928 obsession

So I guess it is safe to conclude that my car has a 2.20 or 2.27 rear end. I've been doing some research and it appears that an '82 euro had the option for a 2.27 or the standard 2.73 Also, I've seen that an '82 euro 5 speed is also a G28 05 gearbox. So I guess it is possible that the orginal owner somehow manage to snag a euro gearbox or maybe at one time it has been opened.

Glenn Evans

The "short" first (ie noticeably greater spread between first and second), and your final drive ratio of 2.27 (34:15), indicate that your transmission is an G28.08, not an G28.05. Page 30-06 refers. As Mark correctly stated, the transmission's main shaft - of which the final drive pinion is an integral part - would have to be changed to change the final drive ratio; gears would have to be pressed off and swapped ... who'd bother?. Even if the car was delivered with a G28.05, a G28.08 has been fitted since.

On what do you base your belief that your transmission is a G28.05? The transmission type and serial number is stamped on a rib underneath the transmission; where the diff housing mates to the transmission case, if I recall correctly.

So Christian, did you use your GPS (Global Positiioning System for Mark) for the speeds you quoted for your father's car, as you did for yours? What size tyres does he run on his 17 inch wheels?

928 obsession

The trasmission ID on my trans is G28.05 11c 1411 It's defiently not an 08. When we orginally bought the car our intent was on it being a race car so we did not mind it did not come with many service records. Anyway I decided I wanted to restore it and use it as my first car. For all I know a previous owner may have swaped out the gears. I do not know, but they defiently did not replace the synchros if it was opened

mark kibort

lift both cars up in the rear by the rear crossmember, put them both in 5th gear. mark the tires in refernce to the ground. rotate the engine one revolution. 2.27 will move not quite a half of a revolution at 158degrees. 2.75 will be over a quarter of a revolution. 130degrees. almost perfectly between a quarter revolution and a half revolution. in otherwords, a quarter revolution, plus 1/8th of a revolution . It will be obious. THEN, all the guess work is removed.

get back to us and let us know what you find.

Glenn Evans

The G28.08 is listed as the US manual transmission for MYs83-84. It occurred to me that Christian's car may be a late MY82, and was fitted with the new transmission but that it retained the old designation - one of those Porsche model development quirks that occasionally comes to light.

The workshop manual reveals that there is a precedent for the G28.05 having a different final drive ratio. Page 30-01 of the workshop manual states that the original G28.03 was fitted worldwide up to June 13, 1980. P30-02 states that the G28.05 was fitted to 928 cars "beginning with 1981 models (June 1980)". While the changes from the G28.03, listed on the same page, include "modified
ring/pinion gear", the combined table for the G28.03 and .05 on p30-05 states that the final drive ratio 12:33 (2.75:1) was retained up to Jan 13, 1981 and that the 11:30 (2.7272:1) was fitted since Jan 14, 1981.

This indicates that, by early 1981, Porsche had not yet adopted the policy of assigning a different type number for transmissions with different final drive ratios. Perhaps it did so only beginning with the '83 model year?

I see that the "928 Final Drive Ratio Chart" on the 928 Specialist site (www.928gt.com) lists the 2.27:1 as optional for Euro 81-83 models. I have looked through the option codes on the same site and cannot see a code for an optional manual transmission for either 78-82 or 83-86. Do you still have the option code sticker under your rear hatch carpet? If so, is there are option code on it which is not listed on the 928 Specialist page? We should be able to find out if it was for the optional transmission.

928 obsession

No it's not there, I plan on eventually doing a PCA option code lookup though. My car was produced sometime in March of '82, so I doubt an '83 transmission was installed but it's possible. I know the 928's had numerous options avaliable, could the optional euro gear ratio of 2.27 possibly been an option for US models? I read that if you were willing to pay, Porsche would customize your car to your requests.