front end shakes (c900)

Get the machine up again and see if you can make the hub move on the ball joints and check the wheel bearings. Check for any obviously missing wheel weights. If you do not find anything - get yourself to any shop offering alignments and have it checked carefully and immediately. It could be axles - but it doesn't sound like it at first read.

It sounds very much like something has come loose rather than worn out and that can be a very dangerous situation in a front wheel drive car at any speed. Maybe simply a missing weight - but maybe not.

Best of luck.

Dexter,

Thanks for the reply. The car has had new tires w/ balancing and alignment within the last few months. It's possible that it threw a weight off, but for something I didn't bother to mention in my initial post: I was briefly on a highway again on the way home, at 60 - 70 mph, and there was no problem. It is definitely somewhat intermittent in nature, which points away from wheel weights. Plus, there is the dependence on whether I'm accelerating, decelerating, or cruising.

Yes, I agree, hence my roadside checking of things to make sure that the wheel wasn't going to actually fall off of the car. Anyway, I think I'll definitely have a look at the driveshafts when I next get a chance, and drive conservatively in the mean time. If the inner drivers or CV joints are wearing, the problem should be getting gradually worse.

Thanks again.

John

I'd be giving the entire driveline/suspension at the front a good inspection. Have a look at the lower control arms and make sure none of the welds are coming apart, and also see if any of the balljoints might have failed. Lower control arm faults have occured before and they're quite well documented though your car is an early-90's C900's so it's not likely to have that problem.

Best thing to do is put spacers under the upper control arms for both front wheels (to release spring tension when the car is lifted), loosen the lugnuts and lift the front of the car. Take off both front wheels (make sure the car is on stands or something else to hold it up - never use just a jack to hold it up!), and have a really good look at everything. Look at the brake calipers, shock mountings, balljoints, etc. and if you can, get someone to sit in the car and turn the steering lock-to-lock while you check out each side and look to see if anything's amiss. Also try turning the wheel hubs by hand with the tranmission disengaged (neutral for manuals and P or N for autos) and see if anything scrapes or clunks other than the brake pads on the disks.

While you have the wheels off, check them too - you might have sustained damage to a tyre and that would certainly cause shaking or strong vibration. It's very unlikely that if a balance weight has come off that you'd get really violent shaking - you might start to feel slight vibrations but the loss of a few grams of weight off a wheel is rarely going to be a problem for regular driving (but if a weight fell off and got stuck in something else it might)

If you can't find anything obviously wrong, broken or out of place, put the front end of the car back together again and take it to a Saab-trained mechanic for a professional assessment.

Regards,

Craig.

Thanks for the suggestions. I replaced the ball joints, shocks, and brake pads over the summer, so if anything's falling apart I should be able to spot it. I'll take a close look at the A-arms, but as you said it's an early 90s car so it's likely fine.

Here's a question though. I want to inspect the inner drive joints. Is it possible to pull the axle from the differential by simply detaching the ball joints from the A-arms, rather than having to separate the ball joints and take the spindle apart? It seems like it would be easier to pull the axle/brake disc assembly as one piece, if possible.

Thanks, John

I've experienced this and the cause was dried out outer u joints. Re-pack with grease and the shake goes away.

Duane

Ok well then it's unlikely to be balljoints, etc. Could be a CV problem though.

Yes you can do that, but the whole swivel member, brake caliper and brake disk assembly will be quite heavy. The Bentley manual has good descriptions on how to deal with all those components - generally you should remove the brake caliper and disk before trying to remove the steering swivel member both to reduce the weight you're working with and give you something less unwieldly size-wise.

Since you're thinking about doing it with the drive axles still attached (via the outer CV joints), you're going to need plenty of things to support the swivel member as it'll pull the inner end of the drive axle out of the inner CV quite easily if not well supported once the balljoints are pulled out of the a-arms.

If you want to replace the outer CV nuts, you could detach the swivel member from the driveshaft and further reduce the weight you're dealing with at one time. I know we probably all re-use outer CV nuts but they're supposed to be replaced (make sure that if you do re-use the old ones that they're staked after re-installation and torquing!). 8-)

Also, beware that you have to torque the outer CV nights to a very high torque - my torque wrench only goes to 150 ft/lb and the torque is supposed to be around 200! I had to literally stand on it to get it up to 150 (on my

1985 900i) and I'm sure that they nuts will be fine. Never ever crack or torque up outer CV nuts with the car off the ground.

Regards,

Craig.

Did they dry out because the boot(s) had failed? I'd be replacing the boots at the same time if grease in the outer CV's needed repacking.

Craig.

Hi,

On the earlier c900s this is the standard procedure for removing the engine. You put spacers in the upper wishbone so it does not come down all the way, then release the balljoint from the lower wishbone then you can pull outwards far enough the hub assembly to make the drive shaft come off the transmission receptacle (what its name).

This is not far off of what you need to do to get the whole axle/hub assembly on a bench. Remove brake caliper, balljoint from top wishbone and undo steering knuckle.

At this point hope you did not need to have had the driveshaft nut undone, say to replace the CV joint, as it should have been undone as the very first item.

==================

I am not sure what you will find by "inspecting" the inner drive shaft hubs. Maybe look for excessive play of the inner CV assembly.

Sorry I can't be of much help.

