Late Model NAG1 Transmission UpgradeWords by Richard Kratz photos by Mike Piraino

CAPTION: The Chrysler NAG1 five speed overdrive transmission.

CAPTION: With the case removed you can see the guts of the transmission. Five speeds, three planetary gearsets.

CAPTION: This is the K-2 clutch pack, third gear, which is considered to be a weak point of this transmission. You can see thediscoloration on the steel disks from overheating.

CAPTION: From left to right we see the NAG1 input shaft, a 727 input shaft and a 904 input shaft. The NAG1 is almostthe same size as the 727. The NAG1 measures out to 22mm while the 727 is 1 inch (22.54mm) so it is very stout.

CAPTION: From left to right here is the NAG1 front planetary, a 727 planetary in the middle and a 904 planetary. The NAG1 has fourplanetary gears like the 727 and is almost the same size and made from steel. To reduce friction the NAG1 uses all bearings for matingsurfaces in the gear set while the 727 uses thrust washers.

CAPTION: This is the bell housing bolted to the stand before the transmission is put back together. Interesting fact: this is the onlypart that separates the Mercedes version from the Chrysler version. Fun fact: the Chrysler plant received all of the German toolingright down to the "Made in Germany" casting on the internal components.

CAPTION: Here are the stock clutches (right) compared to the upgraded clutches (left). The upgraded clutches provide a 40%increase in friction surface area and are made from a more aggressive friction material further increasing their effectiveness.

CAPTION: Here are the completed sub-components before they are loaded back into the case on top of the pump. Most automatics arebuilt by loading the internal components into the case starting from the rear to the front while the NAG1 is the reverse, you loadeverything on the pump starting from the front to rear and then lower the case over the internals.

CAPTION: Another strength of the NAG1 transmission comes from the rear, this transmission is one of the only ones out there wherethe output shaft is supported in the rear by a real ball bearing rather than a bronze/teflon/babbit bushing.

CAPTION: To increase pump life and rigidity especially under the high pressure that the NAG1 uses, cast iron is used for the gearsection of the pump. Westminster Performance Transmission already loaded a new bushing and Viton high temperature seal towithstand the heat from the high stall torque converter. Here it is coated with assembly lube to prevent a dry start up before it isinstalled.

CAPTION: This is the front pump/bell housing with the whole assembly loaded on it. The arrows point to the two reluctor wheelsused for the speed sensors in the valve body. There are two holes in the case where these two wheels provide the signal for the pickups for the input and output speed sensors that stick through those holes. These two sensors allow the TCM to detect clutch slippage ineach gear. Also noted with circles are where Chrysler nicely indicated the direction of ATF flow to and from the transmission cooler.

CAPTION: B&M SFI 29.1 flexplate part number 10340. If you’ve upgraded your transmission and have more than stock power, thisis a highly recommended upgrade. We’ve seen stock flexplates crack and break on pure stock factory cars, much less modified ones.Get one.

Back when Chrysler was owned by Daimler-Benz a new platform of cars was developed for the Chryslerbrands, the LX. This platform underpins the Gen I Chrysler 300, Dodge Charger and Magnum and with a fewdimension changes the Dodge Challenger. The first generation cars have a lot of parts from the Mercedes partsbin—suspension, rear ends, and what we’re interested in here, the transmissions.

Our late model project car, the Maulin’ Magnum a 2007 Dodge Magnum SRT8, sees far more abuse then anystreet car and almost all street/strip cars for that matter. The car has over 50,000 miles on it and nearly 500quarter mile passes, most with nitrous oxide or a supercharger. The car has a tow hitch and pulls a nearly 2,000pound trailer with gear to races all over the southwest. Then we unhitch, swap wheels and tires, strip out someweight and go racing. And the car is a good race car, with Contributing Editor Alex Rogeo at the wheel the carhas made four final rounds and this year earned runner up in the PSCA Street Muscle championship, goingseven rounds in the final race. We continue to be impressed by this wonderful platform and the versatility ofthis Mopar machine.

