Author Topic: 3.27 diff vent seeping  (Read 24758 times)

awolff280sl

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3.27 diff vent seeping
« on: October 05, 2008, 19:28:03 »
I have been doing some high speed driving with my recently installed 3.27 rear end. After the drives, I have noticed some hypoid leaking down from the diff vent. The rest of the diff is dry, and the vent is screwed down tight, so I think the oil is "perculating" up through the vent. I was careful not to overfill the diff with oil, having filled it with the rear wheels on the ground.
Has anyone else seen this? Given how hot the diff is to the touch after these drives, I wonder if it's not surprising to find some oil "boiling" out of the vent?
Andy   Sarasota, FL
'69 280SL 4speed
'06 Mitsubishi Evo

DavidBrough

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Re: 3.27 diff vent seeping
« Reply #1 on: October 06, 2008, 05:53:12 »
Hi Andy,

I had a similar problem with my 3.46 axle which leaked quite badly from the breather on the top of the diff. When I first installed the axle I removed the large breather pipe and plugged the holes as many others had done but the only way I found to cure the leak was to have the left rear chassis modified and re fit the breather. I have now covered about 2,500 miles with no leaks at all.

Have a look at my post and photos from 21 June:-

http://index.php?topic=8490.46



David Brough
1969 280SL Auto with A/C & 3.46 Axle


Garry

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Re: 3.27 diff vent seeping
« Reply #2 on: October 06, 2008, 06:13:43 »
Hi David,

I have just got my car back after fitting the 3.46 diff and I notice that I have a small leak from the removed breather tube outlets.  There is a pool of about 3" under the car after I took it for a drive of about 150 miles at the weekend.  Am keeping an eye on it at this point and hoping that it will settle down.  How much leaked did you get from your diff before you made the decision to re fit the breather.

Other than that the change is fantastic and really makes it a real pleasure to drive now.

Andy, I felt the Diff whilst under there looking at the leak after driving it mainly on open road at 60 mph + and it was not 'hot' at all.
« Last Edit: October 06, 2008, 06:16:32 by Garry »
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awolff280sl

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Re: 3.27 diff vent seeping
« Reply #3 on: October 06, 2008, 07:32:31 »
David,
Looks like I've got the same problem. Did you investigate altering the cooling tube itself rather than making a chassis mod?

Garry,
The several mechanics I've spoken with say that it's normal for the diff to be hot after high speed driving. I hope that's reliable information, though.
Andy   Sarasota, FL
'69 280SL 4speed
'06 Mitsubishi Evo

DavidBrough

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Re: 3.27 diff vent seeping
« Reply #4 on: October 07, 2008, 01:05:16 »
I did look at some sort of modified breather and did try a flexible one first but there just wasn’t enough space and it rubbed on the chassis. I then thought of a smaller bore custom one but that would have been very convoluted to fit and I wasn’t sure if a much smaller bore would still work. What swung it for me was that our UK Pagoda specialists said they always modify the chassis and fit the breather with these axles and they did the mod quickly and cheaply and all is now well.

Mine only leaked when on the move and only from the breather on top of the diff, any leak from the breather plugs should just be a simple sealing issue. I found that only small drops of oil actually reached the floor as most was smeared all over the diff, axle, fuel tank and rear valance from leaks at speed which then dripped to the floor when stopped from just about everywhere at the back. It is surprising just how much mess a small amount of leaking oil will make as there was no real discernable drop in the diff oil level.

I do have to say though that this change makes such a difference and I can’t understand what the original engineers were thinking when they took out the 3.69 diff and replaced it with a 3.92 for the 280. Still, it was the same people that thought it would be a good idea to fit such an unusable first gear in the auto they then had to make it start in second and still had the audacity to call it a 4 speed.
 
David Brough
1969 280SL Auto with A/C & 3.46 Axle


awolff280sl

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Re: 3.27 diff vent seeping
« Reply #5 on: October 07, 2008, 05:08:22 »
From what I'm learning, this diff vent leak issue is so variable among rear end conversions, some have it, some don't; and the reason for this variability is not known.
While I'm learning to live with it (and it's really not all that bad, mostly an affront to perfectionism), I've been playing around with small changes in the diff oil level and using synthetic hypoid oil.
I noticed that even when I filled the oil to the bottom edge of the fill hole with the diff cold and then drove the car, oil would still drip significantly from the fill hole when the plug was subsequently removed. I figure expansion of the oil volume from heat.
With the oil level filled cold to about 1-2cm below the bottom edge of the fill hole, I have no leak from the vent...yet. I would not expect this small difference in oil volume to leave the gears under-lubricated.
Andy   Sarasota, FL
'69 280SL 4speed
'06 Mitsubishi Evo

