Limited Slip vibration/binding on 1982 930....me thinks...

[DaytonaCoupe66]

Hello; looking for opinions/suggestions on hunting down a vibration.

I have a 1982 930, ROW Canadian car, that I bought last year. Stock drivetrain.
When I start off at an intersection with a turn left or right there is a vibration in the rear end that gets worse as the car gets warmer. Starting on a hill with a turn it feels like binding in the rear. It's not there when the car is cold out of the garage, and as the car straightens it quickly subsides to normal. I put in the Kendall LS transmission fluid and it made no difference. This had cured a similar but less pronounced issue in a previous 930 with LSD. The transmission shifts nicely in all gears. Car has 185000 kms. Clutch appears to be fine as there is no slipping on boost.

I replaced the 4 CV joints with new units thinking this was the source. No change. A local mechanic has suggested wheel bearings but I have no heat on the wheel hubs after a lengthy drive, no noise from the bearings, no wheel slop when checked on the lift. And...if I take a corner as in making a perpendicular turn at an intersection with the clutch in to the floor there is no vibration....nice and smooth. As soon as I let out the clutch it's there until I straighten the car, then gradually disappears. It appears to be prevalent at low speeds only. Wheel bearings are on the way nonetheless, and I have the parts on hand change the original motor and transmission mounts this winter. The rear brakes are worn (discs have a significant wear ridge in them), I'll replace all 4 corners as part of the winter refit.

Any thoughts on these symptoms? I note from the service file that the previous owner put synthetic gear oil in the car. With approx 3K kms on the car this summer all eyes will be on the fluid for the drain and change.

Final question; if this ultimately means a new LSD, can the LSD unit be changed with the transmission in the car? I had seen a few utube videos where this had been done on a 997 GT3.

Comments are appreciated as I work through this. Cheers!

[kamaro]

I can only answer your last question, yes you can replace your diff with the trans in the car, I just did that on my car.

[356911930]

Daytona,

The bearings are a good place to start. I would have a close look at the rears.

I do not think these LSD like the synthetic gear oil...too slippery. The problem could be the friction disks are wearing out. Jack up the rear of the car so that both rear wheels are off the ground, spin the one tire, both wheels should spin the same direction. If they spin the opposite direction you have no LSD or the LSD could be worn.

Rahl

[gsxrken]

The wheel bearings are a monster job. I wouldn’t do them unless you absolutely want to do them anyway.
It’s interesting the vibration goes away with the clutch in. I’m no expert but I would have thought the diff clutches would still doing their thing as one wheel travels further than the other around a sharp turn whether or not power is applied. Makes me wonder about the state of the engine and trans mounts too. On my 930 box that Kevin Gross rebuilt, the bearing races that mounted the diff needed to be over bored and new ones pressed in. It was a heat related condition as well.
You want 80w-90 GL5 gear oil with limited slip additive. You can add 1 or 2 bottles of limited slip too as a last ditch effort. Drain out some of the oil first so it isn't overfilled if doing that. I’d try that first. I don’t know if completely worn lsd discs make any noise or just don’t perform the lsd function anymore. Maybe some experts will chime in here.
Good luck man.

[DaytonaCoupe66]

Thanks for the perspectives.

Kamaro; good to know that the LSD can be replaced without removing the gearbox from the car. Did you ultimately add this feature to your 930 transmission? (been reading some of your posts on the open diff).

Rahl; the car does have LSD as per your procedure for testing and it works fine when on the hoist. I've not tried it with one rear wheel on and one rear wheel off the ground for amount of resistance. I'm quite sure that this option was standard on Canadian cars, likely due to our lengthy winters followed by several months of poor skiing.

GSX; the wheel bearing kits for both rears are on order from a firm in the UK. Hugely significant savings vs what the P stealership wanted, but 2 months on backorder. It's a job that should be done on a 38 year old car anyway so it's on the agenda for this winter. No, not looking forward to it. I would think that when the clutches wear they would no longer perform the LSD function, whereas on mine it feels like something is binding. I did drain a bit of oil and added a small bottle of LSD magic, but no change. When I drained the transmission last winter to install the Kendall there were no tell-tale signs of wear on the drain plug or in the fluid.

So, before I tear into the diff as the last resort the plan will be drain gear oil and inspect, change out wheel bearings, motor / transmission mounts, adjust clutch - check bellhousing bolts (just occurring to me that "something" clutch related could be out of alignment?), replace rotors/pads on the brakes, then reassess.

I did a pile of preventive maintenance over last winter, then suffered a recurring but intermittent and annoying 'engine suddenly dying while driving' problem in the spring. Fuel system and all peripherals tested within spec but I had a noisy rear fuel pump. I know it's heresy to throw parts at a problem but with our short driving season and the time it takes to get parts in the new-Covid-age I accumulated a new CDI and rear fuel pump. No change. Rewired the two fuel pump relays via fuseable links to the battery as per a DIY on this site and problem solved. Less than $10 to fix something that I'm sure plagued the PO over the years as well.

Cheers....

[s5uewf]

I would guess the issue is either fluid or LSD clutch wear.
The cheapest thing to test is to drain and replace the trans oil with proper weight and spec. Here is another thread on oil and LSD - I am sure there are several in the forum:

911 Turbo/ 930 gear oil recommendation

If this does not fix it, then possibly LSD clutches. I purchased my LSD clutch discs from Guard transmission when I needed to replace mine.

[kamaro]

Originally Posted by DaytonaCoupe66

Thanks for the perspectives.

