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Had a gentleman call me last night and he has a 68 XR7 with a 4-speed manual in it. Says it's the original tranny and been rebuilt once. I have never actually driven a manual transmission car that old. Just wanted to get someones impression/experience/opinion on them. The 3 speed automatics are loud and have me rocking forward sometimes to help it into 4th gear (don't know why I do that) Is having a 4th gear quiet the tranny at all? I know that they are wide ratio which of course is not ideal for muscle cars.
 

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Unless you are using Gear vendors overdrive a 3 speed only has 3 forward gears in a automatic . Manual transmissions can have a gear growl if there is wear , or a dry gear . The wide ratio was intended for smoother highway driving , you can how ever change this ratio to fit the drivers needs . Rev it up and dump the clutch like you stole it .
 

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Having a 4-speed doen't quiet the transmission. It just keeps RPM's lower at higher speeds like on the highway. Advantage is crusing along you don't have to go all the way into 4th gear. Three speeds wind out more...
 

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A lot has to due with the final ratio's - depending on which rear gears it has as to how many RPM's you are turning. "quiet" is open to a lot of interpretation too....that being said my AOD sure made a huge difference on highway comfort and brought the RPM's down to about 1800 at 65....not that my car is "quiet" with headers and performance muff's....
 

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My 70 XR7 4 speed makes a little bit of noise if I accelerate out of 2nd gear but way low in the gear. Noise goes away after I get firther into that gears power zone. That being said, my 2006 Z06 also has a low end growl in first gear which I found is common from other Z06 owners.
 

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Engine RPM (and engine noise) in top gear will be exactly the same for a 4 speed manual as for a 3 speed manual, since both have a direct (1:1) output. A 3 speed automatic (C4, C6, FMX) also has a 1:1 top gear, but because the torque converter never locks up completely, engine RPMs will be somewhat higher at a given speed than with a manual. The transmissions themselves, whether automatic or manual, should be essentially silent. Noise (other than perhaps a slight whine under acceleration) is an indication of a dry bearing, a worn gear or some other non-normal condition.
With a small block engine, the wide ratio toploader is actually preferable as a performance gearbox in most situations, as the extra torque multiplication helps noticeably with acceleration. The main exception is road racing, where its desirable to keep the engine RPMs in a high and relatively narrow band, and running steeper rear gearing than what would be acceptable in a street car is the norm.
Close ratio gearboxes also make sense behind torquey big block engines, since they don't need the extra gear multiplication. But the "big-input" toploaders used behind 427s, 428s and 429s were all close-ratio from the factory, so it doesn't sound like you're dealing with one of those.
 

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cj750 beat me to it
 
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