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Old 09-08-2013, 08:07 PM   #1
Carbroke
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Default 1939 transmission spec

Just rebuilt my 1936 Pickup tranny, which was a 1939 Mercury car tranny.

Replaced all of the bearings and synchro parts, along with the front and rear second gear thrust washers, etc, etc.

After installing the bearing retainers and checking the main shaft end play, I have about .062 of end play.

Anyone know what this should be? I have searched endlessly for a spec on this through all my ford books, motors, and the web, but can find nothing on the end play. .062 seems a bit large, and as these transmissions have a tendency to pop out of gear, I'd just as soon fix this while still on the bench.

It looks like a lot of the end play is the rear bearing sliding back and forth in the rear retainer. The snap ring is .067 as opposed to the original .065. The front thrust washer was pounded to death when I pulled it all apart. Likely this was why.

Anyone got any ideas? Can a shim be put into the rainer to hold the bearing in place?

Last edited by Carbroke; 09-08-2013 at 08:53 PM. Reason: additional info
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Old 09-08-2013, 08:11 PM   #2
Lawrie
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Default Re: 1939 transmission spec

Talk to Macs Van pelt,he knows them inside out.
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Old 09-08-2013, 08:19 PM   #3
Mac VP
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Default Re: 1939 transmission spec

There is no written spec that i have ever been able to learn. Assuming you are referring to the mainshaft endplay in the case itself, on a closed drive trans, with the rear bearing snap ring installed and the rear gasket in place, install the rear bearing retainer and tighten it with at least two bolts. Then, install the u joint with its special bolt & washer to the mainshaft.

If you can feel any fore & aft movement when you try to move the mainshaft, the best way to minimize that is to use a thicker rear snap ring (51A-7070). We stock them up to .075" thick.

The same scenario for the front bearing snap (b-7026). We carry two brands of trans gaskets as one brand uses thicker paper for their front & rear retainer gaskets than the other. It all adds up and you don't want the input and output shafts moving apart that much.
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Old 09-08-2013, 09:02 PM   #4
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Default Re: 1939 transmission spec

Mac,

The front input shaft is really good. The retainer/bearing/snap ring clearance is not allowing any movement there. The rear bearing can move in and out considerably, accounting for more than 1/2 of the total end play on the main shaft.

Can a thicker snap ring be put in alone, or does it require a bearing change-out as well?

Also, the original gaskets are much thinner than what I am putting on. I agree this would add to the "slop". Maybe I'll just pull the gasket and use a thin layer of blue RTV for the gasket.

Is there a "ballpark" end play figure to shoot for? Appreciate the help, Mac.
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Old 09-09-2013, 05:39 AM   #5
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Default Re: 1939 transmission spec

You can replace the rear snap ring with the rear retainer off and the ball bearing in place. The common snap rings measure about .063" and the thicker gaskets are about 5 thou thicker than the other brand. This can mean up to .017/018" difference. I assume you have the rear oil baffle in place on the mainshaft (just in front of the rear ball bearing).
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Old 09-09-2013, 12:00 PM   #6
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Default Re: 1939 transmission spec

Mac,

Yes, both baffles are in place, as is the front spacer ring on the front of the mainshaft, the "thin" thrust washer ahead of the 2nd gear slider, and the very thick rear thrust washer behing the 2nd gear slider.

When I replaced the "thin" front 2nd gear thrust washer, I measured what I had and ordered accordingly. Is this washer picked based on a measurement somewhere? Maybe the guy before me put some different parts in and mistakenly put in the thin washer instead of the thicker version.

Guess I'll be calling you this morning.
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Old 09-10-2013, 06:00 AM   #7
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Default Re: 1939 transmission spec

Once the rear retainer (rear motor mount) is installed the rear bearing should not be able to move in and out of the transmission housing. It is likely the rear bearing seized at one time and damaged the rear retainer or you have the wrong rear bearing, if the bearing moves with ease in and out of the transmission housing the hole in the housing may also be slightly enlarged, the fit should be very close, both in the housing and the rear retainer. If not, then even a good bearing outer race may rotate or wobble causing more damage.
32-48 85Hp. Transmission Rear B-7065 MRC 306SG, Federal 1306CG, Nachi 6306ZZENR two metal shields, remove the shield on the transmission side.
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Old 09-10-2013, 08:04 AM   #8
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Default Re: 1939 transmission spec

Can't recommend Mac VP's transmission book enough. Very valuable resource, much like Ol' Ron's book and JWL's.
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Old 09-10-2013, 11:08 AM   #9
Carbroke
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Default Re: 1939 transmission spec

Well, the book aside, Mac has been great to work with on the phone too. Like most here, a real helpful guy.

I did what he asked regarding bolting the retainer down and then installing the U-joint. This essentially limits all movement to the movement of the inner race within the bearing (not much) and whatever slop is left in the rear retainer (B-7085-B).

My original snap ring measures .065" but there is a tad over .071" of depth for the ring in the retainer. So I have ordered up the .075" thick snap ring from Mac (his part number is 51A-7070B). This ring (plus a thin gasket) should remove all of the end play, keep the bearing as far forward in the case as possible, which will also keep the rear oil baffle from wiping the rear case as it rotates.

When I get the new snap ring and install it all, I'll get back to this thread and post the actual measured main shaft end play. So far the original .062" slop I started with (sans u-joint) has been markedly decreased to about .006" (slop between thin ring and snap ring cut in retainer) so it should get even better yet.

Can't tell you all how much your help and suggestions are appreciated. And I did order Mac's book for my growing library on old Fords along with some other hard to find parts.

Terry, I had specifically looked for signs of the bearing having spun in the case and in the bearing retainer originally when I tore it all down. There is no sign of it having been spinning in there at all. While the rig sat for 42 years, and the rear bearing had rust on the lower balls, apparently it was sufficiently shot enough to allow the inner race to rotate when we pushed it around for loading. Thanks for the thought though.
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