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Carl v S
 
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Question 915 Transmission Rebuild Problem

Hi Folks, need some help or thoughts on where I've gone wrong.
I recently purchase a 915 bearing retainer plate and though I do not think that it has any bearing ( ha, ha) on my assembly problem perhaps you can share some thoughts as to what may be causing the issue. I have replaced all the bearings and synchro dogs on 1, 2nd and 3rd gear. I also replaced those brake bands and sliders for 1-2 and 3-4. When I tighten all the shaft nuts and the retainer nuts on the CMS plate the trans shafts tighten up and i can not turn them by hand, They will turn with some effort if I use a ratchet. It appears to me that the third gear dog tooth backside is rubbing on the face of the fixed third gear. I can not insert a feeler gauge in that gap.
As soon as I loosen the bearing clamping plate the shafts free up. Almost as if the clearance between fixed third and fourth id too small. By only a few thousands. Ö

Old 02-01-2019, 11:13 AM
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simple..there should never be any clearance on any gear with dog-teeth attached...all the dog-teeth has to be totally flush with the gears...lloks like you do not have them all the way in-on...

Ivan
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Old 02-01-2019, 12:11 PM
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Carl v S
 
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Thanks for the quick reply... but...
The problem is not the gear that the dog tooth is pressed onto but rather that the back of the dog tooth on the 'free 3rd gear" on the main shaft rubs on the fixed third gear face located on the pinion shaft.
Old 02-01-2019, 12:24 PM
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If you're sure all the thrust washers are in the right position on both shafts, try stacking the rest of the pinion shaft pieces on it and snug up the nut on the end to pull everything tight.
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Old 02-01-2019, 12:39 PM
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KTL KTL is offline
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I agree with Ivan that the dog teeth need to sit flush against the side of the gear. That should be corrected anyway. My recollection from Jon B here on the forum is that a dog ring pulling off the gear is a sign of the ball bearings within the tensioning plates/retainers being a loose fit. That allows the pinion shaft to walk and that drives the dog teeth off the gear

915 Teardown - Odd Damage Assessment

So, yes, fixing the dogs flush with the gear will make the problem even worse. But the dogs still need to be put back flush where they belong

I'm with John Walker on this one. Are you sure you have your placement of the thrust washers correct on the shafts? Coincidentally another guy on the forum is having a similar problem with the shafts being tight. He found that the placement of the washers was not correct.

He makes reference to the improper placement of the washers in post #16

915 transmission / LSD question
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Old 02-01-2019, 12:47 PM
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Carl v S
 
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Wow, so much help so fast! First a thank you. I think that I figured out my problem...
Please see photo below and look at the main shaft. I installed shim #3 between 3rd gear (#6) and spider #12. Looks much better now and I have the clearance. Will assemble on bench tomorrows and confirm. Thanks again. This project keeps on giving.

Old 02-01-2019, 01:19 PM
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Quote:
Originally Posted by KTL View Post
Coincidentally another guy on the forum is having a similar problem with the shafts being tight. He found that the placement of the washers was not correct.

He makes reference to the improper placement of the washers in post #16

915 transmission / LSD question
Yep, I am the other guy.. I paid someone to do my gearbox and they put that washer in the wrong spot.. Glad you caught yours before buttoning it all up.
post some photos of the assembly!
Old 02-01-2019, 01:32 PM
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your diagram

Quote:
Originally Posted by carlvs View Post
Wow, so much help so fast! First a thank you. I think that I figured out my problem...
Please see photo below and look at the main shaft. I installed shim #3 between 3rd gear (#6) and spider #12. Looks much better now and I have the clearance. Will assemble on bench tomorrows and confirm. Thanks again. This project keeps on giving.


Hi Carl
can you link me to where you sourced that diagram and the listing for the parts?
It would come in handy with the discussion I am having with the fellow repairing my box.
Thanks
Mike.
Old 02-01-2019, 01:34 PM
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Carl v S
 
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Hi Mike,

Here is a link to the Pelican forum where I found the picture.

Whining of 915 Transmission

Another good source for part numbers etc. and a great "Fiche" is http://www.***********.com/porsche-parts/911-78-83/porsche_911_parts.php

Type in the Model and then year to see parts diagrams for your car. There are also some very good tutorials on Rebuilding the 915 transmission. Just google them. Good luck!

Carl
PS will try and upload some photos this Sunday.
Old 02-01-2019, 02:44 PM
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Carl v S
 
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Oops!
The link was edited by Pelican it goes to a competitor ... In Atlanta...
Old 02-01-2019, 02:50 PM
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Carl v S
 
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Follow up. Gear box assembled and back in the car. Iíve put just over 600 Km on my ROW 78 911 SC and happy to report that I have five forward gear and just one reverse! Shifts much better, gear whine in fifth is gone and pleased with the taller fifth gear ratio that I chose. Time to tackle the AC project.


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Old 04-11-2019, 02:49 AM
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Good result!
Did you isolate the issue causing your shafts to tighten up?
Old 04-11-2019, 12:00 PM
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Carl v S
 
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915 Transmission Rebuild Problem

Yes, I think that I figured out my problem...

Please see photo in previous post and look at the main shaft. I installed shim #3 between 3rd gear (#6) and spider #12. Looks much better now and I have the clearance. Shifts great and the whine in fifth is gone. When I replaced the worn fifth gear I installed a new taller set. Dropped cruising rpm by about 500-600rpm when driving at 65mph.


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Old 04-16-2019, 04:20 PM
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