BC

I have two shims on each side, and I suppose I can buy more and see. The bearings that were in there were not in as good a shape as you have shown in your pics of the ones you reused. The races are actually starting to pit slightly if I hold them up to sunlight - so I really didn't want to take a chance anyway.

John V

I agree with your swapping them out. If I had known they were that cheap, i might have done the same (well maybe not- mine were in great shape). The only thing I would recommend is that you check preload before you get too deep. To do that, you will need to install the diff without the pinion shaft in place. With the side plates torqued down to spec, I would make sure the rear cover is not not outrageosly tight on the pins - AND- that the diff has no side to side play at all. If that checks out OK, then all I'd worry about is backlash.

BTW- you only have 2 shims per side? My gear box had 4 on one side and 6 on the other.

BC

Thanks John. I will check all that when I get the bearings. On the shims - if you are talking about the external shims that are on the OD of the side plates and get claimed between THEM and the trans case itself, then yes, only 2 each side.

John V

Update 1/25/07.

as I assembled the final shift shaft and spring assembly, I decided I wanted to change how the shift lever is spring loaded. I've driven 928's that have no centering spring between the 2/3r &4/5 shift planes. Mine was like this. I have also driven 928's that seemed to be spring loaded into a neutral position in the 4/5 shift plane. My preference is to have the shift levers nuetral axis in the 2/3 shift plane (requiring some pressure to move the lever into the 1/R and 4/5 shift planes). I ended up modifying one of the springs and it appears to have done the trick. I'm not sure how long lived it will be since the torsion spring is working opposite of it's intent (forced into an unwind state) which does decrease life in torsion springs but, since this feature was not there at all, I figured I'd set it up how I like it and hope for the best. I'll post a pic when I figure out how to upload pics to Rennlist (my other account is maxed out).

svp928

John, since I also hve G28-05, I just want to say Thanks for posting your experience here...it is very informative.

My trans only has a spring at the 1/R gate, and I'd like to set it up the way you are doing. I had assumed my spring was broken- it never occured to me that it came that way. Someday, I must pull out the box and fix it. I think it may be easier to saw a hole above the top plate and fix it without pulling it out of the car...? hmm.. ahve to check that out..


Steve

danglerb

Spring in mine goes to 4-5 position, and 2-3 is what I would prefer. These springs are internal to the tranny?

Bill Ball

John:

Very nice thread. I especially like the LSD posts. I have one sitting on the floor still, on my To Do list. Oh, and after driving some 5-speed 928s, I think I agree with your spring position change. 2nd to 3rd is vague.

Vilhuer

This neutral position has been mystery to me for long time in '78-84 boxes. I think I have it figured out now. In '78-81 boxes there is only one spring which is preventing movement from 2/3 to R/1. There is nothing between 2/3 and R/1. Where lever goes when all parts are new is still question mark for me. Think only things affecting that is gravity and possibly forward selector cup.

In '82 MY factory added second weaker spring which will force lever to 4/5. This created two step process for geting into R/1 plane. If I'm reading PET right, seems like second spring can be added to '78-81 box without changing anything else. Making solution which put lever into 2/3 and will last a long time can be difficult. Two springs fighting it out and one of them is bound to get weaker sooner than other.

'85 and later versions are clear as spring system is totally different. None of the versions is really perfect. Been thinking about how to make late style better but haven't figured out a way which would fit inside space available, yet.

Podguy

John,

I am a little fuzzy on the differential set up. I did it on mine but have no confidence that I got it right. Since I was only replaceing the differential and no the pinion gear i only had to check for two things. The first was to get the space between the ring gear and the left side of the case correct that is backlash. I had difficulty measuring the back lash with a dial indicator. Do you have an pictures of how you did it? i managed to get the back lash in the correct range but have not blue printed it yet to be sure.

When settng the left side shims for the back lash I left the shims out of the right side so I could load the bearings. Once the back lash was set I measured the right side gap with a feeler gauge and added shims for zero play from side to side. Is this going to work? I assume like wheel bearing the carrier bearings should not have any pre load. What has me concerned is when the sucker heats up and puts load on the bearings.

