Rear-end ratio on 84 Park Avenue

[Guest]

What's the rear-end ratio on an 84 Park Avenue with the 307 V8. <P>My friend is going to sell the car to me for $500 because it needs a trans and a radiator. I'm thinking of removing the 200-4R and installing a rebuilt th350. Then I'll fix the radiator and sell the car for $1200. Then I'll sell the 200-4R for a few bucks and make some money on the car.<P>I need to know if it will get buy with three speeds.<P>I'm going to sell it to another friend of mine who needs a cheap car. A 200-4R costs twice as much as a 350 and the blue book is only $1200.

[NTX5467]

Sounds like a good deal of work just to make a few hunderd dollars . . . I'm not sure if there will also need to be driveshaft alterations in that deal too, but it's possible (another $100.00 or so for that). Plus the Turbo350 will need to be a BOP case, I suspect, or the one with both of the bolt patterns on the bell housing instead of the more common Chevy pattern.<P>In some respects, getting rid of the OD trans for a 3spd could put the vehicle out of compliance with emissions regulations, as there'll be more "flow" coming out of the pipes as the engine will be running higher rpm during cruise. If the vehicle will not pass emissions because of that, have you really helped your friend that needs a cheap car that might not pass emissions, who could then come back on you for doing the alterations? <P>This issue was pointed out to me years ago by a transmission shop. The theory, even back then, made sense.<P>Unfortunately, there are several things that will "total" those cars out, including buying a reman carb from GM (the new ones were over $1500.00 when they were still available!).<P>The other aspect is that if the 200R4 trans is fixed, the radiator is fixed, and a few other deals attended to, the end result should be a reliable vehicle that will not depreciate too much more in the future. That might be the more advisable course of action.<P>As for the axle ratio, I doubt it's lower geared than a 3.08, more probably a 2.73 even with the OD trans. There are several ways to verify this, though. <P>Easiest way would be to check the Service Parts ID label that might be on the underside of the deck lid, looking for "GU_" or "GT_" codes. A "G80" indicates "Locking differential". With those codes a GM parts person can punch them into their parts catalog database to verify what the codes mean. This would indicate how the vehicle was equipped at the factory. Considering the vehicle, I doubt anyone would have altered things later on.<P>Next hardest way would be to check the stamp codes on the rear axle itself. Typically, about 1/2 way between the center section and the brake flange, passenger side axle tube, hopefully facing toward the front of the car, but might be more toward the top of the axle tube. The code there is the basic "birth certificate" for the axle, noting plant where assembled, dates and such, plus the axle's "guts" are noted by the letter codes on the end of the string of numbers, as in "BP" or "BPT", for example. Again, these codes can be decoded in the charts section of the GM parts database at the dealership.<P>The third hardest would be to remove the rear cover and rotate the ring gear until you hopefully see a stamping on the outer edge of the ring gear, such as 41-10 (which would be a 4.10 ratio) or similar. Number of teeth on the ring gear and the number of teeth on the pinion gear. At that same time, you can look inside the differential carrier housing to see if there are 4 springs or an S-shaped flat spring to indicate a limited slip axle. Taking the cover off would cost you a new gasket and some fresh lube--and might tell you more than you wanted to know about the condition of what was in there.<P>You can use these same methods on pretty much any GM vehicle, as far as I know, at least the ones built from the '60s onward (from what I've seen in the parts books). The labels and such didn't start until the early '80s, if I remember correctly. Without the label, the stamp codes would be the best way.<P>In any event, even with the OD trans, it should be "highway gears" in there, just the matter of degree would be the issue. <P>Just some thoughts . . .<BR>NTX5467

[Guest]

GU1 = 2.41<BR>GU2 = 2.7?<BR>GU3 = 2.9?<BR>GU4 = 3.08<BR>GU5 = 3.23<BR>GU6 = 3.42<BR>GT4 = 3.73<P>Or jack up ONE wheel, spin it twice, and count the driveshaft revolutions.<P>GM put 3.23's behind some non-OD trans. I would be a 3.42 is behind the 200-4R.

[Guest]

<P>Its really hard to help out friends. Thanks for the heads up, i didn't think about that emissions conflict. I think 200-R4's cost like $800 to rebuild. I was hoping to make it reliable for a grand, but now its looking like 1500-2000

[Guest]

It won't effect emissions testing. All emissions testing works off of concentrations, not total flow. The flow may increase with RPM's, but that doesn't necessarily mean that the % or ppms will change.<P>Even if it did work off flows, it would only effect high speed emissions (when the OD would be engaged). Most emissions problems are at idle or accelration, not highway cruising. Many emissions testing equipment works off set RPM's anyway, not speed.

[Guest]

b4black,<P>In California the emissions testing is curretly done on a dyno. They put the wheels in rollers and simulate the engine load by varying dyno resistance at cruising speeds. I didn't think of this until it was brought up since I haven't smogged a car on this new system. I am not sure what other states do this, but California is on the cutting edge of emission testing.

[Guest]

Still a few 100 RPM's isn't going to do much. The effect on emissions will be slight.<P>California is using MTBE as an oxygenate. Dump some ethanol, a different oxygenate, in the tank, and it will more than make up for transmission.