# Trans and Diff ID help needed...



## System (7 mo ago)

My 70 was a factory 4 speed 400 car but the driveline was replaced at some point. The engine is a WT but I haven't figured the trans or rear end yet. The seller did say the trans was from a 66 GTO but had no other info. I'm not sure if the shifter is original to the car or came with the trans? The rear diff is an open carrier so that will need updated. Do these pics help identify?


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## ylwgto (Oct 27, 2009)

On the rear end there are date stampings (sometimes faint) on the passenger axle tube close to the center section. Those can Id the rear.


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## O52 (Jan 27, 2019)

The axle code is on the left side tube a few inches left of the center section. Also has the Julian assembly date. Should be 2-3 weeks prior to the vehicle assembly date, although thats not always true.


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## 1971LemansWisc (Apr 18, 2021)

GM 3846429 is Muncie 4 Speed Transmission Tail Shaft Housing.

3851325 is 1965 Chevy, Corvette, Camaro or Chevelle M20 Transmission 

Shift Lever/Stick - 1965/66 Pontiac GTO Shift Lever/Stick are generally round. 

Your "flat" bar Lever/Stick smacks of Chevy. 

Not an expert - but what this looks like to me.


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## System (7 mo ago)

You guys are awesome! Thanks for the info. Oh, and one more amateur hour question if you would... What is this attached to the throttle linkage? Looks like a throttle position sensor? (Yes, I noticed the missing bolt from the guide. I'm off to remedy that now...)


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## ylwgto (Oct 27, 2009)

that is a kick down switch for a TH400 auto...a remnant of the original transmission set up. with a 4 speed it is doing nothing


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## System (7 mo ago)

You know what, I thought that. And what's more odd is that PHS says that this car was a factory 4 speed so no idea how that got there.


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## BLK69JUDGE (Jun 10, 2010)

325 case muncies were Pontiac also 64-65 not 66
yes a 68 super turbine 300 or 68-72 th400 kickdown
looks like the 7236 hurst bolt on replacement unit for the 69 camaro chevelle


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## System (7 mo ago)

Thanks again for the info folks. This car is kind of a basket case but it's what was affordable so who knows how many times and how many ways it was setup. Now it's time to make it mine....


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## System (7 mo ago)

This is the best pic I can get of the diff numbers. Hard to make anything out at all. I'm thinking that if it has the scalloped cover, it's the correct type rear end for the car and I can order a set of Yukon gears and limited slip? Anyways, pic of the numbers. They were on the passenger side of the diff and not the tube though so maybe I'm looking in the wrong spot...


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## O52 (Jan 27, 2019)

That’s the casting number. The axle code and date is stamped into the left side tube. You may have to sand the paint off to see it. 
you need to make sure of which rear axle you have. There were two different 10 bolt axles, so you need to make sure which one you have before ordering parts


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## System (7 mo ago)

Gotcha. Just checked and couldn't find a darn thing. It must have been pitted before it was last painted as it's pretty rough. What is the next way to verify?


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## 1971LemansWisc (Apr 18, 2021)

Well ... next step might be more than you want to do now. 
That is ... to pull the cover and look at the ring gear. 
Images are of my 1970/71 10-Bolt 8.2 BOP (Buick Oldsmobile Pontiac) Differential
The 2 images of the Ring Gear aren't the best but if you zoom in you'll see "41 16" equating to a 2.56 (41/16) ratio. 
Again, have to zoom in but there is a "70" Date Code stamp. 
I have my Build Sheet and was able to find the Axle Tube stamping of "XB", confirming 2.56 Safe-T-Track Axle. 
After confirming everything I went with the Yukon Dura Grip 3.36 ratio for my build. 
Good Luck!


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## System (7 mo ago)

OK, only last question on the diff. Can anyone be more clear on the 2 different possibilities of rear end I might have. Everything I see in my Google search shows only one 10 bolt BOP diff cover with the reverse scalloped sections of the diff cover on either side looking like the diagram below. The GM corporate 10.2 from a Chevy would be a round cover without the scalloped part. What other possibility could my rear be if not a BOP 8.2 with this shaped cover? I called Randy's and they say if it's got this cover, it's a BOP 8.2.


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## O52 (Jan 27, 2019)

The reason I mentioned two different type of axles was that your car seems to be a mixed bag of components. I saw the scalloped cover and assumed it was an 8.2 but remembered reading there were a few 8.5s with a scalloped cover. See links below.

There are two BOP rear end housings; Pontiac models from 64-72 used an 8.2" ring gear. 71-72 Olds and Buick and very few Pontiacs used a 8.5" ring gear. The 8.5 is the better of the two. 
8.5 normally has a round cover but some Olds models used a scalloped cover similar to the 8.2. 

As mentioned earlier the axle code / date was found on the left side tube. In 71 that changed to the front of the right hand tube near the brake line clip. But as this chart from Wallace Racing shows it could be anywhere depending on the type of axle

1971-1975 : Front of Right hand (passenger) tube,about 3" from carrier
1970 : W/C-lock axles-Front of Right hand (passenger) tube,about 3" from carrier
1970 : non c-lock axles-: Rear of left hand (driver) tube,about 3" from carrier
1967-1969 : Rear of left hand (driver) tube,about 3" from carrier and stamped on left rear brake drum.
1966 : Rear of right hand (passenger) tube
To be absolutely sure, remove the cover and look for the gear ID.







