Alpina B10 Turbo Getrag G290/5 Gearbox Conversion - E34
This information is provided as a reference for those wanting to convert a manual E34 with the Getrag G260/6 or M5 G280 to the G290/5. The G290/5 is an extreme duty box built especially by Getrag for Alpina for use on their twin turbo E34 B10. It uses parts from the 850i manual including the massive 110mmPCD x 40mm thick flex joint (guibo). It is significantly stronger that any other box that fits up to the big six M30 engine and is quite rare to find second hand. I picked mine up from the UK and had is shipped to Australia. I read the stock G260 was very strong and I can believe it. It is amazing in that it tolerated the power without issue but I really wanted the big guibo of the G290 more than anything else as I was killing too many of the stock size, and the added insurance of the stronger box can't hurt.
In summary, a number of modifications must be done, namely:
In summary, a number of modifications must be done, namely:
- The box is longer than the G260 so the shifter arm and shift lever must be shortened.
- The output flange on the G290 uses a 110mm PCD with an 18mm centralising spigot versus the 16mm G260. The drive shaft must be modified with a new 3 larger lug flange and must be shortened.
- The guibo is from an 850i manual and is 110mm PCD x 40mm thick and uses 14mm high tensile bolts versus the stock 96mm PCD x 30mm thick 12mm bolt guibo.
- The stock cross member is modified and relocated on the G290 box to allow it to be bolted up in the stock location on the car
- Depending on your clutch, a new throw out bearing may have to be made.
Gearbox length
The G290 is 574mm from bell housing to output flange versus 537mm for the G260. The difference of 37mm plus the 10 mm difference in guibo thickness means the drive shaft is shortened by 47mm (after attaching a new bigger tripod flange which will be covered later). I could not feel any significant difference in weight during manhandling them both. The input shaft and flywheel spigot bearing are identical for both boxes making the front engine interface 'plug and play'.
G260 on left, G290 on right
G290 on left, here you can see the size of the output flange
In terms of the centre line of the output shaft and shifter linkages relative to the cross member, luckily they are identical for both units, so only the fore/aft position of the cross member is important. This is illustrated below:
The cross member needs to move 22mm forward on the G290 and must have some material removed to clear the box. The actual lugs on the box are modified for this as the member is non-uniform 3d in shape and you have to keep the mounts in the same place relative to the member. Moving the holes on the G290 lugs 22mm forward also needs a hole drilled for the dowel pin on the mount. This is shown in the picture below:
x/member mods on left (scallop out and removal of lip), new 22mm relocated mount position in middle, x/member installed on right.
If at this point you are wondering why I never bought an Alpina mount, its because they cost about $800. This method locates the box exactly as it should be.
Next up the shift arm and lever must be shortened. I'll save you the specific reference dimension, but the aluminium arm must loose 30mm in length and the mild steel shift rod 10mm. The shift rod should also be bent to clear the big guibo. Again, Aplina parts are horrendously expensive. The x/member, shift arm and rod for a Bi-Turbo E34 G290 car would be over a grand in Oz.
Next up the shift arm and lever must be shortened. I'll save you the specific reference dimension, but the aluminium arm must loose 30mm in length and the mild steel shift rod 10mm. The shift rod should also be bent to clear the big guibo. Again, Aplina parts are horrendously expensive. The x/member, shift arm and rod for a Bi-Turbo E34 G290 car would be over a grand in Oz.
Modified shift arm and shift rod (cut and weld).
With all of the above taken care of, the box can bolt right up and the shifter linkages and x/member bolt right in. I took the time to re-tap the x/member holes to M12 from the stock M8.
Sometimes, I wish I had a lift! working on the ground sucks. Here is the G290 going in.
G290 installed with x/member in stock location (left). Modified shifter linkages installed (right).
It should be noted that the output flange and centralising spigot set up on the G290 is exactly the same as a manual 850i so if you can get one of these driveshafts, that would be the way to go as it would be easy to adapt it to the E34. However, since these are rare as rocking horse shit, I modified my E34 driveshaft with a Hardy Spicer custom flange from their Mechanics 'R' range, 110RC-26-7495 which measures 110mm PDC and uses 12mm bolt holes.
This is modified to take 14mm bolts. The centralising bearing is also opened up by 2mm to 18mm for the G290's larger spigot and positioned a little forward so it 'swallow' a reasonable amount of the output shaft spigot. Its welded onto the stock shaft with the flange face 47mm further back (shorter shaft) than stock. This will now allow the existing driveshaft to bolt up to the G290's massive guibo. The joy here is not have to change guibos every few months as those of you with turbo motors probably go through them like I do. This bad boy should take the beating no problem as its designed for the heavy beast of an 850i. My drive shaft also uses a serviceable domestic V8 universal joint in it.
Shortened and balanced drive shaft with larger tripod flange attached.
The new box is quite and smooth albeit a little baulky and stiff when trying to get 1st off the line. 1st and 2nd are shorter than before with 3rd to 4th same as the G260. With the 3.91 diff, 1st and 2nd are very quick and with any boost, just light the tires. Overall, a great improvement. Power delivery is smooth with no twisting weak guibos. The drivetrain now easily handles the torque the car makes.