awolff280sl

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Re: 3.27 diff vent seeping
« Reply #6 on: November 15, 2008, 16:16:17 »
Diff vent seepage eliminated. I installed an oil tolerant, large diameter/thick walled, flexible hose to substitute for the rigid "cooling" pipe. Had to come off the fixed axle side with a 45 degree adapter (indexed to point downward once fully tightened) to avoid hitting the chassis. No leaks along the hose nor at the diff vent. May be a solution for those with the diff vent leak problem that avoids cutting on the chassis.
Andy   Sarasota, FL
'69 280SL 4speed
'06 Mitsubishi Evo

Naj ✝︎

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Re: 3.27 diff vent seeping
« Reply #7 on: November 15, 2008, 17:09:06 »
Andy.

Coukd you post a picture of your new pipe, thanks

naj
« Last Edit: November 15, 2008, 17:12:30 by naj »
68 280SL

awolff280sl

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Re: 3.27 diff vent seeping
« Reply #8 on: November 15, 2008, 20:15:11 »
Here are pictures, broken up into 2 postings. Don't know if you can embed in postings?
Andy   Sarasota, FL
'69 280SL 4speed
'06 Mitsubishi Evo

awolff280sl

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Re: 3.27 diff vent seeping
« Reply #9 on: November 15, 2008, 20:16:13 »
More pictures
Andy   Sarasota, FL
'69 280SL 4speed
'06 Mitsubishi Evo

awolff280sl

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Re: 3.27 diff vent seeping
« Reply #10 on: November 15, 2008, 20:17:35 »
Automatically embeds a thumbnail, cool!
Andy   Sarasota, FL
'69 280SL 4speed
'06 Mitsubishi Evo

Naj ✝︎

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Re: 3.27 diff vent seeping
« Reply #11 on: November 15, 2008, 20:30:08 »
Thanks, Andy.  ;D

naj
68 280SL

hank sound

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Re: 3.27 diff vent seeping
« Reply #12 on: February 09, 2012, 21:53:11 »
Hi Andy,

We'll be installing a 3.27 rear end in my 69 SL, and I'm going to follow your lead as regards the flexible cooling tube.   As good fortune would have it, there is a shop within less than a mile from me here in Burbank that can measure the fittings from the old "U" pipe, incorporate the 45 degree angle fitting and recreate the complete hose for me.

My question - - about how long is your rubber cooling hose?

Cheers & thanks much,

Hank




awolff280sl

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Re: 3.27 diff vent seeping
« Reply #13 on: February 09, 2012, 23:16:12 »
The hose is about the same length as the pipe. One of the problems to avoid is flattening of the hose where it loops back 180 degrees. The proper length will lessen this tendency, but I subsequently went back and slid on a Unicoil to keep the hose nice and round at the bend.
Check here: http://www.gates.com/europe/brochure.cfm?brochure=7718&location_id=11377
You can find them in most sizes in most auto parts stores.
I've also used a Unicoil under the PS reservoir b/o that short hose that tends to flatten.
They work great.
Andy   Sarasota, FL
'69 280SL 4speed
'06 Mitsubishi Evo

hank sound

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Re: 3.27 diff vent seeping
« Reply #14 on: February 10, 2012, 01:01:46 »
 ;D

Well, there you have it !!   The engineers @ MB figured they needed to have a cooling tube in that rear end - and Andy figured out how to make it all work in the W113.   Of course, I'll include the Unicoil feature as well.

Thanks mate,  Hank

awolff280sl

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Re: 3.27 diff vent seeping
« Reply #15 on: February 10, 2012, 03:25:29 »
The so-called "cooling" pipe may in reality be a pressure equalizing device, ie it serves to reduce oil pressure within the diff by providing a shunt off to the axle tube.
That said, after a high speed drive my diff is very hot. and I wonder if it would be that hot if a metal "cooling" pipe was there instead.
Andy   Sarasota, FL
'69 280SL 4speed
'06 Mitsubishi Evo

hank sound

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Re: 3.27 diff vent seeping
« Reply #16 on: February 10, 2012, 03:58:26 »
I wonder how hot it would be if you didn't have anything but plugs in place of the metal pipe.  Honestly, I don't think any demons currently lurk in the 3.27 rear end of your car.  

