[pSun]

Hello,

I am currently working out some kinks in our 90 Plymouth Sundance, 2.5 liter TBI, with the A413, 3 speed automatic transmission. The tachometer isn't currently working and my previous attempts to repair have failed (so far).

I have been told that while traveling with my 3 speed automatic transmission in 3rd gear @ 65 mph, the engine is turning "approximately" 2,800 rpm, near or at maximum torque.

What I would like a bit of help with is the following:

1) At what vehicle speed in 1st gear, is the engine making 2,800 rpm? Lets call this vehicle speed A.
2) At vehicle speed "A", if I shift manually into 2nd gear (without increasing the vehicle speed), what rpm is the engine turning (in second gear)?
3) At what vehicle speed in 2nd gear, is the engine speed 2,800 rpm? Lets call this vehicle speed B.
4) At vehicle speed "B", when I shift manually into 3rd gear (without increasing the vehicle speed), what rpm is the engine turning?
5) At what vehicle speed is the engine rotating 2,800 rpm in 3rd gear?

I don't expect anyone to know these numbers off the top of your heads, so I am actually asking you to, perhaps, today or tomorrow, while running a local errand or driving to work, if you (whomever doesn't mind) don't mind doing a stranger a small, seemingly ridiculous favor, to check these vehicle and engine rpm speed for me.

 

[John Wood]

You might get a few different answers if a few people actually try this out. Those are not normally published and since you have a lockup converter, you have to be sure what condition it is in. For example, when the engine is under load, like in going up a hill, the computer will not provide a lockup signal at the usual 43 MPH and the RPM's will run higher. IIRC, the lockup can only take place when you are in 3rd. For #5 you pretty much answered that yourself. I have noticed that at 70 MPH on my Spirit, I am running about 3050 RPM, but the factory tach could easily be off by 50 or more RPM.

If I get a chance tonight, I'll try to see what speed I am going in 2nd gear at 2800 RPM. It might be tough around here with the traffic congestion but we'll see how it goes.

 

[Bob Lincoln]

You're in luck. Awhile back, I made a table of RPM vs speed vs gear, based on published gear ratios for various cars I owned or considered buying. So here you go:

A-413:
1st gear: 2.69:1
2nd gear: 1.55:1
3rd gear: 1.00:1
Reverse: 2.10:1
Axle: 3.05:1

1st gear at 2800 RPM is about 25 mph
shifting into 2nd at 25 mph, RPM drops to about 1700 RPM
2nd gear at 2800 RPM is about 42 mph
shifting into 3rd at 42 mph, RPM drops to about 1800 RPM
2800 RPM in 3rd gear should be about 65 mph

This will vary a little with tire size, I think this is based on 15" (849 tire revs per mile).

If you want to swap your tach board with my known good one, let me know. I have a partial schematic and can test it functionally, maybe find a bad component if there is one. Make sure the Chrysler P/N is 4375410, that's what I have.

 

[John Wood]

I can confirm the 42 MPH at 2800 in 2nd gear. That is about all I could do on the Spirit on my commute home and I couldn't stay at a constant speed for long because of tight traffic. It takes 35-40 minutes to go 8 miles in this urban sprawl, so we move pretty slow.

 

[pSun]

FELLAS!!!

Thank you so much for even being interested enough to assist me! I was somewhat uncomfortable throwing out "an" assignment for non-involved members to bite on.

John Wood: thanks for taking the time to real world what you could.
Bob Lincoln: thank you for having thought about my dilemma before it happened. I will pull the board again and check the P/N. I can get a hold of replacement used boards and the actual speed o mechanism. Sounds like it is the board; there was a peculiar "red" marker, mark near one of the capacitors on the board. This made me think that perhaps the previous owner had it looked at and a discrepancy was unearthed.

 

[Bob Lincoln]

How is the tach behaving? Is it just dead, or does it flutter/fluctuate all over the scale, or read too high or low? Or work intermittently?

 

[pSun]

Bob it is completely non-active, "dead", the needle rests on the peg. The illumination lamps are working, that is it.

 

[GLHS60]

A-413's have transfer gears that are easy to change and are available in 3 ratios. Most are about 1.05 but some early Omni's had 1.22 for faster acceleration but higher cruising RPM. Early K cars and later Omnis had .91 for slower acceleration but lower cruising RPM. This has nothing to do with your original question that Bob answered but might be of interest if you are trying to lower cruising RPM.

Thanks
Randy