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

[kumba]

I'd just tap it for M14-coarse, grind it down, make a spacer, and drill the plate out to accept the bigger bolt. There is plenty of beef on that boss to hold it as long as you are getting enough thread depth.

If the threads past where it is broke really do look good, I'd still trying running a thread-forming tap through it. Only problem is those tap's aren't cheap: http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=17557249&PMT4NO=81288503

Good news is you'd have one **** of a chaser for anything else that is M12x1.75.

 

[jonheese]

$28 isn't too bad for the thread-forming tap.

If I go with the M14 bolt, I think I'll grind the broken piece off before tapping it, otherwise that'd make for a very interesting drilling/tapping experience...

Okay, so I've got plenty of options now. Thanks guys so much for the recommendations. I'll take stock of the situation once I get a good look at everything and post back here when I decide, and probably again when I get something going.

 

[jonheese]

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.
[youtube]rSzpmP_vCE4[/youtube]

Ah, I didn't see this edit until just now...

18mm of threads, huh?

Well, the shaft of the bolt is 1-5/32" long (all of which is threaded), and the trans mount plate is 5/32" thick, so that leaves 1" of threads sticking out into where the mounting boss should be. The broken section represents about 3/8" of threads, so that leaves 5/8" of threads after I cut/grind off the broken piece. 5/8" =~ 15.9 mm, so that's a no.

Thanks for that very quantitative analysis. That tells me that I'm "close, but no cigar" for just using a loose, un-threaded spacer, if I believe the Machinist's Handbook (and I do).

I guess I will try using aluma-weld/durafix to "weld" an aluminum disc onto the ground-off boss, then drill and tap the whole jobber for an M14x2.0 bolt and call it a day.

Thanks again, guys.

 

[93rev2sev]

When using durafix, I found it likes to pool at the lowest spot and will run off of the part like water if the part is not level

You NEED to make a dam of some sort to form the molten alloy in the shape of the boss. further searching on the web will yield videos that demonstrate this. Also, to get the amazing adhesion that you see in the vids, the PART needs to be 732 degrees and you MUST THEN scratch it up with the stainless brush and use the hot part to melt the rod...NOT the flame. Once the durafix begins to tin the aluminum (like soldering), you are ready.


PRACTICE on something that you don't care about.

 

[jonheese]

Gotcha, good advice, thanks.

 

[kumba]

I wonder if you could use something like a welding bung in the hole so you don't have to worry about filling up the rest of the cavity. From the description it sounds like it would stick or grab it.

 

[jonheese]

I wonder if you could use something like a welding bung in the hole so you don't have to worry about filling up the rest of the cavity. From the description it sounds like it would stick or grab it.

I don't get what you mean...

Here's my plan:

1. Measure boss from end to end to get full length (X)
2. Grind off broken section of boss so it's flat
3. Measure newly-ground boss (Y)
4. Cut 1" diameter alum rod to length defined by X - Y
5. Bevel edges of spacer and remaining boss to roughly 45°
6. Centerpunch and drill 12mm hole in spacer
7. Temporarily bolt spacer to ground-off boss using stock M12 bolt, to hold it in place while Durafixing
8. Heat up & "weld" spacer to boss using Durafix (exact procedure pending)
9. Drill out threads with 12mm bit, tap with M14x2.0 tap

 

[93rev2sev]

thats probably a pretty decent procedure, If I were you, I would bevel the rest of the "land" so that there is a slight gap for the durafix to bleed into.

Also, I would tin the rod and the boss separately with durafix before trying to put anything together. This way, you know both pieces are properly tinned.

 

[jonheese]

thats probably a pretty decent procedure, If I were you, I would bevel the rest of the "land" so that there is a slight gap for the durafix to bleed into.

Do you mean more than just beveling the edges? You saw step 5 above, right?

Edit: Do you mean something like this? (Not drawn to scale, but it's supposed to represent the side view of the spacer and the transmission boss where they meet. The dashed lines are the edges of the hole.)

