915 rebuild: re-assembly phase

[tbitz]

Well I am now ready to start re-assembling my 915 tranny.

I will start with the putting back the differential unit. The axle flange seals were hard to get out. It took alot of heavy blows with a piece of wood, but finally they came off. I followed Jim Sims advice and placed some oil on the new seals and they slide right in (maybe too easy, are they gonna slide out?).

Should I be using any loctite on any of the nuts/bolts in the tranny?

What is the correct torque for the flange bolt to differential (1978)? Bentley says 32ft-lbs(page 390-3) and Haynes says 19-22ft-lbs. Who is right? I wish I had the shop manual for the 915 rebuild.

[Jim Sims]

Hi Tony,

The torque on the axle flange bolts depends on the bolt and washer configuration. If there was a washer under the bolt the torque is the lower value of 18.8 to 21.7 ft-lbs; if your axle flange bolt didn't have a washer under the head then a value of 28.3 to 33.3 ft-lbs is specified. The is due to the design changing during the production run over the years. It isn't recommended to put any locking compund (like loctite) on the threads of these bolts.

I suppose if you can pull the shaft oil seals out with your fingers they are too loose. If they are this loose I would remove them and degrease them (use soap and water on the rubber not a solvent; then rinse and dry them thoroughly. Then I would degrease (a little solvent is okay to use here) and dry the bores in which they mount. The I would lightly "butter up" the OD's of the seals with an oil rated RTV silicone rubber and press them in again. I would clean up the excess RTV silicone with a "Q-tip" and then let the RTV silicone rubber cure for 24 hours before exposing it to much oil or handling. John Walker or others may have a better or alternate solution.

Per the factory shop manual here are some upcoming torque values:

Input shaft flange nut - 115.7 to 130.2 ft-lbs
Input shaft castellated nut - 86.8 to 101.3 ft-lbs
Retaining plate (for the shafts) nuts (note the manual recommends replacing the lock washers under these nuts) - 15.2 to 16.8 ft-lbs
Pinion shaft flange nut (manual says to replace this nut) - 173.6 to 188.1 ft-lbs
Guide fork, shifting nut - 5.8 to 6.5 ft-lbs
Shift detent, transmission housing - 10.8 to 13 ft-lbs
Shift fork nuts - 17.4 to 18.8 ft-lbs
Transmission housing: side and front cover and guide fork cover - 15.9 to 18.1 ft-lbs

Some other notes: The mesh marks (scribes on side of teeth) on the differential ring and pinion gear were for manufacturing purposes; you can ignore them during reassembly. Also the manual recommends lightly coating the running and contact surfaces of the gears in the differential with "Molykote" or MoS2 paste.

Tomorrow Brad and I will assemble his input shaft and get the seals in the front cover installed but we're still waiting on a first gear synchro hub (dogteeth) in order to assemble the pinion shaft.

Good luck and let us know if we can help with any more factory manual information.

Cheers, Jim and Brad

[tbitz]

Thanks Jim.

My axle flange bolt has a washer, so I went with 20ft-lbs.

The axle flange seal went in smooth. I simply pushed it in with my hand. I could probably remove it by hand, but it would require a good pull. Since this is replaceable even with the tranny in the car. I'll leave it and watch for oil leaks. I took the time to clean the tranny case (I think this was the most time consuming job of the rebulid). Now I will be able to clearly isolate any oil leaks.

Thanks for the torque specs. I'll write them down in my Bently book.

I put the dogteeth on my second gear. I simply lubed it with swepco and used my vise with aluminium jaws to press it in. My first gear is too big for my vise and doesn't sit in the center. When I try and squeeze it goes in lob sided. I'll have to find another way.

Thanks for the info.

[Jim Sims]

Tony, A few other pieces of information we've gleaned from the shop manual and experts who have been gracious enough to answer our questions (hint: there is very good value in joining PCA).

1) The factory shop manual states that the parts on the input and pinion shafts that are pressed on (or knocked on if one is using the hammer method) should be pressed on dry; i.e. there shouldn't be oil or other lubricants on the surfaces being assembled with a press.

