Lucas oil in a manual trans

[FundamentalyConfused]

I have a 1990 Legacy L sedan manual trans and I was wondering if I could put Lucas oil in the trans.

[Legacy777]

Is there a reason you're wanting to put it in there?

I've played with additives over the years and for the most part, end up going back to just the appropriate oil for the application.

[FundamentalyConfused]

I've used Lucas engine and trans oils in my GM vehicles and it helped smooth out the car.

There's a noise coming from the trans, I can't describe it, I only hear it when the clutch is out and in gear. When I press in the clutch the noise goes away. I thought that adding some Lucas might help with the noise.

I went ahead and switched my Subaru over to synthetic fluids. I don't know what was in it before I changed the oils but it was dirty. Changing the trans fluid did help with making shifting easier.

My first thought on the noise was it might be the throwout bearing but isn't that supposed to not make noise when the clutch is engaged?

[Legacy777]

So if the clutch is out, not in gear, and the car stopped, you don't hear the noise? Does the pitch of the noise change with engine speed or road speed?

It may be a bearing or something internal to the transmission. The transmission in my Impreza has kind of been noisy like that. I've just ignored, and it's been ok for several years. I first noticed it after changing the fluid from regular to a mix of synthetic blend. These transmissions tend to like regular oil over synthetic.

You can try putting in the lucas oil and see if it helps.

[FundamentalyConfused]

The noise was there before I did the fluid change. The user manual came with the car and it said go with a 75W-90 gear oil. The least expensive and closest thing I could find was Valvoline 80W-90, I figure that should be good enough. The noise didn't seem to change any after the fluid change.

So if the clutch is out, not in gear, and the car stopped, you don't hear the noise?

Correct.

Does the pitch of the noise change with engine speed or road speed?

I'm not sure. I want to say yes but I can't really tell because the cocktail of NVH+bad shocks+miss matched tires makes it difficult to tell after picking up speed.

[Legacy777]

I think you may have eluded to a possible cause. Do you have different tires on all four wheels or just one that is mis-matched. According to Subaru the tires should be within 1/4" circumference of each other. I'd suggest measuring them to see how far off they are from each other. This issue could be causing added stress to the center diff viscous coupling.

Try and listen to see if you can hear any more specifics on the noise.

Do you experience any torque bind or shudder when taking slow tight turns?

[FundamentalyConfused]

I'll have to go measure the tires, they're all the same size but 3 different manufacturers. The ones on the front are the matching pair. They were on the car when I bought it. I do know that I need all 4 tires to be matching or the exact same size because of the AWD. That has been out of my budget for a while.

I haven't been driving an AWD long enough to know what torque bind feels like and I haven't done many slow tight turns, I'll have to try that out in the nearby parking lot.

The only thing I've done with the tires was to take and put the matching pair on the front. They were originally on the drivers side and I don't remember if it was making that noise before I juggled the tires.

[Legacy777]

What I'd suggest doing is measure the tires with a string. Drive over the string and then measure the distance on the string. Every tire will deform differently under load, so one tire may deform more than another, which will affect contact patch and overall circumference.

[FundamentalyConfused]

I didn't get a chance to do the tire check yet but when I went out a little while ago I paid attention to the sound and it is making the sound when not in gear, it's quieter and harder to notice when not in gear.

[Legacy777]

Does it go away when you depress the clutch?

Listen carefully when you depress the clutch and see if you can hear gear teeth come to a stop when you depress the clutch.

[FundamentalyConfused]

So if the clutch is engaged the teeth will be spinning?

[Legacy777]

Yes, with the clutch engaged, the main shaft will continue to spin.

Here's a diagram of the trans and blow up of the main shaft.

http://www.main.experiencetherave.com/s ... iption.jpg
http://www.main.experiencetherave.com/s ... t_assy.jpg

[FundamentalyConfused]

So the ending diagnosis is there is a faint noise when not in gear and with the clutch out. The noise is louder to me when the car is in motion and the clutch is out. There is no noise when the clutch is engaged either stopped or when in motion.
The noise was present before a fluid change to 100% synthetic Valvoline 80W-90 and there was no change in the noise after the fluid change.

I do remember that there was about a half inch thick of metal/sludge, mostly sludge, buildup on the drain plug. It appears to be a magnetic one. Perhaps it really is just a bearing going bad.

I think the only way I'll really find out what it is is if I took it to my trans guy.

[Legacy777]

If you hear noise when the clutch is depressed, ie trans main shaft not spinning, then the problem is most likely the throw out bearing or pilot bearing (most likely throw out bearing).

[FundamentalyConfused]

Great, looks like I need to find a new clutch kit then.

[Legacy777]

Honestly, I'd just keep running it until the noise gets worse, especially if the clutch is fine.

[FundamentalyConfused]

Run it till she pukes eh? I can do that, lol.

[Legacy777]

Maybe not until it completely dies, but at least until it gets worse....that way there's less likely a chance it will leave you stranded somewhere.

[MeinKreuz]

It's definitively the throw out bearing, if it was the pilot bearing it would be squealing all the time, or you would have some pretty rough clutch chatter. I've ran into this problem with one of my trucks. When you push the clutch in it puts pressure on the bearing and quiets it. Your best bet is run it til she blows. You can pick a new clutch up that usually comes with the pilot bearing, throw-out bearing, clutch plate, pressure plate and alignment tool for pretty cheap. Usually the only thing with this is the bearing makes a really nasty noise and gets pretty annoying, but you could still drive on it. Good luck

[FundamentalyConfused]

Thanks for all your input guys.

My plan is to pick up a new clutch kit and have it ready for when the current one goes out.

That's a bit of stress off my mind not having to worry about doing that job right away.