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Old 01-02-2008, 12:04 PM
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T-350 rebuild - what happened to my endplay?

Hey All,

I've got an issue that I hope someone can help out with here - I had decided to rebuild the transmission in my truck (1979 Chevy K10 1/2-ton 4x4 350/350/np203) myself - figured it'd be a good learning experience - and am currently in the process of putting all the pieces back together. The problem I'm having right now is that there appears to be almost no end-play at all, and I don't know if it's because of something I didn't do right, or maybe too much grease (petroleum jelly), or just new parts that haven't fully seated yet. I'm using the Sessions book as my guide, so as it stands:

Checking initial end-play before tear down, I had 0.048" (checked by laying the transmission on its back and pushing on the output shaft).
Doing the same check after rebuild, I had absolutely none. After I tore it down again and removed some of the excess grease, I gained 0.002" of end-play (which makes me wonder if I did use too much grease - or too much to bench test with).

New pieces: all bushings, torrington bearings, thrust washers, frictions, steels, intermediate band, and hardened intermediate race. No shims used before or after.

Thrust washer specs:

Sun gear thrust washer (4-internal tangs):
Old (plastic): 0.0448"
New (metal): 0.0468"

Input ring gear thrust washer (3-external tangs):
Old (plastic): 0.0606"
New (metal): 0.0639"

Output carrier thrust washer (4-external tangs):
Old (metal): 0.0616"
New (metal): 0.0634"

For a grand total of +0.0071" difference in thickness when comparing thrust washers. I know that the intermediate and direct drums are seated fully because I was able to count each time one of the frictions engaged (click - . . . - click - thunk!), and I can spin the input and output shafts both forward and backward after the pump is torqued down. What else do I need to look at, or should look at, to see if something was done incorrectly?

Thanks,
Mike

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Old 01-02-2008, 06:08 PM
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Brimstone, I just put my th350 together using the Ron Sessions book (my first). I also had ..052 nd play overal and that did not change much for rear nd play,. I did however ,like u lose all my front nd play. The shaft turns sweet and all and I have ALL new steels and frictions, bearings etc.
I did not change the front bearing(did not come in the kit) and was not worn that much sp i decided to not to worry about it. I do not use a dial ind. just accurate measuring before teardown and I could not "feel " anf front nd play after rebuild. I do not think I could "feel" .005 anyway.
Hope some one answars this for us.
Check my thread th350 air check
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Old 01-02-2008, 09:23 PM
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When I did mine, I followed Sessions book too. I cked before AS HE SUGGESTS, and made a note of my end play. After I changed EVERYTHING, I had NO endplay. Apparenlty, putting in all new steels and torrington bearings closed up the gap from the previous build. I needed to get some selective washers and got it opened up to spec. If you leave it tight, you will be asking for problems.

If I recall correctly, end play is checked with a dial indicator on the INPUT shaft end and then pushing up on the OUTPUT shaft. It is total play, not just one end. I had mine standing straight up sitting on the edges of 2, 5 gallon cans so I could let it settle after each "up" push on the output shaft.

Did you match the number of frictions and steels that came out of your trans? Some have less than others, but the kit usually has the maximum amount. If you have the pistons that take less and installed all of them, you will have major clearance problems.

Mark
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Old 01-02-2008, 10:51 PM
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did you install a torrington bearing or a tanged thrust washer behind the pump ? while they are interchangeable, it does require using the correct bearing. initially, i had installed the bearing but lost a lot of endplay, so i went back with the washer.
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Old 01-03-2008, 08:51 AM
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350 endplay

Did you change any hard parts? The bushings that you changed, are they fully seated, as in, not sticking up above flush causing you to lose endplay.

Did you change the bushings in the pump, where the input shaft[forward clutch drum] goes? If these bushings are tight it may feel as if you have no endplay.

DHMag brings up a good point about the pump washer/pump bearing issue however, I will take a moment to expound on this.

There are different thickness washers for the pump[ selective ] so a pump washer change could account for your loss of endplay.

I don't remember for sure but I think that in 79 your pump should take a bearing, but someone along the way may have built this trans before and changed the pump to awasher style.

Also the bearing is perhaps .140 in thickness, or so, and the washers will be much thinner so a change here is a huge difference.
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Old 01-03-2008, 10:40 AM
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Jmark - yes, that is the preferred method of checking end-play. When I checked mine beforehand that wasn't an option so I had gone with option #2 - checking endplay with the transmission on its back (Setup the dial indicator - push the input shaft back to find zero, then push on the output shaft to find total endplay). I'm doing the final check the same way, as well.

All bushings were replaced as close to the stock depth/location as I could get them. I used the depth reading on a set of dial calipers to find out the bearing's position, then drove 'em in to that point. For the bushings in the pump, I didn't have a driver that would work, so I "machined" one out of 6061 aluminum on my wood lathe - worked like a charm.

