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Old 09-20-2020, 06:52 PM   #1
Talkwrench
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Default syncro hub position for second

When shifting into second gear should the syncro hub be hard up against second gear ?
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Old 09-21-2020, 05:59 AM   #2
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Default Re: syncro hub position for second

Not sure that it would be “hard up” against second gear,but for sure it’s position would be right next to second gear. I guess there could be a slight gap.......measuring in a few thousandths. I’ve never measured it but I recon it would vary from transmission to transmission. It’s not something that Ford ever gave a specification for.
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Old 09-21-2020, 07:59 AM   #3
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Default Re: syncro hub position for second

I've never measured it, but what I do on a 39 double-detent top is put a hard stop in the top casting (5/16 NF bolt), so when I go into second "in a hurry", the shift rod/rail hits the stop at the right position. This helps guarantee that it is not "over shifted".
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Old 09-21-2020, 09:38 AM   #4
Tim Ayers
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Default Re: syncro hub position for second

Quote:
Originally Posted by Bored&Stroked View Post
I've never measured it, but what I do on a 39 double-detent top is put a hard stop in the top casting (5/16 NF bolt), so when I go into second "in a hurry", the shift rod/rail hits the stop at the right position. This helps guarantee that it is not "over shifted".
Dale:

Do you do this in place of the plug?

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Old 09-21-2020, 11:21 AM   #5
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Default Re: syncro hub position for second

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Dale:

Do you do this in place of the plug?

Tim
No - it is on the opposite side for the 2nd/high shift rail/rod. I drill the top with a 5/16 NF, then install a bolt that is shortened to length, with a jamb nut on the inside of the top.

2016-11-12 17.13.47 copy.jpg

2016-11-12 17.14.02 copy.jpg
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Old 09-21-2020, 11:32 AM   #6
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Default Re: syncro hub position for second

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Quote:
Originally Posted by Bored&Stroked View Post
No - it is on the opposite side for the 2nd/high shift rail/rod. I drill the top with a 5/16 NF, then install a bolt that is shortened to length, with a jamb nut on the inside of the top.

Attachment 442724

Attachment 442725

Got it! Thank you!
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Old 09-21-2020, 11:46 AM   #7
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Default Re: syncro hub position for second

Quote:
Originally Posted by Bored&Stroked View Post
No - it is on the opposite side for the 2nd/high shift rail/rod. I drill the top with a 5/16 NF, then install a bolt that is shortened to length, with a jamb nut on the inside of the top.

Attachment 442724

Attachment 442725
I'm fixing to do the same type of thing on a different transmission.
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Old 09-21-2020, 06:42 PM   #8
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Default Re: syncro hub position for second

I checked mine and it sits off nearly a 1/4" , was just curious as to if this would be another possible cause of jumping out of second ?
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Old 09-22-2020, 06:20 AM   #9
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Default Re: syncro hub position for second

I am confused, the hub is the center part of the syncro and the syncro sleeve is the outer part. On the early syncro with 6 steel balls the hub moves on the splined shaft and the later syncros with blocker rings the hub does not move. What syncro are you talking about??? Are you talking about the sleeve?

If your going to install a 2nd gear shift stop on the transmission top, you may want to consider placing the bolt lock nut on the outside of the top instead of inside IMO.
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Old 09-22-2020, 06:37 PM   #10
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Default Re: syncro hub position for second

The sleeve Terry.
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Old 09-23-2020, 02:21 AM   #11
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Default Re: syncro hub position for second

Rob, I have the dimensions of the travel for the forks and hub for the early and late trans if you want.
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Old 09-23-2020, 06:44 PM   #12
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Default Re: syncro hub position for second

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Rob, I have the dimensions of the travel for the forks and hub for the early and late trans if you want.
Lawrie
That might be handy Lawrie.. post or email me when you get the chance..
Still waiting on all the diff - hub stuff to arrive so I can start on that..
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Old 09-23-2020, 07:16 PM   #13
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Default Re: syncro hub position for second

Note: The following is related to 39-48 transmission setups . . . not the earlier stuff!

Given the discussion is about the transmission popping out of second gear, there is a lot more to think about. What I've found is that the issue is primarily related to tolerances/slop in the overall transmission setup.

