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Discussion Starter · #1 ·
Vigo on Allpar said:

Note that on a non-overdrive like the 3 spd autos your diff ratio and overall top gear ratio would be the same because the highest gear in our 3 speeds is 1:1. 1:1= 1, times X, = X. The 4 speeds have an overdrive 4th gear with a ratio of .69:1.

so if you have the common differential ratio (for the 604) of 3.6:1, and you multiply that by .69, you get the common 2.49 overall top gear ratio. so for every one revolution of your tire, the engine turns 2.49 times in 4th gear. you can also extrapolate the effective differential ratio by going backwards from the otgr with .69. i.e. you have a 2.49 otgr, 2.49 / .69 = ~3.6. I say effective differential ratio because it is actually the combined ratio of the transfer gears on the side of the transmission and the actual ring and pinion gearset in the differential. determining the split between those two is more complicated because the tooth counts/ratios of the transfer gearsets arent really documented here.

so if you are cruising down the road at 65mph and 2000 rpm in 4th, you can do 2000 / 2.49 = 803, so at 2000 rpm in 4th your wheels are spinning at 803 rpm or so. this will actually work for any gear if you know both the gear and differential ratios.




I've got a '93 Spirit ES 3.0 with a column shifter that reads (D)-3-L, and an '89 Spirit ES 3.0 with a floor shifter that reads (D)-D-L. Any difference, or just style points?

Also, I have a '93 LeBaron (AA) 3.0 with a column shifter that reads D-2-1. Does this have a lock-up torque converter, and does that make a difference to the formulas that Vigo presented?

Also, are any of the gears (differential or transmission) swapable in order to create custom ratios? I would love to get a 604 to run at about 1,500 at 65 mph...

Thanks,
Dave
 

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The 604 did have a gear swap, it came from a 2.0 stratus atx, the was the end drive gears that can be swapped, I forget the count of teeth vs. the 604 gears.

Here is a link that might help with the FD gears:
The A604

The Final drive mod for the A604/41te tranny
Well, here it is tried and true.It really works! Given a set of new drive gears from the 99 Dodge stratus with the 2.0 motor (part# 4773275) this mod takes about and hour.The stock gears are a 47/49 tooth count , where as the stratus gears are a 46/50 count,better gear ratio for better acceleration.
 

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Discussion Starter · #5 ·
So the next question is (if anyone knows or can tell by the pix): Are the drive and driven gears interchangable? That is, can I run the 50 tooth as the drive gear and the 46 as the driven gear ( thus giving less power off the line but lower RPMs at freeway speeds?
 

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I believe someone wanted to do that but found the gears did not mesh due to tooth count, someone correct me if i'm wrong!!

If you really want to find out it will take alot of digging over at yahoo chysler3literv6 groups where I originally found out about that mod. I was going to try it but blew my A604 up and swapped to a A543 manual tranny.

Good Luck!
 

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Discussion Starter · #7 ·
I believe someone wanted to do that but found the gears did not mesh due to tooth count, someone correct me if i'm wrong!!

Good Luck!
I just finished unbolting the trans from the engine before lunch, so if all goes well I'll have the answer by the end of the day.

By the way, anyone know how to do the math (or even all the variables) to figure out what I need to change to reach my desired 1,500 RPMs at 65 MPH?

OK, I found an Excel spreadsheet at the Chrsyler3literV6 Yahoo group, and I found that I can get where I want to be by having a gear ratio (GR) of 3.00 (vs. 3.55 for a stock 604). So the bigger question is:

What components make up the gear ratio?

Thanks,
Dave
 

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Discussion Starter · #8 ·
DING!! DING!! DING!! We have a winner!!!

Maybe...

http://www.turbododge.com/forums/f4/f22/121219-trans-differences.html

This chart by 22dodge shows various transfer, output, and pinion/ring combinations used in different 604ish applications over the years.

Are the pinion/ring easy to swap?

