Check Rear Main Seal?

[tjswarbrick]

N55 135i 6MT with ~107k miles. Mild tune (MHD 91 octane Stage 1.)

Just had 3 oil leaks repaired last month: oil pan gasket, valve cover, and a lower oil line (near turbo).

A couple years ago, on a fairly hard launch (3k rpm, quick clutch engagement,) I got slippage instead of motion, and the new C7 got away.
Never happened again.

A few months ago, clutch would occasionally slip upon hard application of throttle from ~3k rpm cruise in 4th or 5th. Didn't happen in lower gears, and 6th held fine. Weird. Not all the time, but a couple times a week. Shifts were fine.
Had those oil leaks repaired. Clutch seemed just dandy, until yesterday, on the return leg of a 600mi round trip weekend.
6th gear, ~2500rpm. Went for a pass, got revs, but no speed. Backed off, it caught, and off I went. Over the course of my 250mi highway slog it probably happened 3 times, but also didn't happen 3 times (laid into it, and it just pulled properly.) After the third instance of slippage I decided to set the CC and just cruise in the last 150 or so miles. Traffic, shifts, passing from a lower gear, and gentle pulls from 6th posed no problem.

I'm wondering if, perhaps, I've got a leaky (rear main?) seal letting some oil come in contact with the clutch.

Anybody know if there's a good way to check, without a teardown?

Would it even do any good to know? If the clutch has wear left in it, but is oil contaminated, does it still need replacement?

I'm figuring I'll drop in a 335is/550i clutch (and new rear main seal) when the time comes, but the credit card hasn't recovered from the oil leak repairs, so I really hope the time is not now.

All help and insight is appreciated!

[The Wind Breezes]

Don't even worry about it, you don't want to change that. Especially if you're asking this.

[tjswarbrick]

I'm not gonna change it. I perform bolt-on mods, but would have my mechanic do it. Probably doesn't matter - most people seem to recommend doing so at clutch replacement time. I'm just trying to figure out if my time has truly come.
I guess what I really want to know is, is there any point in having him perform some sort of inspection to see if the seal could be the culprit.
Thanks.

[chris_flies]

You can generally tell by looking at the area where the transmission meets the engine. You might see some oil residue down there. If there is, clean it off and monitor it over a week or so (if it gets oily again, you know the culprit). If your clutch is slipping, I'd definitely take care of it sooner rather than later, you don't want to find yourself in a situation where you need to go and then you can't; things tend to change very quickly on roads.

Side note: my dad's 2017 GTI started slipping its clutch at just 24k miles on stock power. He could consistently replicate it, but, no matter how hard I tried, it wouldn't slip for me . It sketched him out big-time, and he got it taken care of by the end of the next week. EDIT: It also had a leaking rear main seal because if an issue with the robotic installation at the factory.

[JimD]

Clutches also slip when the pressure plate is not putting enough pressure on the clutch and when the clutch is worn out and the rivets start to touch. Looking for oil as Chris suggests makes sense but if you want to save the pressure plate I wouldn't wait long (if it's the rivets touching it's probably happening to the pressure plate too).

The only car I've had that had a slipping clutch was a Mazda 626 that my late wife bought - her only new car purchase. If she had waited a couple weeks, she could have purchased an automatic which she like better for about the same price but instead she got the manual. She drove it fine, not quickly and not always gracefully but fine. I drove it when we were going somewhere. I noticed one day that the clutch was slipping as I accelerated. It had a little NA four cylinder so I was really surprised. Only about 60K miles. We had the clutch replaced and the pressure plate was fine, the clutch was not worn completely out. I gave the car to my son when she died and he put two more clutches in it. He changed the pressure plate two on the second one and it was working fine when he sold it - with about 250K miles.

Only significance to that story for you is that it is worthwhile to get to the bottom of slipping clutches and it may not be what it appears to be. If you have it done, I would want to see the parts replaced and to check the pressure plate if it is not being replaced. Rear mains seem to last a long time, really long time, these days but that is good questioning attitude too.

last thought, my old rule of thumb for clutches was 100K miles. I haven't had to replace one at that point, however, but I would try and check them. But my last several vehicles have gone up to around 150K on the original clutch and were working fine when we got rid of them. But the clutch life depends a lot on how you drive. Needing a clutch at 100K miles would not be terribly surprising, especially with your hp increase (even though only stage 1) and with what seems like fairly spirited driving.

[tjswarbrick]

Except for a couple (torturous) years ~2010 when my kids were little, I've ALWAYS had a manual.
Beginning in 1984 with a couple YZ80's.
Replaced 1 clutch in a Dodge Colt I had for about 60,000 miles, 0 in my first new car - Sentra SE-R that I held on to for 88k mi; 3 in the Jetta GLX I had for 10 years and 160,000 miles (that was nuts. 1st and last lasted over 60k mi each; 2nd one barely made it 20,000 miles. Perhaps they didn't do the pressure plate on that one), and 1 in the Hyundai Tiburon I tried for a couple years while finishing up my degree.

Generally, once they start going, they're pretty consistent and I could get another couple months out of 'em before slippage becomes uncontrollable.
Put the 1'er to the test twice on the drive home last night, and once this morning on the way in. 2500-3000 rpm in 6th. Nail it until the boost comes on strong and velocity becomes excessive. No slip.

I know it's self-adjusting. I do wonder if it slips a bit, senses wear, adjusts, is good for a bit longer, and repeats.