That said, we begin to notice some shifting anomalies in the early summer which showed up clearly in the datalogs. Something wasn’t right in transmissionville. Now again, remember that this car makes about 660horsepower and has 50K miles on it, 500 quarter mile passes with WOT shifting and hard launches, towing updesert highway grades in 113 degree temperatures, well, you get the point—our 50,000 miles are probably morelike 150,000 or more of normal use.

We took the car to our friends at Westminster Performance Transmission. Father-son owners, Joe and MikePiraino are wizards whose old school/new school experience and knowledge is encyclopedia deep. Joe has beenbuilding street and racing transmissions since way back in the last century and there isn’t a trick he doesn’tknow. Mike schooled in trans tech at his father’s side and went to college and has the mechanical engineeringdegree to prove it—he’s not just an engineer by training but by nature and passion too. Joe and Mike campaigna beautiful twin-turbo dragster in NHRA Division 7 that they built themselves. And you don’t have to take ourword for how nice the dragster is, Joe and Mike have earned the Best Engineered award at Pomona, not oncebut twice.

WPT does a lot of work on the Dodge Chargers of various Southern California law enforcement agencies.Police and service cars see far more abuse than average street cars, they’re similar to our project car in thatregard. Joe and Mike begin to delve into the NAG1 transmission that comes in the V8 Hemi cars and learnedtheir weak points and problem areas. More importantly they learned how to address those areas. According toMike, the NAG1 is a fundamentally strong design especially considering that it is a five-speed with anoverdrive.

The NAG1 is actually a Mercedes transmission, one of the legacies from when Daimler-Benz owned Chryslerand is found in 2005 to 2012 Chrysler, Dodge and Ram vehicles. In Mercedes code the transmission is calledthe W5A580 or WA580 transmission. The Chrysler nomenclature breaks down as follows:

N = NewA = AutomaticG = Gearbox1 = 1st Generation

And the Daimler-Benz nomenclature is:

W= wet (torque converter uses fluid as apposed to a dry clutch)A= auto580= Newton Meters of torque capacity (about 427 pound feet of torque)

Chrysler built NAG1 transmissions at its Indian Transmission Plant II in Kokomo, Indiana. The transmissionhas three planetary gear sets which have four planetary gears each. The transmission utilizes unusually high linepressures, double that of most transmissions at 300 PSI. The torque converter is a lockup type with a multi-platefriction plate/steel plate design.

An electronic Transmission Control Module (TCM) commands the transmission. The TCM is adaptive and hastrim tables that allow the computer to adjust the transmission’s shift characteristics to your driving style.

The good news is that the NAG1 is a strong, yet relatively lightweight unit. It is a complex transmission andeven if you know how to tear down and rebuild a 727 transmission we urge you to think long and hard beforetackling the NAG1. It’s a beast of a different nature.

Joe and Mike put our car up on the rack and pulled the transmission. Tear down revealed burning on the 3rd gearclutches from slippage, so it was definitely time to overall. But Joe and Mike had no intention of just rebuildingour transmission and sending us on our way. They know what our car has to live through and they gave us everytrick they knew to help the trans stay together and shift better under our sadistic automotive abuse program.This is not going to be a step-by-step how to rebuild and upgrade story, first because we already warned youthat this trans is best left to experts and secondly, because Joe and Mike are racers and business people, whichmeans they just aren’t going to give away all of their secrets. Fair enough.

The NAG1 has drums and clutch packs that use five sets of friction and steel clutch disks. One of the first ordersof business is to use either Mercedes AMG drums or custom machine the existing drums (depending onapplication) to make room for more clutch disks. Our transmission now has seven pairs of clutches in eachdrum, a 40% increase in friction area thus increasing power handling capability and durability.