2) You likely know that the needle bearings shouldn't be mixed up but should be assembled with their original races/gears; for good measure we are also retaining the original axial orientation of cages and races. We note that the one needle roller located at the seam of the needle baring cage can slip out easily; the seam needle bearings for 1st and 2nd gears in Brad's transmission seem especially prone to this. They'll stay in place but only with reasonable handling. The stories one reads of people finding a needle roller on the drain plug magnet are easily believeable.

3) Beside the issue of the outer bearing races being a little loose in the transmission (differential) housing (and the red loctite measure to resecure them) one should also check the faces of the retaining plates holding the shafts and bearings up against the transmission housing. If the bearings/races have been improperly turning then the contact faces of these retaining plates may be worn to the point that they do not clamp correctly. If worn it is recommended that they be replaced.

Enough typing; time to get to work!

Cheers, Jim

[tbitz]

Thanks for the info Jim.

I have kept the needle bearings together with each gear. I have not retained the orginal axial direction though . None of my needle bearings came off.

For reassembling the shafts I'll try heating things up before I put them in the shaft. Hopefully they will slide in (I don't think so).

I looked at the bearing retaining plates you mentioned above. Mine look perfectly flat. No groves at all. Thank God.

I got all my new dogteeth in the gears. I borrowed a bigger vise for 1st gear. I heated the dog teeth in boiling water and placed the gear in the freezer. I had to use quite a bit of force on the vise for 1st gear but it went in all the way. I put back the reassembled gears on the bearings on the shaft to make sure they turned smooth. All is well so far

Now for those circle clips Any tricks on getting them back on? I thought removing them was tricky. Note: I am doing all this by myself (no son, only three women in this house). As soon as I have the circle clip open to the best of my abilities, the synchro ring pops off. Looks like another "special" porsche tool is needed. I haven't gotten any yet, I won't start now.

I think I'll take a break and think about the circle clip problem. (aka Miller time...)

Cheers,

[Jim Sims]

Hey Tony,

Regarding the circle clips for the synchro assembly: since you don't have a second pair of big hands available consider either a big plastic cable tie or a big hose clamp around the synchro ring to keep it compressed. If you use the hose clamp then be sure and pad the inside with something so you don't mar the friction coating on the synchro rings. We sort of put the circle clips in by spreading them as much as we could with the snap ring pliers; they tend to buckle out of plane if you spread them too far. Then we started by placing the inward pointing tab in the radial slot and then going around the ring pushing it down as we kept it spread with the pliers; as we pushed it down it snapped inward into the groove. Of course someone was also keeping the synchro ring compressed and down at the same time.

We've put Brad's input shaft together and have taken all the old seals out of the front cover. We'll be cleaning that up and putting in the new seals shortly. I'll post a more detailed account later. We can do a little more cleaning, then we'll be waiting on parts. Sigh!

Cheers, Jim

[tbitz]

Thanks Jim.

I got the circle clips in. A beer and a break always helps. I used some tape to hold the synchro rings in place. I customized my snap ring pliers with a small grove so the holes in the circle clip would not slide out of the snap ring pliers. This made life easy.

Everything went in smoothly for the pinion shaft. For the input shaft I had to heat the needle races and then they just fell into place. I do have one concern. There is a thrust washer which is tapered on one side (Item #7 in Bentley page 350-2). When I took my shaft apart the tapered side was facing the rear of the tranny (towards the clutch/engine). Is this correct? It is not very clear in the Bentley photos.

Cheers,

[Jim Sims]

The tapered or beveled side of that thurst washer faces towards the engine/clutch. This reason for this is apparent; if you look closely you will note that the taper or bevel of the thrust washer ensures that it only contacts the inner race of the ball bearing. Cheers. Jim

[tbitz]

I have assembled both shafts. I placed the thrust washer as you mentioned.

I placed the two shafts beside each other with the gears meshed, and noticed that all the meshed gears don't perfectly line up. If I line up 4th gear, then 1st gear is off by quite a bit. I can see by the wear on the teeth that this is how it was before I messed with it. Do the shop manuals indicate what is the max misalignment between the gears? Here are some pics of what I mean.

