Thought on AWD Bevel gear failures

[befarrer]

Has anybody done any monitoring of oil temperatures or attempted to cool the front bevel gear in the AWD Volvo's? Considering that a hypoid gear can make considerable heat, the bevel gear is located behind the engine, out of the air stream, under the turbo, the hottest part in the engine bay. I hit some parts under my car after a 80KM highway run in -10c weather. The oil pan was 60C, bevel gear was 85C, rear differential 40C. I have brand new tires, but once tires start wearing down slightly between rotations, and add another 30C of ambient temperatures, I can see the bevel gear oil getting well over 100C. I wonder if this is a contributing factor to the failures?

[jimmy57]

The death of angle gears is almost always because the viscous coupling seizes and the rpm differential that the VC provides isn't there. So the AG gets the stresses and builds heat that it is not designed to accommodate. In my experience somewhere around 125K miles is when the VC has often seeped the oil out of the viscous gel and begins to seize. There is a VC test where you lift one rear wheel with gear lever in park (locks the final drive gear in trans and the final drive case is the drive splines for AG spline connector cuff) and a torque wrench on a lug nut positioned radially perpendicular ?? to wheel center should yield with a slow rotation at less than 80 ft-lb +/-. A failed VC will often take enough torque that you tighten the lug bolt and it jumps at something over 125 ft-lb in jerky motions. Or it doesn't move at all and you would break the lug bolt before it would move.

[scot850]

What jimmy57 makes sense, he has a lot of experience, but I have not seen the VC failures he has seen, but my sample size is way smaller.

There are a list of issues that I would add to his suggestions and most are down to relatively simple maintenance or in most Volvo cases, lack there of!

1) Oil changes of the trans/angle gear/rear diff oils. Ask most owners when they were last done and I'll guarantee the regular owner will look at you like you have two heads. I have never been into a dealership and had the service/oil changes ever suggested unless I suggested it. The transmissions (auto) in the 90's Volvo said were 'sealed' for life which in reality was 'bollocks'. The regulars here know full well that 80,000km/ 50,000 miles is probably the max for a flush. The relative cost of the change, even at the dealer (here it about $500 CDN which is stupid) and with a synthetic oil should keep these transmissions in good shape. While not a scientific number, I would suggest every 5 years if you don't do big mileage. If you do it yourself you can increase this frequency. This relates to FWD or AWD's.
2) Angle gear - never had a suggestion from a dealer on changing this. I would suggest the same frequency as trans. I would guarantee most owners have never had this done.
3) Driveshaft/prop-shaft maintenance. More so the prop-shaft. Regular checking of the condition of the front UJ checking for movement and while there the rear seal for the angle gear should be checked for leaks. Then check for condition of the center bearing support, and although I have not seen it often, the rear UJ which seems to lead an easier life than the front one as the front one is right beside the heat for the catalyser.
4) VC (viscous coupling). AS per jimmy57 there is a somewhat sketchy test for the VC operation. The VC itself has no servicing other than checking for leaks from the clutch fluid and more importantly the front bearing which can literally collapse and can be sometimes heard by a 'whoose-whoose' or light grating noise when turning.
5) Rear diff. Again never had a dealer suggest changing this on an AWD. For the first time I have had the recommendation for our 06 XC70 to have the Haldex system serviced. Car is now 14 years old (although only 100,000 miles). That suggestion only came to light when I asked when it should be serviced. Now how good is 14 year old oil and the condition of the filter? Changing the oil in a P80 rear diff is challenging but not impossible. Again check for leaks at the diff axle seals. Again these do leak and take a fair amount of work to replace. A seized rear diff requires the dropping of the whole rear sub-frame as you have to separate the clamshell sub-frame to remove it and the bolts Volvo thoughtfully fitted from the top preventing easy removal. Great design!

If owners understood the cost of replacing these parts relative to the cost of maintenance cost then some might actually do it. Volvo does not help the process, and people understandably get scared when Volvo claim you have to use their ridiculous priced special oils only, but as we now know there are excellent aftermarket oils that are equally good for the purpose.

Some of the issues are just poor design, but the bigger issues are caused by lack of maintenance bad service advice from dealers. Add to that Volvos usually running for a long time after something should be fixed and becoming 'just old cars'.

Final points are again lack of understanding on the old AWD system and probably any AWD system of tires. Particularly the P80 AWD system if you have a tire failure except when the tires are virtually brand new, requires new tires all around. I have have seen many AWD cars, including Volvo where owners have fitted one new tire on a car with half-worn tires as they are cheap. This loads all the AWD system. Also lack of tire rotation adds to these issues.

