Need help with 69 trans and rear end codes

[Joseph H.]

OK, I am still new, so please be gentle, also I know a few things about cars, but not really performance related. Here is my situation I have a 69 350/350 4 spd. I recently purchased the vehicle from another NCRS member. I was able to check the engine stamp prior to purchase, but was not able to verify the rear end and trans. I was told the vehicle had a numbers matching drive train.

So, to the point. I checked the trans and rear end today the trans appears to have the correct vin stamp, but the rest of the code looks to be P9(I think)M22 and the rear end appears to be stamped OAW198E3. I was told the car had an M21 trans with 3.70 posi rear end. I purchased the judging manuals as well as several other manuals. The trans code should have a letter at the end of the code to indicate which muncie trans is in the car, but I do not see an A,B or C after P9M22. Any suggestions on how I can verify the type of trans this is?

In regards to the rear end according to the manuals it appears to be for a big block car and it has 3.08 gears? Any help here also.

I first want to know what exactly I have and since I am not really an expert, what difference do the gear ratios make. I assume one is better for city vs. highway driving and top end performance vs off the line performance, but I do not really know, please inform me. Also I noticed that the speedometer is way off, maybe 10,15 or 20 MPH. It seems to function correctly, just not the right speed. Does the speedometer issue have anything to do with the rear end? I understand you need the correct speedo gears, so I assume that the speedo gears may be correct, but the rear end is the issue.

Thanks for the help. I know this is lengthy, but please help.

Also this is an early 69' VIN 1291 if that helps. The body build date was Sept 11th (bad omen), 1968. How can I tell the exact final assembly date?

Regards,
J Hudec

[Terry M.]

Re: Need help with 69 trans and rear end codes

P9M22
P = Muncie heavy duty 4-speed
9 = model year of transmission
M = August
22 = 22 nd

How does August 22 work with the build date of your car?

Not all transmissions had the letter code following the assembly stamp. If yours doesn't you will have to experiment by charting the indicated road speed at a given rpm. Pick, say 2000 rpm and chart the indicated road speed in gears 1 through 4. The difference between the road speed will tell you which transmission you have. Post those numbers and we will work you through it.

Could the first character be a C, or are you sure it is a 0 or O? AW = 3:08 for all the years, but the 198 looks like a Julian date. Those didn't start on the differential until 1971, so you may have a 1971 or later unit in there. There is a casting date on the differential housing, but someone else will have to tell you where it is.

[Joseph H.]

Re: Need help with 69 trans and rear end codes

Terry, Thanks. I think the August 22nd date works, as my build date is Sept 11th. So, I can still do the test even though I think my speedometer is off (low) by say 15 MPH? I am assuming it is off because of the rear end. The first letter could be a C, it was hard to read, the judging guide indicated, (I think anyway) that the 198 was the mon/day/yr of production, so I assumed it to be jan, 9th, 1968. Plus the guide indicated that the first digit would be a number for the shift, that is why I thought O or 0. CAW would be posi from a 427 car? I could not figure out the E3 on the end, I thought that was E (Eaton), but not sure of the 3?

I will try the speed at all four gears @2000rpm as soon as I can.

[Terry M.]

Re: Need help with 69 trans and rear end codes

Yes the RPM test will work regardless of the accuracy of the speedometer -- assuming the inaccuracy is liner, that is that it is off the same percentage at all speeds -- like it would be if the wrong speedometer gear is in the transmission or the differential is the wrong ratio. We are looking for the differences in speed due to gear changes.

I'm going to need some help from others on the board, but I know those in the know are out there. I believe the close ratio will show relatively the same percentage speed change for each gear. The wide ratio will have a bigger 3 to 4 speed jump.

If the date were January 9, 1968 I would expect the code to be 1 9 68. On the 1968-1970 differentials there is a definite space between the month, day and year numerals.

I can't imagine there is a O or 0 a shift. I would expect 1 2 or 3. Since we don't judge these codes we don't have a lot of experience with them, so I could be wrong, but January seems a long ways from September. One can't rule out anything for sure though. The casting date would help clear it up. I know how hard it is to read those stamped codes. They are often not readable.

I forgot -- yes the E is for Eaton. I'm not sure about the last 3, unless it is the shift it was assembled.

[Joe L.]

Re: Need help with 69 trans and rear end codes

OK, I am still new, so please be gentle, also I know a few things about cars, but not really performance related. Here is my situation I have a 69 350/350 4 spd. I recently purchased the vehicle from another NCRS member. I was able to check the engine stamp prior to purchase, but was not able to verify the rear end and trans. I was told the vehicle had a numbers matching drive train.

So, to the point. I checked the trans and rear end today the trans appears to have the correct vin stamp, but the rest of the code looks to be P9(I think)M22 and the rear end appears to be stamped OAW198E3. I was told the car had an M21 trans with 3.70 posi rear end. I purchased the judging manuals as well as several other manuals. The trans code should have a letter at the end of the code to indicate which muncie trans is in the car, but I do not see an A,B or C after P9M22. Any suggestions on how I can verify the type of trans this is?

