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928 transmission swap out

 
Old 02-22-2011, 05:21 PM
  #46  
cpayne
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Originally Posted by Landseer View Post
I did that on the last one we fixed this fall.

Pulled the clutch and lubricated the short shaft, which needed it.

That gave easy access to bolts. Better for torquing them in the reinstall, too, I think.

Supporting the front of the TT on an adjustable height stool, plus trans jack for the box, gave fantastic control over the unit to allow single person to do the job with less risk to the dog.

I had forgotten about the method for removal with clutch still installed --- will attempt that next time.

Jim Chambers' car is single disc, not sure if that gives more room?
Did you see the Bear under your car!
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Old 03-01-2011, 12:32 AM
  #47  
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as far as diagnosing the previous transmission (holbert) failure, i forgot to mention that there was a huge trannie noise, starting from just before my last race. it sounded like the torque tube , but obviosly it was coming from the trans. in the pits with sean, Brian and gang, i could hear some pretty nasty gearing noise, but again, thought it was the tt going out. im thinking there already was some damaged teeth on the main input shaft. eventually , it just let go.

is there one gear that the main input 5th gear interacts with, regardless of which gear you are in?

if its just 5th gear and the one it attaches too, maybe Ill rebuild it!
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Old 03-01-2011, 02:33 AM
  #48  
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Originally Posted by mark kibort View Post
is there one gear that the main input 5th gear interacts with, regardless of which gear you are in?
Entire lay shaft rotates always with input shaft.

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Old 03-01-2011, 01:38 PM
  #49  
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Thats what I wanted to see! cool. so, i see that when the main shaft gear, strips out a little,it barely makes contact and can drive the layshaft. so, no power can be transfered there. But, how does 5th gear drive the differential, if the Diff is driven off whatever gears are engaged on the layshaft?
In concept, i get it. 5th doesnt required that lower gear set (layshaft), but all other gears do.

I know I dont have a clue how the gears all interact, so I guess it is time to breakout the manual and have a looksy.
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Old 03-01-2011, 02:09 PM
  #50  
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Here's what's 'in the box' when you buy a 5th gearset. Includes the synchro, and is preloaded with the two needle bearings that ride on the pinion.


So if the TT shaft is spinning, so is '5th gear' on the layshaft, and thus the entire layshaft is always spinning too











Erkka-

What are the little notches in the tooth surface of the part of 5th gear that fits on the layshaft? For oil transfer? Noise abatement?

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Old 03-01-2011, 02:30 PM
  #51  
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Great pics! thanks
so, this might be the only damage. but, how does the force transfer to the diff in 5 gear selected, and not use the layshaft connection?

how do those bearings and gears come off the shafts. do you need a press, or gear pullers, or something more elaborate.

is it possible, this is something I could do in my garage, or mostly, if I can borrow presses for parts of the disassembly or assembly?

I still have to consider the $1500 price tag of a new 5th gear. are there any used 5th gears out there?
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Old 03-01-2011, 02:40 PM
  #52  
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I'm sure there are used 5th gear sets out there... you have one of them!

Dan
'91 928GT S/C 475hp/460lb.ft
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Old 03-01-2011, 02:42 PM
  #53  
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But, do 928 s4 transmissions ever break someplace else other than 5th gear related???
Originally Posted by dprantl View Post
I'm sure there are used 5th gear sets out there... you have one of them!

Dan
'91 928GT S/C 475hp/460lb.ft
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Old 03-01-2011, 02:45 PM
  #54  
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http://www.mailordercentral.com/928i...302%20905%2033

$750. Dunno whether they're in stock but they're pretty good about answering the phone, over there.
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Old 03-01-2011, 03:10 PM
  #55  
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Ive heard of these guys! good question? in stock?? probably not

Mk

Originally Posted by Rob Edwards View Post
http://www.mailordercentral.com/928i...302%20905%2033

$750. Dunno whether they're in stock but they're pretty good about answering the phone, over there.
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Old 03-01-2011, 05:02 PM
  #56  
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Originally Posted by mark kibort View Post
But, how does 5th gear drive the differential, if the Diff is driven off whatever gears are engaged on the layshaft?
See that strange looking gear at front end of pinion shaft. 5th gear syncro ring locks input shaft into it through shift sleeve (not in picture) making both shafts rotate in sync. There is picture in archives somewhere which shows how power is transmitted through each gear. I know I did it years ago but can't find it now.

Originally Posted by mark kibort View Post
how do those bearings and gears come off the shafts. do you need a press, or gear pullers, or something more elaborate.
Lay shaft 5th gear is easy to remove. Might not even need puller to get it out after circlip is removed. Changing syncro rings to 1-4 and R mean pinion shaft has to be dismantled almost completely. It can be done with fairly easily available tools. How many different types you need depends on how much you want to use big hammer and how much finesse.

Originally Posted by Rob Edwards View Post
What are the little notches in the tooth surface of the part of 5th gear that fits on the layshaft? For oil transfer? Noise abatement?
Or side product of manufacturing process.
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Old 03-01-2011, 06:30 PM
  #57  
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so, what does it take to pull all this stuff out of the gear box. assuming that all the gears are fine, certainly the synchros were fine, so, if all the gears are untouched, just replace the main 5th gear and the opposing gear on the layshaft, and put it back together. sounds easy.
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Old 03-01-2011, 06:54 PM
  #58  
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OK, here goes---- RTFM!
lol!
Take a minute and look through it, all will be revealed....
Or, quit whining and send it Greg Brown...
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Old 03-01-2011, 07:09 PM
  #59  
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Old 03-01-2011, 08:14 PM
  #60  
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The real issue is not how hard it is to take the transmission apart, or put back together (though that would certainly be an issue for me, as well), it's looking at the disassembled pieces and knowing what is 'good' to put back, and what needs to be replaced. That's the challenge. I can look at the surface of a new synchro and the surface of a used synchro, and tell the difference, but I can't tell you whether the used synchro is any good or whether it's done.
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