1962 Invicta Exact Location of Stamping on Rear Axle Housing Identifying the Gear Ratio

Hi,

I need to know where exactly is the Rear Axle Ratio code stamped on the rear axle housing of a 1962 Buick full-size (LeSabre, Invicta, Electra.) I have information that says it is on the bottom of the housing, but I'd like to know exactly where on the housing?

Here's my story if you are interested. I own a '60 Buick Invicta 2dr hdtp, mild custom. I am on a quest to convert to open driveshaft and 4L60e overdrive transmission. I am planning to use a 61-62 rear differential that will be a direct bolt-in to my 60 axle housing. I want a diff with the 3.23:1 ratio. I've found a guy who has a 62, but he wants to be sure (and I want him to be sure) that it is a 3.23 before he goes to the trouble of pulling it. He told me he did a quick search for the stamped code, but was unsuccessful. (I sent him info on how to determine the ratio by jacking up the car and turning the rear wheel and observing the number of rotations of the drive shaft, but haven't heard anything yet, so if I could point him to the exact location of the code, it would be to my benefit.)

Sure would appreciate some help on this question.

If you want to see my car, just google 1960 Buick Invicta images, and mine is the two toned Island Coral with Black top, scattered about the images (or once I get it right, I hope to have a pic on my profile like some of you other pros.)

Thanks, Bob Whitaker

Bob,

The attached picture is from a 1963 axle with a 3.23 ratio. It is my understanding that the 23 stamped on the housing is what indicates the ratio. I don't have a better picture to show where it is on the housing but you can see it is not a deeply stamped number. I couldn't see it with the rust and grime on the axle until it was cleaned and sand blasted. It may be hard to find if the housing is rusty or dirty.

Hope this helps a little. Good luck.

Bob,

The attached picture is from a 1963 axle with a 3.23 ratio. It is my understanding that the 23 stamped on the housing is what indicates the ratio. I don't have a better picture to show where it is on the housing but you can see it is not a deeply stamped number. I couldn't see it with the rust and grime on the axle until it was cleaned and sand blasted. It may be hard to find if the housing is rusty or dirty.

Hope this helps a little. Good luck.

Thanks. I'm afraid you are pointing out the main problem - if the rear axle is dirty and/or rusty, and you don't know precisely where to look, you would have to do a thorough cleaning, or even blasting, in order to reveal it and with the axle still in the car in an overgrown yard, this might be too much of a pain in the you know what. So, I think I'll just have to hope he will try the "tire rotation method" to estimate the ratio.

I sure appreciate you sharing this info.

Thanks again, Bob Whitaker

Side issue . . . you might have a 3.23 axle ratio currently and it works well with your existing engine calibration, BUT unless it's got a good bit of lower-rpm torque AND some type of electronic fuel injection on the engine, the 3.23 ratio AND .7 OD gear ratio combination will not attain enough rpm at 60mph to use the OD effectively. You might be better off chasing a 3.64 or 3.9 rear axle ratio just so you can use the OD at normal highway speeds with a carburetor. Aim for a mph/1000rpm of about 30-32mph/1000 in OD with your tire size, which a carburetor will tolerate on the highway IF the camshaft is not too far from stock duration specs. Electronic fuel injection can tolerate a 3.08 rear axle ratio in OD, though, as the FI does not rely upon air flow through the throttle body to meter the fuel, it does it "by command of the controller" instead, as the vehicle might have a 1600 rpm cruise in OD at 60mph (on flat ground).

Might need a Buick service manual to determine WHERE on the housing the particular "ratio stamp" is supposed to be located.

Just some thoughts,

NTX5467

Bob,

Any particular reason that you want to use the 4L60E transmission? Doesn't that tranny require a computer to control it? The 4L60E trans is the electronic replacement for the 700-R4, a non electric trans. With the 700-R4, you only need a Throttle Valve cable to control shift points. Plus you can control the vehicle speed at which the torque converter locks with an aftermarket unit.