This is a pic of 4th gear lined up.


But with 4th lined up 1st is not lined up. You can see the wear marks where 1st gear meshes with the input shaft. This is how it was originally.

[Jim Sims]

No, the shop manual doesn't give any tolerances for such misalignment probably because the gears are not supposed to be misaligned to the degree indicated in the image you posted. Something has to be wrong in the parts stack up and I would venture to guess the problem is within the pinion shaft. This misalignment looks to be the thickness of a thrust washer so perhaps one is missing or in the wrong place. Starting from the front (front of the car) of the pinion shaft here are the parts that are contained within the gear housing (this doesn't include any of the 5th/reverse parts): radial roller bearing, thrust washer, 1st speed assembly (1st gear, synchro assembly, needle cage and race), 1st/2nd operating sleeve (slider) and 1st/2nd spider, 2nd speed assembly (2nd gear, synchro assembly, needle cage and race), thurst washer, 3rd speed "fixed" gear, spacer bushing, 4th speed "fixed" gear, forwardmost ball bearing race, ball bearing with retainer or clamp plate around flange of bearing, rearmost ball bearing race and finally the rearmost radial roller bearing. In addition to a missing or misplaced thrust wsher a bearing could perhaps not be seated properly but I doubt the shafts would assemble and run with a bearing out of place. If you don't find anything wrong with the pinion shaft then let me know and I'll send you the assembly sequence for the input shaft. Good luck. Jim

[tbitz]

Jim,

I have all the components you mention for the pinion shaft.

If you have the bentley manual pages 350-2 and 350-4 show the assembly of the two shafts. I have followed these pictures to verify my assembly.

Looking at the input shaft there is a spacer (item #18 on page 350-2 of Bentley. You can see the spacer in the picture above). The only pupose that I can think it serves is to line up the 1st gears. It seems like mine is too long. Can you measure the thickness of yours? Mine is 19.5mm long.

Can you measure the thickness of the various thrust washers? Maybe I have the wrong ones to begin with.

Thanks,

[Jim Sims]

Sorry, I don't have a copy of Bentley handy. Your first gear setup doesn't look like a 915; are you working on a 930 4-speed? The reason I ask is that there is not a spacer bushing between 1st and 2nd fixed gears on a 915. In a 915, 1st gear is part of the shaft itself and 2nd gear registers against radial extensions of the splines. First gear may be removed from a 930 input shaft and there is a spacer bushing between 1st and 2nd gears. From the parts catalog here is the assembly sequence staring at the front (again parts within the gear housing; no reverse parts listed) for a 930 transmission input shaft: radial roller bearing, "fixed" 1st gear, spacer bushing, "fixed" 2nd gear, thrust washer, 3rd assembly (gear, synchro assembly, needle cage and race), spacer ring, 2rd/4th operating sleeve (slider)and 3rd/4th spider, spacer ring, 4th asembly (gear, synchro assembly, needle cage and race), thrust washer, ball bearing race, ball bearing, ball bearing race, radial roller bearing, and flange nut.

I can measure thrust washers but we'll first have to check for parts match (by numbers) between a 915 and 930 if you indeed have a 930. Cheers, Jim

[Jim Sims]

The space between 1st and 2nd gear on Brad's 915 input shaft is 1.55" or about 39.4 mm; there is not a bushing spacing them apart. I can measure the thrust washer thicknesses but it will be several hours or more before I can get to it and post the information; do you still want the thicknesses? Do you know any of the history of your transmission? Was the input shaft repaired?
Cheers, Jim

[tbitz]

Jim,

The tranny is a five speed. I don't think its a 930. The numbers written on the case are 915-303-2211R and 915-61-718-0559.

In your assembly I don't seem to have the "spacer ring"

"....(slider)and 3rd/4th spider, spacer ring, 4th asembly (gear, ......"

I've attached pictures of the assemblies for the two shafts from Bentley. They don't show a spacer ring either.