Charles

Sounds like most of the possibilities have been suggested by correspondents here. One other possibility may also be a grabbing brake caliper. I experienced a similar unexplained on my 9000 and it was traced, by the dealer, to the off-side (UK car) brake caliper not releasing fully. A bit of a long shot, but may be worth a look while you're under the car.

True. It's occurred to me that I should take a look at the motor mounts as well, as the engine bouncing around could certainly cause the symptoms.

If it turns out to be a drive axle problem, I might just replace both axles with complete rebuilt axles, which includes pre-assembled inner and outer joints. Eeuroparts.com appears to sell them for a reasonable price, with return of your old axles.

John

Ok, I took a good look at things today, and took some pictures, available here:

Things that stood out to me: front motor mount has some cracks, but I'm not sure if these are really severe enough to cause vibration. Also, the left inner tripod bearing boot (which is totally covered in engine oil and PS fluid) seems to be somewhat uneven. Is it possible that it's slipping off? Or worse, that the tripod joint is somehow puling apart?

I'd greatly appreciate comments on the pictures.

Thanks,

John

Hi,

I'm hoping a few of you find time to take a peek at some of my high-res photos posted previously, especially the left side inner joint and the front motor mount.

Here's an update: I drove the car about 100 miles today, mostly on the highway (65 - 75 mph), and there was no problem at all. Which makes this an "intermittent" problem. Which will no doubt make it especially tricky to pin down...

John

Also look at the a-arm bushes. I had one replaced during (one of the right-side upper a-arm bushes) the last rego-renewal service but I've noticed from driving my 1983 900S 400 km's from the south-east of Sydney to Newcastle (that's in Australia not the UK!) and back today that when I power against a left-hand turn there's a fair bit of shuddering, but nothing when I do the same against a right-hand turn. I don't really know what to look for with them so I'll be seeking help from another SCCA member who has done bush replacements.

Some people have said to me that shuddeirng when turning is a give-away symptom of a-arm bushings failing. Could well be so based on what the other person says, I'll probably plan to replace all the suspension bushings with poly ones between now and June next year when rego is due again. I'm looking at renewing the shocks too so doing it all at once could be a Good Thing.

Yes that's a good way to go since it means you can do a straight swap of the drive axles, and either take the old ones back for a 'core' refund, or keep them and replace joints, etc. yourself to keep them as spares. Now that I've actually done CV boots, etc. and pulled out driveshafts on my 1985 900i I'm confident at doing it, but the first time is quite daunting with all the steps that need to be done in the right order.

A few places on Ebay have been selling complete driveshafts of late (in the USA though).

CV grease is fun stuff - it's molybdenum-based so be careful about skin exposure.

Regards,

Craig.

Looks like something's happened to that boot over the inner CV. Probably it either wasn't put on properly in the first place and someone tightened up the clamp without realising, or it's been subjected to a 'shadetree' service and the clamp isn't tight enough. It's hard to tell if all the oil is the product of CV grease that's broken down or simply just engine sump oil.

Gotta sleep but I'll look at the rest of the pics tomorrow after work (3.30 am start!).

Craig.

Hi John

Hard to tell if it is a badly fitted clip round the boot or a more serious fault. If you are underneath the car, you can undo the clip and resit it. Don't refit too tight to gibe it a chance to move again ... assuming it is its insides that cause the problem. The inner driveshafts (receptacles coming out of the gearbox) is what will give was over high mileage or abuse of the car. They can wear out or break.

Sorry I can't guess if there is a problem there. But in terms of procedure of getting to it, the method I have you for removing the lower ball joint would not give you any space to work with, so given everything is new I would remove the brake caliper and take off the complete axle + hub off (see my previous message).

For your test, if you are looking at the coupling of outer axle to inner axle, going on motorway is not good enough. You have to make the axle move in/out in relation to the inner axle, ie. uneven surfaces and turns, so it finds the faulty bit on the inner axle and recreates the problem. You first mentioned that the problem happened at particular speed and when the engine was (was not) pulling the car, if the problem is in inner/outer axle joint it should be reasonably constant.

Refit boot. Check that outer axle does not have any play in relation to inner axle (up/down, forwards, backwards) but you will get some play if you try to rotate the axle in relation to the inner axle. Hard to tell how much, if any, is acceptable.

Regards Charles

Looks like the power steering is leaking somewhere, most do.

Yep, that's a long-standing problem. I just top off the reservoir periodically.

John

My vibration problem didn't happen especially when turning one way or the other. It's strange that the shaking was so violent the other night, but has been completely absent since. Even if I replace the entire drive axles, I won't really know whether that solved the problem until I've driven around for months or years without a recurrence. *sigh*

John

in article slrndof779.shf.rotten_NOSPAM snipped-for-privacy@oragam.example.com, John B at rotten_NOSPAM snipped-for-privacy@ccil.org wrote on 25/11/2005 23:23:

Hi! Which wheels do you have? I have the curly 'Aero' wheels and a slight bend gives me the shakes at around 40 MPH ... Apparently quite common with those wheels on C900s and 9000s.

Change your front wheels to the back and see if the problem is still there. If so, that's a quicker fix than starting to replace the drive shafts and associated ancillaries.

Good luck - hope you find the problem.

Paul

1989 900 Turbo S