26-051

DT12 Transmission Cooler Retrofit
FLA COE
FLB COE
FLD Conventional
Business Class
FLC 112 Conventional

Century Class Conventional
Argosy COE
Cargo
Columbia

122SD and Coronado
Business Class M2
> Cascadia
108SD/114SD

Freightliner
Service Bulletin

General Information
An air-to-oil transmission oil cooler is available for vehicles equipped with a DT12 transmission.
It can be added to the vehicle even if it was not originally equipped with a transmission oil cooler or it can
replace a water-to-oil transmission oil cooler located in the bottom tank of the radiator.
The retrofit process involves adding the new cooler to the radiator support frame, updating/adding a new oil
cooler control valve in the transmission, and updating/adding cooler plumbing lines.
Parts that are required for the retrofit include:
• Air-to-oil transmission oil cooler
• Transmission oil cooler plumbing
• 90-degree JIC line fittings
• Transmission oil cooler ports (in transmission)
• Transmission oil control valve (in transmission)
• Hardware
• Transmission Oil-to-Air Cooler Update Kit DSN012T18001
Refer to the Parts Tables at the end of this bulletin to determine which parts are required to retrofit the
transmission cooler. See the detailed BOM information in Table 6 to determine which part list is compatible with
the vehicle.

Work Instructions
Transmission Oil to Air Cooler Installation
1. Park the vehicle on a level surface, shut down the engine, and set the parking brake. Chock the tires.
2. Remove the bumper.
3. Inspect the radiator frame for cooler mounting holes. See Fig. 1. If the radiator frame has cooler mounting
holes and there are no obstructions on your vehicle, it may not be necessary to remove the hood to install
the cooler.

Freightliner Service Bulletin, 09/18/2019

Page 1

26-051

DT12 Transmission Cooler Retrofit

Freightliner
Service Bulletin

FLA COE
FLB COE
FLD Conventional
Business Class
FLC 112 Conventional

Century Class Conventional
Argosy COE
Cargo
Columbia

122SD and Coronado
Business Class M2
> Cascadia
108SD/114SD

A

07/16/2019

f261526

A. Cooler Mounting Holes
Fig. 1, Radiator Frame With Cooler Mounting Holes

4. If necessary, remove the hood.
5. Remove the lower radiator baffle.
6. Remove the side baffles.
6.1

If the radiator frame already has cooler mounting holes, the baffles do not need to be removed.
Proceed with step 7.

6.2

If the vehicle has a multi-baffle system, remove the bottom fasteners that hold the left- and right-side
baffles in place. If not, proceed with step 6.3.

6.3

If the vehicle has a one-piece baffle, remove all the fasteners and adjust it to clear the area at the
bottom of the frame.

7. If the vehicle was originally equipped with a transmission cooler to the radiator, remove the jumper lines
from the radiator.
8. If the radiator frame already has cooler mounting holes, and there are no nuts welded to the back surface
of the flange, install the U-nuts (23-12625-010). Continue with step 13, cutting a pass-through on the lower
air baffle.
9. If the radiator frame needs cooler mounting holes, use the drilling-location template tool (07-24621-000) to
mark the radiator frame for new oil cooler mounting bolts as follows:
9.1

Page 2

Position the template tool on the bottom left corner of the radiator frame as shown in Fig. 2. Mark
the two drilling locations on the left front of the radiator frame.

Freightliner Service Bulletin, 09/18/2019

26-051

DT12 Transmission Cooler Retrofit
FLA COE
FLB COE
FLD Conventional
Business Class
FLC 112 Conventional

Century Class Conventional
Argosy COE
Cargo
Columbia

122SD and Coronado
Business Class M2
> Cascadia
108SD/114SD

Freightliner
Service Bulletin

A. Mark the drilling locations using these two holes.
1. Drilling-Location Template Tool
Fig. 2, Drilling Locations on the Left Front of the Radiator Frame

9.2

Position the template tool on the bottom right corner of the radiator frame as shown in Fig. 3. Mark
the two drilling locations on the right front of the radiator frame.