In regards to the rear end according to the manuals it appears to be for a big block car and it has 3.08 gears? Any help here also.

I first want to know what exactly I have and since I am not really an expert, what difference do the gear ratios make. I assume one is better for city vs. highway driving and top end performance vs off the line performance, but I do not really know, please inform me. Also I noticed that the speedometer is way off, maybe 10,15 or 20 MPH. It seems to function correctly, just not the right speed. Does the speedometer issue have anything to do with the rear end? I understand you need the correct speedo gears, so I assume that the speedo gears may be correct, but the rear end is the issue.

Thanks for the help. I know this is lengthy, but please help.

Also this is an early 69' VIN 1291 if that helps. The body build date was Sept 11th (bad omen), 1968. How can I tell the exact final assembly date?

Regards,
J Hudec

J-----


Early 1969's did not have the suffix code on the transmissions. That practice did not start until late October, 1968. Your transmission was built in August 1968 (for 1969 model year usage) and, thus, would not be expected to have the suffix code.

[Jim T.]

Re: Need help with 69 trans and rear end codes

How are your inboard u-joints retained? My 70's rear end is CAV0702 and has caps to retain the u-joints. The first printing of the NCRS 1968-1982 Corvette Specifications Guide identifies CAV being for a 454. My 70 is base engine 350/300 with turbo 400.

[Terry M.]

Re: Need help with 69 trans and rear end codes

The more recent Spec Guide corrected that. The differentials Chevrolet labeled "heavy duty" were used for all 454, LT1 and all M40.

[Joseph H.]

Re: Need help with 69 trans and rear end codes

Thanks regarding the suffix codes on the trans. That explains the trans and it appears to be original, now I have to just figure out which one it is. Cannot drive it today, as it is raining.

Regarding the inboard u-joints. I just crawled under the car and the inner half shafts are retained to the rear end by u bolts and nuts. The caps on the outer half shafts are retained by inner locking clips. I have a number that I took off of the differential cover, which I believe is 464910.

Thanks in advance.

[Terry M.]

Re: Need help with 69 trans and rear end codes

Sounds like someone has been there before you. The differential case may be the on the car came with, but the internals, and stub axles may not. I believe all M40 came with the so called heavy duty (caps and bolts) on the inboard U-joints.

[Joseph H.]

Re: Need help with 69 trans and rear end codes

Terry, Where is the case casting date? I did not see it when I had the car in the air the other day, but I was really concentrating on the stamped area. Can I get the cast date without any disassembly? Do I have to have the car on a lift or just up on a floor jack?

[Terry M.]

Re: Need help with 69 trans and rear end codes

I am not sure where it is, and was hoping others who have been there would chime in.

[Joseph H.]

Re: Need help with 69 trans and rear end codes

OK, Thanks. I will see if I can get it back in the air this week after the rain stops. I will also perform the speed/rpm/gear test. I am not that worried about the rear end being incorrect, I am more concerned with knowing which trany I have and being able to get the speedo to read the correct speed.
I looked at a couple of differentials on ebay to try and see where the cast date is, but they always show a close up of it and I cannot figure out the orientation of the unit when the picture was taken. I think I will add a new post asking about the cast number.

Your help is much appreciated.

[Joe L.]

Re: Need help with 69 trans and rear end codes

Thanks regarding the suffix codes on the trans. That explains the trans and it appears to be original, now I have to just figure out which one it is. Cannot drive it today, as it is raining.

Regarding the inboard u-joints. I just crawled under the car and the inner half shafts are retained to the rear end by u bolts and nuts. The caps on the outer half shafts are retained by inner locking clips. I have a number that I took off of the differential cover, which I believe is 464910.

Thanks in advance.

Joseph-----


If the cover is GM casting #464910, then that's been replaced. That cover was never originally used for a 1969. It was used for 1978-79 and later became SERVICE for earlier models. However, since this cover uses 7/16" spring retaining bolts, special spacers need to be used when a 2-1/4" wide 63-77 spring is used.

The original cover for your car was GM casting #3871375 and used 9/16" spring retaining bolts.

[Joseph H.]

Re: Need help with 69 trans and rear end codes

Joe,
Thanks, I will be sure to look for that when I can get the car back up in the air, maybe Thursday. I suspect the differential has been changed and I an going to get the casting code off the differential housing when I get it back in the air. That will tell me the date and give me an idea of how to decode the stamped code.

Also I counted the leafs in the spring and there are only 7. I think mine should be nine as it is a small block and it does not have a rear sway bar.

I will let everyone know when I get the info.

[Joe L.]

Re: Need help with 69 trans and rear end codes

Joe,
Thanks, I will be sure to look for that when I can get the car back up in the air, maybe Thursday. I suspect the differential has been changed and I an going to get the casting code off the differential housing when I get it back in the air. That will tell me the date and give me an idea of how to decode the stamped code.

Also I counted the leafs in the spring and there are only 7. I think mine should be nine as it is a small block and it does not have a rear sway bar.

I will let everyone know when I get the info.

Joseph----


Yes, the spring should definitely be 9 leaves AND it should be 2-1/4" wide.