John Hedenberg
November 1, 2003
Contributers: Performance Automatic

Step By Step

View Photo Gallery
0311mm_01z Ford_Focus_ZX5 Front_Side_Drag

0311mm_02z Ford_Focus_ZX5 Undercar_Removing_Transaxle_Pan
Performance Automatic technician Woody Wodridge made sure our 4F27E Focus transaxle was removed and installed properly.
0311mm_17z Ford_Focus_ZX5 Undercar_Valve_Body
The first step was to remove the pan to access the valvebody.
0311mm_focus_04_z
Ford's 4F27E transaxle is a four-speed (three gears plus overdrive) design that has planetary gears much like that found in an AOD-E application. One of the main problems with the factory unit is it was designed with very little line pressure, which slows down the shift feel and response. One of the first modifications PA does is to alter the valvebody to improve line pressure, which increases the firmness of the shift points. Note the arrow. This is the OEM vent tube that vents air trapped in the case.
0311mm_focus_05_z
With the transaxle split in two you can see the front pump assembly and final drive section (the differential). Our transaxle contains a performance 3.91:1 final drive ratio.
0311mm_focus_06_z
With the rear of the transaxle removed you can see the second gear, overdrive band and drum assemblies.
0311mm_focus_07_z
The hot spots (or burned areas) on the band indicate soft shifts and slippage.
0311mm_focus_08_z
The entire planetary set is removed, double-checked and gets a good cleaning before being reinstalled in the case. The planetary ratios are 2.65:1 for reverse, 2.82:1 for first gear, 1.50:1 for second (intermediate), 1.00:1 for third gear (direct) and 0.73:1 for overdrive. The planetary gears in the 4F27E are very similar in design and construction to the AOD-E Mustang unit.
0311mm_focus_09_z
Here is the third gear and overdrive drum disassembled which shows severely smoked clutches, no doubt due to our extreme slippage during the nitrous blasts. Performance Automatic installed a complete new high-performance clutch kit from Alto consisting of four (as opposed to three) Alto Red lined racing clutches and Kolene steels for improved performance and grip. Adding a fourth clutch increases the overall clamping force of the entire unit.
0311mm_focus_10_z
Next the forward clutch and input shaft are laid out on the bench for examination. These clutches are not designed to withstand the added horsepower of a power adder and need to be upgraded if extended performance is to be achieved.
0311mm_focus_11_z
You can see the reverse clutches and band assembly. The old ones (top) are severely burned and smaller in diameter when compared to the new Alto Red clutches.

The Red Hot Chili Pepper has just taken a monumental step in the quest for serious performance. For those of you keeping up with the progress of our Torch Red ZX5 Focus, you are well aware that we plan on installing a turbo kit from Precision Turbo & Engine in the very near future. But while waiting for that kit to be fully developed by its manufacturer, we took up some of the slack with a 75hp nitrous kit from Nitrous Express. It was at that point we encountered obstacles-and we're not talking about the engine.

With the factory automatic transaxle handling the gear changes, the Pepper blistered (Hey, for this car it's blistering!) to a fine 14.92 at 90 mph with the nitrous and a 17.00 at 79 mph on motor. The good thing was we managed to dip into the 14s, but the bad part was that on the nitrous our factory transaxle was not a happy camper. When the little red nitrous button was depressed, all hell broke loose with the slushbox. True the car did perform well, but our shifts were weak and our 60-foot times, even with help from the blue bottle, needed attention for sure. Then the transaxle decided to start slipping.

With fixing our wounded transaxle at the top of our "to do" list, we began researching some companies that had front-drive Ford experience and found just what we were looking for three short hours away. Performance Automatic, located in Gaithersburg, Maryland, has been at the Ford C4 game for eons, but admitted the Focus was a venture they had been exploring for some time.

Shop owner Tom Cyr and performance salesman Harvey Baker assured us they were extremely interested in helping us with our horrid transaxle and explained that there were places where it could be improved. We've covered conventional C4, AOD and AOD-E transmission buildups in the past (some with PA) and have a pretty good idea as to how they work. However, when dealing with the Focus unit, we didn't have a clue as to what made it tick.

"The 4F27E four-speed automatic overdrive unit is unique in that it is completely operated by solenoids," explained Cyr. "The transaxle uses electronic shift control and is designed for operation in transverse powertrains for front-wheel drive vehicles. The 4F27E features a four-element torque converter design that includes a TCC (Torque Converter Clutch) and a gear train that has two planetary gearsets, a transfer-shaft gear final drive and a differential. The hydraulic control system of the 4F27E transaxle has six electronically controlled solenoids for shift feel (through line pressure control), shift scheduling (through shift valve position control) and TCC apply, controlled by Pulse-Width Modulation (PWM)."

The second key ingredient is, as expected, with the torque converter. "The converter we are using for this particular application is a factory unit we cut open and modified to allow for 500-600 additional rpm of stall speed on the line," said Cyr. "It consists of a four-element assembly containing an impeller, a turbine, a reactor and a TCC (Torque Converter Clutch) for increased fuel economy. For the record, we do not alter or eliminate the lock-up feature; that stays the way it is from Ford."

