Drivetrain problem- new tires

[Lonestar245]

New here, just took over driving my wife's 2009 Saab 9.7x after selling my GMC Sierra pickup. I work in telecom construction as an inspector, so I am in the field all day watching construction crews install duct for fiber optic cable, or watching crews install the fiber in the ducts. This requires something with ground clearance to be able to hop curbs all day, and be tall enough not to have the catalytic converter set a field on fire. It helps if the vehicle has limited slip diff, or even 4WD, as sometimes it gets muddy out there. So... when I sold my truck, the Saab seemed like it would fit the bill nicely.

Maybe.

I was backing up along a curb and did not notice I was by a broken catch basin (gutter) that had rebar sticking out, so I destroyed my right front tire. Fortunately, I had road hazard warranty, and it was replaced at little charge. I had a concern that this new tire would cause problems with the Saab's AWD system, as it would be slightly larger than the remaining tires that had around 35k on them. I quickly noticed a shudder or shimmy in my steering wheel at highway speeds (over 55) and started thinking it might be an AWD issue. Still, I took it in to the tire shop again and they rebalanced it and at my request, placed it on the rear. I noticed while it was on the spin balancer it was out of round. I knew then what the problem was. They claimed it would go away after re-balancing, so I humored them as I was short on time.

While there, I noticed my rear tires had a lot of wear on the inside, which would explain the "mudder tire" sound I got a low speeds. The shop tried to tell me I had an alignment problem, to which I asked how to align the solid rear axle. I recognized it was the same problem I had with my '07 GMC pickup with LRD- all the u-turns I make are shredding the insides of the tires. This is not my main concern.

Moving on, I notice the front end is now stable again, but I can feel a lot of vibration coming from the back. I return to the tire shop yesterday and describe all the above, and indicate that no amount of re-balancing will fix this. The tire needs to be replaced. They offered to get one in since it was not in stock, and offered a good price on a second so I would have two new tires on the same axle. I agreed, and then they offered to switch brands to something they had in stock so we cold take care of it right now. After some price haggling, I agreed. I drove home from the shop and I can say that all the vibration is gone, but something is different. Couldn't put my finger on it, but it was just an odd feeling.

Got home, no problems other than the weird feeling. Went back out and as I left my driveway, I notice the loud roar of the engine fan - at least I assume that is what I have been hearing all these years as my wife pulls out of the driveway. It was very hot yesterday- well over 100F, and so I figured to help the AC I would just keep the truck in 1st gear and let that fan spin on "hi". After it eventually settled down, I shifted up to "D" and when I reached the end of the alley, I had to brake a bit before turning onto the street. I again felt an odd sensation, and then a bump in the driveline as I accelerated.

I did not have far to go, and felt this bump every time I moved from a stop. I got the idea in my head that the rear tires are a bit different in diameter, and this is confusing the AWD system, probably causing it to engage. I then have the horrifying thought that I am burning up clutches as the AWD system engages due to speed differential- front vs rear- and I figure I better figure this out quickly before I create a larger problem.

Thus, I found this forum. Looked around and didn't find anything that fit my case exactly. I did take a crude measurement and found the rear tires to be 1" taller- 29-1/8" vs 28-1/8"

So now I am a bit frustrated, and curious. I am wondering if it is the tire size that is causing the problem. I am also wondering if there is a relay I can unplug to disable the AWD from engaging until I can solve the tire problem? I really hate to by the two additional tires as that will set me back about $500. I could give up the AWD for a while.

I also did not know about changing the fluid in the xfer case. I have about 65k, so I will be getting on that ASAP, and since I do so many u-turns, I will probably change the rear diff while I am at it.

OK, I know this is wordy, but I find in these situation if I dont give all the details, I get lots of questions, and I need an answer pretty quick.

Thanks to all who made it this far!

 

[The_Roadie]

Much less than 1" tire diameter difference is going to destroy your transfer case clutches in hours, not days. More than $500 at risk. That AWD system can't be disabled electrically 100%. Have to remove the transfer case encoder motor and rotate the shaft properly. I strongly recommend matching tires before driving at all except to the tire store.

 

[HARDTRAILZ]

An inch difference...I would go back to the idiots at the tire store and demand the same size tire. Metric tires do not vary that much from brand to brand esp in stock sizes. Have them put the same size as your two good old tires and you do not spend anything.

 

[Lonestar245]

Before I received a reply, I pulled the fuse for the AWD and drove it around the block. I did not exhibit the bucking or binding that it did yesterday. I had to go to work and did not have a spare car, so I drove the 30 miles or so to the job site. Called my mechanic and he said what you guys said- don't drive it, get more new tires, of at least tires of the same size. Not much I could do at this point.

I went to the local branch of my preferred tire store after work, and pleaded my case and they made me a very reasonable deal on a matched pair. Call it an offer I could not refuse. Big shout out to Discount Tire on Collins in Arlington Tx! (Hope that doesn't break any forum rules).

As for tire sizes supposed to be the same for a given size- yeah, In theory that is good practice, but the reality is a bit different. I have the correct size on my Volvo and they rub the fender liner pretty bad because the tread is wider than the OEM.

