3K rpm at 50 MPH... What gives?

[RCCDrew]

I have a phone app that tells me how fast I am going. Free download.

[charlie challenger]

I use my wife's flip phone when I need to make a call. 

[734406pk]

Ok great! The transmission shifts into Drive. The next step will be to get accurate travel speed and engine rpm from a cell phone and a hand tach. Drive 50 mph actual and record the rpm from the hand held tach. Post back the results and we can go from there. Drive safe!

[charlie challenger]

Alright, found the problem.  Today I put a spring on the kick down linkage, made sure I had 3.55s by turning the wheels 1 rotation & watching the drive shaft make 3.5 turns, and went and bought a tach.  The tach I hooked up reads way different than the tach that I have in the car.  When mine read 3000 the new tach read 2000.    When my tach read 4000 the new one read 3000.  When my tach read 5000 the new tach read 4000 then I turned it off & anifreeze boiled out of the radiator cap. I was surprised more didn't come out of the overflow tube before blowing the cap.  I'll have to adjust my tach circuit board to where it reads the same as the new one.

What I'm not sure about is when at idle my tach is reading 1000, but the new tach is at 500.  Is that possible?  I've got a mild comp cam with .470 lift.  Can that hold an ide at 500?  It stumbles a bit, and I loose it sometimes and have to restart the car.  I'm going to have to assume it's more accurate than mine though.   

Now my main concern is what the transmission guy pointed out to me... the drive shaft is too short.  I searched for extended slip yokes but couldn't find one.  I need to be in there an inch or an inch and a half more.  Does anyone sell extended yokes, or am I going to have to get a new drive shaft?  I got it back in 2007, and I don't remember what shop it was from.  They really gave me the shaft though!

[charlie challenger]

forgot pic

[anlauto]

Might have a Cuda driveshaft in your Challenger

[joelson6]

uh, this is 2015, right? has anyone heard of a GPS? it's this new technology that connects to satellites and

gives you your exact location on a map in the display. and if you look through the menus, you can find a setting

that gives you your MPH while driving. 

[msbaugh]

uh, this is 2015, right? has anyone heard of a GPS? it's this new technology that connects to satellites and

gives you your exact location on a map in the display. and if you look through the menus, you can find a setting

that gives you your MPH while driving. 

If you read his post you would know a GPS wouldn't have helped. His tach was off not his speedo or speedo gear

[joelson6]

i did read the post and actually it would have helped.  at first he wasn't sure if the tach or the speedo was off. this would have verified the speedo. 

[charlie challenger]

I like to party like it's 1999 with my flip phone.  I'm thinking about getting a pager next.

[anlauto]

I like to party like it's 1999 with my flip phone.  I'm thinking about getting a pager next.

Hey...I'm 49 and don't even have a mobile phone All about my land line baby

[RCCDrew]

You guys need to get with the times. My phone tells me speed, has a dyno, a level and plumb bob, a compass, etc. they can even check engine codes on OBD II. Doesn't make a very good hammer though. 

[charlie challenger]

So does anyone know of anywhere you can get an extended slip yoke, or does that not exist for mopars?

[734406pk]

Might have a Cuda driveshaft in your Challenger

  I don't know where you can get an extended slip yoke but the path I recommend is a longer drive shaft. Appears to be approx. 2" short (Cuda). A new drive shaft can be custom made at a reasonable price.The hand held tach readings seem to be correct, except for that idle speed reading being very low. Also the coolant blowing out is a concern. What is your coolant temperature when this happens? Do you have a thermo-clutch fan? Vee belts tight?
 Also what type of ignition system are you running? Factory electronic, MSD or other?

[burdar]

Post a picture of the seal at the back of the trans.  The stock seal has a dust boot at the end of it.  Some aftermarket seals don't have this extra dust boot.  Without that boot in place, it will LOOK like the driveshaft is short.  There was a guy on Moparts with this problem just a few weeks ago.  It LOOKED like he had the wrong shaft in the car but it was correct.  He was just missing the dust boot on the back of the seal.  Post a picture of what you have.