Ed

Good point! The aftermarket, including GMPerformance, has the stand-alone computers to run the "electronic" Turbo700 trans, though, but that little computer can be pricey. Of course, that 3.06 low gear can be desirable for some, but it then goes to a "Powerglide" low gear ratio for second gear. Might the THM200-4R ODs (non-electronic and less power consumption) or one of the aftermarket adaptations of the GM 6-speed automatic be better? Although ALL have the same basic "top gear OD ratio"? Or does the THM700 family better fit the current transmission tunnel in the floorpan?

Just some thoughts,

NTX5467

Bob,

Any particular reason that you want to use the 4L60E transmission? Doesn't that tranny require a computer to control it? The 4L60E trans is the electronic replacement for the 700-R4, a non electric trans. With the 700-R4, you only need a Throttle Valve cable to control shift points. Plus you can control the vehicle speed at which the torque converter locks with an aftermarket unit.

Ed

Well, the last few posts have certainly made me think I have to give this more thought. A lot to think about, and my old mind moves slowly from one idea to the next. But, I can share part of what is going through it:

One reason I decided on the 4L60e is because I am going to use the 401 compatible bell housing from Russ Martin, to which the 4L60e bolts right up after removing the "chevy" bell housing (the 700R4 has a one piece case/bell housing, which requires using less desirable adapter methods.) Another reason is that everything I've read about that transmission, and the fact that I have one in a 94 Chevy truck, give me confidence in its ability to handle the load. Also, I have conceded the fact that I will have to buy a stand alone electronic device to control that tranny.

The engine in this car is the stock 401 ci Nailhead, with an Edlebrock(600) 4bbl and Pertronix electronic ignition, and dual exhaust. Based on the considerable torque that this engine has, I had thought that it could handle the resultant 2.26 final ratio in OD, in relatively no-load conditions at 70mph, and expecting that the tranny would upshift out of overdrive if the load is too much by virtue of a deeper throttle position. Also, I was thinking that there would be some ability to program some of the overdrive thresholds with the aftermarket computer. These are only my seat-of-the-pants suppositions, I don't have any direct experience with these technologies. I will attempt to calculate engine rpm based on my tire size, road speed and OD ratio, as per the suggestion. (I could also investigate what rear axle ratio is in my '94 Chevy truck, to make a comparison of what kind of loads its 350 engine is accommodating when it is in overdrive - or would the fact that that engine is electronically fuel injected significantly confuse the issue??)

The most scary thing that I hadn't considered - but was brought up - is if the 4L60e will have tunnel clearance issues. Does anybody know the facts about this. (I'd just rather not have to do floor sheet metal modifications as well as everything else.)

Interested in your comments, corrections, and warnings.

Thanks for the reply and information!

The reason the issue of cruise rpm is important, relative to the type of "fuel mixer" on the intake manifold, is that a carburetor relies upon air flow through the throttle body/venture to PULL fuel from the float bowl (hampered by some of the "in channel" restrictions used to calibrate the fuel curve itself) into the air stream and then into the engine. Once you open the throttle, the "response time" related to how quickly the air flow increases from the throttle being opened. If the rpm is too low, the response can be "sluggish" and more opening might make things worse, until the transmission downshifts a gear or two for higher rpm levels.

With electronic fuel injection, whether port or throttle body, as soon as the throttle is opened, addition fuel happens right THEN regardless of what air flow rates might be. One reason that people raved about how much better the '87 GM light-duty pickups ran than the earlier ones with carburetors. Then, at the first oil change, they had complaints about "fuel economy", which relates to what I mentioned above. As soon as the throttle opens, however little, additional fuel is added THEN, not later when air flow increases with rpm levels.

The normal axle ratio for the '87 5.7L Chevy 1/2 ton pickup was 3.08, which could also be had with P235/75R-15 tires. We had one such pickup, with the THM700 automatic in it. It did well in performance and I clocked several tanks at 19-21mpg in mostly easy freeway driving. I thought that was pretty neat, considering we'd had a '78 5.7L V-8 that never got past 11.5mph when it was new, no matter how it was driven. But, we had to start ordering our 1/2 tons with the deeper 3.42 ratio so our sister dealership would dealer trade with us. The 3.42 was "deep" enough to allow for towing boats and such, whereas the 3.08 would not pull it as well.

