how to change oil in a 68 4sp?
10-30-2014, 09:50 AM
#1
Melting Slicks
Thread Starter
how to change oil in a 68 4sp?
Got ready to change the oil in a '68 4sp Muncie and it has a fill plug (good), but no drain plug like the other ones I have seen on later years. So, am I going to have to siphon the oil out like on a rear end with no drain? Or does one of the lower casing bolts work as a drain?
Also, this one is stamped "P8C15c". All in all, the Corvette looks to be very original to a 68. The last letter "c" is smaller than the "P8C15". Is this a M22? or something else?
Much Thanks!
Also, this one is stamped "P8C15c". All in all, the Corvette looks to be very original to a 68. The last letter "c" is smaller than the "P8C15". Is this a M22? or something else?
Much Thanks!
10-30-2014, 11:30 AM
#2
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Hi 20,
I believe the SUFFIX letters decode as:
A 2.52:1 M-20
B 2.20:1 M-21
C 2.20:1 M-22
Regards,
Alan
I believe the SUFFIX letters decode as:
A 2.52:1 M-20
B 2.20:1 M-21
C 2.20:1 M-22
Regards,
Alan
10-30-2014, 11:32 AM
#3
you have to use the siphon method
I used a vacuum pump.
10-31-2014, 11:37 PM
#7
P8C15c decodes to Muncie, 1968 model year, March 15,1968 ... and the c should not be there. The A,B,C suffix stamp started in October 1968, for the 1969 model, 7 months after this transmission was built. As to why there is a small c stamped after the build date, that's open to conjecture. Maybe a past owner rebuilt it to M22 specs? In any event, since you plan to drain the fluid, maybe you can open the sidecase and take a picture of the gears to figure out what you have. And it's pretty easy(if you know how) to drill a hole and tap for a drain plug in the lower boss. In 1968, there were 80 factory M22 transmissions installed in Corvettes, and they were all in the L88, so it's pretty unlikely you have a factory M22.
11-01-2014, 12:26 AM
#8
Melting Slicks
Thread Starter
Ok and thanks for the responses.
So, all M22's have a drain plug.
And yes, for me, the little c at the end was suspicious. I decoded the rest as you say. I checked a stamp on a 72 close ratio M21 and the suffix letter was the same height as the rest of the PXXXX. However, I thought maybe the 68 stuff was different. Good to know and thanks for the responses. Wonder why anybody would stamp a little c, but hey these are 40+ year Corvettes, who knows what all stories they could tell if they could talk!
This also explains why some of my Corvette books do not say anything about a A, B, or C suffix for 68 Muncie's. This suffix business started for the 69 models, ah ha!
I see the boss for a drain, so maybe I will install one when the opportunity arises.
Thanks again!
And yes, for me, the little c at the end was suspicious. I decoded the rest as you say. I checked a stamp on a 72 close ratio M21 and the suffix letter was the same height as the rest of the PXXXX. However, I thought maybe the 68 stuff was different. Good to know and thanks for the responses. Wonder why anybody would stamp a little c, but hey these are 40+ year Corvettes, who knows what all stories they could tell if they could talk!
This also explains why some of my Corvette books do not say anything about a A, B, or C suffix for 68 Muncie's. This suffix business started for the 69 models, ah ha! I see the boss for a drain, so maybe I will install one when the opportunity arises.
Thanks again!
Last edited by 20mercury; 11-01-2014 at 12:31 AM.
12-09-2016, 04:40 PM
#9
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It's been a while but seems like the bottom bolt of the tail housing would sometimes drain it if removed.
Jim.
Jim.
12-09-2016, 07:27 PM
#10
Drifting
Got ready to change the oil in a '68 4sp Muncie and it has a fill plug (good), but no drain plug like the other ones I have seen on later years. So, am I going to have to siphon the oil out like on a rear end with no drain? Or does one of the lower casing bolts work as a drain?
Also, this one is stamped "P8C15c". All in all, the Corvette looks to be very original to a 68. The last letter "c" is smaller than the "P8C15". Is this a M22? or something else?
Much Thanks!
Also, this one is stamped "P8C15c". All in all, the Corvette looks to be very original to a 68. The last letter "c" is smaller than the "P8C15". Is this a M22? or something else?
Much Thanks!
Wes
