Looking to install a high mile LSD from a G28-05 into a low mileage G28-03. Please advise. 77Tony

 

I just did that ( 05 to an 05). I used all the bearings and shims from the open diff and the same ring gear. Set up the same as the original diff when installed.

 

Ducman, Did you also go with the upgraded G.B. mod (post # 3) ?: https://rennlist.com/forums/928-foru...-question.html

 

sure did. mod worked like a champ. i also used the 3-2 5 quart of redline mix. so far no chatter and shifts great as well.

 

You have to use the same ring gear that comes out of the transmission...it is a matched part with the pinion. Differentials are very rarely the exact same...otherwise Porsche would not have to have provided shims to adjust them.

Measure the backlash between the ring and pinon, in the '03, before you remove the differential assembly.

If the bearings and carriers are good in the '03, re-use them. Mark the shims carefully, so that you can put them back in the exact same places that they came from....for now.

You will need to remove the bearings from the '03 differential and install them on the '05....in the same relative location. Once a bearing in worn in with a bearing race, they are a "matched set" forever.

Strip down both differentials so that all the bearings and the ring gear are off.

Disassemble, clean, inspect the limited slip. If you want a more aggreesive limited slip than stock, follow my instructions on Ducman's previous thread.

With all the "guts" removed from the limited slip, carefully clean the surfaces where the two housing pieces bolt together and then bolt them together. Use a minimum of 6 nuts, bolts, and washers (10mm minimum), spaced equally in the ring bear bolt holes to bolt the two pieces together.

Get someone that has accurate measuring tools (within .001") to measure the "overall heights" of both differentials. This dimension will be the measurement from where one bearing sits to the surface where the other bearing sits. Record those dimensions and calculate the difference, if any.

This dimension determines the "pre-load" on the bearings. If the difference is "0", you will not need to compensate for the difference. If there is a difference, simple math will tell you if you need to add or remove shims (under the side carriers) from one side or the other. Remember that if the new carrier is smaller, you will need to subtract that dimension in shim. If the new carrier is bigger, you will need to add that dimension in shim. Note that, at this point, you don't know which side needs to be changed

The second measurements you need to take is the dimension from where the ring gear sits to the bearing race farthest away from this surface...on both differentials. Record these dimensions and calculate the difference, noting which differential is bigger/smaller.

This dimension tells you where the actual ring gear sits, in relationship to the bearings. If the difference is "0", you do not need to compensate for this difference. If the differnce is not "0", you will need to compensate for this difference by moving shims, from side to side.

After you have all the measurements, it is simple math to tell you what and where you need to do with the shims, in order to get the ring gear back to the exact same location as it was with the original carrier.

Let's say, just for example, that the "new" differential is .002" bigger, overall, and the dimension from the ring gear to the far bearing is .002" smaller. You know that you need to "remove" .002" of shim, to have the same preload. You also know that you need to "move" the bearing race on the "non-ring gear side" (that's the side that you had measured) closer to the ring gear .002", for the bearing races to be in the exact same place. In this case, you would simply remove .002" from the right hand side's shims.

Once you have done all the measuring, calculations, and shim correction, (which is actually very simple to do...I've probably made it sound complex), assemble the limited slip, bolt on the ring rear, install the bearings and stuff it into the transmision. If done correctly, the backlash will be exactly the same as it was originally.

Simple.

 

+1 pn matched R&P - it is a must, It will grenade in short time if they're not new or "wear paired" for lack of a better term.
Best of Luck.
Bil

 

Thank you very much Greg, I'll run this past Jeff, the mechanic on this end. Nice new ride Bill, I had a Jet Stream Blue 08 a few years back. T

 

This is great. Thank you very much for the detailed instructions.

 

Just did this for a customer and Greg is spot on as usual. As an aside gas tank removal is not neccessary just use some thought and patience and the diff easily clears the tank and the box

 

Really? What model year? Looks too tight to me on my 89.

 

Maybe it was a manual gear box.