Surfer69

I discovered my drivetrain issue is only a TO brg and not the tranny. But when I pulled the magnetic tranny plug to check oil it was covered in metallic sludge. Tranny is removed and I have poured out the old 90w oil but would like to flush the remaining residual oil out also.

Wondering what to use like acetone? Something that wont hurt seals but will remove heavy 90W oil etc.... THX

toobroketoretire

Its not necessary to flush it out as any crud had settled to the bottom where the drain plug is. Just refill it with 50 weight motor oil.

Pop Chevy

The only good way to clean em out is to take it apart and then you might as well rebuild it. If it's working good just refill it with a good quality GEAR oil. NOT 50wt !

flyeri

Don't flush with a chemical. If I was going to flush it, I would use warm motor oil, 0w20 or such. Let it drain for a while and refill with the proper lubricant.

Kubs

When I "flush" rear ends or transmissions using gear oil, I run a little engine oil through and then run a bit of the new fluid through to push that out. After letting it drip for about 10-15 min I put the plug back in and fill with gear oil. No chemicals.

AzMotorhead

As long as its out and you dont run it under load.
FLush it with ATF. It's a light weight oil and high detergent.
Make a mount to bolt it up to a engine stand. Fill it with ATF, use a electric drill to drive the input run it at a slow speed for a minute or 2.
Pull the plug and let it drain overnight.
refill with the mfg recommended wt gear oil and reinstall.
As a note, on all the Muncies I've rebuilt there's always alot of swarf that collects at the bearing cavity where the mainshaft meets the
input shaft.


FWIW I would rebuild it with a small parts kit, new bearings and snychros while its out.

REELAV8R

How about diesel? Or diesel mixed with ATF? Thin, not harsh, and like Az says ATF has lots of detergent action, so it should work to get junk washed out.
Then fill and run, drain and fill again.

Surfer69

ATF is a good idea. I've always known it has a detergent like base.

Simple enough.

MelWff

You do realize a stock M20 has no drain plug? It only has a fill plug.

7T1vette

You can flush it, but you probably can't get rid of ALL metallic debris from the tranny. It will 'hide' in bearings and recesses, then come out later to do more damage. Seals have also been compromised.

Disassemble it, clean and inspect all metal parts...especially *****/rollers/races on bearings. Metal debris run through bearings is especially bad on them. Gears can live through that damage; bearings/bushings are more at risk.

With the tranny out, rebuilding it is not that big of a job. If you don't want to do it, call around to some LOCAL (not national chain) tranny rebuild shops and get rebuild quotes. Good ones will likely recommend that you replace bearings and bushings, along with seals.

Majoho

The factory original M20 in my 1970 has both a fill plug AND a drain plug. Not sure about other years though. I know some had drain plugs and some didn't.

Jeff_Keryk

My 68 does as well...

sandy laker

Kerosene works for me.

CanadaGrant

Yup, my 69 M20 has one.

dugsgms74

As far as I know it shouldn't, perhaps it was added. I believe the drain plug was added in late 69(M22s had them before that). My Jan build 68 does not have one(M21).

CanadaGrant

My 69 M20 is a late build. Oct 24th 69 and it has both plugs.

MelWff

I have my car since February 1973, the build date is November 1969, no drain plug. Anybody know why some of us have one and others dont?

Surfer69

Adding to the record...my October 69 has no drain. Only filler plug.

Used the ATF which seemed to work well. Lot of gunk came out so cross fingers and hope she survives at least 10K more before rebuild.

Majoho

A search of the forums led me to this information posted by member Joe Lucia:

"As far as drain plugs go, during the 65-69 period, only M-22 model Muncie 4-speeds were originally equipped with a drain plug. Beginning in 1970 with the introduction of the "661" main case, all Muncies got the drain plug. It is very possible, as Stan mentioned, that very late 69s also received the "661" main cases and, consequently, the drain plug. For most Chevrolet car lines (except Corvette and Camaro), the 1970 model year began in the fall of 1969. So, the "661" main case may have been the only one in production by the fall of 1969. My original owner, mid-September 1969 built Corvette has the "660" main case and does not have the drain plug. However, later build 69s (which were built through December) may use the "661" case."

The thread is titled "Need help with Muncie transmission part # and drain plug info".

Hope this answers your question.

Surfer69

7T1 I should have listened to you.

Put new TO bearing in and still tranny is messed up. So out one more time for major rebuild.