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DDS DDS is offline
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Moron gearbox rebuild

pun intended. As some may remeber, I elected to take on rebuilding my own gearbox(es). I have some pics posted here and would really appreciate any comments on teh condition of the synchros and dog teeth as shown.

http://www.syer.net/gearbox_rebuild.htm

I was also wondering....

1) Does the rear cover require the same careful shimming with the correct paper gaskets? Both of mine had the same gasket, and my ebay gasket set only had one rear cover gasket included.

2) My gasket set came with three thicknesses of int. plate/gear housing shims, coloured cream, yellow(ish) and brown. IIRC, these are /004, .006 and .009" respectively. Does it make sense that one box had no shims at all between the int plate and gearbox, while the other had three of the .005" shims? What does shimming accomplish?

3) Does changing the diff change the shimmign requirement?

4) I have a 914/6 box and a 914/4 box, both apart. Which gearing would be preferable for a mainly street driven 2056cc weber carbed, cammed four banger?

TIA, Dave
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Old 05-08-2004, 08:01 PM
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#1. No. It's just a papar gasket. Should only be one in the kit.

#2. There should be at least one at least for sealing. The shims help set the contact between the ring gear on the differential and the pinion gear on the thick shaft.

#3.No shimming with the differential. But, keep the same ring gear.

#4. The gearing on the 6 is a little shorter than the 4 and is set that way because the 6 has a higher rev limit. Unless you plan to have a 6500 rpm 4 cylinder, I'd stick with the 4 cylinder gearing.

Now from your pictures.

Most of the early boxes had the bolt. It's used for the 911 and the 914/6 acellerator linkage.

Yes, that is a factory diff!

If you can slide the synchband around in the dog teeth easily, it's done.

And those dogteeth are done. Don't look at the point, look at the missing scoop in the middle of each tooth.

On first gear, I would use a dremel to repoint both the dogteeth and the slider. I would take a straight file and make sure the area between the "splines" are straight. You can see a little mushrooming on the right side of each spline.

That bearing is the cheaper bearing to replace. If the balls are loose on the bearing with the smaller balls, it is about done.

Reverse looks ugly. Pick the better looking one and use.

That roll pin was from the the 914/6 tranny, which in it's tailshift configuration, has 1 internal roll pin. Was the 914/6 tranny sideshift converted? That is common. I did it to my 914/6.

James
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Old 05-08-2004, 10:23 PM
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Oh yeah, the link to my web-page doesn't work. One to many "http//"'s

James
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Old 05-08-2004, 10:24 PM
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Thanks for all the help James.

I do actually have a 6500 rpm 4 banger - at least I think I do, so that's where I set the rev limiter! HD valve springs, rocker studs, elephant feet, ported, big valves. Seems happy up there and the torque curve seems to work. I'm playing with venturi sizes (may go down from 36 to 32mm) and that may change things.

http://members.rennlist.com/chuxter/901&915ratios.htm

I just had another look and interpret the gearing table as showing that the six actually has the same first gear, a significantly taller second, a slightly taller third (so much closer to its second than on a four), the same fourth, and a slightly shorter fifth. So, "closer ratios" once you get into tall second, and a little shorter/higher rpm in fifth. I'm running tires a bit smaller than stock, maybe use the six gearing with the four's fifth gear for highway use? This might not be necessary as the engine already seems to come 'on song' at about 85mph in 5th! Any thoughts?


Thanks for the dtailed input on the 'box.

It had already been converted to side-shift. I had hoped the broken roll pin was part of the original mech. or a legacy from the failure that necessitated the weld on the rear cover. (probably one and the same.)

When you refer to the scooping of the tooth - do you mean the way the point of the tooth is hollowed across the span of its point? How to describe? - If it were a peaked roof it has a badly sagging ridge, and it should have a straight one? I ask because they also could wear/hollow against the synchro, though the synchros seem - by design - to be getting the worst of that deal.

When you dremel the points - I presume they need to be the same length, and if the above is true, to have 'meat' to the tooth across its depth. Do you bother to level the teeth before repointing them (like sharpening a saw) or just carefully have at it with a stone in a dremel? I suppose they come somewhat prelevelled by grinding against the slider's teeth!

Thanks again, Dave.
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Old 05-09-2004, 03:46 AM
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Repointing:


Cleaning up

Cleaning up

Left before, right after

Left Before

Right After
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Old 05-09-2004, 06:09 AM
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The shorter gears will make it a fun car to blast around in although I would install the taller 5th gear for freeway speeds. Driving down the freeway at 4k gets old.

