Real tech discussion on design, fabrication, testing, development of custom or adapted parts for Pontiac Fieros. Not questions about the power a CAI will give.
I have been soul searching as to why I keep failing my transmissions. The easy answer is too much power, but I am getting tired of replacing the transmission. I am far too good at getting the case apart. A skill I never wished to obtain!
We all know that history has shown that worn diff bearing can cause problems. I think that these worn bearing are the leading cause of my past two failures. In each of these failure, the output shaft has "punched" a hole in the bellhousing around the bearing. Normally, this shouldn't have load in this direction (in forward motion anyway). Obviously, something is causing a force to be directed in that direction or is putting a bending moment on the bearing.
I took apart my Euro Getrag last night and studied it and my failed transmission. My guess is that worn diff bearings are allowing the entire diff to "tilt" under load and apply uneven meshing with between the ring and pinion. This would cause the bearing there to experience loads it wasn't intended to have and lead to cracking the aluminum case around the bearing race. There isn't a lot of meat that holds it together. I want to look more closely at the fracture marks on the bell housing to see if there were signs of cracks and polishing. This would lead me to believe that it was a gradual breakdown over time and finally, a catastrophic failure. Unfortunetaly, I don't know the best way to determine if the diff bearing are "worn". There is over 4500 lb-ft of axle torque with my car. Me checking it with my hands is hardly a reliable test.
I am building this new transmission for the car with all new parts. Hopefully this one will last a bit longer due to that. Just a thought. Let me know what you think.
I don't think there's going to be much argument with your hypothesis, it's pretty well acknowledged that the weakest link in our trans is the diff support. Even in low power applications these worn bearings can cause problems, which in most cars results in leaky axle seals. It's the same story for the FWD cars, same issue. This is also why cheap rebuilds rarely hold up, because even if the bearings are replaced it won't matter unless the proper shims are used with the new bearings. Lots of cheap rebuilds will simply replace blocker rings where necessary and toss in some new bearings where necessary, and as you know the brand new Getrags (from eBay, etc.) are a much better value than any rebuild kit out there.
So, what are your plans for the new trans? Mix and match case halves or reuse an entire Fiero case? Do you have the tool to select your shims for the diff bearings? IIRC, the euro trans uses the FWD style linkage and the shift shaft is slightly different...do you plan on sticking the Fiero parts into it or using a FWD conversion kit (such as Rodney Dickman's)?
You can replace bearings without reshimming. The bearings are sufficiently precise from part to part that there's no real effect on preload in changing bearings. That @$$umes, however, that the preload was right with the original bearings...
Can you post pics of your failed transmissions?
It sounds like you just reached the limits of the 282 case. I think the radial load on that roller bearing from the final drive mesh could easily cause the failures you describe, but I haven't seen the parts.
Can you detail each of the transmission failures you've experienced? I think that would add to our statistical knowledge of how these boxes fail.
In multiple failures described on Old Europe, the right diff bearing boss was simply pushed out of the case. This indicates that the axial load on the diff from the final drive mesh is too great for the case.
The cold preload on a 282 should be .003-.004. If you can move the diff by hand, then your bearings have loosened up that much. If you can't move the diff by hand, then your bearings may have loosened by an amount less than this. Once at operating temp of ~150 degrees, the differential expansion of the diff carrier and the aluminum case brings the preload to zero.
Even if the preload is perfect, there's nothing you can do about case flex. The aluminum is going to move and wiggle and stretch when you apply that load to it. Nothing is perfectly rigid.
Describe your launch technique and the rest of your driveline. You may be able to extend trans life by modifying your technique or installing lower inertia parts.
You might look into a Getrag 284. I haven't taken one apart yet, but I have a couple on the shelf. Externally they're almost identical to the 282, but the case is MUCH thicker and better braced. They also have MUCH larger axle splines and differential bearings. First and 5th overall ratios are the same as the 282, but 2nd, 3rd and 4th are shorter.
You realize that's more than double the torque rating for the Muncie-Getrag 282? According to the GM service manual, the gearbox is only rated for 200 ft-lb.
The Dark Side of Will wrote:You can replace bearings without reshimming. The bearings are sufficiently precise from part to part that there's no real effect on preload in changing bearings. That @$$umes, however, that the preload was right with the original bearings...
Sure you can...but should you? After X thousand miles, 20 years, splitting the case and pressing stuff apart/together, IMO you should check that the shim thickness is ok. Sure, it might be, but like you said that's a very bold assumption. Coming from captain QC, I'm surprised to hear that from you. I'm not saying you need a CMM or anything.
I didn't say you shouldn't CHECK. I said you shouldn't need to change the shims. However, when mixing and matching case halves and diff carriers, you almost certainly will have to reshim.
Anyone have another good bellhousing? I bought an ebay trans about a month ago too... I have the tranny in my car that is good, and the the old tranny out ofmy car which is still functional but the case was cracking around where the rear tranny mount bolts to... so i dont want to use that case unless i have to. Spare getrags are never a bad thing.
LOL, you're suggesting he puts a trans in the car rated for LESS than what hes breaking now? The 287 is only rated for 170, and depending on the model you need a an adapter plate and a way to adapt the slave cylinder, plus all new mounts, etc.
At that point, you might better off just finding a F35 with the LSD from the turbo/supercharged 4cyl. (or a 6speed F40 for that matter)
Jinxmutt wrote:LOL, you're suggesting he puts a trans in the car rated for LESS than what hes breaking now? The 287 is only rated for 170, and depending on the model you need a an adapter plate and a way to adapt the slave cylinder, plus all new mounts, etc.
At that point, you might better off just finding a F35 with the LSD from the turbo/supercharged 4cyl. (or a 6speed F40 for that matter)
Yea what was I thinking! (I have one on a duke right now though I dont know how or why it got there)
Here are pictures of my previous trans failure. It looks like a tooth broke off the pinion and that caused the case to pop. I looked at the first trans I broke (diff failure) and it had a crack on one of the pinion gear teeth also.
The broken tooth on the shaft would have been nice to see from the get-go.
Obviously, when the piece of the tooth breaks off and gets stuck in the root clearance between the pinion and the ring gear, the separation force from the mesh is going to skyrocket. That's what split your case. It's interesting that the output shaft bearing boss broke and not the diff bearing boss. Are any of the ring gear teeth damaged? Any damage in any *valley* between ring gear teeth?
If you want to stay with the 282, then cryo treat the shaft and ring gear, *followed* by REM polishing. The cryo treatment will alter the size of a fraction of grains within the metal. This will cause smooth surfaces like gear teeth to become slightly lumpy. This lessens the contract area fraction of the tooth, which acts *against* durability. You will need to polish the teeth after cryo treatment to account for this. It would be interesting to check root clearance and lash before and after.
If you want some more insurance, convert to a 284. If you want more insurance than that, cryo treat and REM polish the internals from that box.
I know where there's a 284 for $350. LMK if you're interested.
