XC90 rear differential replacement - questions

[chitownV]

When I looked up the Haldex generations, there are some discrepancies about the 2009 XC90. It's a crossover year, so maybe it's related to when yours was manufactured. I am going by just trying to understand the Haldex systems, their design purpose, and how they could work in conjunction with the DSC systems. I remember when DSC was just coming out mainstream to luxury vehicles in the mid to late 90s, so I'm trying to remember that training.

Unfortunately, the best way to check the diff is for you to physically do it. Look for the part number or do the count. Mark and compare revolutions to get the ratio. You can find a lot of info online on how to do this.

Regarding the DSC, the Haldex design roots include, if the input shaft had a different speed from the output shaft then the Haldex would increase the pressure to engage. You can verify this by reading Haldex's generations and history. DSC is purely a traction+going-around-turns system, accounting for yaw, steering angle, engine input, etc., but purely to keep wheels' traction so the vehicle can be driven and steered. How the Haldex may affect that, well you are aware of how interconnected the different systems are and we can see DEM issues can trigger codes.

Haldex also has its roots as a coupling that simply accounts for low-speed turning & parking slip/differences in axle speeds. Unlike other RWD-based AWD systems which can vary & manage the torque fore and aft (manage both fr/rr axles), this Gen Haldex is more of a tiny-part-on/full-on system. If there is a difference in input-to-output speeds, who knows if Haldex will be full-on all the time when the wheels are rolling.

You could search some of the S60 forums. Maybe someone there has asked the question about modifying their vehicle for performance with a Gen 3 Haldex unit that pre-charges.

Good Luck and keep us updated!

[ggleavitt]

Manufacturer: Volvo
Part Number: 36050629
Replaces: 36000566, 36001719, 36002421, 36002516, 8603784, 8603863
Look up the PN you have on your old diff and the new diff. If it's one of these then you're good. If it's not, post the PNs and someone can clarify. There's no difference I can see between the parts though as a start, if gears changed between the variants you would be sure the PNs would change as well. That printout, you sure it's not the TF-80SC final drive ratio being referenced? Change in ratio might make more sense as a variable torque driveline to the Haldex coupler rather than a fixed matched gearset.

Angle gear for V8 is just for V8 as you allude, chassis break and physical change to the part somewhere in the run (post CH 300000 think), you need to buy some extra hardware to fit the new gear housing.

I used a new OE reseller source (https://parts.volvocarslisle.com/) and an old OE reseller source (https://www.tascaparts.com/) as cross references and they're consistent. Think you're probably good.

[chitownV]

Part Number: 36050629
Replaces: 36000566, 36001719, 36002421, 36002516, 8603784, 8603863
Confirming the p/n with the Volvo dealership linked sites took some time. That's good work. Looks like the non-Volvo linked sites use the older versions or databases of VIDA.

Change in ratio might make more sense as a variable torque driveline to the Haldex coupler rather than a fixed matched gearset.

Could you explain more about this or give a link? Variable torque, do you mean the off/low/high pressure? Pretty much 2 settings of torque, besides being off.

[chitownV]

"Change in ratio might make more sense as a variable torque driveline to the Haldex coupler rather than a fixed matched gearset."

@ggleavitt, I don't see anything in your MVS link about variable torque regarding Haldex that you said in the statement above. Unless you mean something else because there isn't variability built into our Haldex units. Again, for torque, there's a low pressure for parking and when AWD is not needed (or it could hurt), then it is full-on (high pressure). It is not variable. In the same way, a transmission manual clutch disc is meant to smooth the differences in engine and transmission speed upon engagement, it is not designed to vary torque output.

- FYI, I know of several auto manufacturers that will disengage their full-time AWD at high speeds, if it's an option in the transfer case design. BMW's XDrive waits until you reach ~80-100mph for later units, ~2012+. If you have ever driven a FT 4WD vehicle on the highway with snow and had all 4 wheels spin out, then you will understand why Haldex will not be full-on (high pressure) at high speeds.

I will publically link the info I was evaluating, not scared to do so. I don't own it so why keep it hidden from other MVS members and Volvo owners? The Gen3/Gen4 changes are to be proactive rather than reactive compared to earlier generations.
- A long thread about swapping from Gen2 to Gen 3 Haldex, good Haldex info. https://www.swedespeed.com/threads/real ... ex.558890/
**Haldex training material (might want to bookmark this one) https://auditttuning.org/2010/12/07/hal ... y-program/

You will see the different Haldex modes below.