Freightliner Service Bulletin, 09/18/2019

Page 3

26-051
Freightliner
Service Bulletin

DT12 Transmission Cooler Retrofit
FLA COE
FLB COE
FLD Conventional
Business Class
FLC 112 Conventional

Century Class Conventional
Argosy COE
Cargo
Columbia

122SD and Coronado
Business Class M2
> Cascadia
108SD/114SD

A. Mark the drilling locations using these two holes.
1. Drilling-Location Template Tool
Fig. 3, Drilling Locations on the Right Front of the Radiator Frame

10. Remove the cooler bushings and test fit the cooler to confirm the locations of the holes are correct.
11. Center-punch the new bolt locations.

NOTE: The radiator frame is very close to the radiator core, which can be easily damaged by a drill.
Insert a drill backing plate to prevent the drill from breaking through the support channel and
damaging the radiator.
12. Using the standard-length drill bit from the tool kit, drill and tap the holes in the radiator frame for the
transmission cooler, as follows:
12.1

Page 4

Set the drill-stop depth so that only 1/2 in (13 mm) of the drill bit protrudes from the stop sleeve. See
Fig. 4.

Freightliner Service Bulletin, 09/18/2019

26-051

DT12 Transmission Cooler Retrofit
FLA COE
FLB COE
FLD Conventional
Business Class
FLC 112 Conventional

Century Class Conventional
Argosy COE
Cargo
Columbia

Freightliner
Service Bulletin

122SD and Coronado
Business Class M2
> Cascadia
108SD/114SD

A. Drill-stop depth measurement: 1/2 in (13 mm)
1. Drill Bit
2. Stop Sleeve
Fig. 4, Setting the Drill-Stop Depth

12.2

Drill the holes.

12.3

Tap the holes to 8 mm x 1.25 metric threads.

13. Mark and cut a pass-through on the lower air baffle. See Fig. 5 for locating the cutout.

A. Measurement: 1-3/8 in (35 mm)

B. Measurement: 3-7/8 in (98 mm)

C. Measurement: 3 in (76 mm)

Fig. 5, Lower Air Baffle Cutout

14. Turn the bushing liners so the flange is facing the radiator frame and install the bushings. See Fig.6.

Freightliner Service Bulletin, 09/18/2019

Page 5

26-051
Freightliner
Service Bulletin

DT12 Transmission Cooler Retrofit
FLA COE
FLB COE
FLD Conventional
Business Class
FLC 112 Conventional

Century Class Conventional
Argosy COE
Cargo
Columbia

122SD and Coronado
Business Class M2
> Cascadia
108SD/114SD

1

A

B
07/16/2019

f261527

1. Bushing Liners
A. Remove Bushing Liners
B. Turn and Install Bushing Liners
Fig. 6, Turn & Install Bushing Liners

15. Install the cooler. Apply medium strength thread locker on the fasteners then tighten the fasteners 7 lbf·ft
(9.5 N·m).
16. Install the jumper-line support bracket.
16.1

Page 6

If the radiator frame already has a drilled hole for the jumper-line support bracket, install the
threaded rivet (23-12631-381) in the radiator frame. See Fig. 7. Proceed to step 20, fitting the
jumper tube assembly.

Freightliner Service Bulletin, 09/18/2019

26-051

DT12 Transmission Cooler Retrofit
FLA COE
FLB COE
FLD Conventional
Business Class
FLC 112 Conventional

Century Class Conventional
Argosy COE
Cargo
Columbia

Freightliner
Service Bulletin

122SD and Coronado
Business Class M2
> Cascadia
108SD/114SD

1
07/16/2019

f261528

1. Threaded Rivet (23-12631-381)
Fig. 7, Threaded Rivet for Jumper-Line Support Bracket

16.2

If the radiator frame does not have a hole for the jumper-line support bracket, position the template
tool (07-24621-000) on the bottom left corner of the radiator frame, and mark the drilling location on
the back of the radiator frame for the jumper-line support bracket hole, as shown in Fig. 8.