I'm also currently using the bearing behind the pump. I had tried the thrust washer as well - but it didn't make a measurable difference at the time. It originally had the bearing, and there was so much sludge in the bottom of the pan (not to mention leaking from every orifice) that it's probably a good bet that it had never been opened before.

I had documented tear down with a digital camera, so I'm 100% positive that I'm using the same number of steels/frictions throughout. Clutch stack clearances were also all in spec as well (~0.025" for the intermediate and forward drums each, and 2 dimes - or 0.100" - for the reverse stack).

I think what I'll do tonight is try the washer on the pump, and if that doesn't do it then I'll use the old output carrier washer as a test (since it's easy to get to) - that alone should give me an extra 0.002" of play. If that works, then I guess I'll look into getting a thinner pump washer somewhere. I'll report back when I've done this experiment.

Thanks,
Mike
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Old 01-04-2008, 11:11 AM
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Well, I managed to do some more testing on this, and have come to the following conclusion: someone please shoot me if I try to rebuild another automatic transmission .

The front pump washer that I have measured out at 0.1031". I had put in the old output carrier thrust washer as a test to see if that helped with the end play any, and tried out these scenarios:

1) Old washer & pump bearing
2) Old washer & pump washer
3) New washer & pump washer

The resulting end play for each attempt? 0.002" - unchanged, no matter the combination. And I really had to push on the output to get that 0.002" too. I was figuring that using the old washer would have given an extra 0.002" clearance, but I guess that was too much to ask for.

*Thinking* maybe I should try it without the bearing or washer on the pump to see if that opens things up - or try just the shims at least. That oughta give some measurable amount of clearance for testing (or maybe I'm using too much common sense, here).
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Old 01-04-2008, 01:44 PM
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350

Common sense is ok, if you have tried all of those different combinations and your clearance does not change common sense would dictate that something else is a bit askew.

But what though. Did you change the case bushing and is it below flush by at least the depth that the thrust bearing has to sit into the case?

I'm starting to run out of ideas here

I will wait to hear your answer.

Last edited by briscoe; 01-04-2008 at 01:45 PM. Reason: spelling
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Old 01-04-2008, 03:37 PM
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Quote:
Originally Posted by brimstone
what happened to my endplay?
I ask my wife this about once a week, but I don't think that's what you're talking about.
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Old 01-04-2008, 03:41 PM
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Yep, case bushing was replaced. I think that's the only one that wasn't installed to the same depth, but I had tried the bearing before-hand and the bushing didn't interfere that I could tell. Guess I can rip it all apart again over the weekend and push it in a hundredth or so just to make sure . . . might as well double-check all the rest while I'm at it too . . . well, good news is I'm getting *real* good at removing the output shaft lock ring
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Old 01-04-2008, 03:47 PM
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Quote:
Originally Posted by curtis73
I ask my wife this about once a week, but I don't think that's what you're talking about.
It's a good thing I'm not married cause I'd be getting a different kind of endplay myself (My "assembly table" is the dining room table - too cold in that unheated, no-insulation, drafty, pole-barn of a garage) .
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Old 01-04-2008, 07:52 PM
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endplay

Case bushing depth is different on a 350 compared to a 700R4, because of bearing design.

When I was a young rebuilder, younger anyway, I made the mistake of not driving the case bushing in far enough and winding up with clearance issues.

You gotta check it.
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Old 01-08-2008, 10:43 AM
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ok, done some more work on the trans. Case bushing is now installed 0.224" down from the bearing face. Since the flange on the bearing is 0.143" long (or thereabouts), that shouldn't cause any interference now. I also measured the output shaft endplay with the low/reverse support installed and that's at 0.125". I haven't gone any farther than this cause I wanted to make sure of something so that I wouldn't have to tear it back down again.

The pic attached is of the channel where the low/reverse support resides in the case (bottom of the pic is the bottom of the transmission. You can see what I'm talking about on the large lug in the center). What I would like to know is is the amount of wear normal, or is that how it's supposed to be? Reason I ask is every time I install the support, the anti-clunk spring "pushes" the support into this grove and it's a real pain to remove when necessary since the lugs no longer line up. Should I look at a case saver, or am I way off base?
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Old 01-08-2008, 11:22 AM
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th350

As best as I can see and I'm not catching a real good look at the bottom lugs, you do not have enough case wear to worry about.

By the way, where was the case bushing sitting, flush, or a little below flush, and if below flush how far below flush, I'm still thinking about your clearance issues.
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Old 01-08-2008, 03:40 PM
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Of course, I didn't bother to take a measurement before I re-visited the case bushing, but if I had to guess I would say that it was installed to somewhere around 0.17 - 0.18" - it was below the bearing surface, but not totally below the NW notch. Now it is totally below the notch floor itself. I'll also try to get more definite measurements on the case wear while I put it back together.

Thanks for all the help, BTW. Hopefully I'll eventually get it. I must say though that I have never had this much trouble with an assembly before - carbs, wiring, steering columns, a manual transmission (ST-10) - nothing has been such an ordeal as this has.
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