The spacer I was talking about before is item #18 on the input shaft assembly shown below. Mine is 19.5mm long (0.767"). You do not have this item?

Hold off on measuring the thickness of the washers. Let's figure out if I have the right parts first.

here is the input shaft components:


Here is the output shaft components:

[tbitz]

Jim,

Also my fist gear is part of the input shaft. It can not be removed. I measured the distance between 1st and 2nd and I read 40.5mm. This is 1mm more than yours. The gears seem to be well pressed against each other.

[Jim Sims]

Tony, The spacer rings are on a 930 tranmission input shaft which you obviously don't have. No, we don't have item 18 but instead the space between first and second gears is determined by radial extensions of the splines which Brad's "fixed" 2nd gear registers axially against. This item 18 bushing isn't shown in any of my parts catalogs diagrams but there is a hint about it for there is a spacer bush (PN 915.302.267.00) listed between the shaft and 2nd gear in the catalog parts listing but it doesn't have a figure reference. It looks like there may have been a change in the input shaft and 2nd gear positioning design between Brad's and your transmission. Another thing to check is if you have any gears flipped around as they can be installed with the axial faces pointing in the wrong axial direction. There is a note about this in the Bentley figures you posted plus here's the way Brad's gears faced. Pinion or output shaft: free 1st gear assembly numbers (numbers etched on side of gears) face forward (front of car is forward), free 2nd gear assembly numbers face backward, "fixed" 3rd gear numbers face backward and "fixed" 4th gear numbers face forward. Input shaft: "fixed" 2nd gear numbers face forward, free 3rd gear assembly numbers face forward and free 4th gear assembly numbers face backward. Good luck! Jim

[tbitz]

Thanks Jim.

The gears are facing the direction you described for both shafts.

I measured the thickness of the parts on the output shaft. Using the item numbers in Bentley (figure above) here are my thicknesses:

#1 (bearing) 20.0 mm
#2 (washer) 3.73 mm
#5 (race) 25.0 mm
#7 (sleeve) 17.0 mm
#10 (race) 25.0 mm
#11 (washer) 3.3mm (this part has cracks on the outer/inner edges. I didn't notice this before. This part maybe too thin)
#12 (3rd gear) 17.5mm (including raised collars on both sides)
#13 (spacer) 36.9mm
#14 (4th gear) 17.5mm (including raised collars on both sides)

I cannot remove the rest of the parts, but I measured the thickness as they are on the shaft.

#16+#17+#18+#19 = 44.0mm

Can you check the thickness of the above parts if it's not asking too much?

Thanks,

[Jim Sims]

#1 20.0 mm
#2 3.71 mm
#5 25.0 mm
#7 16.98 mm (this is actually the hub thickness of 1/2 spider)
#10 25.00 mm
#11 3.35 mm
#12 17.45 mm
#13 36.9 mm
#14 17.45 mm
#16+#17+#18 +#19 = 43.6 mm (this is probably the least accurate measurement due to the fact the ball bearing and front most ball bearing race are not mounted onto the shaft).

Overall not much difference (~.56 mm or .022") with the differences easily accounted for through tolerances and measurement error (I was using a dial caliper).

Doesn't look like the problem's the output (pinion) shaft.

Jim

[tbitz]

Thanks Jim.

Have you placed your two shafts side-by-side to see if all the gears line up? I used the bearing flanges as the start/reference point since they will both be flush to the case when assembled.

Does your 1st gear sit in the middle of the fixed 1st gear on the input shaft?

1:00am here in Canada's Capital and I gotta go to work tomorrow. Time to go to bed...

[Jim Sims]

Haven't checked shafts side by side since we haven't assembled the output (pinion shaft). We're still waiting on the new 1st gear dogteeth. We really didn't notice if the pinion and gear of the 1st gear set were in full axial mesh before disassembly but there are no wear patterns on the teeth to indicate an offset. Factory manual cross-section drawings appear to show the pinion gear (the one that is part of the input shaft) of the 1st gear set to be a little wider than the gear. The 1st gear pinion appears to extend a little more forward but I don't know how reliable these sections are for this level of detail. Cheers, Jim