4R70W Neutrals On 3-4 Shift (Overdrive Band Not Applying)

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March 25, 2019

A common problem with the Ford 4R70W automatic transmission is a neutralling condition that can occur on the 3-4 shift. When this neutral flair or neutral condition occurs while driving down the road, there is an overdrive cancel button that can cause the transmission to go back into gear and confirms that the transmission really did neutral on the 3-4 shift. Generally what causes this is when the band does not apply, but the forward clutch releases. This means that the signal was given to make the 3-4 shift, and everything in the valve body did what it was supposed to do, but there was a mechanical issue of some sort. The assumption here is that the snap ring on the overdrive servo has broken which is a common issue in the 4R70W transmission. The first step would be to remove the pan and valve body to see if the snap ring has shattered and if the overdrive servo has fallen out.

Upon removal of the pan and valve body we have found that the small end pieces of the snap ring have broken off; however, enough of the snap ring remained to hold the overdrive servo in place (shown above). Had the snap ring shattered the servo piston would have fallen out when we removed the valve body.


Upon thorough examination of the valve body we found that one of the broken end pieces of the snap ring passed through an opening below the servo piston and into the valve body, jamming the servo regulator valve. We then removed the broken piece of the snap ring and reassembled the valve body.



For the overdrive servo (shown below), there is a tool that allows you to relieve the pressure of the snap ring, and in this case, help us see that the band was still intact. The remaining broken piece of the snap ring could not be removed with pliers due to missing the notched ends that had broken off. We had no choice but to leave it in the case and make the customer fully aware that we fixed the 3-4 neutral shift at this time by removing the broken piece of the snap ring that jammed the servo regulator valve. We also let the customer know that the issue could arise again when or if pieces of the remaining snap ring break or shatter.

Check out the full video of Raybestos Powertrain Sales & Product Development Support Engineer, Irvin Gers diagnosing and fixing the common problem of the broken snap ring that cause the neutral condition of the 3-4 shift on 4R70W automatic transmissions. https://www.youtube.com/watch?v=TSCZkLWkfdk

 

posted by: Nathan Truncone   comments: 0

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