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Is installing a lsd in a 915 a diy project?

I'm going to have to rebuild my transmission in my 1984 Carrera and would like to add an lsd. I also would like to add a shorter gear set depending on finances. Can adding an lsd be done at home? Do I want factory or aftermarket lsd? I plan on building the engine to a 3.4 in the distant future and would want to take that in consideration of my rebuild also. Thanks in advance for any advice.
Dean
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Old 06-16-2012, 11:31 AM
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Old 06-17-2012, 07:37 PM
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Dean,

It can be done at home, however you'll need to check the R&P backlash and make adjustments as needed using factory shims. Further, the carrier bearings should be carefully checked for wear and replaced if needed (requires a press).

I would be using a Guard LSD for your application.
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Old 06-17-2012, 08:41 PM
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Steve

Thanks for the reply. I was under the assumption that I needed a special tool to do this and that it is expensive. I'm really trying to do all of the repairs and upgrades to the car myself.

I'll definitely use the guard lsd. I'll call you when I'm ready to purchase it. I've talked to you on the phone in the past and you have been very helpful and willing to share your knowledge. Once again thanks.

Dean
Old 06-18-2012, 01:42 PM
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I,ve heard that a" factory" LSD can be installed without re shimming .It still needs to be "inked" to make sure
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Old 06-18-2012, 03:04 PM
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You can do this at home. When replacing the differential with a LSD (factory or Guard) & using same R&P you do need to measure and adjust backlash and carrier bearing preload. It can be done with some obtainable tools. There are threads on it here and good information in Peter Zimmerman's How To Rebuild a 915 tutorial. If you change to a different R &P, that's when you need the expensive tool to measure pinion depth.
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Hope this helps.
Old 06-18-2012, 03:36 PM
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I just did this as part of a rebuild. I will say that it is quite a challenging process especially if you don't already have a large selection of shims available. I had actually preordered shims in anticipation of this but despite that still did not have the correct selection and had to order and wait on delivery from Germany. I did get some generic shims from McMaster-Carr in 0.1mm, 0.2mm, 0.3mm, and 0.5mm thicknesses that aided in estimating final OEM shims. It is a tedious process that involves assembly and disassembly with multiple measurements that are critical.
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Old 06-18-2012, 03:51 PM
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Originally Posted by sjf911 View Post
I just did this as part of a rebuild. I will say that it is quite a challenging process especially if you don't already have a large selection of shims available. I had actually preordered shims in anticipation of this but despite that still did not have the correct selection and had to order and wait on delivery from Germany. I did get some generic shims from McMaster-Carr in 0.1mm, 0.2mm, 0.3mm, and 0.5mm thicknesses that aided in estimating final OEM shims. It is a tedious process that involves assembly and disassembly with multiple measurements that are critical.
Thanks for the info. I don't even know what shims look like. Could you point me in the right direction in the McMaster catalog. Buying shims to mock it up is a great idea. How many should I buy of each size? This is going to be my winter project so I'm collecting the parts I'll need.
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Old 06-18-2012, 08:41 PM
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Quote:
Originally Posted by 911dean View Post
Thanks for the info. I don't even know what shims look like. Could you point me in the right direction in the McMaster catalog. Buying shims to mock it up is a great idea. How many should I buy of each size? This is going to be my winter project so I'm collecting the parts I'll need.
Dean
The shims I purchased were 50mmX62mm:

98089A501 0.1mm stainless steel
98055A429 0.2mm spring steel
98055A431 0.3mm
98055A433 0.5mm
98055A435 1.0mm

McMaster-Carr

I only purchased one package of each because I used them in combination with the OEM shims to achieve various combinations of stack thickness. They have to be ground down on one side to fit the locating pin on the speedometer side.
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Old 06-19-2012, 02:49 PM
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Old 10-16-2014, 10:35 AM
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Any updates on this. I want to also put a LSD in my trans

Thanks

David
Old 09-11-2019, 04:51 PM
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Wow zombie thread.

I did my own by precision measuring my well working oem diff, the old bearings, the new bearings, and the new diff. Then putting the new diff in the same spot.

I used 996 shims, they're much cheaper than 915 shims, the same dimensions, and available in better increments.

I verified my work with paint marking.

You definitely can't do this if you have to set up a diff form scratch (aka do the pinion depth.) And it's not the "proper" way, but it works if you are meticulous. I had access to a surface plate, 123 blocks, and a calibrated height gauge in the machine shop at work.

It's been in for several years / a few thousand miles.
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Old 09-11-2019, 06:20 PM
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Quote:
Originally Posted by Harpo View Post
Any updates on this. I want to also put a LSD in my trans

Thanks

David
It's covered in the Workshop manual and here. How-To: Porsche 915 Transmission Repair Tutorial Part 5 - Porsche Wiki

Read Peter's wiki and decide if you are up for it.
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Old 09-11-2019, 07:26 PM
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The problem with the “put it back exactly where you found it” approach is these things are so old it’s often no longer in the right place when you take it apart. Sidecovers flex. Bearings wear and may be out of spec. If you get it printed to run where it was you may be putting it right back in the wrong place and accelerate the wear on it.

Porsche Classic has recently started selling 915 ring and pinions again. They are $3-4K. Finding a good used one is getting hard and rarely under a grand. If you’ve got a couple gearboxes to fiddle with maybe you do it. If it’s your one and only and required to be able to drive your car? I suggest paying a professional.
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Last edited by Matt Monson; 09-11-2019 at 07:40 PM..
Old 09-11-2019, 07:38 PM
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I rebuilt my tranny on my own a couple years ago with the help of a very experienced Porsche mechanic. I have a factory lsd and rebuilt that also. Checked everything as per factory manual. Side bearing races are easily replaced with heat. No press required. They literally fall out and in. Proper shiming was checked as per manual by measuring space between cover and case once cover race is touching bearing. Tranny works so much better than before the rebuild.
Old 09-11-2019, 08:23 PM
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Oh yeah, I forgot about that cover gap check for bearing tension, I did that too.

Again, I highly recommend against doing it how I did it. I was comfortable with the risks involved in my method, and the backup checks I used were enough to satisfy me. My LSD is up there as one of my favorite upgrades, as I use my car primarily for autocross.
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Old 09-12-2019, 07:20 AM
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The very hard to do DIY step is setting pinion depth without the Porsche (or a certain VW) tool. You are essentially measuring the distance from the end of the pinion shaft to the centerline of the differential output.

You can use a dial indicator and some scrap iron to measure backlash, and the feeler gauge method for preload. Swapping shims around is a pain unless you have a special puller for the bearings. A trick a mechanic showed me is to get used bearings, and hone them some so things are a slip fit for the shimming - when you get it right, put in the new bearings. This is based on the assumption, which is a pretty good one, that the bearings are all well within their tolerance.

But I don't think you can count on the new LSD having exactly the same side to side dimensions as the open diff you removed. They don't have to have exact dimensions, because the shims are used to get that right.
Old 09-13-2019, 10:04 PM
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I agree with Matt Monson.

I think this is one area where it can pay big dividends to engage a professional with appropriate experience.

Ring and pinion sets are really hard to find as good used (I have one for sale in the Classifieds) and new ones ain't cheap.
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Old 09-14-2019, 01:56 PM
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