I know it'll need replacement sooner rather than later, but hate to do so prematurely.
The biggest expense is labor. I'll definitely go for the full kit which includes disc, pressure plate, throwout bearing, fork lever and bolts. And do the seal at the same time as is so often recommended for this powertrain.
I'm more concerned about being able to re-use the DMFW. Those buggers are not cheap.

[Dackelone]

I would have the transmission fluid level checked. Could be low. ? Maybe even have it changed.

The California Transmission Supply Company sells kits of the ZF boxes... but I am not sure about the 7 speed DSG box. ? I would contact them for some advice on a trans fluid kit.


https://www.thectsc.com/catalog/trans-fluid-56.html


I don't think your rear mail seal is leaking. I mean it could be... but its quite rare. I would clean off the underside of the engine and check for leaks. You can use a UV dye for the engine oil to see IF you have a rear main seal and use a cheap UV led test light to look for leaks.

Dack

[dtla1]

Originally Posted by Dackelone

I would have the transmission fluid level checked. Could be low. ? Maybe even have it changed.

The California Transmission Supply Company sells kits of the ZF boxes... but I am not sure about the 7 speed DSG box. ? I would contact them for some advice on a trans fluid kit.


https://www.thectsc.com/catalog/trans-fluid-56.html


I don't think your rear mail seal is leaking. I mean it could be... but its quite rare. I would clean off the underside of the engine and check for leaks. You can use a UV dye for the engine oil to see IF you have a rear main seal and use a cheap UV led test light to look for leaks.

Dack

Not as rare for the RMS to leak as you might think Dack. I had mine replaced (under warranty thank goodness) somewhere around 50-60k miles. And I also remember seeing tons of threads about it at the time. It's as much of a pain as changing the seal at the mechatronics sleeve on DCT cars, transmissions gotta come out.

[tjswarbrick]

Originally Posted by Dackelone

I would have the transmission fluid level checked. Could be low. ? Maybe even have it changed.

The California Transmission Supply Company sells kits of the ZF boxes... but I am not sure about the 7 speed DSG box. ? I would contact them for some advice on a trans fluid kit.


https://www.thectsc.com/catalog/trans-fluid-56.html


I don't think your rear mail seal is leaking. I mean it could be... but its quite rare. I would clean off the underside of the engine and check for leaks. You can use a UV dye for the engine oil to see IF you have a rear main seal and use a cheap UV led test light to look for leaks.

Dack

After the OFH went 2 years ago, cheap filter spewed oil last year, and the latest 3 leaks - the underside of the engine is a MESS. Do have a couple cans of engine degreaser - suppose it's time to get to work.
I do have 2 bottles of the dye, as well. I'll try to get down there and clean up / check things out.
Replaced the tranny fluid with Redline ATF 2 years ago, and level checked last summer. All was fine. Wouldn't hurt to get another looksee, I suppose, but it shifts brilliantly.

[Horigan]

I had a mild rear main seal leak that we monitored, then ended up addressing when the clutch started slipping as you describe. Replaced the rear seal, clutch, and pressure plate. All good now. The leak is apparent if you look at the bottom of the engine/transmission interface.

[chris_flies]

Originally Posted by tjswarbrick

The biggest expense is labor. I'll definitely go for the full kit which includes disc, pressure plate, throwout bearing, fork lever and bolts. And do the seal at the same time as is so often recommended for this powertrain.
I'm more concerned about being able to re-use the DMFW. Those buggers are not cheap.

For the 128i, Valeo (a BMW OEM) makes a single-mass flywheel conversion (not lightweight). I don't know about fitments for the 135i, but that'd be a great route for future longevity when you eventually replace the clutch.

[tjswarbrick]

Made an appointment for 110k service (SES light was on), oil change, brake flush, and clutch slippage investigation.
New shop to me, but well respected locally for top-notch service, long labor warranty, and they tune/race too.
Just had an interesting chat with an advisor/mechanic:

a) He advised that GC 0w40 is "kinda thin" and he prefers something thicker "like 10w30." But that isn't thicker when it's hot! (I explained that I've been happy with the 0w40 (GC only), and Blackstone has come back clean, safe, and recommending fairly long intervals (8k mi) so I'm happy. Says they use 20w-60 in race cars. Mine is not raced - just spirited street driving. And not an Sxx engine - just an N55. They'll put in the 0w40 at my request, but recommend 5w30 or 10w30.

b) Wanted to know my weight, preferred specs, and likely use to set the alignment. That sounds good.

c) Said the oil change, inspection, brake flush and clutch inspection is a full day. Clutch R&R, if needed, is another day! Also - they do the flywheel with clutch every time (BMW recommended procedure), but don't do the rear main seal unless it's leaking.
(I'm going with 335is/550i clutch "upgrade" regardless.)
Seems most on here like to do the seal during clutch job since it's accessible and good preventative maintenance. I tend to concur.

4) These are the guys who told me last week "If your SES light is on and your clutch is slipping, don't drive the car!"
Clutch has been slipping, only under full throttle in top gear, for several months. If I don't get on it, it hooks up fine.
SES light is not "Check Engine" light - it's "Service Soon." Also turned itself off today for some reason.

Oh, since it's my DD, for stock-like action and no chatter I'm going to pass on the SM FW. Would love to spring for a lighter DMFW option - 1M unit costs the same; weighs, what, 4lb less; bolts up with same 6-bolt pattern. But it seems the bearing interface between the flywheel and crank are different, so it wouldn't work.

Trying to figure out if I should suck it up, take their advice and use the warranty if it doesn't work out; stop second-guessing myself and do what I feel is right; or find another shop whose procedures and values align more with my own. (I'm not a mechanic, but it's always fun to try to think like one.)

Thoughts?