SIL 16-WT-20
December 08, 2020
Page 1 of 4
SUBJECT:

3000, 4000 Series Retarder Accumulator – Piston and Seal Improvements

MODELS AFFECTED:

3000, 4000, B300, B400, T200, T300, T400, T500 and B500

INTRODUCTION:
As a continuing product improvement, the internal Piston Seals and Piston (items #3 and #5, Figure 1) of the
3000 and 4000 Series Retarder Accumulator have been redesigned. The Air Solenoid Valve Nipple (item #12,
Figure 1) and Air Solenoid Valve Fitting with orifice (item #14, Figure 1) have also been improved with the addition
of thread sealant.

Figure 1. Accumulator Assembly Exploded View
MC / SL8744EN

5255067

Copyright © 2020 Allison Transmission, Inc. All Rights Reserved.

SIL 16-WT-20
December 08, 2020
Page 2 of 4
Table 1.
TIDA, TIDB
3000

4000

Part Number
Ref
No.

Part Name

Qty per
Assembly

Former

Current

1

Accumulator and Solenoid Valve Assembly

29553476

29563813

1

Accumulator and Solenoid Valve Assembly

29553478

29563815

3

Seal (Piston)

2

29527008

29563171

5

Piston

1

29527007

29564913

12

Air Solenoid Valve Nipple

1

443981

29563216

14

Air Solenoid Valve Nipple 4K only, Painted green

1

29514765

29566363

SERVICEABILITY:
The new Piston, Piston Seal, and Nipple fittings are backward compatible with former 3000 and 4000 Series
accumulator assemblies. See Table 1. The new Piston and new Piston Seal must be used together and not
intermixed with former Piston or Piston Seal designs. The former Piston, Piston Seal, and Nipple fittings without
sealant will be completely cancelled.
Two new service kits have been introduced to upgrade former and service current assemblies. See Table 2. Kit
P/N 29563811 is to be used to maintain current accumulator assemblies (P/N 29553476 and P/N 29553478).
Conversion kit (P/N 29565564) is to be used with former accumulator designs to upgrade them to current design.

IDENTIFICATION:
The current Piston Seal is slightly narrower in cross section and the Piston Seal Grooves are slightly narrower to
correspond. The lip of the current seal is no longer beveled. See Figure 2.
The new Piston contains an “A” marking on the concave surface for identification purposes. See Figure 3.

Copyright © 2020 Allison Transmission, Inc. All Rights Reserved.

SIL 16-WT-20
December 08, 2020
Page 3 of 4

Figure 2. Former (Left) Current (Right)

Figure 3. Piston “A” Marking

Copyright © 2020 Allison Transmission, Inc. All Rights Reserved.

SIL 16-WT-20
December 08, 2020
Page 4 of 4
Table 2.
Seal Kits
3000

4000

Ref
No.
N/A
3

Part Name (indent indicates content)

Qty

P/N

Status

29535973

Cancelled

2

29527008

Cancelled

1

29527009

Maintained
in kits
below

2

29527010

Released

2

29534489

Maintained
in kits
below

29563811

Released

Seal & Gasket Kit
Seal, Piston Lip
Sealring (Slide Ring)

4
9

O-Ring, End Cap (Steel)
End Cap O-Ring (Aluminum)

9
N/A

Seal Kit (for use with current Accumulators)

3

Piston Lip Seal

2

29563171

Released

4

Sealring (Slide Ring)

1

29527009

Released

9

End Cap O-Ring (for use with Aluminum
endcaps)

2

29534489

Released

29565564

Released

N/A

Seal, Piston, Nipple Conversion Kit (for use with former
Accumulators)
Instruction Sheet #367

1

29565591

Released

3

Sealring (Slide Ring)

1

29527009

Released

4

Piston Lip Seal

2

29563171

Released

5

Piston

1

29564913

Released

9

End Cap O-Ring (for use with Aluminum
endcaps)

2

29534489

Released

9

End Cap O-Ring (for use with Steel endcaps)

2

29527010

Released

12

Nipple With Sealant

1

29563216

Released

N/A

NOTE: "Released" in Status column indicates the part is also serviceable by its own part number.

ASSEMBLY:
For assembly instructions, see Instruction Sheet #367 on the Allison Hub.

TID 1, 2 and 3 MODEL ACCUMULATORS:
The newly released Piston Seal and Piston found in conversion kit (P/N 29565564) are backwards compatible
with TID 1, 2, 3 Accumulator Assemblies.

Copyright © 2020 Allison Transmission, Inc. All Rights Reserved.