Moving forward, I'm going to change the fluid in the xfer case ASAP, and probably both diff too.hopefully I won't be rebuilding my xfer case.

Thanks for the replies. Glad to know this forum exist.

 

[Wooluf1952]

Glad you got your truck working again and

Welcome


In case you haven't heard:

http://gmtnation.com/forums/topic/218-welcome-to-gmtnationcom-heres-the-story/L]

 

[djthumper]

Glad you got things working again.

Welcome!

 

[Lonestar245]

I wrote my response while at the tire store, on my phone, so I hope it was not too much of a mess to read. That tiny screen, my bad eyes and big fingers are simply a bad combination. Anyway, I drove it home on the new tires, and it did not exhibit any drive line issues, although I confess I have yet to replace the AWD fuse. I figured all it does is solidly engage the AWD clutches in the transfer case when a rear wheel spins, transferring power to the front. In case I created a problem during my 30+ mile drive across the metromess- like say burned up fluid and chunks of clutch material- I figured to just give the thing a break until I can change it. After all, I had 30 miles of 70mph highway ahead of me to get home. This morning, I have a short errand and figured I would put the fuse back in for a quick test, just so I would know if there is already a problem I can be studying on what might be involved to fix it.

I also had a chance to do some searching around on this site and found a lot of useful information. Now that I am more familiar with how it works I might not post so many newbie questions that are already answered.

Sticking with the subject, when the need arises, should I rebuild the transfer case at home? Is this fairly easy to remove and is there any reason I cannot rebuild it myself? I am not exactly inexperienced at mechanics, although I confess I didn't know much about this vehicle since it was my wife's vehicle, and covered by a generous 50k mile warranty as well as included all service items up until a year or so ago. So I just didn't pay it much attention and assumed the dealer would take care of it. Probably should have asked them to service the transfer case at 49,999.0!

I would be inclined to rebuild the transfer case myself if it is easy enough to get out. I know the fluid is Auto Trak II, but what is the brand/part number of the friction modifier I keep reading about? I want to source this at the LAPS if possible- O'Reilly has the Auto Trak II, possibly they have the friction modifier too.

As for the tires- I ended up with a set of Pirelli Scorpion Verde All Season with 50k mileage warranty. These are designed and marketed to tree huggers- not that there is anything wrong with that- with several key features appealing to the type. One is supposed to be improved fuel mileage. We shall see. That usually means lower rolling resistance (which they claim to have), and I can already tell you these casing are firmer than the Falkens I was riding on, so the ride is not quite as luxurious. More bumpy, bouncy, for sure. I can only say I hope I dont come to hate them for this. They might need a bit less air in them- because I typically find the tire store over inflates. On the plus side, they are super quiet! I read a few reviews after I got home yesterday (and there are very few) and the one guy who had them on a small Mercedes SUV said he only got 20k out of them, they could not be kept in balance, rode poorly, etc... but that is one guy.

More to come...

Update: Replaced the fuse, vehicle operated perfectly normal for the 10 miles or so I drove it. Slow, fast, tight turns, no bumps, pops, binding, etc.... Still going to change the fluid, inspect it for color, content, volume. Also, have not tested on a slick surface to see if the front positively engages. Again, hot and dry here, no place to test. And I wonder, is it supposed to come on gradually or firmly? Say if a tire slips under a heavy engine load will it normally hit pretty hard - as mine has done in the recent past?

I do hear an electrical whine when rolling down my alley between fences with the windows down. Might have always been there and I never noticed as I have never tried to listen for anything before, save the obviously loud serpentine belt idler pulley bearing.

 

[Wooluf1952]

I would be inclined to rebuild the transfer case myself if it is easy enough to get out. I know the fluid is Auto Trak II, but what is the brand/part number of the friction modifier I keep reading about? I want to source this at the LAPS if possible- O'Reilly has the Auto Trak II, possibly they have the friction modifier too.

The only friction modifier I'm aware of is for the rear differential. And since only the SS has the posi rear, our G80 locker doesn't need it. You can buy Mobil 1 diff fluid with the LS additive. It won't hurt anything.

 

[Lonestar245]

The only friction modifier I'm aware of is for the rear differential. And since only the SS has the posi rear, our G80 locker doesn't need it. You can buy Mobil 1 diff fluid with the LS additive. It won't hurt anything.

Thanks for that explanation. I guess I got the two things confused.

I am curious, does the SS AWD have the same set up as my 9.7x as far as the transfer case? Regardless, what model TC do I have? I want to see how it works.

I also wonder- would my 2009 be covered by the GM 5 year 100k mile powertrain warranty?

 

[Instrumental]

Pretty sure the Saab does have the limited slip, it does need the friction modifier in the rear differential.. As mentioned, only Auto Trak II in the transfer case. I got mine at NAPA, many get it at the dealer.

A dealer can run your vin and tell you exactly what coverages you have, but anything warranty or recall related has to be at a Saab dealer, GM dealers are not allowed to do the work. I had to drive 45 minutes each way for the window switch repair, my local dealer wanted to do it but found they couldn't.

