No comments on these dog teeth ??

Do they look ok to those of you with the experience to tell the difference since I can't !

Looks to me like you've got a pretty solid builder there. I'm not sure I would even be replacing the sliders, let alone dog teeth.

Have you measured the synchros yet? If they measure within spec, see how much effort is required to push the slider down onto the corresponding gear.

If the dog teeth look that good, install a new synchro ring and measure it. If it is in spec, and all the teeth look as good as those shown, there is a strong possibility that you will get away with only synchro rings & sliders. Obviously, consider this a long-distance observation, there is nothing better than being able to actually inspect each item.

Lucky dog. that box is in decent rebuildable shape with just synchros and maybe 1/2 slider.

For the large bearing stuck on the output shaft, a bearing puller, and some heat from a heat gun.

On the input shaft gear stack, remember that home made socket tool I mentioned at the very beginning of the post. now is the time to make/find/borrow that one. You already have old clutch plate.

Thats good to hear things don't look too bad. I haven't measured the synchros yet. I will read up on that in Pete's tutorial. I can push the sliders onto the gear with effort but it is not too difficult.

I think I will replace all synchro rings and 1-2,3-4 sliders as I believe these are always done . At $600 for the 5-R slider I think I might skip that one as Inever had any issues going into fifth.

The cost of these parts is scarey. With a full clutch rebuild as part of this project ( and the reason it started) I have about $3k worth of parts and I have not considered the spun bearing repair so I don't know if I would consider myself lucky


Do you always replace the break bands and stops when the synchro rings are replaced ?

Input shaft nut removal
 

After a long delay I am back at this gearbox rebuilt. My parts order got tied up in Customs for several weeks.

I have my case repaired and installed new synchro rings on 1st , 2nd gear, as well as new 1-2 slider.

I am now trying to remove the nut on the input shaft but its not budging . I pryed out the indent and welded a 1" deep socket to my old clutch plate to make a fitting I can put a breaker bar on. I think I am going to have to get a better vise set-up to hold the nut.

Does removal of this nut usually require an impact gun ??

Picture of homemade tool. ( Asbestos has since been removed)

http://forums.pelicanparts.com/uploa...1291083835.jpg

Heat.....use mapp gas

I welded up the 1/2 extension bar to the side of a large 3/4 socket that fits the nut. Slide the home-made tool over the shaft. Screw the used clutch plate to a piece of 3/4 plywood which is screwed to the studs in the garage wall. Slide the gear stack into the clutch plate, engage a long 1/2 breaker bar with a cheater pipe while supporting the other end of the gear stack to keep it from flopping around, and off it came.

I bet you can't do that now since you welded up the socket to the clutch plate. Sorry, no help.

Joe Bob, I was a little nervous using the mapp gas next to the bearing I was planning on reusing but maybe some heat won't hurt. Thoughts ?


I saw the pics of the yelcab1 setup but I thought my arrangement would work equally as well and since the torque is centered on the input shaft I thought it might be more accurate.

Hvae someone put tension on the "tool" while you heat it.

I hate to mention this, but...

How-To: Porsche 915 Transmission Repair Tutorial Part 6 - Porsche Wiki

...the M/S nut tool is easy to duplicate. You need a half-inch drive socket, and a length of thick-wall galvanized pipe. Part the socket, and weld each half to one end of the pipe. Secure the M/S and remove/tighten the nut.

If you need actual measurements let me know and I'll measure my factory pieces. The first few pictures in the above link will show you what you need...

Peter ,

I am aware of that tool and your tutorial section. I think I have read it through about 10 times now as it is my bible for this job.

The problem with the extra deep socket ( and I originally was going to make one) was that it would require a special Porsche tool to hold the shaft ( which I don't have and can't easily fabricate) as I would not be able to use the clutch plate spline ie it would be in the way of the deep socket.

The next logical approach was the welded crowfoot socket as described by Yelcab1 which I said OK this approach should work fine but then in my wisdom I said to ensure an accurate torque upon reassembly , I would go with the modified socket I had welded up and show in the picture with the 1/2" deep socket securely welded to the clutch plate core. This permits me to loosen the shaft away from the held nut.

I think my tool will work I just a better vise to hold the nut more securely ( my vise mount to my workbench is not up for the task) as the torque required to loosen is substantial.

I don't mind upgrading the vise/mount as this gets used often. Special Porsche tranny tools don't, also even with the proper shaft restraint it requires the solid vise the hold the tool so I probably have the same issue with it.

Peter or others have you ever used heat to loosen this nut or should I continue with brute strength keeping in mind that I plan to reuse the bearing?

I didn't order any replacement bearings due to the escalating cost of the project ( I probably have $4000 in parts/case repairs/duties/taxes already as this started as a clutch job) and my bearings appear to be in fine shape. If I get a bearing failure in the near future I guess it is live and learn but that is why I have this "hobby " car. If I have to go back in I am sure it will be much easier a second time.

I've never used heat, but have encountered that nut, in some transmissions, to be so damn tight I can't tell you (the Tutorial trans was one of them!). Please, please, please don't take this question as an insult, but because you're turning the shaft, and holding the nut, you must turn the M/S the opposite direction to loosen it, right? In other words, to loosen the shaft you must turn it clockwise, right?

