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

[jonheese]

EDIT: See last post for current state of affairs... Thanks.

Okay, I've found a new problem with the replacement transmission for my '90:

I don't have the transmission mount bolts in front of me, but does that one go deep enough to be okay with the boss broken like that? If not, can I drill the hole deeper and helicoil or tap it bigger and use a longer bolt?

I'm starting to think that this transmission case is a lost cause...

Also, the thin plate between the trans and the engine: Necessary or not? I can't find mine and I'm not exactly sure what its purpose is anyway...

Thanks in advance.

 

[jonheese]

Okay, never mind about the damaged transmission mount boss... I found the bolts (duh, they were still threaded halfway into the "old" transmission so I wouldn't lose them ), and I think there's plenty of thread to engage and hold the transmission to the mount just fine.

Here's some shots of it assembled (I should've gotten shots of the bolt up next to the broken boss to illustrate how much good thread was left, but I didn't):

So now the only question is about the thin sheet metal plate that goes between the transmission and the engine...

What say you all? Do I need it?

 

[SuperHO]

isn't that just a dust shield for the clutch/flywheel?

 

[LJRuddy]

I left mine off my last SHO only because I forgot to put it back on... Never had any issues.

 

[jonheese]

isn't that just a dust shield for the clutch/flywheel?

I'm not sure, Josh's clutch replacement procedure just calls it "the plate between the tranny and the engine", and it specifically says "Make sure [it] is installed as required." And the clutch how-to procedure doesn't mention it at all.

If that's all it is, does that mean that it may not be necessary (if I can't find it)?

I left mine off my last SHO only because I forgot to put it back on... Never had any issues.

Aha. Okay, that sounds like as good an endorsement as any.

If anyone thinks it is necessary, or will cause damage/problems if left out, please chime in. In the meantime, I think I'll just keep on truckin' here.

Thanks.

 

[raff18]

mines been off for 20k atleast noprobs so far

 

[kumba]

At this point, why not just use this replacement trans for parts, and rebuild the original since it's already out of the car?

Seems like you are taking unnecessary shortcuts on something that obviously has external issues. I would at least want to pop it open and check out the internals. If the guts are all good then just change housings. Worse case scenario you waste a couple hours checking it out and have some pretty good peace of mind later.

 

[jonheese]

At this point, why not just use this replacement trans for parts, and rebuild the original since it's already out of the car?

Seems like you are taking unnecessary shortcuts on something that obviously has external issues. I would at least want to pop it open and check out the internals. If the guts are all good then just change housings. Worse case scenario you waste a couple hours checking it out and have some pretty good peace of mind later.

I can definitely see your point, and I do agree with you to a certain degree...

However, "a couple hours"? Really? I maybe overestimated it, but I figured I'd be stuck for the rest of the weekend on the transmission if I had to open them up.

If I were to go that route, would I need any special transmission tools (diff shims?)? I do have Josh's Quaife/MTX Disassembly video, but I had really planned to use it more for a post-mortem on the old trans...

 

[jonheese]

And let me add to that that the original transmission's issues are:

- Chattering noise when driving in 5th gear, mostly when under power
- No speedometer input, probably bad speedo drive gear on the diff (and no, it's definitely not the VSS driven gear)

So... If I were to swap all the good bits out of the replacement trans into the original case, I would almost certainly have to swap the diff as well, so that would require the diff shim tools and a selection of shims, right?

 

[shospeed143]

that plate is there to keep dirt and anything else that could hurt the clutch out. the other part is the plate is there to keep the starter gap at the right spot. without it your starter teeth will get wear out faster and same with your flywheel. you may not see any change but there will always be problems with keeping it off in the long run. if you cant find your I have a extra one that I could send you at the cost of shipping. just send me a pm and I could get back to you.

 

[Off Road SHO]

You are correct. It is a .025" thick shim plate that keeps the starter in the right place and more importantly, keeps water splashed by the right front tire out of the bell housing area. The distance between the oil pan and the tranny bell housing is .027". It's easy to put in after the fact, IF, you loosen up the engine to tranny bolts and remove the starter.

Tom

 

[jonheese]

Okay, I'm convinced. I will take shospeed143 up on the offer to send me one, and thanks Tom for that explanation. Makes sense to me.

 

[jonheese]

Okay, so here's the update on the transmission swap...

I disassembled the original transmission (per Josh's MTX/Quaife video), and I cannot for the life of me see anything wrong with anything there.

I know that the car made a clack-clack-clack noise in 5th gear in time with engine RPM, and I know that the speedo gear in the VSS didn't spin with the diff.... But now, with the case apart, I spun the diff and I could clearly see the little square hole spinning with it, and I even used my finger to put resistance on the speedo output and it still spun (one of George's theories was that a bad speedo cable in the car's past had put too much resistance on the speedo gears in the tranny and somehow damaged the speedo drive gear on the diff to where it wouldn't spin the cable, but it would spin the VSS so the cruise still worked).

I also took out the 5th gear shaft, and all of the bits on it looked good... The synchro and blocking rings looked good, the gear teeth all looked good... So that's a mystery.