Not trying to scare the crap out of folks, but maintenance is key here more than anything.

Last final point is driving style. The systems are fairly robust but like many things in life you get some drivers who are just rough on their cars. It is hard to tell how an old car has been driven, so it is always an unknown. All you can go by is maintenance history.

If you need any further advice feel free to PM me.

Neil.

[abscate]

Update on this in 2022

Volvo calls for two different oils in the diff and angle gear , the angle gear one is a so called “low foaming “ version of GL5 with a BOT spec

Is this important? I have no clue

[scot850]

When I don't know I use the real stuff and don't ask. Biggest issue is lack of servicing in my opinion and people driving their cars like idiots. Last angle gear I tried to pull I ended up leaving as the internals had no oil but only a very badly burnt substance that looked like a dried out grease. The collar teeth were so madly stripped they had also stripped the teeth on the splines as well on the input shaft for the angle gear.

As with the diff on these cars, I will guarantee most owners never service them. It is the same as auto and probably manual trans oils and rear diffs and Haldex systems where fitted. I have spoken t many owners about these service items and their eyes glaze over with the idea of spending money on these repairs. They are happier to blame Volvo for making crap cars. Clearly the issues are not of their doing........!

Neil.

[Pacolamerguez]

Hello,

I'm interested in your discussion about servicing the Volvo AWD system, particularly on the Volvo 850 and V70 Phase 1, as I own a model of this type.

I have a 1998 Volvo V70 XC AWD, M58 manual gearbox.
I would like to maintain it properly and prevent any possible breakdowns... Even though it already has 305,000 km...

My questions concern the oil capacity of the bevel gear and the rear differential. As well as the grade of oil to use.
To be honest, I've already "rebuilt" the angular gear by changing all the seals and bearings inside (and if you know the torque to apply to the preload ring, I'd be happy to see if I've done anything stupid), and there's still a slight "hissing" sound when I drive at a steady speed of 100/110 km/H.

Could this indicate a lack of oil? Should I increase the grade of oil to make up for the mechanical play?

Finally, I would welcome any information or tips you may have.

Sorry if my English isn't perfect! I'll do my best

Thank you for your answers

[abscate]

Bon jour!

The angle gear and rear differential take a bit less than one liter each. Many use synthetic 75W-90 gear oil in both, but Volvo actually has a special non foaming gear oil they call for in the angle gear.

We are very jealous of your AWD with m58. Add it the Louvre, Versailles, baguette, and fromage of beautiful French things

Here is a picture of the Volvo recommended oils for bevel and the rear differential

[Pacolamerguez]

Thanks for your reply! It made me laugh a lot

Maybe when the time comes, I'll donate it to a museum haha
But yes, in the meantime I use it to buy bread and cheese

Right for the oil! I found on different sites that the capacity of the angle gear was about 800mL, and that of the rear differential about 1.3-1.5L.

Incidentally, I sucked about 1.1L of "dirty" oil from my rear differential, knowing that it was leaking through the driveshafts joints... Which I replaced of course
I put 1.3L of oil back into the rear differential. And I have the impression that it's the one that's "whistling" at a steady speed of around 100km/h.
But maybe it's the angle gear after all... If 200ml of oil is missing, it's possible!
I'll try adding 100mL to see if that changes anything.

I didn't know you were a fan of the M58 gearbox
It's obviously quite a rare version (and very difficult to find front driveshafts )
Incidentally, I have some questions about how this AWD system works.

Do you know what the "TRACS" button does, please?

And are we in agreement that the M58 gearbox and rear differential have no autoblocker or limited slip? They are "classic" differentials?

And thank you for your answers and help

[abscate]

You could have a limited slip differential in your rear differential but I don’t think it’s necessary with an AWD car

The TRACS button turns OFF the traction control,which is limits wheel speed difference at low speed. I can’t remember if it works only on the front or on all four wheels. It uses hydraulic brake pressure to slow the spinning wheel.

The system is on by default ( défaut )when you start the car, the button is if the driver wants to turn it off for some reason

[erikv11]

Bon jour!

The angle gear and rear differential take a bit less than one liter each. Many use synthetic 75W-90 gear oil in both, but Volvo actually has a special non foaming gear oil they call for in the angle gear.

We are very jealous of your AWD with m58. Add it the Louvre, Versailles, baguette, and fromage of beautiful French things

Here is a picture of the Volvo recommended oils for bevel and the rear differential

So far I've used use synthetic 75W-90 gear oil in both

But I have no interest in stressing out the angle gear ... has anyone seen an appropriate low foaming gear oil for sale anywhere?