I pay particular attention to the dimensions on the main-shaft (the front caged roller bearing area) - it needs to be as close to the original specs as possible. If the bearing area is worn, this can really contribute to the problem. I do not run worn mainshafts in my rebuilds . . . I cherry pick the best ones I can find - in many cases NOS ones.

Also, I believe that having any slop in the fitment of second gear to the main shaft is also an issue (and this is common!). I've been working with Charlie NY and having him re-bush all my second gears - for an exact/tight fitment to the specific mainshaft I'm going to use (I send him the complete mainshaft assembly).

I have built two 39 trans with Zephyr gears in the last couple of years - with perfect mainshafts and the newly bushed 2nd gears and they do not pop out of second gear (even under hi-rev abuse). Just try to get anybody who rebuilds these transmissions to guarantee they "won't pop out of second gear" . . . good luck with that! . That is why I build my own. (Am building four 39 boxes when I get back from vacation - all are setup as I note in this thread).

Another area that I concentrate on is having a really good cluster shaft - either original Ford stuff, or I make my own. All of the repop shafts that I have bought are undersize - usually .001 to .002 . . . which adds slop to the cluster setup. Also, when I stack my gears up on the mainshaft, I setup the thrust clearance to be exactly .004 - the lowest end of the spec.

I've found that the tighter you run ALL the clearances, using the highest quality parts . . . the better. As a youngster, I always put up with my 39 boxes popping out of 2nd under high revs and deceleration - as an "Old Goat" I now try to build transmissions where I don't have to hold them in second! LOL

Hope this helps! B&S
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Old 09-23-2020, 11:24 PM   #14
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Default Re: syncro hub position for second

That info will help a lot Dale, I did go through all of that. The problem is [and Im sure for most] is having a lot of spare parts to choose from to make a good setup.
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Old 09-25-2020, 07:38 AM   #15
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Default Re: syncro hub position for second

Quote:
Originally Posted by Talkwrench View Post
That info will help a lot Dale, I did go through all of that. The problem is [and Im sure for most] is having a lot of spare parts to choose from to make a good setup.
We all know the feeling! I tend to start "collecting parts" long before I do the rebuilds. The parts that I pay the most attention too are the mainshaft and the cluster shaft - I try to find the best ones I can. If I have to install a used mainshaft, then I make sure there is very little wear on the bearing surface - hopefully none.

I do believe that having a precision fitment on second gear (bushing to main shaft clearance) is one of the important "tricks" to helping 2nd gear stay in gear, but that is a hunch that Charlie NY and I share. Most of the guys on the site share information - we are all trying to rebuild the best transmissions in the best ways possible and nobody can claim to know all the secrets.
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Old 09-25-2020, 10:40 AM   #16
Tim Ayers
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Default Re: syncro hub position for second

Quote:
Originally Posted by Bored&Stroked View Post
We all know the feeling! I tend to start "collecting parts" long before I do the rebuilds. The parts that I pay the most attention too are the mainshaft and the cluster shaft - I try to find the best ones I can. If I have to install a used mainshaft, then I make sure there is very little wear on the bearing surface - hopefully none.

I do believe that having a precision fitment on second gear (bushing to main shaft clearance) is one of the important "tricks" to helping 2nd gear stay in gear, but that is a hunch that Charlie NY and I share. Most of the guys on the site share information - we are all trying to rebuild the best transmissions in the best ways possible and nobody can claim to know all the secrets.

**Edit: I should have read all of Dale's post. As usual, he's spot on and covers my comments.

I am no expert, but after having many chats with MacVP, I also think the backlash setting of the cluster is also a crucial measurement. Too much and the cluster wants to thrust upward. When you let off the gas, the cluster then drops causing the synchro to move.
This movement, which the synchro is under load, pushes/forces it "pop" out of gear.

When this happens, no fix except a hook on the dash for the stick will keep it in second gear under deacceleration.

Good thing Mac sells shims off various thicknesses to get this measurement spot on. This measurement is a by product of wear to the thrust surfaces fore and aft in the case.

Too much movement also can grenade the clusters since they will makes contact with one another. Reason why many hi-po or OHV swaps cause a blow out of the transmissions.

Finding the best case you can is also an important part of the rebuilding process.

Last edited by Tim Ayers; 09-25-2020 at 11:21 AM.
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