Up until 1996 Mercedes used friction disks with material on both sides, alternating friction disks with steeldisks. The problem with this arrangement is that the steel in the friction plate, sandwiched between the twofriction surfaces, has very little area through which it can shed heat. Heat is the enemy of transmissions, heat notonly breaks down the transmission fluid but it also reduces the coefficient of friction for the clutches, all elsebeing equal cooler parts have a higher coefficient of friction. So the NAG1 uses Mercede’s improved singlesided friction design for better cooling. Joe and Mike used single sided clutches with a more aggressive frictionmaterial than the factory uses, and with 40% more of them the transmission can handle a lot more power then itcould from the factory. Some transmission performance shops use the old double sided style of clutches as an‘upgrade’ and Joe and Mike advise against that.

Other tricks include modifications to the transmission pump; Joe modified the lube flow circuit to improvecirculation and used a Teflon coated backing plate on the pump. Seals were upgraded, tolerances checked andthe new improved unit was reassembled. Since we’re running a supercharger and we kind of like not having ourcar cut in two, we went and ahead installed B&M’s new Mopar Hemi SFI 29.1 flexplate (part number 10340). Ifyou take your car to the track be sure to take a photo of the flexplate installed in the vehicle and keep a printoutin your car or a photo on your cell phone, sometimes tech inspectors ask for proof that the part is installed.

LAT Oil’s awesome ATF was poured into the transmission, see our November 2012 issue for a full review ofthis outstanding ATF. This fluid is used by Pro Mod racers because it works even at the 600F temperaturesthose cars subject their fluid to.

And we were off towing and racing again. The transmission has an upgraded valve body that we covered in ourAugust 2012 issue and we use the Mercedes “Blue Top” solenoids in the valve body. The results of WPT’swork is impressive to say the least. Combined with a new Mopar TCM (Transmission Control Module) thetransmission shifted perfectly at the next race. The data logs from before the Westminster Wizards touched theNAG1 always showed a lot of variability in the RPM trace during a run. For one thing, the shift points weren’t

always nice sharp points and the actual RPM at which each shift occurred varied considerable on average for allgears through out a weekend.

After the WPT guys improved the transmission, we saw lap after lap where the shifts for all gears occurred witha variability of only 15 RPM from lap to lap. The RPM traces are solid and show perfect shark tooth sharppeaks and valleys. Alex reports that the transmission shifts solid and instantly and inspires confidence. On thestreet the car is fun to drive and the shifts have a nice, quick and firm feel to them.

IMAGE: NAG1_Datalog_Bad.pngCAPTION: This is a data log of RPM and speed from before the Westminster Performance Transmissionupgrade. Note that the RPM at the 2-3 shift (vertical yellow line) is showing 5690 RPM. The 3-4 shift occurredat 5990 RPM. Both shifts should be occurring at the same RPM. Also note the shape of the 2-3 and 3-4 shiftpeaks, you see a little flattening of peak instead of a sharp point.

IMAGE: NAG1_Datalog_Good.pngCAPTION: And here’s a data log from a race after the Westminster Performance Transmission upgrade. Forthis race, through the Diablosport Trinity hand held programmer we targeted 6200 RPM as the shift point for 2-3 and 3-4 shifts. Note that the 2-3 shift here occurred at 6201 RPM, it doesn’t get any more perfect than that,and the 2-3 shift occurred at 6209 RPM. Only an 8 RPM difference and within 10 RPM of target is outstanding.Note also the nice saw tooth sharp shapes of the shift peaks.

Assuming you have no broken parts, a full upgrade rebuild like ours will run about $4,500 from WestminsterPerformance Transmission. If you’re not in the Southern California area you can ship your transmission tothem, just give them a call to make arrangements. If you’ve got a power adder on your car, or nitrous oxide, orhead and cam upgrade, or if you track your car regularly, you will need to upgrade your transmission. Notmight, WILL. The good news is, the basic NAG1 design is sound, strong and capable. With a little tenderloving care from someone like WPT, the NAG1 will reward you with great shifts and long life.

CONTACT INFO:

Westminster Performance Transmissionwestminstertransmission.com7032 Westminster AveWestminster CA 92683(714) 897-6611

B&M Racing & Performancebmracing.com100 Stony Point Rd., Suite 125

Santa Rosa, CA 95401(707) 544-4761 Option 2

LAT Oillatracingoils.com(888) LAT-OILS