What the hey, yo - did this thread inspire you to go feeling around your car's rear end :):) after a spirited drive........... just for fun?   But I like the fact that you're looking for perfection.   My take, is that you've come up with a totally viable approach to this particular issue associated with a diff swap.   

The company that will make my "diff hose", makes hoses for heavy industry.    I will approach them regarding group pricing on this item.

Cheers, Hank

« Last Edit: February 10, 2012, 04:07:57 by hank sound »

Benz Dr.

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Re: 3.27 diff vent seeping
« Reply #17 on: February 10, 2012, 13:28:24 »
The pipe is for cooling the rear axle lube in the heavier 4.5  The lighter 280SL shouldn't need this tube at all. A rubber hose won't provide much in the way of cooling compared to a metal one.
« Last Edit: March 16, 2017, 18:09:06 by Benz Dr. »
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hank sound

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Re: 3.27 diff vent seeping
« Reply #18 on: February 10, 2012, 14:04:45 »
Hi Dan,

Well, why then does this thread exist in the first place?   Later today, I'll ask one of the techs at the hydraulics hose shop for their take on this subject, and I'll post their thoughts.

Cheers, Hank

GGR

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Re: 3.27 diff vent seeping
« Reply #19 on: February 10, 2012, 18:02:36 »
Could someone post a picture of the chasssis modification needed to fit the original tube ? The one a few posts above is not available anymore.

Another question : I have a 3,27 on my W111 Coupe with the cooling pipe fitted. I have slightly overfilled the rear end with three quarts instead of 2.5L (overfilled by 0.4L). I first had no problem but I then drove the car on the highway with a lot of weight in the trunk (temporarily) provoking a strong negative camber. When I reached home I noted the diff was all wet in oil, with a drip coming from up. I guess it's from the vent. Can the combination of overfill and negative camber (therefore sending all the oil that are in the tubes towards the diff) provoke a seapage, even with the cooling tube in place ?

Thanks !

pagoden

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Re: 3.27 diff vent seeping
« Reply #20 on: February 11, 2012, 06:15:30 »
Yeah, it doesn't take much to overfill them; care must be taken to level the diff both ways as well as keep the camber close to zero.  And somewhere in the older books I think there's a specified time to let it set after filling, with the fill-cap still removed, in order to allow any overfill to overcome the meniscus effect and drain out.  [On reflection, that's probably from transaxles, not our diffs, but it is so German, n.v.?  There's also a spec timing the rate of drips when draining engine oil during a change procedure, like when it slowed to no more than x number of drips in a minute you could consider it drained.]  Probably best to underfill it very slightly if anything; if you "settle' the car a little after filling, the slight loss of camber should do it.  It's one of those times to let things 'breathe' a bit in between.  There's a filtered vent to atmosphere up near TDC and centerline.

Love what you're doing with those cars,
Denny
1968/69 280SL, just+100k mi, manual 4, 3.46, both tops, 717/904

pagoden

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Re: 3.27 rear end seaping
« Reply #21 on: February 11, 2012, 06:37:10 »

Thanks, Andy; your fix has a lot going for it.  In a lot of searching nationwide over a week or two I could find only one hose product with a diameter suitable for fitting over the existing tube (to be cut off near its fittings) for a solution similar to yours, and that hose was rated for milk.  Getting hydraulic fittings made up to the heavy-duty high pressure hose and then welded to our metric fittings was going to run two or three hundred dollars in our market, so I took Walter's advice and just bent it out of the way, pretty much the way your hose goes.  ["Just" bent it isn't really accurate; it's challenging in the cramped areas upside-down and underneath, and took a goodly portion of my levers and tweakers and odd-shaped wrenches.]  Not pretty but after several re-tightenings of the threaded fittings, no leaks or rubbing in the ensuing few thousand miles.  'Twere more neatly and easily done prior to installing the axle -- and with a torch to smooth things -- but then it's hard to know just where it needs to move to and how much.  [Though two or three swaps ought to teach that.]
It's a much cleaner and more elegant swap with the external circulating tube removed and the holes plugged neatly with M-B oil drain plugs.  And for, let's say, 80% of these swaps that is the way it's done: viola!  Mine looked all nice like that when it left Joe's shop.  By the time I arrived home a day's drive later, at least 75% of the nice new lube was gone, except for what was all over the rear - - underside sopping and outside slick.  So what determines the difference between those of our swaps that blow out their contents and those that don't?  Where's the variable? 
I'd much rather we proactively find and fix it - control the situation at its source - than have to mess around coming up with improvised reactions to unpredictable crisis. 
I'm not at all pleased that I haven't been up to the challenge myself.  I've asked some of the most experienced and respected 113 pros about it with little result.  In Britain they carve off a bit of the understructure to clear the tube. 
Here's a fairly major failure that occurs, apparently randomly, in 20% (?) of one of our largest and most favorite improvements, and we haven't figured it out -- yet.

