FUN WITH TRANSMISSIONS Late Model Honda by Bill Brayton Today s late model Accords have changed; removing the unit from the car isn t always necessary to correct a shift problem. Remember when you had a shifting problem with an old F4 Accord and you just knew it was because throttle valve A was sticking? Back then your choices were pretty easy. To correct the problem you could choose between either pulling the unit out or pulling the unit out. But today s late model Accords have changed; removing the unit from the car isn t always necessary to correct a shift problem. In this edition of Fun with Transmissions, we ll take a look at a few of the more important elements of these transmissions, including line pressure control, solenoid operation, diagnosis, and which parts need to be changed on every rebuild. Before any transmission diagnosis can begin, a good understanding of how the transmission operates is a must. The 1998-and-newer Accords come with BAXA/MAXA (4-cylinder), and B7XA (V6) model transaxles. Similar transaxles are also used in the 1997- and-newer Prelude (M6HA), 1998-and- 46 GEARS August 2002
Accord Transmissions: It s Not an F4 Anymore and by Mike Van Dyke newer Odyssey van (MDWA, B7TA), 1998-and-newer Acura 2.3 CL (B6VA), and 1997-and-newer 3.0 CL (B7ZA, M7ZA) vehicles. These model codes can be found on the transmission case housing (figure 1, page 48). All of these transmissions are shifted by the computer, using three shift solenoids. The line pressure control is handled by two A/T Clutch Pressure Control (CPC) solenoids. These pressure control solenoids don t actually control line pressure in this unit; rather, they control clutch apply pressures. This unit, much like the KM transmissions, works on a fixed line pressure. Clutch apply pressure is modulated during the shifts by CPC solenoids A and B. The combined operation of these solenoids constantly switches the clutch apply pressure from CPC pressure and mainline pressure to control shift feel. See figure 2 (page 48) for a complete guide to shift solenoid operation. Notice that there s a different solenoid pattern during the shift versus the steady state operation. GEARS August 2002 47
Late Model Honda Accord Transmissions Figure 1 Figure 2 Gear Position Shift Control Solenoid Valves A B C Shifting from N to D3 or D4 ON ON ON D3 or D4, 1 st gear OFF ON ON D3 or D4, shifting gears between 1 st and 2 nd ON ON ON D3 or D4, 2 nd gear ON ON OFF D3 or D4, shifting gears between 2 nd and 3 rd ON OFF OFF D3 or D4, 3 rd gear ON OFF ON D4, shifting gears between 3 rd and 4 th OFF OFF ON D4, 4 th gear OFF OFF OFF Manual 2, 2 nd gear ON ON OFF Manual 1, 1 st gear OFF ON ON Shifting into Reverse from Park or Neutral OFF ON ON Reverse engaged OFF ON OFF Park OFF ON OFF Neutral OFF ON OFF Figure 3 Now let s take a look at shift solenoid operation and how a shift is accomplished: Hold on to your hat and tie down your boat, because this is going to get a bit hairy. But once you understand how the system operates, shift problems will be fun to solve. For this example we ll use the 1-2 shift, keeping in mind that the other shifts are accomplished in a similar manner. In figure 3 the shift valves are in the 1 st gear position. One thing about these schematics: The green oil, which is called clutch oil, switches between mainline oil and control oil. In this schematic, shift solenoids (SS) B and C are on, and SS A is off, with the 1 st clutch applied. Here s where it gets tricky. As vehicle speed increases, the computer commands the 1-2 shift, and turns SS A on. This strokes shift valve A. When this happens, 1 st clutch apply pressure switches from mainline, to control pressure from CPC valve A, and CPC valve B control pressure is routed to the 2 nd clutch. The first thing that stands out in the schematic in figure 4 is that both the 1 st and 2 nd clutches are applied. Now you might be thinking, won t this cause a bindup with both clutches applied? Well no, because what s actually happening is that, as the 2 nd applies, the 1 st releases, through the oper- 48 GEARS August 2002
