Diff gear recommendations

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I've emailed Cass about options and where they're made.
Professor Fate said:
Doctor Diff- manufacturer seems to depend on the ratio and carrier. Not sure of the country of origin on some of them, some (like the 3.55/741) seem to be his own brand. Could always ask him. Not a bad price, either.
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4spdragtop said:
Hey all, I'm contemplating a diff gear change from our factory 323 to 355.
I'm not looking for top of the line, but want quality and NA made, if possible. Next to zero track time(once for the bucket list)
Mfg recommendations??
Thanks
Steve
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Steve, I'm considering the exact same thing so I'll ride along on your thread!!. Like you, I'm 99.9% street. Wouldn't mind taking it down the strip a time or two but really just want to have fun on the street. Don't do a ton of highway so that's not an issue.

I'm also running 3:23 Surgrip, but it's a 742 pig. 5.9 warmed up a bit with a PTC 9.5" convertor.

Please let us know what Cass says.
 
Cool! :thumbsup: Ride shotgun! As I mentioned the engine runs great but would like to add oomph. I probably drive 80-90% street or very short highway stints.
66fyssh said:
Steve, I'm considering the exact same thing so I'll ride along on your thread!!. Like you, I'm 99.9% street. Wouldn't mind taking it down the strip a time or two but really just want to have fun on the street. Don't do a ton of highway so that's not an issue.

I'm also running 3:23 Surgrip, but it's a 742 pig. 5.9 warmed up a bit with a PTC 9.5" convertor.

Please let us know what Cass says.
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I went with 3.55s for my 741 case I used Motive performance gears. Very happy with the quality and they are quiet.
 
Your cam may be too big for lo end street performance and your rear tires too tall.
A stock style cam and stock rims / tires will probably get you what you want
This will pin you in your seat from 1000 rpm to well past highway speeds with 3.23
gears, be a blast to drive and probably get 20 mpg,
Mopar got the 340 A body cars right. Now if you are going racing you will need some changes
 
Keep the 323's and get a 3500 stall converter. . It will drive normal and kick *** power on acceleration. I went from 323's - 355's -391's -410's still had a hard time spinning a set of factory size tires riding the brake.

I installed a cheap 3500 GER converter and went right back to 323's . It torches the tires from a throttle stab with no brake.

All the 340 cars I bought in the 70's brake stalled at 2800- 3000 if they had a factory 340 converter. Put that same converter behind a 383 or 440 and it brake stalled at 3300 -3500. I did it many times on many different cars.

I had one RR that had a chrysler New Yorker trans put in. That converter turned the car into a real pooch. Back in the 80's the turbo action XX was the replacement for 340 and Hemi. advertised stall 3000- 3500

Believe me skip the gear change and get a converter. What trans do you have a 727 or 904 and what year?
 
I have used high stall converters and they will provide lo end tire spin but that's about it and for me the novelty wore off for street use. They are no fun driving on hilly or curvy roads at speeds. It's a learning experience and a constant battle driving through them which i grew to dislike. But will certainly provide you with burnouts from idle
and are well suited for racing.
 
ir3333 said:
I have used high stall converters and they will provide lo end tire spin but that's about it and for me the novelty wore off for street use. They are no fun driving on hilly or curvy roads at speeds. It's a learning experience and a constant battle driving through them which i grew to dislike. But will certainly provide you with burnouts from idle
and are well suited for racing.
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If they provided tire spin, you need more traction, not less convertor.

If you have a high quality, proper flash stall convertor, built for your engine, chassis and application, you won't even notice it's in there until you matt the go pedal.
 
I hated 3.55s either 3.23s or 3.91s
I agree with 273 good verter with 3.23s for the win
What cam do you have?
 
3.55s for a 741 case are available new from Dr. Diff and others.

My rear end builder thought they were going to be noisy because of the grind (3 face vs 5 face or something like that) but was very pleased with the results. He got a great pattern on bothe drive and coast side

No noise that I have noticed.
 
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Hi Steve. I don't know anything about your combo. Could you please share.
 
For a street machine I'd be worried about offshore gears and noise.
 
4spdragtop said:
Looks like 741, I'm a dumbass.
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Looks like the Motive Gear is your best bet cost wise. ......but I gotta say it. IMO, the 3.55 is the most useless as tits on a boarhog ratio there is. lol I mean, the 3.23 is the perfect balance between highway and performance. The 3.55, while it's not a big change, IS a change and you WILL notice it. I would just go straight to the 3.73. And the reason I say that is because the mileage difference between the 3.55 and 3.73 will be absolutely minimal, yet the performance difference between the 3.23 and 3.73 will be huge.
 
4spdragtop said:
Cool! :thumbsup: Ride shotgun! As I mentioned the engine runs great but would like to add oomph. I probably drive 80-90% street or very short highway stints.
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80-90% street, and very short highway trips.
Sounds like 3.73s to me. I like to see at least a half ratio change to make the expense worthwhile. Add a converter with about 500-750 rpm more stall than you have now (500 would probably be best) and you will have a completely different car. If you find that the 3.73s seem a bit too much, run the tallest tire that will fit in the wheelwell.

Edit: my performance street car runs a 4500 converter, and 3.91s. My other car, I bought a 4.10 pig to change out the 3.50s, so take my advice with a grain of salt, or two.