If so, than it looks (if I have any idea what I'm talking about) like 46, 50, 54, and 59 tooth gears are available for the 16/60 pinion/ring combo, while 46, 47, 49, 50, 54, 55, 58, and 59 tooth gears are available for the 17/59 pinion/ring combo.

If the transfer and output gears happen to be interchangable, the number of combinations would be...um...big.
 

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Are the pinion/ring easy to swap?
It would require pulling the tranny to work on the differential, if going that far install some diff pin savers which are cheap from the dealer!

IF the ring/pinion from a 2.0 status are the usable, then that paired with the 2.0 gears would be the best bet since it has a over all ratio of 4.07, the 16/60 make it 3.75:1 alone, while the 17/59 are only 3.45:1

That paired with taller tires should get quite bit better fuel economy.
 

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So, doing this for fun, but if my calcs are right.

to get near 1500rpm @ 65mph, you need 3.17FD + 45" tall tires

(65x3.17x336)/45 = 1538.506... rpm

I guess I was wrong thinking higher FD = lower rpm on the 4.07 since that paired with 45" tires will be:

(65x4.07x336)/45 = 1975.30666... rpm

with the 4.07FD you need about 60" tires to get around 1481rpm at 65mph
 

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Discussion Starter · #11 ·
Wow, would 45" tires really fit my car? :eek:



Sorry, couldn't resist. If I have the 17/59, then I'll go with the 54/59 combo from the 3.8 Imperial. If not, then I'll see if I can swap the 17/59 in. The donor was a scrapper, and I don't recall the year. I can check the tranny tag tomorrow.

Many folks talk about how weak the 604 is, and 22dodge/Allmotor mentioned that he does over 100 upgrades to make them better. I PM'd him but he hasn't responded yet, so does anyone else know what the list of upgrades is (or at least the list of most likely to fail parts)? I have the time and reasonable funds :two cents: to build it right, I just need the build list.

Thanks,
Dave
 

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Just to let you know, those calcs are wrong, you need to know overall ratio (those are just FD ratio). I found that using Final drive ratio is wrong and must use Overall ratio which is 4th on the A604 x Final Drive ratio to find true engine RPM for a given speed!

I was trying with my A543 with 3.77FD and my 15" tires (205/60R/15's) which should be about 24.65" tall

with that at 40mph:
(40x3.77FDx336)/24.65= 2052.2rpm. When testing that today at 40mph in 5th gear its just under 1500rpm.

I found the overall ratio is 2.68:1, so lets do this again
(40x2.68x336)/24.65 = 1461.23rpm. THATS MORE LIKE IT!

So with this you need to find your Overall ratio before going trying diiff tire sizes!

Either way, 3.17FD would be your best bet to lower engine RPM at 65mph
 

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Discussion Starter · #13 ·
Re: 604 gear swap? Now with teeth...

Well, I counted my teeth today. Turns out I've got 59 on the top and 54 on the bottom. This may seem like a strange number for a human, but I am a Chrysler enthusiast... :D :p

According to 22dodge's chart, this 3.17 ratio should only have been available with the 3.8 AY body (which makes sense because the extra power would allow it to lope along). I pulled mine from a 3.0 AA body. Go figure.

Reaper1 (thanks man) turned me on to ASOG, which has a list of a604 build ideas here:
ASOG.net - A604 Information

What do you guys think of the list? Any ideas on where to get these parts? Why doesn't TD have a list like this? Should I do a pictorial of my tranny build and post it? Will you have my baby?

Thanks,
Dave

"Don't taze me, bro!" :party2:
 

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Discussion Starter · #14 ·
Either way, 3.17FD would be your best bet to lower engine RPM at 65mph
chysler3literv6 has an Excel spreadsheet that does the math for me. A 3.17 with 215/60 16s (as it happens, I have 16's) will run about 1,800 at 65 MPH.

Oh Happy Dave!
 
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