ATB install: remove tranny or take the shortcut?

Well, my new potential mechanic just told me. "To do it right, I need to take the transaxle out and do measurements on a bench perfect. But I know that many do it on the car, and I can do that too. 15 hrs the right way, 7 the other way." So how does one measure backlash on the car? Is there a tool that this mechanic may not have, and therefore feels better about installing the ATB on a bench? Thanks for your feedback.

To do it as per the factory manual and set it up perfectly the gearbox needs to be out of the car. There are various shims in the gearbox that do everything from preloading the bearings to keeping the ring and pinion in their quiet spot. The correct process is labor intensive. If the new differential is not dimensionally identical to a very tight tolerance then the whole unit needs to be re-shimmed which is a trial and error process.

Apparently Quaife TBDs are perfect (or nearly so) in dimension to the stock units and are not requiring shims, etc. What are the symptoms of a potentially less than perfect installation? The installation of my TBD was done with the transaxle in the car and I have yet to have any known problems (knock wood) after 30K + street miles and over 5K track miles. Also, a good tech can do the installation in the car in less than four hours, not seven. [Edit] Cheers,

Transaxle noise from and premature wear are the most likely possible issues. The premature wear would not necessarily be a quick thing. I would say given your mileage you won't be hvaing any problems soon.

Guys, still can't decide which option to go with. I know the proper / safest is to remove the transmission. But, could one remove the diff and compare dimensionally to the new one, and the assess if transmission removal is warranted or not. Another related question. My car has 8,000 miles. Should I replace or reuse the bearings that are on my diff? Finally, I am sure that one can swap a diff in 4 hours. But I bet that getting it positioned just right takes time, I am willing to pay for that. I do agree that 7 seems little high. Again, your help is appreciated.

If you are starting from scratch, like when installing a new diff into a new tranny, then you need to do it as described in the Porsche manual. However, if swapping one diff for another, and make the assumption that the old one was installed correctly and the existing bearings are still good, then you can do the "shortcut". The key to making this work is to measure each differential (old and new) and change the shims so the new diff matches the old diff. Do a search for some of the previous posts on this subject -- they will give more detail on the actual process involved. BTW, the Quaiffe diffs are very close in size to the stock ones, but I wouldn't just pop one in without measuring first. Of the four that I've installed, only one didn't require a shim change.

I got mine installed by RUFF and they did it the quick way and to date I have had no problems. The cost was just at 400 bucks. So I think anyway you go you can't go wrong

Not all are a "perfect" fit. Mine required shims. The bearings are pressed on/off and deform in the process. Some may reuse them to save a few bucks, but I chose to use new bearings at the recommendation of my dealer's Gold Meister Tech who did the install. Seemed like cheap insurance to me. YMMV.

My bearings were heated/cooled so that they wouldn't be deformed by trying to bang them off with a sledge hammer. Anyway, I talked to Mike at Guard Transmission about the need to pull the tranny and his response was that a "good" shop with the right tools could do it with the tranny still in the car, that doing it on a bench was not absolutely necessary. He said many mechanics preferred to do it on the bench because it was easier to do that way, but that it was not an absolute requirement to do it that way. When my Quaife was put in, one item was checked with a tool (backlash or preload I forget which) and another was checked by markings, indication and "feel". To date I've got 15K or so on the Quaife unit with no signs of trouble, in fact when my engine/tranny was apart they inspected the diff for me and saw no issues. Mine did not require shims as many have reported, although some have. Probably those cars originally built on Monday.

They deform when initially installed, as do all pressed fittings. Maybe inconsequential, or maybe not. :cheers:

My solution to the question of whether or not to take the tranny out was to install a lightweight flywheel along with the Quaife. Then the tranny must come out, but the Quaife install can be precisely shimmed, and you get 2 great performance mods for the cost of a single tranny removal (2 birds with one stone).

I thought briefly about it. My Cayman (for now) is going to stay relatively stock. I definitely will not install components that can make weird noises, like a flywheel could. IMHO, this is a more "advanced" modification. I have a 2000 Audi S4 with cage, monoball suspension mounts, race seats... all that. Cayman is my daily driver. I know I have it reversed, but that is a function of history. I am thinking of selling the ATB on eBay as well, but probably will install it. My plan is ATB, Eibach springs, SRP, some exhaust mod - currently Fabspeed (but awaiting your research), and then Porsche add ons - such as GT3 steering wheel, Sport Seats, etc.

Just my two cents, I have been in my current profession for 30 years, it involves maintaining various makes and models of machines of the very expensive nature. I can tell you without question to take the time (and money) to do the job correctly. Short cuts, skipping procedures, and generally not following OEM standards leads to a less than desirable end that you will most likely not be pleased with. "BEEN THERE DONE THAT AND HAD TO DO IT AGAIN, THE RIGHT WAY."