Vibration when turning tightly with factory LSD equipped '87 911

iwhelan · iwhelan's Garage

Hello everyone,

I've done some reading on this and have seen different opinions, but here goes. I have an '87 911 with G50 and factory LSD. I don't know what oil was in the gearbox when I purchased the car a few years ago so last year I changed the oil to Mobil Delvac that is recommended by some. The shifts are a bit smoother, so that part of it is great. However, when turning tightly I get a bit of vibration until I get the car going mostly straight, like out of a driveway or tight intersection Obviously the LSD is not slipping very much and the LSD is trying to do eagerly do its job when its not quite necessary.

I've read that some people add a slip additive to reduce this issue, but I can live with it as long as nothing bad is happening, like premature wear on the LSD clutches. Can anyone weigh in on this? I have read other accounts that they don't feel this issue with their own factory LSD. I'm not sure if this gearbox has ever been apart, as the car only had 79k miles on it when I bought it and is in excellent condition.

Thoughts? Thanks.

Trakrat · 07-26-2017, 12:42 PM

Does it happen when turning in both directions?
Does it happen when going in reverse in both directions?
Where are you feeling the vibration at?
Can you test turning it in neutral with the engine off? (have someone push it while you turn)

iwhelan · iwhelan's Garage

Btw, it was not happening with the previous oil, so that one may have had a friction modifier in it.

I believe that it is happening when turning in both directions. I don't recall it happening in reverse, but maybe I wasn't turning sharply enough. I'm feeling the vibration through the whole car, and even my passenger can feel it.

I'll have to try it in neutral with the engine off. I haven't tried that yet.

Thanks.

manbridge 74 · 07-26-2017, 01:07 PM

I would check CV bolt torque pronto.

iwhelan · iwhelan's Garage

I can check that soon, thanks.

Btw, I also don't recall it happening when pulling into parking spots, even if they're tight. It's mostly when applying power, like pulling out onto a road from a driveway or a red light.

Cook&Dunning · 07-26-2017, 02:13 PM

I have fresh Delvac in my 89 with motorsport lsd. I also added 1 bottle of Kendall lsd additive. When the gear oil is cold, and I do low speed tight turns, it is slightly noticeable - not chatter, not crunchy, but a slight shudder - if that is a way to describe it. Once warmed up - and that may be 15+ minutes of normal driving for me - all is good.

I have read a bunch - maybe all - of the gear oil threads here - and there are guys that have forgotten more than I will ever know about gear oil - but my takeaway was Delvac is great for the track - and there may also be more suitable products for the street. Also - when I first changed out the oil, I drove it for a short stint without additive, and there was definitely some vibration / shudder - pick your descriptor - note gear oil was cold, and I did not travel far enough to warm it up.

iwhelan · iwhelan's Garage

Thanks for that info Vince! Its funny, I can remember it more clearly happening in instances when the oil was probably cold. I can't remember for sure if it was happening once warmed up, because how many times am I really turning that tightly? I will have to verify this weekend when I drive the car.

It is a shutter like you described. I don't mind this effect if its not causing any problems, as it happens so infrequently.

Is there anything different about the motorsport LSD?

Thanks,
Ian

Cook&Dunning · 07-26-2017, 02:58 PM

Hello Ian - I hope some experts will chime in on which LS differential is the best - again I am not the expert - my car has a Porsche Motorsport LSD, not the original factory option version. My sense - again from reading here - is the motorsport lsd is not the best, and that all of these have a shelf life.

Maybe all you need is a bottle of additive?

shrtshck · 07-26-2017, 04:52 PM

Experienced same issue after changing the oil in my 87 LSD, a bottle of the friction modifier resolved the issue.

Techno Duck · Techno Duck's Garage

I added about 1/2 bottle of Redline Friction modifier to Redline 75w90NS. It is silent now. Previously, tight turns were very loud and could be felt in the seat of my pants.

G50 with LSD gear oil

Matt Monson · 07-26-2017, 05:58 PM

Delvac can be pretty chattery on those old lsds. An ounce of friction modifier will generally resolve it. Or Swepco 203 with moly if it's a street car rarely driven in anger.

iwhelan · iwhelan's Garage

Thanks for the insight everyone. The big question is whether adding the friction modifier is just to reduce the vibration / shutter or am I actually going to prevent premature wear on the LSD clutches?

If there's no issue with leaving it as-is, I might consider that since it's not that big of a problem.

Also, I don't want to add extra wear to the syncros by adding the modifier. I wonder about the usage of this in a gearbox w/LSD vs using in a completely separate rear-end differential.

If I do add a bit of friction modifier, what's the best one for delvac? Kendall, Redline?

Thanks,
Ian

Matt Monson · 07-27-2017, 07:06 AM

Don't overthink it.

wayne robson · wayne robson's Garage

iwhelan, good advice is to do what others have said, add a bottle of additive
since you drained the old oil, that probably had it in originally .
Any vibration or chattering that can be herd or felt in your car is not good
and can only get worse if not corrected.
Years ago with GM classics Chevrolets Buicks i have owned with LSD
additive, i always used ,infact GM sells a good one,i an not advising is ok for
Porsche, came in a 4 oz bottle, but get a bottle that is approved for Porsche
and use ,to keep your 911 running smooth.

tcar · 07-28-2017, 07:46 AM

Quote:

Originally Posted by iwhelan

... whether adding the friction modifier is just to reduce the vibration / shutter ...

It should decrease SHUDDER... and help the clutches... if that's the issue.

(I have shutters on my windows....

)

Also, try the other tests mentioned above... hot cold, reverse, power off.

Does it stop when you press the clutch pedal?

Could be a CV issue also.

iwhelan · iwhelan's Garage

Thanks for the comments, everyone.

Good point about the shudder vs shutters!

I'll have to see if happens with the clutch in. It happens so briefly because before you know it you're not turning anymore and then that's that.

I understand about the CV issue, but it seems like that would be a coincidence since it started post oil change.

Also, I respect what you guys are saying about adding the friction modifier, but I also see accounts of people who have run LSDs without modifiers without any problem for years and years. They're saying the modifier is just to reduce NVH (noise, vibration, harshness).

Anyway, I'll see if it is happening once the oil warms up, with power off, in reverse, etc. That's a good starting point!

Peter Zimmermann · 03:12 PM

Use Kendall additive, and don't look back. The additive comes in 4 oz bottles, and the rule of thumb is generally 1 oz/pint, so you'll need about one and a half bottles. That'll quiet things down, and will not hurt the life expectancy of the synchros, but might add years to the life of your LSD. BTW; Kendall also makes a terrific synthetic gear oil, 75W/90, for future consideration to use in your G 50.