Also, I would tin the rod and the boss separately with durafix before trying to put anything together. This way, you know both pieces are properly tinned.

Okay, cool. I plan on practicing with the Durafix quite a bit before actually attempting the repair. Thanks again.

 

[93rev2sev]

Yep, like that. Doesn't need to be perfect...in fact, the rougher the finish, the better the "bite"

 

[shoon]

... Also, to get the amazing adhesion that you see in the vids, the PART needs to be 732 degrees...

Does heating it that hot remove the temper from the metal? I was trying to get some races pulled from my case half and someone had mentioned getting the metal hotter than ~300 removes the temper.

+ a propane torch might not work, you "might" need an acetylene torch to get that hot. There is a fair bit of metal mass; so it sinks a lot of the heat that you are putting into it.

 

[jonheese]

Does heating it that hot remove the temper from the metal? I was trying to get some races pulled from my case half and someone had mentioned getting the metal hotter than ~300 removes the temper.

Hmm.... 300°, huh? If so, then Durafix/Aluma-weld wouldn't really be good fixes for structural aluminum, but they are billed as such... Of course, I'm not suggesting that a company wouldn't over-promise something when a profit is involved, but that would be pretty stupid of them to sell a product that, under normal use, de-tempers the base metal...

Edit: Also, if heating it above 300°F detempered it, then it'd be impossible to weld the case, since Aluminum melts above 1,000°F.

+ a propane torch might not work, you "might" need an acetylene torch to get that hot. There is a fair bit of metal mass; so it sinks a lot of the heat that you are putting into it.

I've got a MAPP torch, which burns near 3,650°F (compared to Oxy-acetylene around 5,800°F). If propane won't do it, I think MAPP should be plenty hot to get to 732°F, even with the heat-sinking effect of the case.

Edit: Does anyone know what grade of aluminum the transmission cases are made out of? 6061? If so, MATweb says that I have to hold it at 320°F for 8hours to age (temper) it... Does that mean that 30 seconds of 732°F will be okay?

Edit 2: Never mind, the trans case is cast aluminum, and I don't think 6061 can be/is normally cast... I guess it's probably 319, 356, 535, or A206. Still, all of the MATweb pages for those alloys show that the aging process takes from 2-8 hours at +300°F, and although that doesn't guarantee that 30 seconds of 732°F won't ruin the hardness/strength/temper on the metal, I'm betting that it won't.
319: http://www.matweb.com/search/DataSheet.aspx?MatGUID=f8b5559f5c864f9cbb0a0f45d811545e
356: http://www.matweb.com/search/DataSheet.aspx?MatGUID=4314a54124a84c619d472a09ede7f0fe
535: http://www.matweb.com/search/DataSheet.aspx?MatGUID=60b23f8c4fde40e6b59a773b221999b4
A206: http://www.matweb.com/search/DataSheet.aspx?MatGUID=28da9c9490bc4bfebf987d14afe02f61

 

[jonheese]

Does heating it that hot remove the temper from the metal? I was trying to get some races pulled from my case half and someone had mentioned getting the metal hotter than ~300 removes the temper.

Okay, I e-mailed the Durafix guys ([email protected]) to find out their take on using Durafix to repair cast aluminum, specifically whether the 732°F would de-temper it. The guy responded thusly:

Jon,

I think you have been misinformed about the temps. required to weaken aluminum.
Give me a call. I can best answer your questions by phone.

Thanks, Randy Weeks 800 5479353

So I called him up, and we chatted for a few minutes about it. I could tell from his voice that he's the same guy who demonstrates the product in the videos on the site.

He said that to de-temper cast aluminum like that used in a transmission case, you'd need to heat it up near 1,100°F for at least a few minutes. He said all alloys of cast aluminum will retain full strength when heated to 732°F.

