Technical Hate to do this…GM Rear end ID needed

Sorry guys, I hate to do this, I thought I would be able to find the answer, but so far, no luck. I have GM rear end in my '51 Merc that I need to ID to be able to buy parts…specifically a u-joint at the moment. I know that it is a second series 7.5/7.625 10 bolt, but I can not for the life of me find out what it came out of. The assembly code stamped on the passenger side axle tube reads FC 6K214. The casting code on the bottom front of the carrier reads 551635. I know the gears have been changed out to 3.73(?) from 2.something and I think that swap may have required a different carrier….so the carrier may not be as originally equipped. I have been unable to find any charts with these codes listed to tell me what the rear end came out of. I had assumed the rear end came out of the same '85 IROC Z the engine came out of, but I can not confirm that with the codes I have.

Here's my bottom line dilemma: I have to have a drive shaft made and the shop needs me to confirm that my yoke is not bad since the driveshaft gives them reason to think it might be. He asked me to get a new u joint and check for play between the u-joint and the stops on the ends of the yoke. Problem is I've been unsuccessful at trying to ID what the rear end came out of so I what year/car to ask for a u-joint for at the parts store….since the 18 year old working the counter is only going to know is what the computer tells him….not that I have a GM rear end in a '51 Merc.

 

measure the u joint. Most likely 3.219" x 1.062" which is a Spicer 1310 series. Very common...Precision 369, Spicer 5-153x, etc. Fits over 5000 different models of Chevrolets, for example.

 

Thanks Squirrel, that was fast. Unfortunately, I sent the u joint with the drive shaft to be checked (and they had to send it to their other shop 30 miles away). The tech I talked to today who asked me to check the yoke said the u joint was for a 72-ish Camaro/Nova. I was surprised, but OK with that since it would match the rear steer Camaro/Nova front clip. But when I got under the car tonight, I could see it certainly was not that style rear end but the newer 7.5. So, after having no luck with the codes, I'm just totally confused. I can call him in the morning and have him measure the u-joint I sent over. I guess my concern now is that the u-joint that was in it doesn't actually match the rear end in the first place, likely causing my problem. Just want to make sure I get the right u-joint now to build the new drive shaft to.

 

Measure your yoke, then you know which u-joint fits it. I seem to recall from my off-roader days there was an "adapter" u-joint available that had one size cap/cross on one side and a larger cap/cross the other way for swapping in say 1/2 ton drive shafts to 3/4 ton axles. Might be something to look into if needed.

 

http://www.thecamaro.com/Decoding/Chevy-Axle-Rear-End-Decoding/index.php

Did you look here yet ??

 

Nope, I hadn't. Ran right over, entered my code…not in their data base. Thank you for trying, though. I book marked it just the same…never know when it will come in handy.

 

The other likely U joint is Spicer 5-3147x, or Precision 534, which has 1.125" diameter caps.

That's what's listed for an 85 camaro. They were also used on many other Chevys over the years.

 

Thanks guys for the help! I will hit it hard with your suggestions tomorrow.

 

Of course not , did you read any of the ways they are identified?
Any chance the way you read the code is incorrect or illegible or a 6 is really a zero and such? It would be an odd situation if your code is correct and un identifiable- quite common to read stamped numbers wrong though.

 

Do you happen to know what the width of the rear end is? Wheel mount to wheel mount?

 

I have always just measured the yoke that the U-joint goes into, you need the overall length and the cap diameters. Should be fairly easy to measure, at least all of the ones I have worked on were easy. Should not need an application (year and model) as the dimensions alone should ID it. Most U-joints I have worked with are common across different makes and models (same joints are used in both chevy and fords for example). Also, as stated above, some joints are the same size for all four caps and some have two of one size and two of another size.

 

The code will be 3 letters stamped in a row on one of the axle tubes.

 

Yes, I did read how they are identified, on that page and many others. My rear end does not have a casting code on the the top web on the passenger side as so many sites list, only a casting code in the front if the carrier. Most of the info I had found was on 8.5 10 bolts a 12 bolts, but I have found very little on the 7.5 10 bolts. FC as a code has not come up in any of the listings I have found. Pretty sure I'm reading it correctly though.