Thanks for any insight.

heinrich

I've driven them all and later style is far better, it remains in the 2-3 plane, left is a hard spring to keep R-1 plane safe, abd a weaker spring keeps driver from selecting 4-5 plane. So, when you drive, 2-3 are always there, you have o go right against the light spring for 4-5 and left against the hard spring for 1-R. Much better driving experience.

In earlier cars, it takes some intuition and knowledge of what ear you're in, to find the 2-3 plane. Easy to accidentally select the 1-R plane or 4-5 plane.

John V

I'll post a pic of what I did to the spring to center on the 2/3 gate. It feels really good but as I said, I don't know how long lived this setup will be. I'm inclined to think it will last years given that the spings deflection range is so small.

Podguy-

I haven't seen any specs in the manual regarding preload. My experience with bearing preload comes from my job. I'm not saying that what you did will be a problem but it's not how I would have recommended you do it. All bearings reguire some pre-load. Absent that preload, they are much more susceptiable to skidding, which often leads to premature failure. My observations of the assembly suggest that the case, diff asembly, side plates and shims establish a certain amount of preload. This is independant of the pinion/ring gear interaction. My fear with shimmig to a 0 preload as you did is that under hard acceleration, the ring and pinion gears interact in such a way as to generate force in 2 axes- the first is in turning the ring gear (we want this force), but the second force moment tends to push the diff and ring gear "away" from the pinion gear (like seperating the meshing gears ). This "sepration force" will have a tendancy to load up the bearing in thrust, and unload the bearing on the other side. If there is no preload in that bearing, my fear is that it may skid.

In adjusting the backlash, I chose to use all the shims and just swap sides. This ensures no change in the preload, but adjusts the backlash. if you ended up with extra shims, your backlash might be fine but your preload is likley light. Keep in mind that we are talking about using all the same parts that came out of a gearbox- not new ones. When new parts are introduced, be it bearings, LSD unit.. etc. the shim pack as whole needs to be evaluated since the new parts could effect clearances. In my case, I measured the distance between bearing flanges on my old open diff. versus my new LSD. They were within .003 (LSD being larger) so I decided that I prefered .003 more preload than .001 less (the thinnest shim I had was .004). I hope this made sense.

John V

Sorry- missed some posts,

I didn't take pics of the dial indictaor setup but I think they have one in the manual.

I don't think you could effect these changes (to the springs) with the gear box in the car. The hole you'd need to cut would be quite large.

Vilhuer

WSM has procedure which shows how to measure and count all shim thicknessees in gearbox. Some seriously expensive special tools are needed when backslash measurement is done in factory style. While doing relatives gearbox we did it differently. Seems to work fine.

https://rennlist.com/forums/928-forum/184546-differential-adjusments.html
https://rennlist.com/forums/928-forum/181881-ring-and-pinion-gear-contact-pattern.html

John V

Erkka-

Nice posts... although I don't know why I didn't find them when I searched before embarking on this project.

I thought I was going to get some gup for changing what Porsche "intended" on the shifter position but neither of the early gearboxes shifter methodology appeals to me. You've described both systems exactly like I understood their intent, it just seems so odd compared to any other 3 gate pattern.

Also, to do this, I actually used the 83-84 spring, I just reversed how it is implemented so that instead of having the centering force to the 4/5 gate- it goes to the 2/3 gate. The springs really aren't fighting each other becuase of how the larger spring is held in tension by the spring pin and lever arm wire. It really does feel fantastic and fits perfectly within the space allocated for the spring. If I were to really be ****, I would wind a new custom torsion spring to defelct in the right direction - then I don't thing longevity would be a concern at all... it may even work in the newer gear boxes?

hupp

The shift plane on my '79 is at 2-3. The plane can be adjusted at the rear coupler. The shift lever must be at a specific angle per WSM prior to tightening the pinch bolt at the coupler.