LS4 / F40 swap - fieroguru (Page 132/216)
Rickady88GT MAR 05, 09:45 PM
It looks like the AWD unit was only offered on the 4cyl?
And that the AWD unit is driven by one side of the differential, the output for the passenger side wheel? If this is true, those spider gears are reasonable for driving 3 of the 4 wheels?
I am not familiar with this system, so how does the front differential work, left to right with the unit attached?

[This message has been edited by Rickady88GT (edited 03-05-2018).]

fieroguru MAR 06, 09:07 AM
Across all models, the AWD was used with the high feature V6 as well as Turbo 4s (gas and diesel). The transaxle differential carrier has a hollow stub shaft that protrudes from the transmission case with splines that drives the AWD unit. The passenger axle passes through this stub shaft, but there is no mechanical connection between the axle and this stub shaft - they are free to spin independently of each other. This is the same method for a transverse AWD setup that Ford, GM, Chrysler and several imports use. Cases and gearset designed within the AWD unit vary, but the use of the hollow spline stub shaft off the differential carrier to drive the AWD unit is very common.

The nice part about doing it this way is the final drive of the transaxle differential is then applied to both front and rear wheels. The gear ratio of the AWD unit just matches the remote mounted differential (the rear one in the stock layout, it will be the front one in the Fiero). So you can change the final drive in the transaxle w/o needing to mess with the gear sets in the AWD or remote differential.

This direct coupling between the transaxle differential carrier and the AWD unit means there will be zero slip between the two, which I think is a good thing. I plan to run shorter tires in the front and install a high torque 1 way clutch that will allow the front wheels to rotate faster than the rears. Looking for a 2-5% slip so the rears will be the primary tractive force until they slip about 1" and then the 1 way clutch will lock and the fronts will get power to limit the rear wheel slippage.

Several of these remote differentials are also electronically controlled, so with the flip of a switch I can break the connection making the car 2wd again. This would be helpful with backing up as with the shorter front wheels and the 1 way clutch setup, I will drag the front tires some when reversing, so this electrical lockout would help with that.

[This message has been edited by fieroguru (edited 03-06-2018).]

Rickady88GT MAR 06, 10:03 AM
Ok, this makes sense. The diagram just does not have the passenger side detail. So, how much torque is this AWD unit and drive shaft capable of handling? What diameter is the inner passenger shaft?
Rickady88GT MAR 06, 10:42 AM
Now that I have this on my mind,...I can't imagine how the AWD unit and left drive shaft both link to the differential independent of each other?
fieroguru MAR 06, 08:58 PM
The 2009 Vauxhall Insignia VXR 4x4 has 320 hp and 321 lb-ft.

Power flows from the main output shaft to the differential ring gear, that is bolted to the differential carrier, which houses the spider gears. The spider gears are splined to accept the axles from both sides, but the spider gears are free to bias speed from side to side while the differential rotates at a constant speed. With the rear wheels off the ground, and the car idling at say 10 mph. Stop the driver side wheels and it has 0 speed, the differential is still spinning at 10 mph, and the passenger wheel is spinning at 20 mph. This is the way the stock Fiero transaxle (and every open differential) works.

The difference with the AWD unit is that the differential carrier has a hollow splined shaft that engages the AWD unit and puts power to the remote differential. The passenger side axle passed through the hollow splined shaft to engage the spider gears. The passenger side axle is free to be anywhere from 0 rotation to 200% differential rotation speed, just like the scenario above, while the AWD unit has to match rotational speed with the differnetial carrier it is directly coupled to.

Here is a picture of the Buick AWD unit that is very similar to the Saab one. You can see the smaller/longer splined shaft is the passenger axle and will engage the spider gear. It is poking through a shorter/larger splined shaft that couples the AWD unit to the transaxle differential carrier.


[This message has been edited by fieroguru (edited 03-06-2018).]

Rickady88GT MAR 07, 12:10 AM
Ok, got it thanks.
The AWD unit can not bolt to a 2WD trans. The differential and bearings are specific to the AWD, and I would imagine that the trans case is as well?
fieroguru MAR 07, 08:33 AM

quote
Originally posted by Rickady88GT:

Ok, got it thanks.
The AWD unit can not bolt to a 2WD trans. The differential and bearings are specific to the AWD, and I would imagine that the trans case is as well?



Yes and no.

The differential carrier for sure is different between the 2WD and AWD versions due to the extra splined shaft.
There are 2WD cases that have the proper differential case bolt pattern for the AWD unit to bolt directly to (you just have to removed the axle seal), but the G6 F40 case is not one of them. A couple pages back I show the difference in the differential housing bolt patterns between the G6 case and the 3.09 case from Europe. The 3.09 case would allow the AWD unit to bolt to it.

So for my application, I will need the differential carrier from an AWD F40, then I was planning to make a new case that bolts to the transaxle (so I can flip the output shaft to the remote differential 180 degrees so it will go under the oil pan) and accepts the stock AWD extension housing to for the passenger axle. While I make this part, I will correct the differential housing bolt pattern at the same time.
Rickady88GT MAR 07, 09:48 AM

quote
Originally posted by fieroguru:


Yes and no.

The differential carrier for sure is different between the 2WD and AWD versions due to the extra splined shaft.
There are 2WD cases that have the proper differential case bolt pattern for the AWD unit to bolt directly to (you just have to removed the axle seal), but the G6 F40 case is not one of them. A couple pages back I show the difference in the differential housing bolt patterns between the G6 case and the 3.09 case from Europe. The 3.09 case would allow the AWD unit to bolt to it.

So for my application, I will need the differential carrier from an AWD F40, then I was planning to make a new case that bolts to the transaxle (so I can flip the output shaft to the remote differential 180 degrees so it will go under the oil pan) and accepts the stock AWD extension housing to for the passenger axle. While I make this part, I will correct the differential housing bolt pattern at the same time.



You will also need to flip the front differential. But from what I see, they are low pinion, flipping it would make it a hi pinion. Not that big a deal, if the gear oil still gets where it needs to go and not leak out.
fieroguru MAR 07, 06:10 PM

quote
Originally posted by Rickady88GT:
You will also need to flip the front differential.



Correct.
GreyElf MAR 07, 08:22 PM
My Saab Mechanic can't find any individual ratio P/N's...Sorry