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> (automatic) Transmission Alignment
Jimthecopierwrench
Posted: April 10, 2018 01:06 am
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Couldn't even guess how many of re&re'd or swapped for something different - but the alignment to the engine - or rather centering the crankshaft output to tranny input - never really crossed my mind. The dowel pins simply make it happen.

This at the top of my mind wondering (just thinking, not necessarily planning) how hard it would be to home spin oddball adapter plates.

At a glance it seems simple enough, and then just a spacer (between crank and flexplate) the same thickness as the adapter - at least as far as that direction goes, but it wouldn't take a lot of radial misalignment to chew out a rear bearing and seal .. or a front pump shaft. Intuitively in the range of .005 - a typical enough rear bearing oil clearance.

Makes me think that the dowel holes are machined after casting on a special jig .. but unit to unit tolerances probably aren't that good, and if this was so engines and trannys would be a married pair for life.

(When you think of it' it's almost odd that the casings are mated, and then the reciprocating bits - the exception being manual trannys)

So I guess the flexplate and converter just take up a fair bit of mess then??

Enough for a carefully hand measured, center punched, and drilled out adapter you think?


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MacFromOK
Posted: April 10, 2018 01:38 am
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I'm pretty sure dowel locations are within tight tolerances on OEM engines/trannies. If the "flex plate" flexes very much, it will crack.

However... If you want to make an adapter, all you need is a cheap runout dial indicator from Harbor Freight (or somewhere similar) and a bit of ingenuity. You can then make sure the adapter is centered on both the engine and tranny before assembly. beer.gif


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gremlinsa
Posted: April 18, 2018 08:52 pm
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Done many a tranny drop on several different makes and models.

Every one of them have a little bit of 'slop' in the input-shaft, in fact if you look closely to the design of each one, the input shaft is on a single swivel bearing with a single main gear behind it. Then it has a pin bearing onto the output-shaft. This allows the shaft quite a bit of radial misalignment.. also with the seal directly infront of the bearing, the shaft tip can move about 3mm (~1/8 in) off center and barely put any undue pressure on the seal.

This obviously allows a quite a lot of tolerance on the dowel positions and also takes care of any parallel or angular misalignment..

Actually its a genius design, because you have no need for universal or CV on the shaft, meaning less that can break.


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MacFromOK
Posted: April 18, 2018 11:58 pm
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QUOTE (gremlinsa @ April 18, 2018 02:52 pm)
Every one of them have a little bit of 'slop' in the input-shaft, in fact if you look closely to the design of each one, the input shaft is on a single swivel bearing with a single main gear behind it. Then it has a pin bearing onto the output-shaft. This allows the shaft quite a bit of radial misalignment.. also with the seal directly infront of the bearing, the shaft tip can move about 3mm (~1/8 in) off center and barely put any undue pressure on the seal.

But the seal isn't the problem.

Working as a diesel mechanic in my brother's shop, we had a truck come in with the hubs broken out of its clutch plates. Further inspection revealed that the bell housing's dowel holes were larger than the dowels mounted in the engine.

So... we removed the dowels, and and mounted the bell housing "snugly" (not tightly) onto the engine. With a dial indicator mounted on the crank, we tapped the bell housing into proper position so runout was negligible. We then tightened down the bolts, and re-drilled the dowel holes to an available oversize.

Did a lot of work for the customer after that, but not for broken clutch hubs.

FWIW, the flex-plate in a clutch and the flex-plate (flywheel) in an automatic tranny setup both perform the same function - compensation for minute errors in alignment. beer.gif


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Jimthecopierwrench
Posted: April 19, 2018 01:56 am
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Well from experience I know that (at least into the early 90's) cast iron block tolerances could be atrocious. You just don't see it until you start measuring. I realized a very long time ago that exactly because of this, that a daily street engine doesn't require about 4/5 of the machining that a typical rebuilder performs. Ie, assembly boring of the journals, cutting down and boring rods, crank undercutting big ends, deck cutting, etc. etc. Unless something is broke, hand scuff the crank and toss in the same sized shells that came out.

They must have found a way to mitigate alignment .. either by design as suggested by Gremlins, or an extra precision after cast procedure on both bellhousings and block bosses - ie precision placement of the dowels, which would mean that the holes would have been machined with dedicated equipment. Otherwise just about anything not made by the Germans would have a hell of a time swapping.

Hadn't really though about it before this thread, but when you consider that I've swapped trannys manufactured both decades and different in type from each other to the same block .. it's almost surprising that they fit.

Of course again .. street driven daily's that rarely see 3000 RPM ..

Replaced a whole lot of tail shaft seals from bad U joints or driveline angles .. but don't ever recall a front pump seal going.

Maybe those oddball pains from the bad old years that would chew through multiple rear main seals were a result of a bad mating.


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