Measuring Housings of complex shapes

I have been rebuilding a particular make/model of FWD manual transmission. Some of these trannys consistently eat differential bearings, and I haven't yet found any reason why.

I suspect the aluminum housings are either machined incorrectly, warping under heavy load, stretching under heavy load, or all of the above. So that the bearings end up misaligned and wearing out prematurely. This is my theory.

At work we have a wonderful CMM machine that can measure the bores, locate the centers, verify face runouts, etc. It would be perfect, but our company has a very strict policy against personal use of equipment. I fear that contracting someone to CMM it would be exorbitant.

I would love to measure them myself by hand - I have depth micrometers, bore gauges, and 12" dial calipers. But the bearing bores are at all different depths relative to the machined face where the housing is split, so my hand measuring tools appear to be of no obvious use.

What kind of cheaper approaches might work to measure the bearing bores for position, depth, and face alignment? What kind of machine shops might be able to measure them for less than the cost of a new housing?

Suggestions please.

Dave

Reply to
David Geesaman
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If you find out that the bores are not lined up (in your borken case), what are you going to do with that info? Request warranty? Try to remachine them? Important consideration when you're considering your costs.

CMMs are pretty quick actually. While time in a quality lab could be expensive, you likely wouldn't need very much.

How much is a new housing? Important info here.

Do you know how far out is *too* far? CMMs are pretty accurate, but they are not magic bullets.

To solicit a useful solution, more info is a good idea.

Regards,

Robin

Reply to
Robin S.

Reply to
David Billington

Wow, thanks for the detailed responses.

The bearing preload on these differentials comes from housing stretch - .004-.006" IIRC. My rebuilding is done on a tight budget, so housings get re-used unless they have visible damage. So the idea would be to discard bad housings that aren't good and replace with new. I would have to consult with the bearing mfr's recommendations for misalignment, but I'm guessing that since these are tapered rollers that it might require measuring true position to within .001" or so.

The housing halves cost around $300/ea, and one reason I want to inspect them is because many of these trannys had problems at very low mileage, so I suspect buying a new housing might not solve anything.

If it turns out that all of the housings have reasonably good dimensional specs, I would abandon the practice. But I've done my best to investigate nearly every other possible variable and cannot find a smoking gun for the accelerated bearing wear.

Based on the cost of a CMM and labor, I'm guessing that it will cost over $100 to do a pair of housings, and even that's assuming that I would send enough their way to have them set up a program.

Boy, it sure would be nice if I could use the one at work. But that really is out of the question - if I made a mistake and damaged something my head would roll.

Dave

Reply to
David Geesaman

Before CMM's came along, inspection was accomplished on a surface plate with a height gage and Cadillac Pla-Chek. Given a bit of experience, there's not much you can't inspect by that method, although it is somewhat slow as compared modern methods.

Harold.

Reply to
Harold and Susan Vordos

Can you do a functional check of some kind? Obviously you don't have access to the manufacturing drawings, but perhaps you can figure out what dimension(s) are critical and make a simple go/no-go fixed gage or a simple measurement or two.

Whatever it is should reduce to figuring out the datum features on the part (for each dimension) and making measurements from those, as it would with a CMM. Sounds like you have two possible contenders- misalignment of bores (coaxiality?), and a critical linear dimension for the preload(?). With access to some basic tools (including a lathe) and maybe a surface plate and some stock accurate materials such as +/-5 tenths ground shafts you should be able to make something that works.

Best regards, Spehro Pefhany

Reply to
Spehro Pefhany

Thats what I was going to suggest. Surface plate, quality height gage, Cadillac Master and maybe a fixture or large angle plate should cover most of it.

Gunner

Rule #35 "That which does not kill you, has made a huge tactical error"

Reply to
Gunner

===================== It appears you don't really care what or need the actual dimensions are, but rather how a "bad" case is different than a "good" case.

If this is correct, it may be sufficient to make several accurately machined, or better yet ground, "plugs" that fit the bearing locations with accurate, possibly lapped, concentric holes. Drill rod is very accurately ground, so you can get a very good fit between the drill rod and the holes in the plugs. A suitable hole or two should allow you to use a test [not drop] indicator to check the alignment between the holes, and an inside tubular mike or telescope gauge can measure between the plugs. Adjustable parallels can be used to measure the distance between two drill rod test bars installed in the plugs to determine skew.

In any even, I suggest that you determine what the difference is between a "good" and "bad" case. Nothing worse that spending time and money fixing something that's not the problem.

Good luck, and let us know what you find.

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

Reply to
F. George McDuffee

Greetings Dave, If the housing moves under load but relaxes back to the original shape when the load is removed it may be impossible to measure a case to find out what the problem is. However, you may be able to tell by analyzing the bearings. For example, if a particular bearing is loaded off to one side then wear will be worse in one area. So see if you can analyze the bearing and gear wear patterns. Some bearing companies will be happy to consult with you. I've had good luck with SKF and NSK. Cheers, Eric

Reply to
Eric R Snow

Thanks Eric, I've explored those avenues to some extent but so far I've seen no conclusive evidence. The bearing cups don't appear to be moving in the bores. The gears just simply show normal polishing wear. It usually is the diff carrier bearings, but IMHO it's because these have the least design margin against failure.

Obviously I will continue to pay sharp attention to this kind of evidence. I've done around a dozen of these trannys, and so far on the ones where the bearings weren't completely trashed (we're talking bearing surfaces as rough as cement), I've seen nothing pointing toward an obvious cause.

If the problem is housing flex, I might be able to devise a test with a dial indicator and a weight scale to measure case stiffness. I'm actually thinking about doing a complete engineering analysis of the design, complete with bearing life estimation, housing deformation and stress by FEA, etc. But that's a huge undertaking as well.

Dave

Reply to
David Geesaman

This is true. At this point I don't even know if the condition of the housings are the problem. First I need to find out of the housings even have significant dimensional differences.

I think that if I decide that every housing merits a detailed inspection, that this is the final solution. Unfortunately I have no metalworking equipment to speak of, and I suspect paying a shop to build these tools would be putting the cart ahead of the horse. I do these rebuilds out of the spare space in my one-car garage (with a car in it). In the future I'd like to have a shop with some machining and measuring tools, but for now I'm absolutely stuck with hand tools and a tiny workbench.

Yep, that's why I'm beginning to think CMM is the best bang/buck at this point since it could provide such comprehensive and accurate information quickly and with little investment. Even if I find a shop that will do a good inspection with less fancy tools (surface plate, cadillac Pla-Chek, etc) I kinda think the CMM will be more useful for diagnostics.

Will do. Thanks for your help. Unfortunately this problem may remain unfeasible to solve. The fact that the OEM never even put out a Technical Service Bulletin for their dealer mechanics on this issue doesn't make me too confident.

Dave

Reply to
David Geesaman

============ I wondered where the Pinto and Corvair engineers went....

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

Reply to
F. George McDuffee

If something about the design is marginal, improved lubrication might be beneficial. Ford recommended that some transmissions be flushed and refilled with an improved synthetic lubricant. You might explore whether you can add lubricant channels or deflectors to increase the supply to the bearings. A good bearing engineer might be able to recommend a better bearing for the application.

I would definitely try to have a bearing engineer inspect as many failed bearings as possible.

Don Young

Reply to
Don Young

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