How about adding a vertical 4x4 board/post from the floor to the bench immediately under your vise?

Peter,

Thanks and its not an insult I assure you. I had to think about it twice to be sure but I am rotating the correct clockwise direction. I am going to reenforce the vise and give it another try,

Thanks

Ross

Ross

Have you tried a half inch air impact wrench (or any kind, for that matter)?

Last one I took off came off easily. Of course, I had made up a tool similar to what Peter describes, so I think very little of the impact got cushioned by twisting of my tool before it got to the nut. It might be that the mainshaft will twist enough to lessen or negate the benefit of the impacts. For a guy with a welder, and especially if he has access to some cheap pipe, the tool, even for a once ever task, is really worth it. Because you will have to tighten this sucker for reassembly, and the torque (which got raised to an even higher level somewhere along the 915's career) is fearsome.

I'd put a mattress down on the floor under it so things don't get damaged if it all jumps out of the vice!

If you can obtain a junk 5th gear hub (whatever the splined piece is on that end) you can use that as a holder of that end of the shaft should you fabricate a socket.

I didn't have such a holder piece, and was temporizing with aluminum bits on my vice jaws. While still some 50 lbs/ft shy of what I needed I got scared and took it to my friendly local Porsche transmission shop. He used his really big vice, tools, and 3/4" torque wrench on it. You don't have someone like that handy, but your local machinist should at a minimum have a stouter vice.

Do you suppose that tightening the vice enough to give you the grip you need (especially to hold the shaft horizontal!) is distorting the nut? A vertical position might require less compression, though it looks like you would have to put the gears topside. You could even perhaps make a tool to go in the vice - a large socket bored out and with some plating welded to it.

At least you could take some lumber and make a holder which takes the vertical load with the shaft still horizontal, leaving the vice to serve as a kind of giant crescent wrench.

Which reminds me - I used a very large crescent wrench with a cheater bar on this nut the first time I did it. Won't get you torque measurement (other than by doing leverage math), but to get it off that doesn't matter. You have an admirable holder for the shaft already. And the ingenious yelcab showed how you can make use of your garage's studs to hold things!

I am dubious about heat being beneficial here. For one thing, corrosion is not a factor here. Unlike exhaust studs, this nut and threaded shaft spent their whole life bathed in oil, and never got above maybe 200 degrees F, achieving that temperature fairly slowly and evenly, and cooling the same.

And you aren't going to use heat on reassembly - this isn't a shrink fit deal.

If you aren't going to reuse the nut (I always have - the dimple seems to end up in a different place so that's not an issue), maybe you could get out your trusty Dremel with a cut-off wheel, and weaken the nut with some judicious cutting? Again, even if successful this just puts off facing how you are going to retorque.

Thanks everyone for their advise. Before remounting my old vise on a better platform or replacing it I thought I would try Peter's suggestion to give it better support with a leg under the vice.

It took 2 minutes and a scrap piece of 3" abs cut to length in the chop saw to make a leg.

This made the difference and I was able to get the nut off without heat or an impact wrench. I thought of the impact wrench but did not want to risk damaging the splines on the input shaft

Thanks again Peter to such a simple suggestion, that saved me time and money. I don't know how I overlooked it .

Now to disassemble the shaft and replace some worn synchros and slider.

the price of stupidity
 

I thought I would post another update on progress in this refresh.

I have the shafts reassembled and back in the case. Everything went reasonably well so far except for one thing.

I overtightened one detent plug bolt with required I make a heli coil repair. A $100 in repair supplies later I had it fixed. Live and learn. Time to buy a better low range torgue wrench.

I never removed my shift forks so when the shafts went back together the shift forks were within spec. One item of note is the alignment of the gears . A couple of the sets line up perfect . Some others are not quite aligned , probably 0.5mm offset at max., and first gear off by about 2mm.

I was quite concerned until I reviewed the before disassembly photos and see that it appears to match so in my case the gear alignment was not perfect. I was aware of the 1st gear alignment issue but was unaware the other gears gould be off as well, just to a much lower degree. At this point I don't have the retaining plates torqued to spec and the pinion shaft nut torqued so maybe the situation will improve slightly.

I have a question for those with the experience . Are break bands usually replaced to get a good shift. I did not replace any brake bands but saw a comment from John Walker indicating that they should be replaced. Do these wear out typically ?

Photos


http://forums.pelicanparts.com/uploa...1291773738.jpg
http://forums.pelicanparts.com/uploa...1291773778.jpg
http://forums.pelicanparts.com/uploa...1291773803.jpg
http://forums.pelicanparts.com/uploa...1291773834.jpg

http://forums.pelicanparts.com/uploa...1291798260.jpg
http://forums.pelicanparts.com/uploa...1291798293.jpg

I noticed that also during my last rebuild this spring. Pondered it, ignored it. Tranny works OK.

Given the nature of the brake bands, I have had trouble seeing why they should be replaced unless obviously damaged. This last go around I found that of the blocks had broken. But the bands have always looked OK to me. Of course, that might be because I don't understand them entirely, though I think I am gradually gaining understanding.

I don't recall who posted it, but one of our experts noted that the gears are supposed to be slightly offset to ensure clearance between the fixed gear and the dog teeth on the free gear.

Mike