Freightliner Service Bulletin, 09/18/2019

Page 7

26-051
Freightliner
Service Bulletin

DT12 Transmission Cooler Retrofit
FLA COE
FLB COE
FLD Conventional
Business Class
FLC 112 Conventional

Century Class Conventional
Argosy COE
Cargo
Columbia

122SD and Coronado
Business Class M2
> Cascadia
108SD/114SD

A. Mark the drilling location using this hole.
1. Drilling-Location Template Tool
Fig. 8, Drilling Location on the Back of the Radiator Frame

17. Test fit the jumper tubes and the line clamp bracket to confirm the location of the hole is correct. Once
confirmed, remove the jumper tube/bracket assembly.
18. Use a center punch to mark the drilling location.

NOTE: As long as the drill is kept parallel with the bottom of the lower radiator support channel, the
lower radiator tank is above the drilling location. Use care to prevent damage to the lower radiator
tank.
19. Using the short drill bit from the tool kit, drill the hole in the back of the radiator frame, then tap the hole to
8 mm x 1.25 metric threads.

NOTE: If the radiator frame was pre-drilled, and the riv-nut was installed, do not apply thread locker
to the jumper-tube support-bracket fastener.
20. Fit the jumper-tube assembly to the cooler, the jumper cushion-clamp, and the support bracket, then apply
medium-strength thread locker to the jumper-tube support-bracket fastener. Confirm the tube assembly is
not in a bind from the support clamp.
21. Tighten the clamp-support-bracket to radiator fastener 11 lbf·ft (15 N·m).
22. Tighten the jumper-tube to oil-cooler fasteners 14 to 16 lbf·ft (19 to 22 N·m).

Page 8

Freightliner Service Bulletin, 09/18/2019

26-051

DT12 Transmission Cooler Retrofit
FLA COE
FLB COE
FLD Conventional
Business Class
FLC 112 Conventional

Century Class Conventional
Argosy COE
Cargo
Columbia

122SD and Coronado
Business Class M2
> Cascadia
108SD/114SD

Freightliner
Service Bulletin

23. Tighten the jumper-line cushion-clamp screw 11 lbf·ft (15 N·m).
24. Install the side and lower radiator baffles.

Transmission Update
NOTE: The oil cooler control valve for air-to-oil is different than the control valve for water-to-oil and
must be replaced if the transmission was originally equipped with a water-to-oil cooler.
1. Drain the transmission oil.
2. Install a new seal ring on the drain plug, then install the drain plug and tighten it 45 lbf·ft (60 N·m).

Note: Make sure the seal rings from the cooler port plugs don’t stick to the transmission housing,
preventing the face of the adapter from sealing to the transmission.
3. If the vehicle was originally not equipped with a transmission cooler, remove the cooler port plugs in the
transmission. Install the JIC fittings, and tighten them 56 lbf·ft (76 N·m).
4. Remove the pump cover from the back of the transmission See Fig. 9.

Fig. 9, Transmission Pump Cover

5. Remove the original control valve if replacing a water to oil cooler. See Fig. 10.

Freightliner Service Bulletin, 09/18/2019

Page 9

26-051
Freightliner
Service Bulletin

DT12 Transmission Cooler Retrofit
FLA COE
FLB COE
FLD Conventional
Business Class
FLC 112 Conventional

Century Class Conventional
Argosy COE
Cargo
Columbia

122SD and Coronado
Business Class M2
> Cascadia
108SD/114SD

Fig. 10, Original Control Valve

6. Clean the sealant from the transmission housing and the pump cover.
7. If the oil pump drive shaft, hub, and rotor come out during the cover removal, install the oil pump and drive
shaft (Fig. 11) in the transmission housing. Confirm the dots on the hub and rotor are visible after the pump
elements are installed.

02/07/2017

f261491

Fig. 11, Oil Pump and Drive Shaft

8. Clean the bore for the oil control valve. This helps the O-ring retain the spring pressure while the cover is
being installed.
9. Apply sealant to the pump cover. See Fig. 12.

Page 10

Freightliner Service Bulletin, 09/18/2019

26-051

DT12 Transmission Cooler Retrofit
FLA COE
FLB COE
FLD Conventional
Business Class
FLC 112 Conventional

Century Class Conventional
Argosy COE