Kamaro; good to know that the LSD can be replaced without removing the gearbox from the car. Did you ultimately add this feature to your 930 transmission? (been reading some of your posts on the open diff).

Cheers....

No, I just re-adjusted the diff, I had some whining when I test drove the car and when I took it apart it had a missing shim on one side. I just finished checking the pre-load and the backlash which both were with in specs now, I will test drive it tomorrow and hopefully that will fix it. If I ever need to put an LSD diff I would do the exact same steps, which are not horribly difficult, actually taking the diff out and in again takes no more than 1 hour from start to finish. good luck!

[DaytonaCoupe66]

Hey S5; I guess it makes sense where if the clutches are too slippery, they causes a vibration so worn clutches would likely do the same, even if the proper/stickier GL5 dino oil is in the case. Thanks - some good info offered by all that will be helpful. I'll follow up when I land on the solution. Cheers!

[kevingross]

There's nothing wrong using a good quality synthetic fluid with your 930's factory LSD. I've recommended to my customers, street and race, (and used personally) Mobil 1 and Delvac for 25 years. Works great.

I'm not sure what's causing your vibration. Typically LSD noise shows up as juddering when you make very tight parking-lot turns. There are additives that work well in reducing the juddering, and you might want to try one to see whether its helps.

You don't need a new LSD, if indeed there is a wear issue with it. The service parts to rebuild your LSD are available, and the work to rebuild it is about as simple as it gets. Good luck!

[DaytonaCoupe66]

Hey Kevin; thank you for the comments. I added the Kendal with LSD purchased from our host in the spring of 2020, then added a small bottle of GM LSD additive a few weeks ago. No change. I'll hope that some of the scheduled maintenance items this winter will hit the mark. Cheers....Denis

[flightlead404]

Its a wild shot in the dark but I had a very similar problem a few years ago that turned out to be a nut/bolt on the swing plate on one side had loosened and fallen out.

[Matt Monson]

Originally Posted by DaytonaCoupe66

Hey Kevin; thank you for the comments. I added the Kendal with LSD purchased from our host in the spring of 2020, then added a small bottle of GM LSD additive a few weeks ago. No change. I'll hope that some of the scheduled maintenance items this winter will hit the mark. Cheers....Denis

Change you oil. LSD additives are friction modifiers. That much LSD additive will be way too slippery for your synchros and will wear them out prematurely.

A worn out ZF lsd usually acts like an open diff. It’s unlikely the lsd is the problem unless it’s got broken gears inside of it. I don’t even make replacement clutches for them anymore because so many of them have bad gears or bad housings and really the whole unit is due to be thrown out.

[DaytonaCoupe66]

A great suggestion Flightlead; I'll give the swing plates a check. I may be way off in what I suspect.

Matt; I don't think the car was abused (broken gears?), based on previous ownership but this is only a faith based opinion. Who knows. I'll drain the gear oil - I've only taken one local trip since doubling up on the additive.

Much appreciated!

[DaytonaCoupe66]

"Its a wild shot in the dark but I had a very similar problem a few years ago that turned out to be a nut/bolt on the swing plate on one side had loosened and fallen out".

Working down the checklist of possibilities I took the car in for an alignment as the driver side rear tire is scrubbing off the rubber on the outer edge, and confirmed that the numbers are off. The mechanic did find an issue with the left side trailing arm, and couldn't complete the alignment. The aluminum casting edge/end that captures what I believe is the toe eccentric bolt is broken off. No other damage to this area is evident so perhaps caused by a pry bar or hammer? Geez. I ordered a new trailing arm from the Dealer. Ouch on the price. The few used units available cost almost as much as new.

Looks like a sporting job to get the old one out and new one in, but at least I don't have the remove the old bearings; and, there's no decision to make on whether to do the rear bearings while it's on or off the car.

Photo of the right side that is OK, and left side that isn't. The picture isn't the greatest quality, but tells the story.

Cheers

[stownsen914]

Yikes, sorry to hear. Someone beat the crap out of that.

[DaytonaCoupe66]

I removed the banana/trailing arm left side. No trouble with the upper bolt as the nut was on the transmission side and the bolt on the wheel side so enough room to get sockets in. Surprisingly no more than 25 ft/lb on the nut.

Pics show the damage clearly. The bearing has very limited axial play and turns smoothly.

But, the bolts that affix the trailing arm to the spring plate were also not tightly torqued (likely 25 ft/lb max), and the photo shows some friction wear on the threads.

What's the chance that the rear left wheel mounting points have been sloppy enough to allow chatter under torque on corners, causing the vibration? Thinking out loud, and of course remaining hopeful that this may be the problem.

New trailing arm will hopefully be here this week. I tried to get the hub off the arm with a slide hammer but no go. I'll look for a sized metal tube to pound it out from the back as per the manual.

The info on this site has been a great help!

Cheer.

[DaytonaCoupe66]

Can't get a pic to load into the last window so adding this one.

[Matt Monson]

Yikes.

[DaytonaCoupe66]

The new trailing arm sure is purdy. Actually less $$ from the dealer than what I could find on flea bay used, by the time exchange and shipping are added. Also peace of mind that the part is perfect.

Now to clean up the parts being transferred, new bearings, grease seals, and crush sleeve, and get it installed. I'll find a non-amateur to help me with the final torqueing. I've done enough crying over this part.

[Gianni at Pelican Parts]

Happy you were able to properly diagnose the problem and start the process of fixing it. Thanks for the "shot in the dark" flightlead.