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Speedometer way off!..and third gear rpm question #962346
03/30/11 11:39 AM 03/30/11 11:39 AM
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451 D*O*D*G*E Offline OP
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451 D*O*D*G*E  Offline OP
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My Chall has 255/60/15's on the rear,auto and sure grip .First off my spedo is 20mph off till about 50 then climbs to 30 miles off consistantly.At 75 on the GPS my speedo is on 120.Any ideas??Alos guy i bought the car from claims it has 3.91's but 4000rpm's at 70 mph seem right??.Thats flat azz screamin!Thanks for any help.

1970 Challenger R/T clone 2010 Dodge Journey R/T black,awd,
Re: Speedometer way off!..and third gear rpm question [Re: 451 D*O*D*G*E] #962347
03/30/11 11:49 AM 03/30/11 11:49 AM
Joined: Jan 2003
Posts: 24,562
Brookeville, Md
Mr.Yuck Offline
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Jack the car up and count the number of times the driveshaft turns per one rotation of the wheel. 3 1/2 turns = 3.55, almost 4 = 3.91's a tad more than 4 = 4.10's.... 4k at 70 seems high to me however I usually run 275/60/15's and they are about 1" taller 27" vs 27.99"

whoops forgot, you need the right speedo gear. find out what rear and check e-bay for the correct gear.

[IMG]http://i66.tinypic.com/pui5j.jpg[/IMG]
Coming soon!!!!
Re: Speedometer way off!..and third gear rpm question [Re: 451 D*O*D*G*E] #962348
03/30/11 11:55 AM 03/30/11 11:55 AM
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With a 27" tall tire at 70 MPH, 4000 RPM's sounds more like 4.56 gear. Did you check that 70MPH with the gps or the speedo? You would also need to switch the speedo gear in the trans to compensate. 44 tooth gear I believe. 70 with 3.91"s should put you in the 3400 rpm range.

There are differences in shaft length on the speedo gear, so make sure which one you have. Also when changing the gear you have to use the correct setting on the case.
Re: Speedometer way off!..and third gear rpm question [Re: Mopar_Country] #962349
03/30/11 12:06 PM 03/30/11 12:06 PM
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451 D*O*D*G*E Offline OP
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Quote:

With a 27" tall tire at 70 MPH, 4000 RPM's sounds more like 4.56 gear. Did you check that 70MPH with the gps or the speedo? You would also need to switch the speedo gear in the trans to compensate. 44 tooth gear I believe. 70 with 3.91"s should put you in the 3400 rpm range.



...with the gps.The 4g's was 120(on the speedo) or basically pegged but showing a consistant 70mph(gps) on a wide open highway with no hills or satillite obstruction.
I'll go out and turn the wheels and let you guys know what i found out.First gear only good for tire spinning.

Last edited by 451 D*O*D*G*E; 03/30/11 12:07 PM.
1970 Challenger R/T clone 2010 Dodge Journey R/T black,awd,
Re: Speedometer way off!..and third gear rpm question [Re: Mopar_Country] #962350
03/30/11 12:08 PM 03/30/11 12:08 PM
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451 D*O*D*G*E Offline OP
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Quote:

With a 27" tall tire at 70 MPH, 4000 RPM's sounds more like 4.56 gear. Did you check that 70MPH with the gps or the speedo? You would also need to switch the speedo gear in the trans to compensate. 44 tooth gear I believe. 70 with 3.91"s should put you in the 3400 rpm range.

There are differences in shaft length on the speedo gear, so make sure which one you have. Also when changing the gear you have to use the correct setting on the case.





Hey i'll go out and do it now..be back in half hour thanks

1970 Challenger R/T clone 2010 Dodge Journey R/T black,awd,
Re: Speedometer way off!..and third gear rpm question [Re: 451 D*O*D*G*E] #962351
03/30/11 02:46 PM 03/30/11 02:46 PM
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451 D*O*D*G*E Offline OP
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Half hour turns into three,uncle had heart attack,duaghter is sick had to go get her,well they are definetly 3.91,just shy of 4 revolutions..would the 3500 stall make any difference?I will check the setting on the trans this weekend thanks for all the help!!!

1970 Challenger R/T clone 2010 Dodge Journey R/T black,awd,
Re: Speedometer way off!..and third gear rpm question [Re: 451 D*O*D*G*E] #962352
03/30/11 03:00 PM 03/30/11 03:00 PM
Joined: Apr 2010
Posts: 1,216
Under My Car
Mopar_Country Offline
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You may have to physically change the gear in the trans, simply setting the adapter will not fix the problem. 27" tall tire 3.91 should be 38 tooth gear. If it's not that is why your speedo is whacko.
Re: Speedometer way off!..and third gear rpm question [Re: 451 D*O*D*G*E] #962353
03/30/11 03:00 PM 03/30/11 03:00 PM
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Rio Linda, CA
John_Kunkel Offline
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With 255/60/15's and 3.91 gears you need a 38-tooth speedo pinion. (Color blue P/N 52068060)

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Re: Speedometer way off!..and third gear rpm question [Re: John_Kunkel] #962354
03/30/11 08:36 PM 03/30/11 08:36 PM
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451 D*O*D*G*E Offline OP
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Ok,i'll order that one.What is the setting on the trans for,fine tuning?Still 4000 at 70 on the GPS..i'll get the wife to follow me out the highway some night.Dont know the accuracy of the gps.Thanks again.

