Slug off the line.

[Bob Booth #33372]

I have a question about gearing for my '72 coupe. It has a C.R. 4sp box and 3:08 rear. The problem is that while 2nd, 3rd and 4th gears are ok, 1st gear seems way too tall. I realize that the 3:08 is for fuel economy and is better suited to land speed record runs than around-the-town driving. My question(s) is/are; Is this usual with this trans. and is it possible/feasible to just change 1st gear to a lower one (higher numerically) or should I just go to a 3:70 ring & pinion and sacrifice top end (I don't do much highway driving and don't care much about fuel economy).


Thanks,


Bob Booth

[Wayne M.]

Re: Slug off the line.

Bob --- I assume (if your car is original) that you have either the LS5 or a ZR1, as those are the only two motor options with which you could get a close-ratio transmission and a 3.08 final drive ratio.


If you have the 454, it shouldn't be a "slug", with all that torque. Your best bet would be to switch to a wide-ratio trans, which would give you the "feel" of a 3.55 (3.52, to split hairs) in the first 3 gears, then a wide gap to fourth (direct drive). Remember, the "ratio" between 1-2, 2-3 shifts with wide and close ratios are identical. I don't believe you can change just one gear with the Muncie, as it involved the cluster gear as well; they probably figured two trans gearset choices (combined with 5 final drive ratios) would pretty well cover the spectrum.


In your case, it may boil down to the cost of a transmission swap, versus rear end swap, as you don't do much highway driving, but the wide ratio gives you the best of both worlds.

[Bob Booth #33372]

Re: Slug off the line. Maybe not a C.R. box?...

Wayne,


After reading your response it got me thinking. It's not an LS5 or ZR1 (I wish) and almost nothing on the car is original. The engine is a 350/300, nothing special. I assumed that it was a c.r. box because the shifts go very quick (more like a 6 sp. dirt bike) even compared to some of the race cars I've driven. If what you say is true (that the ratio between 1-2, 3-4 is the same with c.r. and w.r.) then god knows what's in there. Also, if the ratios are the same, then what's the difference between them? I crawled under the car to take a look and the only numbers I can see (pass. side) are as follows. Maybe someone out there can help me identify it;


392566 GENERAL MOTORS CORP. U.S.PAT. NO. 3088366


3978764 GM

[Bob Booth #33372]

Maybe not a C.R. box?...additional numbers...

I failed to give the stamped numbers on the trans.;


P2BO3A 1255137?1


Thanks again, Bob Booth

[Wayne M.]

Re: Maybe not a C.R. box?...additional numbers...

Bob --- The P2B03A tells us the trans was assembled on Feb 02,1972, and the letter "A" indicates WIDE RATIO. (B=close ratio, C=M22 "heavy duty" close ratio). Not sure about the other #'s; could it be 12'S"(for St.Louis)5137x1, and does the VIN # of your car end in 137x1 ? If so, this trans could be the original unit for your car, because its assembly date code would correspond with the timeframe of the VIN.


The maincase # has another digit; 3925660 or 661. I don't have the proper source books, but the 661 might be correct for a '72. Others would have to confirm the tailshaft (extension) #.


But the real acid test for close versus wide ratio is to compare indicated speed at the same RPM's in first and 4th gear. If the speed in 4th is 2.52 times the reading in 1st, you have the wide ratio. (Also, the 3-4 shift will indicate a bigger gap / drop in RPM, holding constant speed, than the 2-3 shift w/constant speed). If the speed in 4th is only 2.2 times the speed in 1st at the same RPM, then you have the close ratio. This method doesn't depend on having the correct sending (speedo) gear in the transmission, nor stock tire sizes. You do need a speedometer that is in correct linear calibration, though.

[Bob Booth #33372]

Re: Maybe not a C.R. box?...Thanks Wayne...

...for the response. Yes, the third character in the VIN is an S. I caught it after my posting last night and tried to update you but this *%#@*^ white screen scourge is drivin' me nuts! It keeps bootin' me off or loses my postings somewhere in cyberspace. Anyway, I also caught Joe's posting below on the M-20 which echoed what you said. As far as the trans. being original to my car, I don't know because thr car has a state issued VIN. Apparently the car was stolen and recovered at some point so there's really no way for me to track it's history unless I can find a tank sticker (which I plan to look for) or track the VIN on the trans. somehow. In any case, you gave me the info I needed and I thank you for that.


Regards,


Bob Booth