Need Some help Please

rabidscoobie

rabidscoobie

10 Year Member
Jun 21, 2007
616
12
48
College Station,TX
#1
Ok my car is in my sig.

Heres the deal.I took my car into Ford under 3rd party warranty for a noise in the rear.
Well turns out the bearings went and screwed the whole housing or something along those lines.Ford says that the entire rear needs replaced,warranty inspects and agrees.
Warranty company wouldnt let Ford use their parts rather warranty company wanted to buy and send the parts to Ford.
What they sent to Ford was a rebuilt 2003 Mach 1 rearend.I told Ford several times to make sure the speedo would be right since I know Mach owners like droppin 4.10's in em.

Well guess what I got it back yesterday and took it for a test run on the highway while following a friend and my speedo is exactly 10mph fast.So anyone know by that mph what gear ratio it is.

Im gonna call Ford in the morn and let them know,but I have a feeling they might give me the run around on it.I would love for it to have the 4.10's in it but i want be speedo right also.

Also if Ford will not fix it whats that part I can buy to correct the speedo after gear install's....just in case.
 

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#3
Not enough information to solve the equation.

Jack the rear end of the car up and with the trans in neutral, turn one of the wheels one full revolution and count how many times the driveshaft spins around - that number is your rear-axle ratio.

If your trak-loc is worn out or the friction of the transmissions guts are to much for it to overcome and the other wheel spins backwards instead of the driveshaft turning then lower one wheel to the ground and spin the other wheel two full revolutions and that'll be your number.
 
#4
We'd need to know how fast your friend was going in addition to the difference in speed. However, we can make an estimate. If your friend was going 70MPH and your speedo read 80MPH, then the ratio between the two speeds is ~1.143:1 (you:him). In other words, you're reading about 14.3% high. If your car's tune is setup for OE spec 3.55 gears then to get a speedo error like that you'd have to have 3.55*1.143 or 4.05:1 in the rear. This is pretty close to 4.10:1.

If he was showing 60MPH then the ratio is 1.167 and the gear calc would be 4.14:1 -- again, very close to 4.10:1. Even if he was going 80 and you indicated 90, the ratio (1.125x) would give a rear of 3.99:1. You can see you're edging toward 3.90:1 as a possible ratio too. That's why you need absolute speed and the error.

I'm guessing it looks like you've got 4.10s in it. You can verify with patman's suggestion: Get it up in the air and count revolutions. I'd suggest turning the road wheel 10 times (not just once) to get a more accurate reading. It'd take more time but it's easier to count whole revolutions than fractions. If you have 4.10:1, you'd have to count 4.1 revs of the driveshaft...not easy to estimate 0.1 of a rev. If you turn the wheel 10 times you'd count 41 turns of the driveshaft. Takes longer but is way more accurate. Expect 39 turns for 3.90s, ~37 turns for 3.73s, 35.5 turns for 3.55s etc.
 
#5
trinity_gt said:
I'm guessing it looks like you've got 4.10s in it. You can verify with patman's suggestion: Get it up in the air and count revolutions. I'd suggest turning the road wheel 10 times (not just once) to get a more accurate reading. It'd take more time but it's easier to count whole revolutions than fractions. If you have 4.10:1, you'd have to count 4.1 revs of the driveshaft...not easy to estimate 0.1 of a rev. If you turn the wheel 10 times you'd count 41 turns of the driveshaft. Takes longer but is way more accurate. Expect 39 turns for 3.90s, ~37 turns for 3.73s, 35.5 turns for 3.55s etc.
Click to expand...

Before you start turning the wheel, you should mark the driveshaft with a piece of masking tape at the bottom so you don't lose track of where you started. Same for the wheel, because I know with me... I start thinkng, did 5 spokes pass or 4 or what?
 
#6
Thx everyone.

I knew there was a way to check like that but couldnt remember.

Im pretty sure its 4.10's cause the speed difference was friend-70 and me showing 80.Plus I last night I looked up tranny gear specs then went out a got a couple rpm readings with a few different speed ratings and used an online gear calculator and all rpm/mph readings came back with 4.10's being the answer which is fine by me.
Now that the warranty has expired,thats all I was waiting for so I could start with modding crap...:D 4.10's and headers was on my list this year anyway,well 4.10's are out of the way and it didnt cost me a penny..:nice:

Thx again
 
#7
Ok lets make sure I have this right.Since Ford says that I am wrong.

At 70mph my speedo reads 80mph at 2500 RPM's.I have paced another car and used one of those police radar trailers to confirm.
Before Ford replaced the entire rear end my speedo was correct(verified with the warning ticket I recieved the week before I took it in),70mph speedo read 70mph at 2000rpm's.