Geoff
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Old 05-09-2004, 11:20 AM
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Great pics, thanks James - I'll post some wild ones later - more failures. I was given a gear set (still on shafts and intermediate plate) from a box that had recently been rebuilt. Tore it down today - your instructions are right on the mark. Some perfect (new) dog teeth and synchros, oddly second was worn. The box had a bearing go bang, lots of damage.

Any idea if those bearings are available through industrial channels?

Geoff - that was kind of what I was thinking about the gears, though I have no experience playing around with it. I suppose part of the equation is what I do with the webers and what that does to the torque curve. I do intend to install a six so it might be wise to build accordingly.

Dave
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Old 05-09-2004, 12:25 PM
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Forget finding the bearings somewhere else as they are "special" and have a ridge on them to seat them.
Rebuild everything you can afford to now and go with the shorter gears as they will be fun even with the four except go with the four 5th gear for reasonable freeway driving.
Change all the synchros that look like there is any wear on them, they are cheap and keep you from trashing the dogteeth($$$)
Geoff
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Old 05-09-2004, 03:24 PM
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Uh, the synchro's are not cheap. They are $60 each these days.

If a synchro looks pretty good, turn it around and use the "back side".

Unfortunately, the way the bearing was made, it is special. I think we can get a $25 bearing which will work, except it would need to have a groove machined in and a circlip installed. This would probably be more than the $150 for the bearing.

James
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Old 05-09-2004, 07:30 PM
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Now that is really going cheap, to turn the synchros around. That I don't buy, $60 is still pretty cheap compared to the cost of sliders. Even if you just do 1st, 2nd and 3rd gears that isnt that bad money wise to fix something right.
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Old 05-09-2004, 09:06 PM
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914 owners are notoriously cheap. The synch band flip gives you an unused side on the band. The Factory manual says to flip any synchro's you don't replace.

Replace all 5 and it's $300.

But the best thing is...as soon as the box starts to grind, replace the synchro.

James
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Last edited by red-beard; 05-10-2004 at 06:28 AM..
Old 05-10-2004, 04:32 AM
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I just think on some things you should do it right so you don't have to redo it later. Fixing a tranny is one of them. Who wants to keep having to fool around with a tranny, much more fun to drive the car.
Geoff
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Old 05-10-2004, 06:00 AM
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James-Geoff

I agree with both of you....However I think James is looking out for the Low end Poorsche owner in these times of Economic Break down-but if you have the Ducats it is best to have it done the best you can......I wish our current Presidential Admin would have James mind set, but that is another barrel of oil!
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Old 05-10-2004, 11:18 AM
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Tooth wear

For those who are interested, worn vs new dog-teeth. How bad are the bad ones James?

Dave

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Old 05-13-2004, 06:32 PM
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Hard to tell in that pic..........They shouldn't be very rounded also look at the sliders.

Geoff
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Old 05-13-2004, 07:16 PM
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With three boxes apart, I'm getting plenty of evidence of wear and failures, and can now see wht James meant by 'scooped'. The gear dog teeth tend to get undercut rather than rounded/blunted, (though that happens too) because the teeth of the slider are not as tall as than those on the gear. The slider teeth therefore do round over. So, while you can't see the point from the top in the pic, you can see that the meat of the tooth below the top has been 'eroded' by the slider tooth. Innnterrresting!
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Old 05-14-2004, 02:59 AM
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That set of dog teeth is in pretty good shape. There is some damage, but they look useable. The really bad ones the "scoop" goes down below the what should be pointed surface.

James
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Guys, I still am not able to indetify the "Scoop" on the dog teeth. Is the new dog teeth the light colored one adjacent to the avatar?
L. mcC
Old 05-15-2004, 03:34 AM
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Look between the photos. I tried to highlight the "scoop"



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Old 05-15-2004, 04:28 AM
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So far so good. I have two good bearings intermediate plate bearings and a pile of frsh synchros and dog-teeth. That synchro hub tool is indispensible as is James' site.

Turns out my 914/6 gearbox had been assembled without shims, and with silicone as a gasket. Pretty sure I shouldn't trust the pinion depth!
Since I will be mixing and matching parts, I'd be happier setting the various shim stacks/preloads and such properly. the haynes manual says leave it to the dealer. Is that absolutely necessary? Is there a DIY way to set this thing up?

TIA, Dave
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Old 05-20-2004, 05:53 PM
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