Yours in motoring happiness,
Denny       ;~) 
1968/69 280SL, just+100k mi, manual 4, 3.46, both tops, 717/904

GGR

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Re: 3.27 diff vent seeping
« Reply #22 on: February 11, 2012, 11:06:20 »
I think the reason for it to happen is that the oil is drawn up by the gear and hits a perpendicular surface where the plug is. Then I guess depending on the oil's properties, it emulsifies more or less and ends up overflowing through the vent. The difference between the lucky and the unlucky ones may be due to oil properties and how fast and how long the car is driven on the highway.

The best solution is to reshape the tube so that it clears the chassis. We should document this as indeed it's easier to do it when the rear end is not in yet.



Love what you're doing with those cars


Thanks ! We're not far from each other. We could meet one day so that I can see on your car what's  involved to clear the chassis with thatt tube, and you could have a drive in my 5.0L coupe and tell me what you think.
« Last Edit: February 11, 2012, 11:13:59 by GGR »

Benz Dr.

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Re: 3.27 diff vent seeping
« Reply #23 on: February 11, 2012, 22:42:04 »
Hi Dan,

Well, why then does this thread exist in the first place?   Later today, I'll ask one of the techs at the hydraulics hose shop for their take on this subject, and I'll post their thoughts.

Cheers, Hank

Why? Because we can.

Rubber insulates. Try placing your hand on the rubber hose near your IP thermostat and then place it on the thermostat housing with the engine fully warmed. Your hand won't stay there very long. In most cases involving gear oil or hydraulic fluids, a rubber hose usually goes to a metal one that goes to a tank or oil cooler. In this case, the oil cooler is the metal tube. The crown gear throws oil off as it spins and some of this oil hits the opening for the tube and runs down until it gets picked up by the crown gear and the cylcle is repeated over again. The crown gear and differential carrier are capable of moving the oil around inside of the axle to the extent that it will keep everything well lubed. The problem withn the 4.5 was the gear oil would get too hot without a cooler.

If you fit a rubber hose so the gear lube can circulate it won't be about cooling. The 4.5 and 280SL have similar power to weight ratios at 16 and 15 to 1 respectively. The 280 engine has more than enough power to push the car down the road with the 3.27 axle so maybe this problem has a different source.
Overfilling is probably 90% of it yet I've seen 3.92 axles that were somewhat overfilled and they didn't really leak out very much. The problem could be something as simple as the 3.27 gear ratio. Lower gearing spins the pinion gear faster but seems to produce less heat because it requires less torque to turn the gears.

I've seen this on tractors. As long as I was running in a low enough gear the fluids inside the transmission and rear axle would run cool. When I tried to run in a higher gear the oil would over heat and I had to stop and let everything cool down. Oil lvel also played a key roll as too low would make it over heat just as quickly as too much fluid. I was running a 155 HP 2WD with a 22 foot cultivator behind me. Conditions were less than ideal so it was pulling hard. This system had an oil cooler in front of the rad.

I think that gear ratio and load ( weight ) play a factor. I'm thinking they placed a cooling tube on the axle because of the gear ratio and the extra heat it would produce. Since the 280SL is almost 1,000 pounds lighter than a 4.5 you really shouldn't need the tube at all. Lower the oil volume slightly in the axle and use a good quality synthetic.   
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

1970  3.5 Coupe
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1985   300CD  Turbo Coupe
1981  300SD
2013  GMC  Sierra
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1967 250SL
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1988 560SEC

hank sound

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Re: 3.27 diff vent seeping
« Reply #24 on: February 12, 2012, 00:54:26 »
WOW - thanks Dan,

"OVERFILL", don't go there !!!    Your post was greatly appreciated - at least a full day's worth in the lecture room !!

Cheers mate,

Hank