big to give me all of the thread width.

Now, if I went to a M14x1.5 size instead, then the minimum diameter would be ~12.376mm and I could easily over-tap the original M12x1.75 hole to that and get full threads.

(As far as I can tell, M14x1.75 doesn't exist, but if it did, the ISO-68-1 formulae tell me that the minimum diameter would be 12.106mm.)

So, do I go to the fine-thread M14 (x1.5) to make sure that I'm getting the full (albeit narrower) threads, or do I stick with the coarse-thread M14 (x2.0) and lose ~0.165mm of overall thread diameter (~0.0825mm off the inside of each thread)? Is that even enough to care about?

Consider that the overall thread height (from trough to peak) on a M14x2.0 bolt is ~1.0825mm, and (in theory), drilling and tapping a M12x1.75 hole to M14x2.0 would give me a thread height of ~1.0000mm.

OR, do I go up to M16?

 

[93rev2sev]

If I were you I'd try durafix. You've already got the case apart. Just don't use anything hotter than mapp gas.

 

[jonheese]

Wait a minute... I'm a total idiot... I just realized that if I'm using a thread insert like a Timesert, the actual hole that I'd drill into the case is bigger than the final hole size, because the insert itself has a thickness. So never mind on that, I'd be fine with a regular thread repair insert...

Durafix, huh? Never heard of it, but I'm looking at the website now...

So I could "durafix" my spacer to the ground-off damaged boss, then drill and tap the whole job as a single unit? Almost as good as welding, I guess?

FYI, I don't have the case apart on the replacement (broken) transmission, I had the old trans apart to do a quick inspection. Could I damage anything inside the case if I Durafix'd it without taking it apart? (I'm guessing yes).

Edit: WOW... I just watched the demonstration videos on the Durafix site, and I have to say, if this stuff can really do what they show it doing, I am seriously impressed... They even show the guy putting a steel bolt into a hole in a thick aluminum plate, then filling the space around the bolt with the molten durafix, and when it cools, because the Durafix adhere to the aluminum but now the bolt, he just backs the bolt out, and presto... perfectly tapped threads.

I think I'm gonna buy a 1 pound kit anyway, even if I don't end up using it on this.

Also, if Durafix melts at 732°F, is MAPP a little overkill? IIRC, Propane burns at ~1000°F and MAPP burns at ~3600°F.

 

[SHO1]

Okay, so who has a diff shim kit available? I see SHO Nut has a rental for $60 (plus a deposit). Is that the way most people do it?

Don't know, but Shonut is prob best bet if you don't have something/someone nearby that you could get shims from.