For the curious person, the gear ratios in the 4F27E transaxle are 2.65:1 for reverse, 2.82:1 for first gear (low), 1.50:1 for second (intermediate), 1.00:1 for high gear (direct), and 0.73:1 for overdrive. The final drive ratio (the ring and pinion) will be either a 3.68:1, 3.91:1 or 4.15:1, depending on the year of the unit. Our ZX5 has a 3.91:1 final drive ratio.

Tom explained the main problem with the 4F27E transaxle is a lack of line pressure. Ford designed the unit to shift rather softly and when introduced to a power adder the shifts need to be firmed up significantly or the life expectancy and performance of the unit will be greatly reduced. As opposed to upgrading the computer chip, which will also raise the line pressure, PA alters the valvebody solenoids and operation and says it is the wiser route to take as opposed to fooling with the electronics (computer) of the car. Before Tom and shop mechanic, Woody Wodridge began dissecting our Focus, Tom explained some of the weaknesses with the factory assembled unit and went over some of the modifications they would be performing. "Ford designed the 4F27E with very mild line pressure," said Cyr. "One of the items we will address will be with the valvebody, which is a hydraulic system consisting of hydraulic control valves and electro-hydraulic actuators. We recalibrate the pressure regulator circuits and the accumulator circuits to instill the unit with five-percent more overall line pressure. This will allow the unit to generate crisper, firmer shifts by activating the system with additional pressure. We will then disassemble the unit and replace all the reverse, direct, forward and low/reverse clutch plates and the intermediate/overdrive band (applied in second gear and overdrive) with high-performance components from Alto." The 4F27E converter operates much the same as a conventional unit and has a lock-up feature for improved fuel economy. The impeller and cover assembly drives the impeller blades and pump. It contains hydraulic fluid and provides a mating surface for the TCC piston and damper assembly. The turbine is driven by fluid from the impeller and transmits power to the turbine shaft and planetary gears. The reactor redirects fluid flow returned from the turbine to the impeller so that it rotates in the same direction as the impeller. This action assists in torque multiplication. The reactor has a one-way clutch to hold it stationary during torque multiplication (at lower vehicle speeds) to allow it to rotate at higher speeds.

One popular modification is altering the performance of an electronically operated automatic trans with a computer chip. This can work to a point, according to Cyr, but on the PA Focus unit it's not necessary. "All a computer chip does is add a slight amount of line pressure to the valvebody electronically," Cyr said. "You can, in effect, accomplish the same features by altering the pressure regulator circuits and accumulator circuits in the valvebody, which is what we've done. We didn't want to mess with a chip, because it may affect the way the unit operates as a whole and possibly do more harm than good. The correct way to increase the shift feel is with the valvebody."

With the transaxle out of the car and on the bench, Cyr and Wodridge performed the modifications above and slipped in the new (modified stock) converter. They jacked up the unit and reattached it to the rear of the block the same as with a conventional RWD platform. With the stock CV joints plugged back in the differential, the car was returned to the ground and the unit was filled with 6 quarts of automatic transmission fluid.

After test driving the car, it became apparent immediately the modified converter had an easy 600 more stall rpm. The unmodified unit would stall to 2,500 rpm (while powerbraking), but the PA converter can be pushed to 3,000 rpm without creeping 1 inch. This will allow us to leave the line harder and decrease our 60-foot times, as well.

With the car back in New Jersey we wasted no time and cruised over to Englishtown's Raceway Park to record our findings. As mentioned before, our best (engine only) time was a 17.00 at 79 mph. With the new PA unit in place, our shift feel was improved dramatically and we ran 7.83 at 77.51 mph, but did so in far worst weather conditions. Our 17-flat was in early April, where the weather is ideal for making optimum horsepower, but our 17.8-second time was accomplished in the extreme humidity of August. Small engines don't respond well to humidity and the Pepper is no exception. Needless to say, the PA unit is doing its job and is ready for a little boost.

We wondered if shifting the trans manually would unleash extra performance. On our first run we did our normal routine and left the shifter in drive with the overdrive off and stalled the converter to 2,500 rpm. After leaving the line the car seemed to stay in first and didn't shift properly. It was later discovered the computer went into what Tom defined as fail-safe mode, because it saw engine rpm but no vehicle speed due to the looser converter. Tom recommended we shift it manually and that solved our problem on the very next run.

With a professional overhaul from Performance Automatic, we can now safely run upwards of 100hp nitrous jets in our kit and the transaxle will have no problem keeping up with the demands. The PA converter feels terrific on the street and the shifts are much crisper and positive. Now bring on the boost baby!

The Focus Transbrake Is Coming
Performance Automatic is currently testing a street/strip transbrake assembly for the 4F27E Focus transaxle. The unit will be able to be installed by the customer with simple hand tools and should dramatically decrease quarter-mile times. The transbrake design will still retain automatic shifting characteristics while allowing the driver to employ all of the advantages of a conventional transbrake. Turbocharged, supercharged and nitrous-equipped engines with higher stall-speed converters will respond well to the addition of the brake and will gain additional starting line control from the locked feature off the line.

Our ZX5 project car featured here was scheduled for a transbrake, but due to time constraints and the fact that the unit is still in its early stages, we weren't able to have that luxury at this time. Stay tuned though, because we definitely plan on upgrading our new unit with a brake as soon as it becomes available-J.H.