rodneybeauchamp

Rear axle flush on ‘38 Special

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OK, so I have drained all the old goop ( brownish oil) from the rear axle and have cleaned out the bottom of the axle  housing as best I could. I’m considering doing a flush as recommended by the shop manual, however I have made up a very nice gasket and resealed the cover. So reluctant to disturb that good work but will remove the lower bolt to drain any flushing oil. Reseal the bolt back with Permatex.

 

Shop manual says SAE 10 or a light flushing oil while running in high gear on stands, ( I can do that)

 

Would Auto trans fluid or diesel fuel oil be a suitable flushing oil as these both have detergent properties?

 

any thoughts please?

 

Rodney 😀😀😀😀😀

 

 

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Not sure you want a detergent oil in the rear end. I would (and just did)  use # 10, it worked well for me.

 

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I think if you just fill it and go you won't have any troubles. I presume that you hosed it down with some solvent or brake cleaner or something while you had it open so anything that's left in there should be pretty benign. Fill with gear oil of your choice (I prefer 140 weight) and you should be good to go. The oils we have to day are vastly superior to those of the past and the parts are very robust. Given the light usage that the cars experience today, it should outlast us all. It's important not to over-think things like this--I did when I changed the gear oil on my '41 and it sidelined the car for more than a year. Get the oil back in it and start having fun!

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I filled mine with diesel and ran it at about 10 mph on jack stands for 30 minutes. Drained it and repeated procedure for another 10 minutes. Refilled with correct oil and 5 years later the oil still looks good.  

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6 hours ago, Matt Harwood said:

I presume that you hosed it down with some solvent or brake cleaner or something while you had it open so anything that's left in there should be pretty benign. 

 

Hi Matt,

thats what I did not do, the shop manual clearly states not to use a solvent such as kerosene or gasoline, so I got out what I could with a rag and my fingers, but still not 100% happy with that. The old stuff was very “goopy”, brown and pretty yuck. Glad I got in there.

 

Was thinking two possibilities, refill with new oil, and run it on stands, then drain and refill. The other was to flush with a lighter oil then refill!

 

4 hours ago, raydurr said:

I filled mine with diesel and ran it at about 10 mph on jack stands for 30 minutes. Drained it and repeated procedure for another 10 minutes. Refilled with correct oil and 5 years later the oil still looks good.  

 

Hi Ray, this was my thoughts too, but see what else is posted.

 

6 hours ago, Jack Welch said:

Not sure you want a detergent oil in the rear end. I would (and just did)  use # 10, it worked well for me.

 

 

Hi Jack, SAE 10 is what is listed in the shop manual, so might look at that. Might buy enough to do the flush twice, but will see what others post.

 

Rodney 😀😀😀😀😀😀😀

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Rodney, careful and do not overfill.  The rear end lube does not lube the wheel bearings. You are probably good to go without flushing but does not hurt to do so as the shop manual sayes.

 

  Ben

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5 hours ago, Ben Bruce aka First Born said:

Rodney, careful and do not overfill.  The rear end lube does not lube the wheel bearings. You are probably good to go without flushing but does not hurt to do so as the shop manual sayes.

 

  Ben

 

Thanks for that advice,  BTW, what would you use as a flushing oil?

Rodney😀😀😀😀

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What do you think the thick stuff you removed was? A semi-fluid grease (or really thick oil) or sludge because the oil was very old, like more than 70 years old (i.e. no- or low-additive oil).

 

If it was very old oil that had turned to sludge, a flush might be in order.

 

But if it were very thick oil or semi fluid grease, like some on these fora recommend - mainly to stop leaks, which is pretty dumb reason to chose an oil - I would just refill with oil of your choice and anything left will be slowly mixed in if it is in a splash or turbulant zone. Remember that the diff. oil is slung about all over the place, creating a sort of thick oil fog, during operation.

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5 hours ago, rodneybeauchamp said:

 

Thanks for that advice,  BTW, what would you use as a flushing oil?

Rodney😀😀😀😀

 

 If anything probably the 10 w mentioned in the manual. If It had already been cleaned as has your's, probably not worry bout it. But then, I have not seen your's.

 

  Ben

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I would use a light colored light weight oil and then when you drain the flush you can see what comes out.  If there is little color change  and no particles coming out, no need for further flushing.

 

Bob Engle

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Just a quick update. 

 

Used a 15W-40 mineral oil to  flush the differential. Popped it on a set of jack stands and ran it in high gear at varying speeds using the hand throttle. Also ran it in reverse for a short time, in total 40minutes.

 

Drained the oil using the bottom bolt and it drained quite nicely as it was a thin oil. Interesting is that after 40 minute run time, the drained oil and the differential were quite cold (ambient temperature about 14-16 C). The drained oil had a brownish colour and a few metallic specks but These were all soft and certainly not harmful.

 

I then repeated the process next day, noticing the colour of the drainant (oil that has be drained) was significantly cleaner and a lighter brown colour, a few flecks of rubbish, but again all soft and insignificant. Again it was cold. Photo shows the two drainants, the one on the RHS jar is first flush.

 

One thing I noticed was that on initial start and running, both rear wheels were turning, then after a short time the LH stopped altogether ( maybe it got tired of going nowhere).

 

On the second flush, the RH side was stationary and the LH was turning. Maybe they take it in turns. 😀😀

 

Replaced the lower bolt and sealed the threads with a Loctite thread sealer (not a locker) 

 

Filled the rear axle with a Penrite Mild EP GL4 hypoid oil and sealed the drain plug with the same Loctite sealer and test run on the stands. It took 3 litres of oil to be just below the drain plug.

 

Will do a road test when I have the manifold gasket replaced.

 

anyway a few photos ( otherwise it never happened) 

 

In hindsight, any light bodied mineral oil will be suitable as a flushing oil, no need to overthink this one at oil! 😀😀😀😀

Rodney

 

 

08864139-FBDE-47E9-9B93-5DE05F4D76CF.jpeg

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C19A3390-3855-43BF-A5AD-080B79CF74D6.jpeg

60A70FBB-B86C-4D21-BC01-07BA9A28CFF3.jpeg

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