 

[Wooluf1952]

Pretty sure the Saab does have the limited slip, it does need the friction modifier in the rear differential.. As mentioned, only Auto Trak II in the transfer case. I got mine at NAPA, many get it at the dealer.

A dealer can run your vin and tell you exactly what coverages you have, but anything warranty or recall related has to be at a Saab dealer, GM dealers are not allowed to do the work. I had to drive 45 minutes each way for the window switch repair, my local dealer wanted to do it but found they couldn't.

Sorry. I think you're right. I forgot about the Saab.

 

[meerschm]

save the obviously loud serpentine belt idler pulley bearing.

Don't think the idler bearing should be making noise.

you might want to take care of that too.

 

[Chickenhawk]

Don't worry about rebuilding the transfer case. Change the fluid and you'll likely be fine.

Now, between this and other forums, many of us have extensive experience with tires and tire pressures. For our information, could you detail the following so we can help you further with some practical advice:
- What was the make and size of the tires you took off?
- What was the make and size of the new tire they initially tried to sell you?
- What is the size of the new Pirelli tires?
- What tire pressure did the dealer put in?
- What tire pressures are recommended on your door sticker?
- Did they inflate the tires with high-performance nitrogen or with old-fashioned analog air?

Just some quick thoughts. Many Falken tires (and some Pirelli tires, for that matter) are what are called "price-point tires." They are designed to sell at an attractive price. They compromise ride, wear, handling and most important quality of manufacturing to sell for a low price. This is likely why they started wearing on the inside.

It has been our experience that tires that wear excessively on the inside when it is not an alignment problem are because of cheap tires.

(And, by the way, the question on nitrogen was just a test to see how honest your tire dealer really is. Nitrogen is the biggest consumer scam of the decade and there isn't one single, justifiable scientific reason for nitrogen aside from padding the dealer's pocket.)

One other point I am concerned about. Your clutch fan should NOT come on for more than a few seconds at startup. One of the problems is that they have a high failure rate; they can fail gradually and owners seem to get used to a few minutes of jet engine noise while driving down the lane, and new owners of used vehicles may think this noise is normal.

When normal, the fan clutch only kicks in on very hot days, especially idling in traffic. It should not kick in on startup for more than a few seconds, if at all. We have two Trailblazers in our family and neither one kicks in at all at startup.

When you first start it in the morning, is the fan clutch on? It makes an unmistakable jet engine noise that can be heard from a block away. If you know what you are doing, one can press a rag against the spinning shroud to see how easy it is to stop the fan from spinning. A normal fan clutch will stop spinning with very little pressure. (Be VERY careful doing this, and if you are not sure what you are doing, do not attempt.)

So let us know the info above and we can help get your truck running better than it was before.

 

[Instrumental]

Does the AC affect the fan clutch being on? I know in other vehicles I've owned the AC will force the fan to always be on.

 

[Wooluf1952]

Does the AC affect the fan clutch being on? I know in other vehicles I've owned the AC will force the fan to always be on.

Having the AC on might activate the fan a little sooner. I'm not sure. But my fan has never been loud with the AC on even in hot city traffic.

Also, as meerschm stated, the idler pulley and tensioner pulley should not be noisy.

 

[C-ya]

When I park my truck and the weather is warm at all, the next time I start it and drive, the fan roars for a few seconds.

 

[Wooluf1952]

When I park my truck and the weather is warm at all, the next time I start it and drive, the fan roars for a few seconds.

That's not unusual. Mine does that at times even in cool weather. IIRC, a lot depends on the position of the fan when the engine was last stopped.

 

[TexazReece]

Same here my fan does the samething. Welcome to The Nation by the way

 

[SaabScott]

Great to see another Saab owner on here! Even more glad to hear that you are sorting things out.

 

[Lonestar245]

Wow, not sure why I missed all these responses??? thought I had this set up to email me when they came in. Well, maybe I have been under a rock? Anyway, that is another issue I'll work on later. To answer or reply to some of the comments above-

The tires I had were Falkens in the OEM size- P255-55-18R. I liked them much more than the Dunlops that came on the truck. They rode quite nicely. About $165 per tire.

The replacement tires are Pirelli Scorpion Verde All Season P255-55-18R. $212 per tire Much firmer ride. Harsh, actually. No doubt due to the "lower rolling resistance". Also, about 1" taller than the Falkens- which had 30k on them.

The rear has limited slip, but I believe I read somewhere it is the Eaton G80 locker, no additive required like the TBSS with its clutches, although the manual calls for it. I suspect the Aero (6.0L) uses the same diff as the TBSS with the clutches.

The fan clutch is viscous (old school) and runs off the water pump. They can be locked up when cold, and are supposed to lock up when they sense a high heat load. It is operating normally, as it always has.

The idler bearing was replaced by me back when it went bad. The point was, I did it even when the truck was under original Saab warranty, not realizing I could have had the dealer do it.

 

[DJones]

I have Falken's right now too. Overall, I like them.