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Discussion Starter · #1 ·
ok first off motor and tranny is out of a 84 fifth avenue. 2barrel and all. the rearend is out of 89 dodge Dakota with v8. im going to double check my gear ratio tomorrow. but think its a 355 or 390. all this under a 52 dodge truck. im hoping the a904 is correct on transmission. looks like all the things I can find online. the speedometer cable gear. is grn and has 22 teeth. I put a aftermarket speedometer in the truck. I have been driving the truck locally working bugs out. my speedometer is off badly. its reading that im going faster than I am. for instance I kept it at 40mph and my gps on my phone says I was doing 22mph. so roughly 18mphs off. I stopped by a transmission shop today and he told me I need a smaller gear for transmission. I was thinking I needed bigger. but im no transmission guy. also I was looking and they don't make a smaller tooth gear. so could I change it to electronic readout vss. and use a cable x box? I have one of those from another past project. found a speed sensor for fifth avenue on rockauto and wondering if I could use that. or am I just screwed.
 

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Its the driven gear that needs to be replaced with a larger one.
The gear housing hole is usually offset with 4 positions to accommodate different size gears.
Thanks
Randy

SPEEDO CHART CHRYSLER.jpg
 

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You don't mention it but another problem is probably going to be the torque converter. It is set to lock around 45 mph with the 2.2 gearing of the donor car. It will lock up way too soon with the steeper gears. You need to replace the spring or disable the lockup or the transmission may not last.
 

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Discussion Starter · #4 ·
Ok from what I have read on chart I have 3.55 rearend. 27ish tall tire. So I need 34 tooth gear. Also did some more research. And the factory speedometer out of fifth avenue doesn't read the same as aftermarket speedometer one. So I think that where my issue is. I'm going to check the rearend from fifth avenue and see what ratio it is. I may swap rearends. As the current one has pinion leak. Now to find a 34 tooth gear
 

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The Fifth Avenue has 2.2 gears unless they were swapped out. Great for the highway but a dog off the line.
 

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Discussion Starter · #6 ·
Yes the drive gear is 22 tooth. It's not a dog off the line anymore. I put the motor,transmission, front suspension, in a 52 dodge truck. It pulls out great and runs great. Just speedometer is off in the reading. When stomped to the floor at take off it will get sideways on dry pavement. Just like to fix the speedometer reading on aftermarket gauge
 

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Discussion Starter · #7 ·
Ok I check factory rearend out of the fifth avenue. With 205 75 15 tire. Marked my tire and mark the drives haft and rearend. Rotated tire around twice. Since only one wheel turned when both raised. It goes 2.25. Check few times make sure I was correct. Didn't think they made rear with that ratio. Or would it go to 2.75 rear?
 

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Ok I check factory rearend out of the fifth avenue. With 205 75 15 tire. Marked my tire and mark the drives haft and rearend. Rotated tire around twice. Since only one wheel turned when both raised. It goes 2.25. Check few times make sure I was correct. Didn't think they made rear with that ratio. Or would it go to 2.75 rear?
Like I said before EVERY Chrysler Fifth Avenue (the RWD ones) came with 2.2 gears. That was the only one they offered, no other options.
 
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Ok I check factory rearend out of the fifth avenue. With 205 75 15 tire. Marked my tire and mark the drives haft and rearend. Rotated tire around twice. Since only one wheel turned when both raised. It goes 2.25. Check few times make sure I was correct. Didn't think they made rear with that ratio. Or would it go to 2.75 rear?
What it is, Chrysler had a very sloppy method of determining the axle ratios, so ones that were advertised as 2.20 were actually 2.25 as your accurate, modern method is no doubt confirming.!! LOL

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Ransy
 

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Like I said before EVERY Chrysler Fifth Avenue (the RWD ones) came with 2.2 gears. That was the only one they offered, no other options.
From a 1985 parts manual; which is a little confusing; they listed a 2.26 for both the 7 1/4" and 8 1/4" rear ends. And a 2.94 for the 8 1/4" R.E. only. Maybe for the Diplomat cop cars?
 

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Doobie; there should also be a metal tag attached under a rear end housing cover bolt which states the ratio. A 2.25 ratio will be pretty doggy off the line. And if you swapped rears, spring C to C distance, yolk size, driveshaft length, E brake cables, etc must be considered.
 

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From a 1985 parts manual; which is a little confusing; they listed a 2.26 for both the 7 1/4" and 8 1/4" rear ends. And a 2.94 for the 8 1/4" R.E. only. Maybe for the Diplomat cop cars?
2.94 gears were only used in cop cars. They were standard on 318-4 cop cars and sometimes optional on 318-2 cop cars. All civilian M bodies with a V8 got 2.2 gears. Before 1980 there were a few other option for the early M bodies.
 
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Discussion Starter · #13 ·
Pt006. I did measure all that. The fifth avenue rear is little narrower than the current one. By like 3 inches.
If I could change rearend would that solve my speedometer issue?
It's not a race truck by no means just a driver. I put pressure cats and cat off the fifth avenue and put under it.
 

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I would leave the Dakota rear end in it if it were mine.
That leaves two issues.
First is the lockup torque converter. I'd disable it:
http://www.magnumgt.com/lockup-torque-convertors/
or
http://www.superior-transmission.com/Product_Page.cfm?ID=44
Then next would be to correct the speedometer/odometer.
Once you have the rear tires you want, you can easily figure out the plastic gear to replace in the transmission (at the speedometer cable end).
You can use the chart above or even more accurate drive the vehicle a known distance like 10 miles and see what the odometer records. The ratio of recorded miles vs. actual miles gives you a a factor to multiply by the number of teeth on the current gear in the transmission.
 

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Discussion Starter · #15 ·
Well drove it alot farther than neighborhood today. And turned around came back. Gotta do something with the gearing. So I think I will put the fifth rearend under it. If everything lines up. Which from the measuring I did it should. But today at lunch I went to 3 differant transmission shops. And none has or can get the gear tooth I need. Mine is not the one with metal rod. It's all plastic. They look like the one in pics. Not sure about the whole spring lockup thing. This truck going to drive not try to haul anything or race anything. Just drive and enjoy it.
 

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Doobie; I think you would enjoy the truck more with a 2.94 rear end. And the lock-up converter working, which could be done in the future. [there is an aftermarket kit for ~ $100.00]. I don't know the ratios of the Dakotas, Valiant 67 might. This might not apply to you, but older Dodge trucks had the spring perches welded to the top of the housing, and cars were welded to the bottom.
 

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He is probably correct that the Dakota axle is a 3.5 or 3.9 which can be a lot without an overdrive. But the 2.2 swings too far the other way. 2.9 or 3.2 would be nice but maybe since the 2.2 is already there they'll work ok. Dakota spring perches are on the bottom of the axle for 2wd and above for 4wd.
 
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Discussion Starter · #18 ·
Yes. The spring perches was on top. Being 2wd truck. Have had a few of those trucks. Still got one I have owned for 15 yrs. Bagged and bodied dakota. With alot of modifications. And as far the rearend out of the fifth avenue I drove the car before I tore it apart to put in truck. Run great. So what I'm using it for to drive and enjoy I think if it fit I put the fifth avenue rear under it. And just drive. Gotta get a electric fan or build shroud for it. Or both. It gets little warmer than I like it too.
 

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Dakotas with automatics had either 3.55 or 3.9 rear axle. The 3.55 gave 1800 RPM at 65 mph with the 4-speed auto, and in 3rd gear (which is direct drive as in an A904), engine speed is 2600 RPM at 65 mph.
 
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