But anyway, here's what I'm thinking:

I've already got a boss brace (repair edition) on its way from Jose to fix the broken shifter boss, but the broken trans mount boss is still bugging me. So, tell me if this sounds like a good plan:

I take the back case half (the "top" of the transmission if it's sitting face-down on the bench) from the old transmission, with its fully intact trans mount bosses, and swap that over to the "new" transmission, thus "fixing" the broken trans mount boss.

Now, here are my concerns with this plan:

1. The shims at the top of the cups/cones at the top of the gear shafts. If they're different from one transmission to the other (and I'm guessing they probably will be), how do I make sure that I shim it correctly with a different case half?

2. The diff shims. Does the "back" case half affect the diff clearances? If I'm not mistaken, both case halves affect this, don't they? So if I change the back half, do I need to re-shim the diff?

Thanks in advance for any help you all can provide on this.

 

[kumba]

I would check the shift forks for wear. I had a problem where the shift fork looked great but was actually worn down from someone using it as an armrest when driving. The part of the shift ford that goes down over the sleeve that engages the gears should look the same on both forks. If one is thinner then it is causing partial engagement and grinding. It's usually the higher gears too where it's more likely to be at on longer trips and at cruise.

Something else to check is to grab the actual gear and see if you have any movement (other then radial/spinning). The actual gear itself (not the brass synchro) should have very little axial movement (front/back, side/side). If it does then the needle bearings are shot or worse.

The only other thing I can think of is the teeth on the coupler and/or the gear being ground down or having big burrs from crappy shifts. Do all the teeth look the same as the other gears? If it's anything like the other Mazda transmissions I've been in then it's kind of pointed with a backward slope. If the tooth is rounded then it needs replaced. If there is just some slight burrs then you can potentially file the burr off as long as it doesn't effect the whole tooth face.

There's should be a list of shaft spec's that should be checked with a feeler gauge while you have easy access. For all you know you could just need a new shim to adjust for wear. No clue what those spec's are but I'm sure someone here has them.

I'd still say that once you've explored the old trans enough to feel comfortable, crack the new one open and give it a once over.

As far as specialty tools go I haven't a clue. I would recommend finding a good manual. If it was an automatic I would suggest an ATSG but no clue what to use for a manual. The previous manual I rebuild I just bought the Ford repair CD-Rom and followed the spec's in it. Wish I could find one for my '95 ATX but the manual seems to go from an '89 to a '96.

Also: http://www.shoforum.com/showthread.php?p=1140665

Lots of pretty pics in there of what I am talking about. The worn/bad teeth can be seen in the OP's second and third picture from the bottom of the original post. The second pics from the bottom is what I would consider too far gone to reuse if I was going to keep the car. The third pic up from the bottom is what I would consider passable as long as I'm not expecting to get another 100K+ out of the car trouble free.

Not sure if that helps but it's my take on your situation.

 

[jonheese]

Thanks for the tips... But honestly, I'm nearly as worried about finding the problem(s) with the "old" transmission as I am with making the "new" transmission work.

I can always take my time diagnosing the old transmission once I get the car out of the garage.

Any opinions on swapping the back case half from my old trans to the new one? How important are those shims on top of the gear shafts? Are they often different from one transmission to the next? How do I measure for proper clearance there with a given shim?

Thanks.

 

[jonheese]

Okay, I just watched Josh's MTX disassembly video further, and I see that the shims at the tops of the gear shafts are all identical, and thus there is no shim selection procedure... You just put one in there and go.

However, I'm not 100% sure about the diff shim. If I change the case "top" (the non-clutch housing half of the case), should I expect that to affect the shim clearance, and thus require me to go through the shim selection process?

As you can probably tell, I'm hoping not to have to do that...

 

[jonheese]

Does anyone know whether I have to re-shim the diff when I change the "back" case half?

This project is on hold until I can find a definitive answer...

Thanks.

 

[jonheese]

Ooh... What about this...

I grind the broken trans mount boss off so it's flush with the broken piece, then cut a disc of aluminum (and tap it? I can't decide), and use it as a spacer between the trans mount and the trans case.

At first I thought about drilling and tapping the spacer, so I would get back those lost threads, but the more I think about the process of screwing in the bolt and torquing it down while making sure there's no gap between the spacer and the case boss, the more I think an untapped hole (bigger than the bolt threads) is a better idea.

Here's my Windows Paint rendition of the modification:

The cut, marked in green:

The simulated spacer, also designated in green:

If nothing else, it will allow me to properly torque down the mount-to-trans bolt there, whereas the way it is now, as I torque it down, it just sorta leans towards the gap and doesn't have a flush surface to mate up against.

Anyone think this is a terrible idea? I know it's not as good as a case swap, but without knowing whether or not I need to re-shim the diff, I really can't go ahead with that plan.

Thanks in advance.

 

[SHO1]

Definately need to check the diff. shim clearance. Might be lucky and not actually have to "reshim" it, but for sure need to check.

 

[jonheese]

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?