48RE Transmission Modifications for Towing

We selected ATO Racing Transmissions in Rancho Cordova, California, to build a 48RE transmission for our 2007 Dodge Mega Cab dually diesel 4WD especially for towing. We researched the TDR forums and talked to other transmission builders and truck owners before deciding to have Jim Galatioto, owner of ATO, build the transmission. ATO is a small company with Jim doing all the assembly work and Jeff and Jim doing the cleaning, parts preparation and R and R tasks.

Jim has been associated with racing transmissions since 1967, when he started working with well known Southern California racing transmission builder Tony Rossi. Jim has had his own shop in Sacramento area since 1980. He is quite well known for producing transmissions that can handle a LOT of power.

I noticed 3 Dodge diesels in the shop during my visit and 2 more were in the parking lot.

What impressed me most when I walked into the shop area was how clean it was. Jim had a Ford diesel transmission ready to build set up on 2 work tables and every part was in rows and stacks ready for assembly. The equipment in the shop was top quality, clean and well cared for. Jim uses over 200 blue cloth towels a week, plus even more lint free paper towels.

Jim has a prop in his show room to demonstrate the advantages of Torrington bearings over thrust washers and was quite willing to answer my questions and educate me with what his experience has taught him is the best way to build a transmission. Jim is very knowledgeable and easy to talk to. He understands transmission modifications and how to get the most bang for the buck. He feels the stock 48RE was built for the mass market and came in well under budget. Jim purchases no parts from Chrysler Corp for his upgrade/rebuild kits. He is not partnered with any particular vendor or supplier so he can use parts from any source he chooses.

Jim's opinion is a stock 48RE transmission with recommended fluid changes, filter changes, and band adjustments in a truck with a 3.73 ratio rear end, standard size tires and no added power can be reasonably expected to tow up to 10,000 pounds for 150,000 miles. He thinks the 48RE is the best core to start with because it has steel front and rear planetaries and a thicker drive shell.

He feels the 3 biggest weaknesses in the stock 48RE transmission are the intermediate band, the thrust washers and the torque converter. The thrust washers are the part with the highest failure rate.

Jim and I discussed his ideas about what changes were needed to improve our 48RE for towing. Improvements in these areas are where you get the biggest returns:

1. Using better than stock materials for gaskets and seals
2. Replacing or modifying components so they don't create as much heat, withstand heat better or dissipate heat more efficiently
3. Setting up the shift to eliminate wear
4. Using billet components where additional strength is needed

We decided on the ATO 48RE Super Heavy Duty performance kit, ATO 48RE extreme duty torque converter, BD billet flex plate P/N 1041210 and Sonnax billet input shaft P/N 22121B-01.

Jim feels that by improving the areas of the transmission that contribute to wear, his transmissions should last at least 300K miles (with fluid changes every 20-25K miles) before needing attention, and go 50K miles between band adjustments.

D&P Products Torque Converter Build

Jim has his torque converters built by Matt at D&P Products in Sacramento. They have provided high quality, trouble free triple disk converters for all Jim's Dodge diesel truck high performance automatics. The only parts reused from the stock 48RE torque converter are the impeller and turbine.

The following new parts are used:

1. Solid 1 piece CNC billet front cover assembly
2. Multi disk clutches with much wider friction surfaces
3. 4130 chrome moly flanged impellor hub
4. Sonnax 4340 hardened turbine hub and splines
5. Sonnax Torrington high performance stator bearing
6. Sonnax stator cap with locking tabs
7. Sonnax spring retainer

Derrick at D&P stated all the billet parts used in their torque converters are made in the USA. They use an original D&P design for their billet dampner piston assembly. They use a lot of Sonnax parts, and they modify some parts to customize the converter to the customer's needs. D&P does several additional modifications that are proprietary. They don't install bearings in non-load areas of the torque converter or in areas where the bearings are likely to fail due to lack of lubrication.