Here are pics of the rear I have. Sorry, I would have posted some last night, but my phone died while I was under the car after taking the first pic. Lol




Here is the assembly code. No other markings on this tube or misplaced letters. I was expecting 3 letters at the beginning also, but not the case.


This is the casting code on the front side of the carrier at the bottom.

Guess my best bet is to call the shop today and have him measure the u joint that was in it and also measure the saddle in the yoke and see what I come up with. Thanks a ton guys!





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I'm still confused as to why you don't measure the yoke you have on the rear axle? Or you could go to the local parts store and buy both of the U joints Squirrel listed, and take back the one that doesn't fit your yoke.

 

Fc is a 76 2.73 chevy nova 6 banger rear , number then 2 alphas would indicate a late 70's ( about 78 ) 80s rear ( metric series )

1970s Gm used both 2 and 3 letter codes

 

Yes, that is my plan today. Couldn't get back out in the shop late last night to measure, but that is my plan at this point. My hope was I could positively ID the rear for future reference, but doing it this way will solve my problem facing me now for sure.

 

Thanks!!

 

I have never measured it, but I will when I get back under the car.

 

Dr the u joint should be a standard 1310 series ( percision 369 or 280 )

a dead giveaway on the 7.5 if its a 3-4th rd gen f body is the bolt mount near the pinion for the torque arm ( s-10s and novas do not have this ) and signs of the radius arm/coil spring mounts at the ends

 

Thanks Stimpy. I'll double check those things, but I do not recall seeing them, so I guess it rules out the F-body. Pretty sure it was a factory leaf rear end, I don't recall any evidence of coil mounts having been cut off.

 

You sure its not an 8.5 10 bolt?

 

Beats me....I'm a bodywork, upholstery and "fun stuff" guy....not a driveline guy. LOL When I read and looked at pictures of id'ing these rear ends, the 8.5 10 bolts looked like the bottom corners of the case by the cover were more triangle shaped and the 7.5 10 bolts had the bottom corners that looked more like lugs like mine does in the pic above. So that's what I was going by to say I thought I had a 7.5 10 bolt.

Anyhoo, the good news is I have a u joint. The winner is a Precision 369. I have confirmed I don't have a worn yoke and the shop can now proceed with the new driveshaft. The current problem has been solved. Now, heaven help me when it comes time to buy brake parts, but that is a problem for another day.

Thank you each and everyone of you who took the time to read this and offer suggestions and direction. I truly appreciate everyone one of you!


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Your right on the ID doc easieist way to tell the difference is the 8.5 has what we call blocks on the bottom corners , and the 7.5 has litterally fangs on them ( they bite you if your not paying attention ) and a 8.2 BOP has nothing its smooth ( thats How I I.D. them without pulling covers )

 

Have you checked here:

http://www.crankshaftcoalition.com/wiki/Rearend_identification

 

Thanks Stimpy. That helps.

Fred, I think I may have been on that site, but I just went through it again. I followed all the links for codes, but alas, the FC code didn't show up anyplace. Great site, though, since it kinda catalogs most all the sites I had been to. Good central site to start with.

 

It makes more sense that the housing is Nova or even 2nd gen Camaro. The 3rd gen is really too wide for these early cars and needs modification to install in a leaf spring car.

 

All 2nd gen Camaro 10 bolts were 8.5", and that's not an 8.5" 10 bolt. The problem with trying to figure out what it is and the U joint size, is it may have had a yoke replaced. So even if you figure what it is, it STILL needs to be measured.

 

That's a question I have floating in the back of my head, too. Even though the 369 u joint is a match to the yoke, I have no clue if the yoke has been changed at some point in its past. I guess I could pull the yoke and count the splines, but it's not leaking and I hate to mess with a goo thing. I guess I'll leave sleeping dogs lie and when the day comes for brakes, I'll just take the parts in with me to the parts store and just see what matches. LOL


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Looks like I'm about 54.5-ish flange to flange (outside) and 45.5 center of spring mount to center if spring mount. No evidence of ever having been a coil spring rear end nor does it have the mount holes by the pinion for a stabilizer bar.


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No, that's to the outside of the flanges where the backing plates bolt on. I might have time later to get the wheels off and I can measure to the drum faces.


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