1970 Challenger R/T clone 2010 Dodge Journey R/T black,awd,
Re: Speedometer way off!..and third gear rpm question [Re: 451 D*O*D*G*E] #962355
03/30/11 08:51 PM 03/30/11 08:51 PM
Joined: Nov 2007
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Kirkland, Washington
Pacnorthcuda Offline
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Quote:

Ok,i'll order that one.What is the setting on the trans for,fine tuning?



If you mean the clocking of the pinion housing....no. Its because pinions with more teeth are larger than those with less. The 'center' hole in the housing is not centered, for that reason. Correct clocking will ensure correct tooth engagement with the worm gear portion of the output shaft of the tranny.
It has no 'fine-tuning' effect whatsoever.
Re: Speedometer way off!..and third gear rpm question [Re: Pacnorthcuda] #962356
03/30/11 08:55 PM 03/30/11 08:55 PM
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With the 38 tooth set it just like the chart I posted above. If you look at the speedo cable threaded portion you can see it's not centered on the adapter.

You should be able to find one on ebag, I just picked up one for 20 bucks, in great condition. If you can't find one there Brewers Performance should have one.
Re: Speedometer way off!..and third gear rpm question [Re: 451 D*O*D*G*E] #962357
03/30/11 09:25 PM 03/30/11 09:25 PM
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Sunny South Florida
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Quote:

i'll get the wife to follow me out the highway some night.Dont know the accuracy of the gps.Thanks again.



just take her car and the gps, and see for yourself. you'll know in a matter of seconds, if it's accurate. if it knows you're going 23 mph it should know your going 70. if the convertor is slipping, your rpms will be excessive. are you positive it's shifting into third? run through the gears manually, and see what is what.

"When Tyranny Becomes Law, Rebellion Becomes Duty"
Re: Speedometer way off!..and third gear rpm question [Re: Golden-Arm] #962358
03/30/11 09:49 PM 03/30/11 09:49 PM
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ky.
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You've got a set of 4.56's.
Re: Speedometer way off!..and third gear rpm question [Re: Golden-Arm] #962359
03/30/11 09:51 PM 03/30/11 09:51 PM
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451 D*O*D*G*E Offline OP
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I just never messed with that part of the housing other than taking the speedo cable off..thanks for all the help i have a manual valvebody and i am definetly getting into third.

just take her car and the gps, and see for yourself. you'll know in a matter of seconds, if it's accurate.Yeah it works great but didnt know if a gps can be affected by weather.Dont know much about them.Her Edge and Garmin are dead on together.

Appreciate the help..been into Mopars since '91 striaght through and definetly dont know everything,even some simple stuff like this which was foriegn to me.I enjoy learning..so much appreciated men.

1970 Challenger R/T clone 2010 Dodge Journey R/T black,awd,
Re: Speedometer way off!..and third gear rpm question [Re: 451 D*O*D*G*E] #962360
03/30/11 09:54 PM 03/30/11 09:54 PM
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ky.
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If you really have 3.91's your convertor is operating at about 80-82%. And that's not good. 4000 at 70 and that's what it comes out to.
Re: Speedometer way off!..and third gear rpm question [Re: kenworth_goose] #962361
03/30/11 09:55 PM 03/30/11 09:55 PM
Joined: Apr 2010
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Quote:

You've got a set of 4.56's.



That's what I'm thinkin'.


Let us know what you find out, inquiring minds want to know.

Re: Speedometer way off!..and third gear rpm question [Re: Mopar_Country] #962362
03/31/11 09:34 AM 03/31/11 09:34 AM
Joined: Jan 2003
Posts: 24,562
Brookeville, Md
Mr.Yuck Offline
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Quote:

Quote:

You've got a set of 4.56's.



That's what I'm thinkin'.


Let us know what you find out, inquiring minds want to know.



I think he counted the rotation of the wheel vs. the driveshaft. He said it went almost 4 complete turns.
Re: Speedometer way off!..and third gear rpm question [Re: John_Kunkel] #962363
03/31/11 10:25 AM 03/31/11 10:25 AM
Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
patrick Offline
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without converter slip, 70mph with those tires and gears is 3400, I'd expect actual cruise RPM to be 3600-3700...the loose converter might be slipping more, getting up to 3800-3900....

275/60R15's drop that 100 RPM.

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Re: Speedometer way off!..and third gear rpm question [Re: patrick] #962364
03/31/11 10:49 AM 03/31/11 10:49 AM
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451 D*O*D*G*E Offline OP
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Yeah i put her on stands and marked the driveshaft on the bottom and the inner pass side tire so i could spin drivers and read the other side..just barely 4 so we know the ratio..so the converter is possible not locking up all the way?..maybe?Wow i think the best thing for me to do is a make a video and post in car of Garmin and my tack readings and the fact you cant hold a conversation with full exhaust at 70mph .
I'll try to put this together today and get back on here..week of vacation has been fun..couple honeydoo's to do but after that i'll try to get video put together...stay tuned...

1970 Challenger R/T clone 2010 Dodge Journey R/T black,awd,
Re: Speedometer way off!..and third gear rpm question [Re: 451 D*O*D*G*E] #962365
03/31/11 11:29 AM 03/31/11 11:29 AM
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Re: Speedometer way off!..and third gear rpm question [Re: Mopar_Country] #962366
03/31/11 03:57 PM 03/31/11 03:57 PM
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451 D*O*D*G*E Offline OP
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Sh** dude you're gonna need another bag.Its raining pretty good now.Camera is charged and honeydoos are done so hope the rain stops.I gots no heater,wipers..nothin

The car was a QUART low on trans fluid i know pints but it took a whole quart in nuetral to get it up to fulll line.Foamy as well.Be back soon as weather will allow.

1970 Challenger R/T clone 2010 Dodge Journey R/T black,awd,
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