Ford’s 6F35N transmission is popular in Ford light to medium-duty front-wheel drive applications. They have logged several millions of miles and have proven to be very reliable. However, with any mechanical device, they have their areas of concern. As time takes its toll on these vehicles, we see some common patterned failures. Today, we will look at some of these areas of concern, the causes, and fixes!
SHIFT QUALITY ISSUES
Today’s drivers have become accustomed to smooth-shifting vehicles. Therefore, any shift sequence or torque converter apply or release that doesn’t feel good causes alarm. If they see ripples in their morning cup of coffee, it could warrant a trip to the local transmission shop!
The 6F35N transmission is a very polite shifting unit on most occasions. With engine torque management combined with fully electronic controls for the transmission, shift timing, torque converter scheduling, and overall shift feel, it provides a comfortable driving experience. However, as the vehicle ages, shift quality begins to deteriorate. Of course, several factors come into play. So, let’s look inside the transmission first.
NORMAL WEAR AND TEAR
It is critical to ensure that all bushing-to-journal clearances are within specifications. If you run worn bushings in this unit, you will have intermittent shift quality concerns that will not go away. The oil pump supply volume provides just enough flow to keep the pressure regulator valve balanced for adequate lubrication and pressure for all driving demand conditions. When bushings wear, there is a greater demand for lubrication flow. The added demand causes the pressure regulator valve to be out of balance more often. The result is a delayed response to changes in line pressure demand and clutch fill timing, affecting shift quality.
A typical bushing that wears is the sun gear bushing (figure 1). It is known to cause an intermittently hard or firm 3-2 downshift. It is important to note that you may not experience this shifting issue with the vehicle coming into the shop on an initial repair. Contaminated fluid tends to be ‘thicker’ and can mask bushing wear-related issues.
THE VALVE BODY
Valve bore, and general valve body wear are common concerns. Issues in the valve body cause flared shifts, tie-ups, and harsh or soft shifts. Often, problems here will get worse as the transmission reaches operating temperature. Let’s look at some valves and valve bores that wear in this unit.
The Solenoid Regulator valve is notorious for wear, especially if the vehicle is driven in city traffic regularly (figure 2). Concerns exist primarily with the First Generation units (2009-2013 ½). A common fault associated with excessive wear in this valve bore is the loss of 4th through 6th gears. Therefore, it is imperative that this valve and bore are checked and verified to be in good working order. There are several aftermarket repair solutions for this valve.
The Torque Converter Clutch Regulator valve bore is another high-wear area for this valve body (figure 2). Given the fact that the computer strategy is designed to apply the torque converter clutch as often as possible, this valve gets a lot of cycling. Again, the First Generation units suffer more than the later applications. There are aftermarket solutions that address wear concerns in this location.
Another valve prone to wear is the Pressure Regulator valve (figure 3). Again, the First Generation units tend to be more inclined to have excessive wear here. The Pressure Regulator valve is located in the pump, separate from the valve body. You want to verify that this valve bore is not worn and is free. Once the unit is installed, you cannot service this valve.
Ford updated the separator plate for the First Generation unit due to durability issues. It is common to see significant check ball seat wear on the plate surface. Sometimes check balls become impacted into the plate. Complaints of flared 2-3 shift, harsh 2-3 shift, and harsh engagement into reverse directly result from the Drive 2 check ball damaging the check ball seat (figure 4). Note that if the Drive 2 check ball blows through the plate, there will be no reverse and a 2-3 neutral. If it gets stuck, a harsh reverse engagement and 2-3 shift will result. The First Generation plate is available from the Ford dealership under part number DV6Z-7Z490-B.
Finally, remember to check the accumulators! Wear in the valve body bore needs to be addressed. Also, accumulator valves with the rubber end must be replaced when servicing the valve body. A collapsed tip will allow control oil to pass, causing shift quality issues and possible clutch slippage or failure.
It is fair to note that Second Generation valve bodies seem to have fewer wear-related concerns than First Generation units. However, in light of all the valve body-related problems mentioned here, assessing the overall health of the valve body is critical in making the best call for repair. In some cases, purchasing a new valve body from the OEM or a reliable aftermarket source may be best. Also, make sure that the latest computer programming strategy is installed. Ford made programming strategy updates to reduce valve body-related wear issues. You can contact your local Ford service department with the VIN of the vehicle you are working on to see if an update is needed.
THE CASE
With time, the case wears at the differential housing bearing surface on the main case half. The wear area appears like the surface was intentionally machined. However, if a ledge is observed where the Torrington bearing rides (figure 5), that’s a problem! Excessive clearance here can cause a complaint of clunking on and off the accelerator or bearing failure and internal unit damage. You can purchase a new case half from the OEM, or shims are available from the aftermarket to fix this problem.
Premature wear of the driver’s side axle bushing (Ford part #AL8Z- 7025-A) has been an ongoing concern for this unit. Make sure that you service this whenever you rebuild one of these transmissions. There are aftermarket bushings available for this application. If you have a 6F35N with a leaking driver’s side seal, an aftermarket tool kit is available through your soft parts supplier that will allow you to service the seal and bushing without removing the transmission.
THE LOW ONE-WAY ASSEMBLY
As these units age and get higher mileage, other issues rear their ugly heads. One area of concern is the Low One-Way element. The element spends most of its life in freewheel mode. With time, debris and metal filings can get into the assembly and cause it to malfunction. If the assembly doesn’t rotate freely, you may experience a bind on the 1-2 shift. Replace this assembly as needed.
THE OTHER RELATED ISSUES
It is common knowledge that engine-related concerns will cause transmission-related problems with most modern vehicle applications. The 6F35N is prone to respond adversely to neglected maintenance items. For example, a dirty or restricted air filter will cause harsh coasting downshifts and firm upshifts.
Low engine oil levels are typical when a Ford vehicle with a four-cylinder engine is not regularly checked and topped off as needed. Since these engines use variable valve timing, which is controlled by solenoids in the lubrication system, oil-related issues will cause malfunctions. In addition, low engine oil levels, dirty oil, or the wrong viscosity can cause issues with powertrain management that will affect shift quality, timing, and TCC scheduling. Therefore, checking engine oil on initial diagnosis is imperative to avoid a misdiagnosis.
Numerous vehicles equipped with the 2.0L motor and the 6F35N transmission come into shops with a knocking complaint. An initial diagnosis indicates that the noise is coming from the bell housing area of the transmission. It is common to have a broken flexplate with these applications. There is an updated flexplate to address this issue. However, you must also verify that the crankshaft and torque converter pilot area are not worn. The crankshaft surface is soft and tends to wear. If you replace the flexplate and torque converter with the crankshaft pilot worn, you will likely have a repeat flexplate failure! There is no known repair for this at this time.
Units that are commonly seen in shops will continue to have added concerns as they age. Our attention to detail is necessary to catch these issues as they arise so we are not caught off guard. Knowing patterned failures and areas of concern will always help you deliver the goods to the customer to ensure they will leave your shop with confidence that you did the job right the first time!