Rear end ID Please - PY Online Forums - Bringing the Pontiac Hobby Together


Rear end ID Please Pontiac - Street



forums.maxperformanceinc.com





Tell me about 8.5" 10 bolts - Page 2 - PY Online Forums - Bringing the Pontiac Hobby Together


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## System (7 mo ago)

Excellent! Thanks again for the info... I guess I need to get under there with a disc grinder and really do some searching or pull the cover....


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## O52 (Jan 27, 2019)

Quite often the ID stamp was very light. A disc grinder will remove the stamp impression with one pass. Recommend 80 grit sandpaper


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## System (7 mo ago)

Will do...


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## 1971LemansWisc (Apr 18, 2021)

Front of Right hand (Passenger) tube, about 3" from Carrier, just left of the Vent. 

To O52's point, I was very careful and used a rotary wire brush wheel to remove the rust in this area as not to damage what was left of the stamping. 

Even with that, I am only able to make out "P" for Pontiac, a portion of the Julian Date when the axle was assembled and the "XB" 2.56 Code. 

The bad metal pitting is complements of Midwest Winters and Road Salt.


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## System (7 mo ago)

So, even if I find something, it won't necessarily be enough do differentiate between a possible 8.5 and a correct 8.2. I'm willing to bet it's an 8.2 though....


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## O52 (Jan 27, 2019)

So am I. 

Probably the original


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## System (7 mo ago)

The only reason I question it being original to the car is that it's an open diff and PHS says Safe-T-Track...


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## O52 (Jan 27, 2019)

ah, how did you confirm it's an open diff? I'm not grilling you, just trying to lay the groundwork.


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## System (7 mo ago)

Jacked the rear and rolled a tire Ed. They go opposite directions so open diff or so the story goes... (Although the interwebs say this method isn't 100% accurate and a surprise might be in order...) I have some seepage from the gasket so I may pull the cover and look regardless. Either way I need to up my gearing. 1st gear is very high and feels like you're taking off in second so I'm guessing there must be low (numerical) gears in there. I'm surprised the sheet from PHS doesn't mention gear ratio?


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## O52 (Jan 27, 2019)

Look at box 18 labeled 'AXLE' Should have a two letter code.


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## System (7 mo ago)

I spend an hour under the car today cleaning the axle and still couldn't find the code. Perhaps one of the previous owners went monkey strong with a grinder cleaning off the rust and removed it. Anyways, I did some more searching and on another forum I read this... If that car had an 8.5" swapped in at some point the tangs on the corners of the center section would be full and squared and if they are flush or open like mine, it's an 8.2". True? Here is one of mine.










Here is a squared one from an 8.5" that I pulled from the Google machine.


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## System (7 mo ago)

So I think I have it sorted. Pulled the cover today. 42-13 gears which I see is 3.23. The date on the ring gear is 1970 so I'm guessing that means it must be an 8.2 according to @O52 and @1971LemansWisc ? Open carrier. Time or order parts...


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## 1971LemansWisc (Apr 18, 2021)

Very cool - looks very familiar to me 
If any indication - the inside the Carrier and Gear Teeth look good.
Based on Wallaceracing.com going to guess yours is a WF 8.2 BOP axle. (Mine is XB 8.2 BOP axle.)


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## System (7 mo ago)

I did find an issue though. The previous "mechanic" ie: butcher... broke off one of the diff cover bolts. He then tried to drill it and turned the hole into an oval before giving up and just loading it up with RTV. So, when I send the car to my diff guy for new gears and a limited slip, I'll have him address it somehow. Perhaps making it bigger and doing a helicoil. At least they are very low torque bolts so a fix will hold.


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## System (7 mo ago)

OK, quick update on the diff overhaul. I found a great source is anyone is in the market for parts! Quick Performance out of IA. You have to call to get the best pricing as it will be more on both their Amazon storefront and even on their website. When you call, you get the owner direct who is very knowledgeable and patient with questions. He sold me a Yukon DuraGrip, DANA 3.55 gearset, mater overhaul kid and posi additive for $640 all in. That included free 2 day air shipping. I ordered Monday and brown santa just delivered them today... I also bought an aluminum TA brand diff cover from them. Now to book time to get it all installed...

Anyways, if anyone needs a vendor recommendation, talk to Bryden at 641-751-8060. Their website is here: Quick Performance: Differential Parts & Components


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## 1971LemansWisc (Apr 18, 2021)

Agree, QP is great!

I went same Yukon Dura Grip but opted for 3.36 ratio based upon my numbers. 

They install well, the Clutches are tight and overall little to no chatter. 

You will have lots of fun! (Of course your rear tires may have a different opinion  )


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## System (7 mo ago)

The diff upgrade will be going behind a 428 I'm dropping in so this should be an adventure... 😁


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