Matt said the factory 48RE torque converter is made very loose so the turbo has time to spool up when you step on the accelerator. It has a stall speed of 2700 RPM compared with a D&P triple disk converter stall speed of 1750. He said with a D&P converter everything happens at a lower RPM, the firmness of the shift varies directly with throttle pressure, the EGT drops and the vehicle accelerates faster after the torque converter locks up. He does not recommend a stall speed lower than 1750 on the 5.9, because the 5.9 idle speed is set a little higher and the truck will creep at stop lights if the torque converter stall speed is set lower than around 1750. He also said turning the idle down to compensate is not a good idea because it causes a lot of other problems.

D&P Products is located in Sacramento, CA. Their phone number is 916 921-6600. The turn around time is generally one day and the torque converter is not painted, just cleaned up after welding.

Building the 48RE Jim's Way:

After the initial disassembly, the parts are evaluated for replacement or reuse. The case is washed with high temperature soap and water, rinsed and then media blasted as required. Jim is proud of the appearance of the transmissions that leave his shop. We requested "no paint" to maintain a stock appearance and Jim said, "no problem" and suggested a light coat of clear to seal the exterior of the case so it wouldn't stain so easily.

All shafts and drums, the ring gear, drive shell, sun gear, and sun shell and the pump housing are put in a vibratory tumbler for 2 hours to remove any flashing from gear teeth and improve the finish on the parts so they look brand new. The exception is Billet steel drums because they already have a nice finish. Jim also polishes all the journals on the shafts so everything slips together amazingly smoothly.

Jim uses parts developed for other brands of transmissions if they suit his application. Part of the Super Heavy duty kit is a DNJ Components Governor Solenoid kit originally built for GM 4L60E transmissions. Jim feels it provides more consistent and reliable governor pressure.

Jim uses Raybestos clutches because the material is stronger and can absorb more heat as well as providing a better shift feel. He stated both the tan and the green clutches are good.

The assembly lube he uses is synthetic grease on bushings and Mercon III on bearings.

He likes to spin the rotating assembly as he assembles the transmission to make sure everything is fitting together correctly and spinning smoothly.

When the transmission is assembled, no sealer is used because Jim insures the mating surfaces are flat enough they won't leak.

The circuitry in the valve body is modified to allow more fluid to flow through it.

The valve body modifications are some of the most significant changes Jim makes to the transmission and they are considered proprietary.

The reworked valve body in an ATO 48RE transmission is designed to provide 80 PSI pressure at idle and 150 psi at full throttle to insure a firm shift that isn't harsh.

The overdrive is tightened up by valve body modification or through changes in the clutch pack or both. The modifications depend on the vehicle and its planned use.

Note: Dummy shaft is used while assembling the overdrive section in picture above.

Jim machines the front ring gear on both sides for bearings, and the rear planetary for one bearing on the top side and one bearing on the bottom side.

Several additional modifications are made which are proprietary and based on Jim's long experience building racing transmissions.

During assembly Jim uses a torque wrench on the valve body, the pump and the pan.

Jim uses 7 clutches instead of 5 in the direct clutch pack. He machines the top pressure plate and selects clutches and steels thin enough to allow 7 clutches to be installed and get the correct height.

Jim uses a steel intermediate band because it doesn't stretch and has no rivets. He uses Redline or Raybestos bands, (not Kevlar because Kevlar tends to flake apart).

Teflon seals are used on the accumulator and the input shaft. Hardened chrome rings are used on the direct clutch and the input drum.

Jim said the difference we will notice between stock and our new ATO transmission is in the shift feel, the shift points being different and the transmission having a more progressive lock up, so you feel more distinctly when the torque converter locks up.

Frequently Asked Questions:

What is the difference between racing and towing transmissions?

Racing transmissions are built with a billet intermediate and output shafts and the valve body is set up to shift harder.

How much torque can the engine develop before you recommend a billet output shaft, billet forward drum and billet intermediate shaft?

A billet output shaft, billet intermediate shaft, and billet forward drum are recommended if the engine produces over 800-1000 pound feet of torque.

How many RPM will a stock 48RE transmission handle safely? 3200 RPM ATO modified transmission? 4000 or 5000 RPM

Do you soak the clutches in ATF before you put them into the clutch pack?

No, because if they are soaked in fluid, you can't feel internal problems such as a tight spot on a bushing or a rough bearing.

How is the torque converter dampened?

