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Speedometer Revolutions #


Dsherm112's Avatar
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09-15-02, 01:55 PM   #1  
Speedometer Revolutions #

1979 Olds Cutlass Supreme Brougham, 305 engine, 3506C Tranny replacement tranny, original tranny was 200 Metric.

I'm unable to find the number for revolutions/mile for the speedometer. It's supposed to be in small #'s on the bottom of the speedometer. The speedometer dial goes from 0-85, if that helps.

Can anyone suggest where I should look?

Thanks,

Sherm

 
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09-15-02, 06:20 PM   #2  
Joe_F
I suggest you take this one to a tranny shop. They have come across this before and can hook you up with the right driven and drive gear to get your speedo as accurate as possible. Either that or any GM dealer should be able to get you the right gears.

As I recall (please keep all posts on the same vehicle together), you are trying to fix the speedometer calibration? It won't be accurate to any great degree with non stock tires as well as a different tranny than original.

Additionally, the low numerical rating of the gearing may have an effect on the car's performance in the long haul. Most combinations are they way they are for a reason (balance of fuel economy, mileage and performance)

 
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09-16-02, 08:11 AM   #3  
I tried to cover all bases before changing the tranny from a 200 Metric to a 3506 C. I talked to my mechanic and the rebuilders tech support people. I also posted here and nothing was ever mentioned about the matching of the tranny to the gear ratio. I was basically told to go for it because the 3506C was a better tranny.

Now that I've done it what can I expect performance wise. It now has a 3506C tranny with a 2.41 rear end. Is this going to improve or decrease performance and mpg. I have noticed that the low gear is not as low as before.

I have worked out the calculations for the speedometer gears, but I'm still trying to determine the cable revolutions/minute to make sure they're ok. I can't find it on the speedometer. Anyone know where it is.

Thanks,

Sherm

 
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09-16-02, 09:00 AM   #4  
Joe_F
Low numerical gears tend to do that with such a tranny .

The original question as you posted it was, "Is this a better tranny". The answer is yes beyond a shadow of a doubt.

The 200C is junk, no doubt about it. A turbo 350 is a wise choice for it, and a 700R4 (overdrive even better).

As I mentioned before without the right size tires, the speedo will not be right.

I believe you had some calculations on the # of teeth you needed for the driven and drive gears in another post (that's why I recommend you keep them all together! ). If so, just take those to any GM dealer and they can match it up on the charts in the parts book.

Just tell them you need a drive gear with X teeth and a driven gear with Y teeth. The parts book should show what you need.

Also there is no "3506C" transmission. It's either a Turbo 350 or a Turbo 350C. The C means "converter clutch", i.e, the clutch locks up as opposed to a non locking converter (done for fuel economy) of the same trans type.

 
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09-16-02, 09:47 AM   #5  
I have used the Bowling and Grippo calculator to figure the speedo gearing. But it requires the revolutions/mile on the cable to make the calculation. I can't find this number to make the calc. It's not on the face. The speedo dial is 0-85.

The calculations I sent previously assumed 1000 revolutions/mile. But in order to be accurate I must recalculate with the proper # for revolutions/mile.

Do you know how I can find the revolutions/mile to make my calcs.

Thanks,

Sherm

 
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09-16-02, 09:52 AM   #6  
Joe_F
Not aware of where that would be but there has to be a way to figure it out.

I know the Firebird and Camaro guys on the internet do it all the time, I have seen it in the forum there.

I don't deviate from stock, so I don't have that problem, sorry .

 
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