New Tow Arms are Now Used On Certain Asphalt Pavers {7121} Caterpillar

Asphalt Paver

AP1000F (S/N: AC41-368)

AP1055F (S/N: TJ51-731; RLM1-107)

AP600F (S/N: AP61-175; LR61-121)

AP655F (S/N: 4801-121; 4521-102; 4531-102; P651-128; 6551-101; MH61-313; ML61-119; 4791-150)

AP655F L (S/N: AC61-101)

Description Of Change: New tow arms are now used for rear mounted extender screed applications on machines listed above. The new tow arm design moves the screed 30 mm (1.18 inch) closer to the rear of the paver because the new tow arms have been shortened 30 mm (1.18 inch) between the screed mounting pad and screed lift cylinder pin. This assists in reducing the center line segregation and thermal segregation.

Adaptable To:

Replace the existing tow arms with new part numbers listed in Table 1.

Rework Instructions for Older Machines with Older Tow Arms

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Do not operate or work on this product unless you have read and understood the instruction and warnings in the relevant Operation and Maintenance Manuals and relevant service literature. Failure to follow the instructions or heed the warnings could result in injury or death. Proper care is your responsibility.

Illustration 1	g06271163
(5) 550-7476 Spacer As

Machines with older tow arms may install spacers (5) in the gaps of forward portion of the tow arm, to move the screed 30 mm (1.18 inch) closer to the paver. Follow the below steps to install the spacer.

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Illustration 2	g06271498
(A) Pin (B) Tow arm gap

1. Float screed to the ground.  Extend both tow points 75% of full travel. Slightly propel machine in reverse to move tow arm gap (B) towards the front. Raise or lower tow point until pin (A) feels free.
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   Illustration 3	g06271763
   (A) Pin (C) Snap ring (D) Washer (E) Inboard side (F) Outboard side

2. Remove snap ring (C) and washer (D). Slide pin (A) inward as shown in Illustration 3.

   Note: Do not remove the pin fully.

   Place one spacer (5) on the inboard side (E). Move the screed thickness screw slightly to make the installation easier. Slide pin (A) back to normal position. Pin head will retain the spacer (5).

   Install one spacer (5) on the outboard side (F). Install washer (D) and snap ring (C). Washer (D) will retain the spacer.

   Repeat the same process for the other side.

   Note: Do not use the spacers (5) in conjunction with the new tow arms. Interference between the screed and paver will occur as the new tow arms are shorter.

   Note: Front-mounted extender screeds, or vibratory-tamper (VT) screeds do not benefit from moving the screed closer to the paver.  These applications, when equipped with new part number tow arms, will utilize 550-7951 Spacers, in between the paver and screed arms. These spacers require longer bolts. These parts will be included with machines that are listed in the serial number effectivity.

   Note: If one of the older part number tow arm is damaged, and needs to be replaced, both tow arms must be replaced with the new part numbers.  Old and new part number tow arms cannot be mixed, due to the difference in length.

Installation of New Part Number Tow Arms on Older Machines

If new part number tow arms are installed on an older machine, it is necessary to change the fittings on the lower port of the screed lift cylinder and re-orient the screed lift / lock valve. This is to prevent the tow arm from contacting the valve in certain conditions.

1. Float the screed to the ground
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   Illustration 4	g06271827
   (G) Lower screed lift cylinder (H) Adapter fitting (J) Adapter fitting (K) 396-7157 Solenoid Valve Gp

2. Remove fitting (H) and fitting (J) between the lower cylinder port and valve (K).

3. Install 3K-0360 O-Ring Seal (7) onto 8T-0249 Elbow (6) and install to lower cylinder port. Do not tighten.

4. Install 6V-8398 O-Ring Seal (9) and 3K-0360 O-Ring Seal (7) onto 6V-9002 Elbow (8). Install adapter (8) to the CR port of valve (K).

5. Join the adapter fittings.  Orient the valve approximately 10 degrees from the vertical position, as shown in Illustration 4, with the top of the valve pointing towards the front of the paver.  Tighten all fittings.

Repeat the same process for other side screed lift cylinder.