2nd edit: Rusty's #41 posted while I was typing. I agree.

3rd edit: don't be afraid of the "weak" 741 reputation. Check out Dr Diffs comparison of the 741, 742, and 489 pinions. Smallest part of all three is the same. Extra metal elsewhere doesn't mean much. Remember weakest link. Weakest link of all three pinions is the same.
 
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I made the change from 3.23 to 3.55.. it did increase the Rpms to the point I bought taller tires to get the 3.23 feel back.



RustyRatRod said:
Looks like the Motive Gear is your best bet cost wise. ......but I gotta say it. IMO, the 3.55 is the most useless as tits on a boarhog ratio there is. lol I mean, the 3.23 is the perfect balance between highway and performance. The 3.55, while it's not a big change, IS a change and you WILL notice it. I would just go straight to the 3.73. And the reason I say that is because the mileage difference between the 3.55 and 3.73 will be absolutely minimal, yet the performance difference between the 3.23 and 3.73 will be huge.
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I hated 3.55's and higher. What most don't realize is that cruising on the highway at 2800 isn't really much on paper compared to 2500 but it is in the car. The increased rpm includes the fan, water pump, fuel pump, alternator, power steering pump, oil pump, crankshaft, camshaft, distributor. driveshaft, universals, etc. This magnifies all the noise, vibrations and harmonics and will produces a ride many won't like. (especially us older guys)
Modern vehicles drive smooth and quiet because they cruise at or below 2000 rpm.3.23's are not bad but 3.55's or higher as a driver...Run Forest Run!
I can hear all the murmurs
And Rocco....my hi stall converter was spec'd for my engine and car by Frank Lupo, and for a race application worked fine. My posts are based on what i found and i like or dislike.
 
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ir3333 said:
I hated 3.55's and higher. What most don't realize is that cruising on the highway at 2800 isn't really much on paper compared to 2500 but it is in the car. The increased rpm includes the fan, water pump, fuel pump, alternator, power steering pump, oil pump, crankshaft, camshaft, distributor. driveshaft, universals, etc. This magnifies all the noise, vibrations and harmonics producing a dreadful ride for most (especially us older guys) Modern vehicles drive smooth and quiet because they cruise at or below 2000 rpm.
3.23's are not bad but 3.55's or higher as a driver...Run Forest Run!
I can hear all the murmurs
And Rocco....my hi stall converter was spec'd for my engine and car by Frank Lupo. My posts are based on what i
found and i like or dislike.
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As an older guy I must disagree. I downshift to hear that noise.:poke::steering:
 
junkyardhero said:
ohh! now you done did it. just you wait till AJ gets here!
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OP,
IMO
there is no better mod to a city-cruizer, than a 2800/4bbl.
In your case, IMO, Rear gears are just to fine-tune the fun factor.
Around town, with a 2800,
you'll be hard pressed to notice the 10% increase in Torque-multiplication, from gearing. This is because for most of the time, you will be in Second gear, and when you increase the throttle-opening, the PT KD will shift you into First which will give you an instant 69% boost in torque multiplication, in addition to the horsepower increase from the higher rpm, in addition to whatever might be going on inside the convertor.. What's 10% on top of that?
Therefore. I recommend to install the 2800 FIRST, then just drive it. The increase in stall is/was, to me, ridiculously satisfying.
THEN decide if you still want the gearing.
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As for me;
Ok so, there are exactly two reasons that I run 3.55s over 3.23s , in my M/T car;
1) so I can idle around the parking lot at 3.5>4 mph with a manual trans, and
2) is to hit 93mph at WOT, at a more favorable rpm, in Second-over.

I actually LIKE 3.23s better, but in overdrive, I get NO BETTER mpgs, so the 3.55s can stay.
I actually liked 2.76s the best. And so with the GVod, 3.55x .78=2.77, that's another reason I have 3.55s; they are a means to an end.
If/whenever I had a factory 318, I would also have a 2800 stall, no exceptions. With a 2800, BAM!,
I like 2.76s, with a 4bbl; why? cuz 5500=60 mph in first gear.
What? your factory low-compression 318 won't go 5500?
Yes it will. You just gotta ask nicely.
If it goes 60@ 5500, it will go 50@4600, and thus; 25@2300, which, with a factory cam, is at about peak torque. So then, when you downshift at 25, into first gear, Bam! you are ready to rock with the factory cam. And besides all that;

With a 2800, 2.76s, and a Thermoquad; When you floor it off the line, the TQ will whack wide open, and moan for as long as you dare stay in it. 15/16/17/maybe18 seconds to ~80 mph, which with headers and dual 3inch exhaust, is music to the Soul.
And yes, I tried the A904 with 4.30s as well, lol.
>But with a manual trans/overdrive; I hit it with everything I had up to 5.38's
Did you know that;
4.88s with a double overdrive seven speed is 2.70 for cruizing, lol.
I still have those 4.88s if anyone asks........
 
AJ...what cam have you installed in these cars to require a converter that stalls at 2800 rpm. My last build was
a stock low compression 340 dart with 1.88" intake valves and a small 204/214 melling replacement cam with
3.23 rear gears. Launching with care would pin you in your seat to well past highway speeds and launching carelessly would just produce tire spin. I had the torque converter custom built for the engine and car combination and it stalled around 2450 rpm.
 
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