[matthew1]

Guys, you must stop bickering. I'm going to go through your posts in this thread and remove non-Volvo content.

[ggleavitt]

Appreciate including the Swedespeed link, lots of good information in there (29 pages worth with additional reference links).

For my own edification I went looking in VIDA 2014D for AOC and DEM (Design and Function, 465 final drive, front and rear). I see the pump (on or off with no variability) and the axial solenoid (PWM from DEM controls pressure to the wet clutch plates) clearly described.
Per VIDA: The Differential Electronic Module (DEM) is directly secured onto the clutch unit and together with the axial solenoid and control valve constitutes one unit. Amongst other things the Differential Electronic Module (DEM) communicates with the Engine Control Module (ECM) and the Brake Control Module (BCM) via the Controller Area Network (CAN). Conducted by the sensor signals, the Differential Electronic Module (DEM) controls the oil pressure to the clutch driven plates by adjusting the axial solenoid. The axial solenoid has variable control over the control valve by means of a pulse width modulated (PWM) signal. The basic pressure in the system is built up by the electrical feed pump. The oil pressure to the clutch driven plates is decisive for how much torque can be transferred to the rear wheels.

Per the posted chart (general Haldex training), there may indeed be “phasing” of the PWM signal to provide distinct modes of solenoid operability via the DEM duty cycle but there’s no mention explicitly in VIDA of any overt state change, just variability of the torque to the rear wheels. Excluding pre-charge, this is how I’ve always understood the system to function, a “fixed” rotational reference from the driveline being applied with on-demand variability to the rear differential via the AOC. Modal variability perhaps, wouldn’t discount that. But variability nevertheless.

Can see the link below for another data point, someone trying to mimic a GEN2 DEM after a FWD to AWD mechanical conversion- https://forum.arduino.cc/t/using-an-ard ... nge/679505 . There are visuals in the post relating to modal operation although the OP does not elaborate and the post closes with no further progress.

Sure someone who has done a deep dive into the V8 DEM software can articulate the axial solenoid PWM characteristics. To be sure you could put a scope on the waveform, that would visually demonstrate modal versus linear operability.

edsit 041323- fix Arduino link, add carriage return.

[chitownV]

I see you copied info from VIDA.

Again, modal, pulsing, like duty cycle, is not varying torque like other AWD systems between front or rear axles. I explained this in earlier posts. Just like a manual transmission, the clutch is not “variable torque” as you stated. While driving, there is a low and high pressure with the Haldex, that’s it. Binary in operation for the rear axle.

Can you tell me what you are actually saying as “variable torque” because you have not actually explained it in your own words, since you made the statement about Haldex. Your own words would help for clarification of your meaning.

Appreciate it.

[ylwgto]

Thanks both for all the solid info.
I'm less concerned about the Haldex unit than I am the differential (maybe being naive). The Haldex units look identical.

So here are all the part numbers I can see. More listed for the new unit as the placement of the diff in the car does not let me see some of the part numbers, which is probably what I need...

EXISTING UNIT IN MY 2009 3.2 R-DESIGN:
HALDEX NUMBERS
(ON VARIOUS STICKERS) S6109547

DIFF NUMBERS
(CAST INTO HOUSING) ?
(ON LABEL) ?
(ON CAST GEAR COVER) 1023870

NEW UNIT FROM 2008 3.2:
HALDEX NUMBERS
(ON VARIOUS STICKERS) 105945, P30735118, S1337934, HAP542, 5W933504-01, 109205-01, 00108803, 01337934

DIFF NUMBERS
(CAST INTO HOUSING) 36114-7, 01023869
(ON LABEL) P1216626 V8/SI6, T123498 2,58
(ON CAST GEAR COVER) 1023870

Thanks

[Stovinator]

Any updates on the diff replacement? Everything work fine or did you need to find a different one?

I’m curious as I’m in the process of sourcing a used rear diff for my 2010 3.2.

Thanks.

[cn90]

I am afraid your problem is a stripped sleeve and not a rear diff.

Correct diagnosis is important.