Late Model Honda Accord Transmissions Figure 4 ation of the CPC valves. The CPC valves (controlled by the CPC solenoids) actually control the drain and apply rate for both clutch packs, to achieve a smooth shift. CPC valve A controls the drain of the 1 st clutch pack, while CPC valve B controls the 2 nd clutch apply. As all of this occurs, the computer is watching for a speed change from the mainshaft and countershaft speed sensor inputs. When the shaft speeds reach a prescribed value, the computer says okay, the shift is complete; now let s turn the CPC pressure off and switch back to mainline pressure. To do this, the computer turns SS C off, which allows shift valve C to stroke up, which switches 2 nd clutch apply pressure from CPC pressure to mainline pressure, and finishes exhausting pressure from the first clutch drum. PRESTO! The transmission is now in 2 nd gear (figure 5). There are also two pressure switches: a 2 nd clutch and 3 rd clutch pressure switch. These switches close at about 36 PSI and open at 30 PSI (figure 6). These switches let the computer know when clutch apply is happening, and it uses these inputs to control clutch apply and release rates during shifts. Now that you know how the transmission shifts inside, you can get a pretty good idea of what s going on from the outside. For example: You have a complaint of a harsh shift after rebuild. If the line pressure is good and solenoids are operating properly, chances are you have a stuck CPC A or B valve, depending on which shift is harsh. Now let s talk about some of the things we are going to do on every rebuild. Of course we want to use the highest quality paper and rubber kit we can. Next and this is critical here use equipment that meets (OE) specifications, to avoid shift problems (harsh, soft, slides, etc). Also, spend the time looking at fluids to determine the fluid your using meets OE specifications, this will ensure consistent results. And it s a good idea to replace the clutch pressure switches, A/T pressure control solenoids and the shift solenoids. Here at the ATRA Helpline, we receive a lot of tech calls regarding shift quality problems. Many of these complaints are due to non-oem compatible clutch plate-steel plate-fluid combinations, or contaminated solenoids. I can see the bosses out there squirming in their seats right about now, because these items aren t cheap. But a job that goes out and stays out is always more profitable than one that sits on the rack and gets these parts replaced one at a time. A few other considerations on these units: After the transmission has been rebuilt, installed, and filled with the proper fluid, the technician runs the car through the gears, only to find that the transmission won t shift past 2 nd. This is totally normal while the car is on the lift. Just let the car down, take it for a spin, and you should have all the gears. During rebuild always watch for cracked drums; Honda drums have always been notorious for cracking, and these units are no different. Pay attention to the differential bearings; they ve been known to fail and send metal through the entire transmission. This was due to a manufacturing flaw in the bearing. The telltale here is to look for a leak at the axle seal when the vehicle first comes into the shop. These Accord transmissions can be complicated, and the best way to deal with a complicated unit is to be prepared before the transmission is ever 50 GEARS August 2002
removed from the car. Proper diagnosis and rebuilding procedures will keep your profits up and your comebacks down. Until the next time, remember: have Fun With Transmissions! Join Bill Friday, October 11, at 9 AM for EXPO 1st Session Seminar: Fun with the 5R55N, A Look at Ford s New Transmission. Join Mike Sunday, October 13, at 12:30 PM for 1st Session Seminar: CD4E / LA4AEL, Common Problems, Parts Interchange, Troubleshooting, and Repair. Figure 6 Figure 5 Lifts and holds Allison 1000 & 2000/400lbs. Built for rebuilders by rebuilders. Used by the Pros, Atra, Transonline, ATSG Loads directly from transmission jack Capable of mounting most front and rear wheel drive transmissions Complete work bench when using parts tray and tool trays Adapts to bench mount fixtures An approved vendor in the General Motors Dealer Equipment Program. Toll Free 1.866.767.5438 www.rnrebuilder.com NOLIFT TRANSMISSION REBUILDING SYSTEM UNIVERSAL WITH ADD A PLATE MOUNTING. GEARS August 2002 51