The torque converter is dampened by springs in the torque converter clutch because it reduces the shock load on the drivetrain.

How much tighter do you want the torque converter for towing? 300 RPM What do you mean by tighter? Lower stall speed

What happens if the torque converter is set up too tight?

If the torque converter is set up too tight, it will increase the spool up time and bog the engine down.

How is the torque converter balanced?

The torque converter is balanced by installing everything in reference to dead center and verifying runout is less then .003-.004. The fluid will also center balance the unit, similarly to how a crankshaft fluid dampener balances on a crankshaft.

What do you look for in a billet flex plate?

A billet flex plate should be machined out of good quality steel, not stamped. Jim likes the BD billet flex plate part number 1041210.

How can you tell if a flex plate flexes?

If you want to see the flex plate flex: 1. Make sure the truck is on jack stands with the wheels off the ground 2. With the vehicle running put the transmission in reverse and do a stall test. 3. As you bring the engine up to 2000 RPM the flex plate will push forward

When do you recommend a transmission temperature gauge?

It is always a good idea to have a transmission temperature gauge, because it lets you know about a clogged transmission cooler line or other problem early on. You can monitor the fluid temperature and ease off if you see it climb past 180 degrees. If you can keep the transmission fluid temperature below 150 degrees, it will last a lot longer.

Where is the best place to install the temperature sending unit for the temp gauge, in the Mag-Hytek pan or in the transmission cooler feed line?

Jim recommends installing the sending unit in the pan.

What is the most common mistake people make when pulling trailers with an automatic transmission that causes excessive transmission wear or damage?

Towing in overdrive up a steep hill with a lot of weight is a common mistake. When the engine starts to waver, take the transmission out of overdrive.

Should you always use tow/haul mode when towing? Yes

What can you do driving-wise to extend your transmission life?

When backing the vehicle up, always stop completely before you put the transmission in drive. If you are still moving backward when you shift, there is a possibility you will take out the rear sprag and break the case.

Matt at D&P suggested shifting into neutral when stopped at traffic lights in stop and go traffic. This allows the fluid to circulate through the coolers and helps keep the fluid temperature down.

Why does the 48RE hunt? How do your modified transmissions eliminate "hunting"?

Hunting is not a transmission issue. Hunting is caused by the transmission controller computer becoming confused by vehicle speed, engine RPM and throttle position. The overdrive and lockup solenoids are piggybacked on the same manifold, both see 12V when the engine is on and are energized by ground signals from the vehicles computer. The apply solenoid has a .020 hole that squirts fluid and doesn't allow enough pressure to build to open the valve against the spring pressure until the solenoid is energized by closing the exhaust orifice.

Matt at D&P said, "To minimize "hunting" problems keep all the grounds clean and snug. This applies to the computer chassis ground as well as all of the grounding straps." He recommends adding an extra ground strap from the alternator bracket to the frame or negative battery terminal. He mentioned keeping the battery terminals clean and corrosion free because they frequently get corroded and cause problems.

What codes do modified transmissions cause and what is changed to cause the computer to throw a code?

As long as the DNG governor solenoid is used, an ATO transmission should not throw a code. Codes can be caused by the governor solenoid shorting, pressure transducer shorting or if the engine computer is picking up a code from something else.

What is the most common mistake installers make when installing an automatic transmission?

You have to know your converter end play and make sure the torque converter is fully engaged in the pump before tightening the case.

What is the design limit number of pound feet of torque a modified 48RE transmission will reliably stand up to? 1400 pound feet

Is the stock transmission cooler large enough? In most cases, yes.

When do you recommend auxiliary transmission cooling and what kind of cooler works best?

If you are pulling a 5th wheel with a combined GVW over 25000 pounds, it is a good idea to run an auxiliary transmission cooler. They can be installed under the bed with a thermostatically controlled fan. Derale makes a nice remote mount cooler with temperature sensors.

What is the easiest way to check that sufficient fluid is going through the transmission cooler?

The fluid must be warm to do this test. It is a 2 person job. Pull the return line from the transmission cooler at the transmission end and slip a clear 3' long 3/8" diameter tube over the end of it. Start the engine with the truck in neutral and hold the engine at 1000 RPM. The fluid should fill a one gallon jug in 45 seconds or less. "Good return flow is a good thing".