We also discussed my plan for repairing the transmission boss, and he said he thought Durafix would work well, as long as I could make sure that it stayed put while it was "wet", same as 93rev2sev indicated. I'm thinking of some ideas on that front, and once my Durafix gets here, I will be playing around with it, practicing, and hopefully I'll work out a good way to do this repair successfully.

He also gave me a couple tips that I didn't see on the website:
- Once the fix is done, don't just take the flame away immediately or it'll cool too fast and get brittle and fall out. Instead, fan the nozzle at the repair area while slowly pulling it further and further away. This allows it to cool more slowly and results in a stronger repair
- Propane gives a 2100°F flame, so it usually does the job fine on all but the thickest and coldest aluminum. MAPP gas is good only if you can't get the Durafix to flow properly with propane.
- Warm up a large section of the piece around the repair area, and this will allow the heat to stay in the work area longer.

I've already got an order in for the stuff, and I'll definitely post back here after I've had a chance to play with it a bit.

 

[kumba]

I'd put some anti-sieze on the bolt you are using to make sure the weld doesn't seize it in there. Probably have to get the copper exhaust anti-sieze to make it stand up to the heat.

A welding bung (or whatever people like to call it) is a ceramic cone/plug/dowel looking thing that you put into a hole when welding to prevent you from welding inside the hole and also for alignment. It sounds like you will be using the bolt to fulfill these purposes.

 

[jonheese]

Yes, the bolt will 1) plug the hole, 2) hold the spacer to the boss, and 3) align the hole in the spacer with the hole in the boss. Honestly, I'm not too worried about the original hole, since it's going to be drilled out to 12mm in the next step anyway.

As far as anti-seize goes, do you really think it'll seize? Isn't the thermal expansion coeff of aluminum almost twice that of steel? Especially since I will be heating the aluminum directly and the bolt indirectly, I expected that the boss would expand faster than the bolt, thus freeing it up in the hole slightly, if anything.

I wasn't planning on using anti-seize, but I guess it's cheap insurance that I can get the bolt out easily afterwards, just in case.

Edit: I see now that you said "to make sure the weld doesn't seize it in there." The Durafix stuff doesn't stick to steel, and in fact, they demonstrate that it can be used to "tap" an over-drilled hole by dropping a bolt into the hole and back-filling it with Durafix, then unscrewing the bolt after it cools. In the video demonstration, it does appear to take a healthy amount of torque to get the bolt out after cooling, but that's with full thread contact all the way around, and the difference in thermal expansion coefficients in that case work against you, because the tolerance is 0 when hot and the aluminum will shrink further than the steel given the same cooling.

 

[jonheese]

Update (it's a LOOOONG one): I got my Durafix on Friday (<4 days from order to arrival), and played with it a little for a few hours on Friday night. Most of my testing was with 1" diam aluminum rod, since that's pretty close to what I'd be actually working with on the trans case.

I cut the alum rod clean through with a hacksaw and beveled the edges a bit. I then heated both pieces up with MAPP, cleaned the oxidation off with the included stainless steel wire brush, then "tinned" them with the Durafix rod, using the brush again to help work the melted metal into the pores. Then I clamped them into my bench vise, heated them up again, and flowed some Durafix into the gap created by the bevel.

I immediately learned that the molten Durafix rod flows very well, as 93revs2sev said. Brazing flat aluminum bars or square tube together would have been pretty easy, since gravity isn't constantly pulling the molten material away, but the round rod was quite difficult.

So, I took some 12ga 1" wide steel flat stock and bent it into a 1" ID circle, thus making a collar that fit perfectly around the aluminum rod, but with a gap between the ends of the steel, so it's like a C-shape. The idea here was to wrap this steel piece around the rods at the joint, so I can hold the Durafix in the gap between them. Since Durafix doesn't stick to steel, once everything cooled, I'd be able to slide it off and the joint would remain intact.