Also now at around 40-45mph Im running about 2500+ rpm's(I matbe wrong cant remeber exactly),so now I dont cruise town in 4th anymore...its now 5th.
Now I used a gear ratio calculator online that asked for this info:
Tranny gear =4th 1.00 Since it wouldnt let me enter 5th's ratio wich is .62
Speed =70
rpm =3750 or so Hard to tell on the Mach's tach
sidewall tire =40
rim size =17
tire width = 275

the answer I get is 4.0999 or something similar...4.10's right?

I also did this to make sure.jacked up the rear put a mark on the tire pointing straight down,marked the yoke at the rearend,turned to tire 1 full turn until the mark was pointing back down.
The yoke mark pasted exactly 4 times.
Thats 4.10's right? Or am I doing something wrong.

I have argued with the Ford tech all morning over this.He says this:

1. he connected his computer and took it on the highway and said the speedo was reading about 10mph fast.OK
2. He also says that reading comes from each wheels speed sensor,and since the speed comes from those that there is noway a different gear ratio can affect the speedo( I call BS there).He says that the rebuilt rear end that the warranty company provided isnt at fault,therefore the warrany doent wanna pay to correct the speedo.
3.He also says that since Im running 275/40/17 and they are worn,that may be causing it too....whatever.They arnt that worn,tread still above the wear bars.

Someone please tell me that Im right on this,Im sure that I am but before I get to bent outta shape with Ford,just confirm.
 
#10
hey bro there is a video in the sticky that shows where ur rpms will be at different speeds with 410s ... u can also use a sct tuner to correct the speedo and or figure out what gears u have by switching the gear ratio in the tuner til u find the one who matches ur buddys car ...
 
#17
rabidscoobie said:
Ok lets make sure I have this right.Since Ford says that I am wrong.
...
1. he connected his computer and took it on the highway and said the speedo was reading about 10mph fast.OK
2. He also says that reading comes from each wheels speed sensor,and since the speed comes from those that there is noway a different gear ratio can affect the speedo( I call BS there).He says that the rebuilt rear end that the warranty company provided isnt at fault,therefore the warrany doent wanna pay to correct the speedo.
3.He also says that since Im running 275/40/17 and they are worn,that may be causing it too....whatever.They arnt that worn,tread still above the wear bars.

Someone please tell me that Im right on this,Im sure that I am but before I get to bent outta shape with Ford,just confirm.
Click to expand...

The speedo is definitely affected by a change in rear gear ratio. The speedo is driven by a signal off the transmission, not the wheel sensors - which is why Ford sells replacement speedo gears for early transmissions and a recalibrator box for later electronic speedo transmissions. Whatever info the computer gets from the wheel sensors is used for ABS and TCS. If the wheel sensors are reading markedly different from the speed showing on the speedometer then that should be evidence right there that something is not right.

There is no way tire wear could account for a 10 MPH discrepancy in speedometer accuracy - there's not enough tread to wear away to make that kind of difference. Even if you shaved off an inch of height off the tire it'd only be a 4% or 5% difference which would amount to a couple MPH error at 70 MPH.

275/40/17 should be within a percent or two of the stock 245/45/17 stock tire size - maybe tack on another MPH of error in worst case scenario? Still not enough for 10 MPH off.
 
#18
patman0911 said:
The speedo is definitely affected by a change in rear gear ratio. The speedo is driven by a signal off the transmission, not the wheel sensors - which is why Ford sells replacement speedo gears for early transmissions and a recalibrator box for later electronic speedo transmissions. Whatever info the computer gets from the wheel sensors is used for ABS and TCS. If the wheel sensors are reading markedly different from the speed showing on the speedometer then that should be evidence right there that something is not right.

There is no way tire wear could account for a 10 MPH discrepancy in speedometer accuracy - there's not enough tread to wear away to make that kind of difference. Even if you shaved off an inch of height off the tire it'd only be a 4% or 5% difference which would amount to a couple MPH error at 70 MPH.

275/40/17 should be within a percent or two of the stock 245/45/17 stock tire size - maybe tack on another MPH of error in worst case scenario? Still not enough for 10 MPH off.
Click to expand...

Thats exactly what I thought,just comon sense really,and I said something similar to the tech,he disagreed.:bs:

He told me that while going down the highway all 4 speed sensors read the same speed while moving...well no &^*#...that because all 4 tires are on the ground turning at the same speed. And since the 2 back sensors matched the 2 from,then the problem was elsewhere.:rlaugh:
I dont know where they got this guy from,but I think he needs to be retrained.Hell Im gonna print these replies out so he can read them when I go back up there.:rolleyes:

Are any of you Ford techs by any chance,yall seem to know much more than him.:nice:
 
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