When the rear axle is too high (lower number), what happens at highway speeds is . . . the pickup will run fine until a small incline is encountered, then it'll unlock the torque converter and then downshift (in that hierarchy order, sometimes simultaneously). Then, as soon as the rise is past, throttle input decreases, the trans upshifts and the converter locks-up again. The 3.08 in our truck didn't do that, but for the dealers who ordered their vehicles "not knowing" with a 2.56 rear axle ratio, I-45 between DFW and Houston resulted in "shift busyness". One man with that situation called up and wondered what was happening. He described the situation and I told him we needed to check the rear axle ratio code. Turned out it was a 2.56 ratio. He then inquired as to how much a lower ratio gearset would be . . . about $1000.00 installed. I told him what was happening was "as designed", but I also suggested that the only way to get away from that deal was to get a different pickup with the deeper rear axle ratio when he could afford it. These things still happen in the newer vehicles, just that the computer controls make everything happen so seamlessly that unless you have a tachometer or a sensitive ear for things, it happens unnoticed.

FEW roadways are completely flat or without inclines, even in "flat" west Texas. Or at least you "think" they are until the trans downshifts due to an incline or overpass that seems "normal". Now, if you opt for the non-electronic THM700, you can manually tune these things with vacuum switches (for torque converter lockup and unlock modes) and also when downshifts might be "load generated", somewhat. With the electronic version, the vendor should supply something to do it electronically, I suspect, as some do with the newer add-on fuel injection units.

The OTHER thing is that a great many people I've known who wanted to replace their THM350s with a THM700 (for the OD ratio) ALL had to install lower rear axle ratios just so they could use OD under 70mph or so. Otherwise, all they gained was the added performance from the deep low gear of the THM700 transmission. All carbureted engines.

If you might use the THM200-4R OD transmission, you'll have a throttle linkage you can play with (which the non-electronic 700 might also have, as I recall, just that it adjusts "backwards" from what you might expect it to, as our transmission tech found out earlier on) . . . this way, some of the downshifting can be tweaked a little, but not much.

We know the 401 has really good lower to mid-range rpm torque. With the smaller "nail head" valves, that can also mean that port velocity can be decently-high, for higher manifold vacuum levels and flow velocity at lower rpms . . . at least that's the theory I'm operating with. It MIGHT carry the higher ratio in OD better than expected, but that would be a huge "cut and try" situation, so seeking out the deeper rear axle ratio to start with would be your judgment call . . . with a carbureted engine.

The THM200-4R swap is something that many in the Riviera community have done to their cars, for the OD ratio. Many of them already had the lower rear axle ratios, though probably not that much lower to start with, but closer to the 3.64 area than not. You might post an inquiry in their forum about transmission case sizes and such, plus ask what their rear axle ratios were on their carbureted cars. Just click on the "Riviera" forum is all that's required to get there, then you can look around and search for those posts.

As it turns out, there is a huge following for the THM200-4R trans in the street rod world, even behind stout big-block Chevy V-8s (with proper internal upgrades). Its ratios are a little more evenly-spaced. 2.74/1.74/1.00/.70 , or thereabouts. Plus, no electronics to fool with or add to the vehicle.

Happy Holidays!

NTX5467

Bob,

How did you do on this project? Is it finished? I just bought my project and intend to do the exact same transplant that you described. I am very curious how yours turned out, what you learned etc.

Looking forward to hearing an update,

Doug

Doug,

Sorry for such a delayed response - I am easily distracted.  I am just starting on this project now.  I finally have the car up on jack stands and am getting ready to start "ripping" things out.  I have ordered a 4l60e from my local auto trans shop, and have procured the bell housing, flex plate and torque converter-to-crankshaft adapter bushing from Russ Martin.  I have been talking with my welder/fabricator friend, and we have kinda agreed on a triangulated 4 link suspension set-up.  (I don't want to go with the pickup truck trailing arms because there will be clearance issues when I let the air out of the air bags to lower the car at shows.

Have you begun your project yet?  Perhaps you are farther along, or even finished, and it may turn out that you know more about the conversion than I do.

Thanks, Bob