However, even with the steel collar in place, I found that the surface tension in the molten Durafix was not high enough. It still found little holes to flow through (and end up in cool splatters on my garage floor and workbench). I was able to remedy this by decreasing the size of the gap between the two aluminum rods. However, since it was hot as dickens and clamped into my bench vise, instead of grinding down the beveled material, I just adjusted one rod so it wasn't in-line with the other, in effect skewing the joint so the final piece would look bent at the joint. This decreased the size of the gap on one side but increased it on the other. I didn't really care about this, as I just wanted to make sure that I could get it to flow properly into the narrower gap. This was just a test after all.

Well, this worked splendidly, with my steel collar in place. Here are my results:

It ain't pretty, and it certainly ain't a "good" joint, but it's very strong. I tried to break it over my knee for quite a while, and even put it in my vise and tried to hang on the end for a while, but I was afraid of breaking my benchtop so I stopped after a while. The black marks you see are melted plastic from a pair of old work gloves I used as a rag when moving the hot work piece around.

So, with this test piece (somewhat) successfully brazed, and with a good set of guidelines for amount of bevel and preferred gap size, I started the work of repairing the transmission boss yesterday morning.

I started by cutting off a short (~3/8") piece of the 1" diam aluminum rod, for the spacer. I center-punched it and drilled a 12mm hole in it, then test-fitted it on the trans boss. I then removed the transmission from the engine and removed the case half. I also removed the little spring and pin from the detent rod area on the case, and the reverse sensor, since I didn't want them getting as hot as I was planning on getting the case. I also made sure that the 3 shaft bearing cups and shims were on the tops of the internal gear shafts and not in the case. Using my pneumatic cutoff wheel, I removed the broken portion of the boss and beveled the flat edges slightly (not too much).

I then set out to heat up the case with my MAPP torch in order to "tin" it with the Durafix rod. I heated it. And I heated it. And I heated it some more. I sat with that torch pointed at the case for almost an hour and a half. After about 20 minutes, my infrared thermometer told me that the surface of the broken boss was around 390°F. After about 45 minutes, it was at 400-410°F. After an hour and a half, it was still at 410°F. I was quickly learning that the mass of the case half was no match for its surface area.

The night before, it took me about 20 minutes to heat up the 1" aluminum round rod to 732°F, and it held the heat for a good 40 minutes before I could touch it with my bare hands. But the transmission case half was very good at shedding heat. Not only sinking it away, but also radiating and convecting it off into the 50°F air. I could see that I would never get the metal up to 732°F with MAPP gas. MAPP in pure oxygen or oxy-acetylene might have worked, but I'm not even sure about that.

So, I regrouped and came up with a different plan. According to the machinist's handbook (Thanks 92revs2sev), I need a minimum of 18mm of threads to safely secure the M12 bolt, and the mounting hole (after flattening out the beveling) went a good 25mm into the transmission boss, although not all of it was threaded. So, I took my M12x1.75 tap and tapped the hole as far down as I could, and that gave me ~24 mm of threads to work with.

So, I took my spacer, which has an un-threaded 12mm hole through the middle, slapped it in there, and used a 35mm long M12x1.75 bolt to bolt the transmission to the mount. This seems to work well, and with almost 22mm of threads, I think it will do a good job of repairing the original damage. Here are a couple shots of the finished repair:

So yeah, much ado about nothing with the Durafix, but you can be sure I'll get some use out of it in the future, as it is some pretty neat stuff.

Thanks again to everyone who posted help here!

 

[93rev2sev]

Good deal. Glad it was that easy.

I guess you would have to preheat the case in the oven to help get the temp you need?

 

[jonheese]

Yeah, I thought of that, and I was considering measuring my oven for clearance, but I think the axle seal (and the wife ) would have complained a bit about that... Plus, how much time would I have had until the Colorado air defeated the pre-heating?

After all that, I figured it was just a better idea to go with the simpler solution of a mechanically free spacer and deeper threads. In the end, this may indeed fail, and I'm prepared for that contingency with a spare case half, I'll just have to break down and re-shim the diff at that point.