Do you recommend removing the anti drain-back valve from the return line? If so, what do you replace it with or do you recommend leaving the transmission in neutral for a few seconds to fill the torque converter?

Removing the anti drain back valve from the return line is a good idea, because they tend to get clogged. Removing the valve will allow the fluid to drain out of the torque converter back into the pan, so when you start the truck, put the transmission in neutral for 30 seconds so the torque converter can refill.

Why would a transmission lose its fluid?

The transmission will lose its fluid if a cooler line breaks, the front pump seal fails or if one of the pressure port test plugs gets loose. It could be the servo, governor, or accumulator port plug.

What is the startup procedure for a newly installed transmission?

It can be difficult to purge the air out of a freshly built transmission, so Jim recommends this start up procedure to purge all the air out of the transmission before it is put under a load:

1. Raise the wheels off the ground.
2. Put 5 quarts of fluid in the pan (8qt with Mag-Hytec pan).
3. Start the engine with the transmission in Neutral then quickly add 4 more quarts.
4. Check the fluid level and put more in to bring the level to the "add" mark.
5. Put the transmission in Reverse for 30 seconds, then step on the brake. After the wheels stop, shift into Drive.
6. After the engine reaches operating temperature, add fluid to the transmission until it reaches the "full" mark.
7. With OD off, put the transmission in manual Low and accelerate, then shift to Second and accelerate. Shift to Drive and accelerate, then go to OD (30 seconds in each gear).
8. Repeat this sequence 3 or 4 times.
9. Make sure the wheels are stopped then put it in Reverse, then apply the brakes, shift to Neutral and check the fluid level.
10. At this point you should have an accurate reading.

This procedure might seem a bit elaborate, but sometimes the transmission is hard to fill.

How does the transmission lubricate? What modification do you do to improve the lubrication system?

The 48RE lubricates by fluid coming in from the cooler return line, going down through the case and out through orifices in the intermediate shaft. The 48RE design is a good one that properly lubricates all areas of the transmission.

How often should you change the fluid?

Drain the transmission pan every other engine oil change or at least every 15K miles, every year drop the pan and change the filter (the stock filter is a good filter).

How often should you check the fluid level?

Check the fluid once a month for the correct level, smell and color. Keep a quart of new fluid on hand and compare it with the smell and look of the fluid in the transmission.

The transmission fluids Jim recommends are Cat 30W, Amsoil Racing Fluid, Swepco 20 or ATF+4. He feels that changing the fluid every 20-25K, if the transmission is working hard, contributes to long transmission life.

Common Problems with Dodge Automatic Transmissions:

47RE and earlier need the stock intermediate servo lever changed from its 3.8 ratio to either 4.0, 4.2 or 5.0. (Jim recommended 5.0 ratio for our transmission.)

The stock band struts and anchor struts are too thin and made out of poor quality cast iron. They will bend and flex and should be replaced with heavy duty parts to prevent breakage.

Conclusions and Contact Information

Jim has improved his processes during 42 years of transmission building, to the point the parts not only have the correct dimensions, tolerances and finish but also feel silky smooth as they mesh together. Jim builds arguably the best working and best looking transmission in Northern California. Each transmission is built for a specific vehicle and application with the buyers requirements being the most important factor. Jim really listens to what the vehicle owner wants. When Jim finishes a transmission it is a precision piece of equipment that has been assembled with meticulous attention to detail.

Jim's transmissions come with a 3 year 36,000 mile warranty.

You can contact Jim at ATO Racing Transmissions, his number is 916 636-3283.

Jim's email address is: ATOracingtransmissions@yahoo.com

Visit Jim's website at:

Click on picture below to read about Jim's 2004 Dodge Truck

Article written by Joe Leonard June 2010

Author's disclosure: We negotiated the price of our transmission with Jim before we decided to write the article. Jim was able to build the transmission with the features we wanted and stayed within our budget. We feel Jim offers an extraordinary level of expertise and we are delighted to share our experience with our friends and customers.

Joe Leonard 2010-06-23