Audi 0A2 into base 986

[Marc_986]

Just before the summer I bought an old 97 Boxster base model with the intention of (in due time) swapping in a Audi V8 (BBK engine is what my eye is looking for).

The biggest unknown for me is the gearbox / driveshaft side of things. So I picked up a brand new Audi 0A2 gearbox yesterday. If my info is correct this should essentially be a G87.20 box, but with the tall diesel gearing.



I plan to drop the gearbox from the Boxster sometime next month or November. That should tell me whether the bolts will align between engine and gearbox. The clutch doesn't worry me too much, as both are made for 240mm clutch, I am sure I can find a combination that works on both the engine and the gearbox.

Now the biggest question will be on the driveshafts. Is there any default shaft set that will fit. Or do I need either different flanges on the gearbox or different hubs on the car?

Any info would be greatly appreciated.

[78F350]

I have not done it myself, but I'm pretty sure that with that transmission you can swap the flanges from a 5-speed 986 transmission. The flanges on that Audi transmission are spaced wider and take larger bolts than the '97 axles.

Check this if you haven't already seen it: Audi transmission Swap DIY Thread

It should bolt to the engine. Have you looked at shift linkage and mounts? I'm not sure about those. It might have the same attachment points.

[Marc_986]

I didn't look at shift linkage yet, but sure that can be resolved easily enough.

The box I have seems a bit different from the one in the other thread (it doesn't list a transmission code, but that short gearing is not available in this box). Difference with the 986 5 speed is at least that the flanges are asymmetric. So assuming I will keep engine and box centered in the car, one side will need a shorter driveshaft than the other side. Quite sure that this is, again, similar to the 987 setup.

However, would 987 shafts fit the 986 non-S? Would they fit the S? Or neither? I am not aware of the details of the rear suspension between 986 and 987, would the width from hub to hub be the same?

I'll be looking into more detail on part numbers etc. , but any available info could help me underway much quicker. Seeing the prices of the Porsche boxes, I am quite happy to have found this Audi one new for about $ 500.

[Marc_986]

So I did a bit of research and this is what I have found:

Axle width (distance between hub flanges) is very similar between 986 and 987.
Inner diameter of the bearing is same for all, but 986 base has smaller wheel bearings.
Wheel side spline of the driveshafts is equal for all.

986 S and 987 driveshafts will not fit the 986 base wheel carrier / upright. The issue is in the diameter of the shaft end not fitting.

Rear suspension of 987 is nearly indentical to 986.

All 986 and 987 have the same rear brake caliper
986 base and 987 base have the same front brake caliper
986 S and 987 S also have same front brake caliper.

So my best bet seems to go for 987 wheel carriers / uprights and 987 driveshafts. The 987 has same wheel carrier for both the base and the S, so I guess any brake disc will fit, but will check.

The only catch seems to be the diameter of the strut being larger on the 987. So likely I will need 987 struts as well. Any other issue I might be overlooking?

[Marc_986]

So, more research done. The 987 axles are not going to work due to the difference in ABS sensors and resulting difference in axle side CV joint.

After measuring the old G86.00 against the 0A2 it seems that they are very close in where the axles are relative to the engine as well as relative to each other. And if my info is correct, the later 2.7 shafts are thicker and have the same / similar splines as the 986 S and the 987. So likely they will fit with the 987 CV joint on them.

In the mean time I pulled the old gearbox out. Comparing the two, it seems the 0A2 will mate directly to the engine and even input spline looks the same. Will take the clutch of the engine to trial fit later this week.

[1thenaton1]

Using belt driven Audi V8 and stock transmission/driveshaft/axles is a proven solution. Any reason you are trying to use BBK engine with timing chain?

[Marc_986]

Nothing too specific other than some reasoning (which might prove wrong..)

- Chain drive engines are more compact, so hoping to give easier fit.
- Less ancilleries driven at the front of the engine, so might be easier to make the front mount
- Low mileage engines available (but I do need to check for availability on belt driven ones)
- Also using 7.1.1 DME, so that should be equally easy / hard.
- Could find the 0A2 transmission new and cheap. Current 5 speed is really tired and I do like a bit lower revs when cruising. As I read on bellhousing difference between V8 generations around this time frame I was worried other engines would not fit. Looking at it now, I think any Audi V8 will bolt up to 0A2.

Maybe I should open my eye for a damaged engine to better estimate the impact.

Other than the chain drive itself being known to have its troubles, any reason against the chain driven V8s?

[Marc_986]

Slowly gathering more parts;

- 987 Transmission mounts used
- New Sachs clutch for the base 986
- 987 shifter + cables
- New 987 driveshaft flanges, see below;



Also I have some parts to fix the current 2.5 engine. So will complete that first, than sort out the shift linkage of the 0A2 and mount it.

One question on the shift linkage; It seems the 987 uses a stiff spring to prevent accidental engagement of reverse. This spring must be in the transmission and it should be somewhere on the selector shaft. Can anyone confirm that it is the G87.20/21 specific selector shaft that is responsible? Stock Audi transmission doesn't have this, reverse lockout is in the shifter instead.

Just wondering whether it would make sense to insert a new selector shaft or just add the reverse spring in the shift mechanism.

[Marc_986]

The gearbox swap is progressing well, time to share some info back to the community.

I sourced a Porsche G87/21 transmission and this one is now in the car, behind the stock 2.5L. This box is indeed very similar to the Audi 0A2. There seem to be two difference (other than the gear ratios, obviously);
- Porsche selector shaft contains the ramp for added resistance in reverse engagement.
- The tail housing of the box is slightly different. Porsche unit has mounting holes for that steel weight and for the exhaust. The Audi has neither.

I'll work out which gearbox is going to be best for the V8 and mount that (+ swap what is needed across).

Other things to note:
- The gearbox is in the original 987 mounts
- Stock (new) 986 clutch.
- Using 987 shift cables (much shorter than 986 ones) and shifter (986 shifter was worn)
- OEM muffler doesn't fit behind the box. Found a used sausage muffler which just clears.
- Using 987 driveshafts and 987 wheel carriers. Requires 987 shocks.
- The 986 parking brake cable needs to be used, the 987 e-brake mechanism inside the car differs.
- I've used 987 brake discs and made brackets to hold the brakeline. Brake hose is routed differently in 987 due to the exhaust in the wheel well.

So while pulling it all apart I replaced the suspension arms, top mounts and springs (M030). Basically the back of the car is refreshed now and should be good for some time. Main things left are to create a bracket to hold the muffler and solve the ABS speed sensor difference.