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2008 fx4 4.0 reverse gear whine. automatic


kburley

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hey guys. i bought a 2008 fx4 automatic yesterday. this afternoon i noticed a strange whining noise in reverse that i hadnt heard previously.

when in reverse, there is a very high pitched whine that changes in tone and intensity in line with engine RPMS

when i shift to drive from reverse, the same whine continues at high intensity for a fraction of a second then disappears. everything else about the trans seems to be operating fine.

there are no other conditions under which i can re-create the noise, which rules out vaccum leaks for me.

i checked the trans fluid and it seems brand new. a service muatve been done on it quite recently.

can anyone provide insight on what may cause this? the truck came with a 30 day powertrain warranty so if its anything remotely major ill likely bring it back to the dealer to look at. thanks in advance
 


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Uncle Gump

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Are you sure it's a transmission noise?

Rear ends tend to whine a bit in reverse and increase with speed.

Try holding your foot on the brake while in reverse and brake torque it a bit. If the noise is still there... it's probably the transmission. If not... it could very well be the rear end whine you're hearing.
 

kburley

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Are you sure it's a transmission noise?

Rear ends tend to whine a bit in reverse and increase with speed.

Try holding your foot on the brake while in reverse and brake torque it a bit. If the noise is still there... it's probably the transmission. If not... it could very well be the rear end whine you're hearing.
yes im sure. it does this even when the truck isnt moving. i tried it with the brakes on as well. i should add that i heard from a mechanic friend it has to do with the square cut gears that they use in reverse and that i shouldnt worry about it. but the problem also happens a very slight amount in drive as well
 

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those square cut gears aren't rotating unless the truck is moving. I'm not sure they still use square cut gears for reverse in modern trannys.
have the dealer listen to the noise, get it documented.
when the noise is happening, pump the brakes a few times. any change?
 
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kburley

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those square cut gears aren't rotating unless the truck is moving. I'm not sure they still use square cut gears for reverse in modern trannys.
have the dealer listen to the noise, get it documented.
when the noise is happening, pump the brakes a few times. any change?
The noise is independent of breaking. When in reverse I had tapped the breaks to see if the noise stops I have concluded that it is following engine RPMs and not vehicle speed. The same issue also transpires at low RPM in drive gear once the vehicle is warmed up.
 

Transman304

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No straight cut gears in that transmission. Sounds like a cross leak or failing pump. The line pressure is raised when in reverse and could be leaking from a bad gasket or loose valve body. Pump whine can occur when demand for higher pressure is from poor fitting gears. Likely the previous owner had problems that they tried to repair from fluid change of flush since you say the fluid is clean.
 

kburley

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No straight cut gears in that transmission. Sounds like a cross leak or failing pump. The line pressure is raised when in reverse and could be leaking from a bad gasket or loose valve body. Pump whine can occur when demand for higher pressure is from poor fitting gears. Likely the previous owner had problems that they tried to repair from fluid change of flush since you say the fluid is clean.
yes, i had the truck in a trans shop today and thats what they told me. the dealer wont cover it and they say theyll let me return the truck. so now im back in my shitbox rusty mazda looking for a truck again. thanks for the help.
 

Transman304

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kburley

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Good luck!
had it in two transmission shops. neither can find the issue. it has had an EPC solenoid and both valve body gaskets, a fluid change and a filter change. there was no sludge or metal shavings in the pan. im just gonna drive it and see if it breaks. at this point im thinking it may not even be transmission related.
 

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What about the transfer case? Engaging the TC make any difference?
 


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