John Deere — Fan and Alternator Belts Tension or Replacement
Maintenance · Fan and alternator drive belts
From a John Deere operator's manual covering: 4039, 4045, 6059, 6068, RG4697. Check it applies to your exact model before use.
Applies to: John Deere 4039, John Deere 4045, John Deere 6059, John Deere 6068
Before you start
- Do not pry against the alternator rear frame
- Do not tighten or loosen belts while they are hot
Procedure
- Inspect belts for cracks, fraying, or stretched out areas. Replace if necessary.
- Using JDG529 Tension Gauge or belt tension tester and straightedge, check tension of warm belts.
- If adjustment is necessary, loosen alternator bracket cap screw and nut on mounting bolt. Pull alternator frame outward until belts are correctly tensioned.
- Tighten alternator bracket cap screw and nut firmly.
- After a new or used belt has run for 10 minutes, recheck belt tension.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Standard V-Belt: 89 N (20 lb force) applied halfway between pulleys should deflect belt by 19 mm (3/4 in.)
- Poly V-Belt: 130 N (30 lb force) applied halfway between pulleys should deflect belt by 13 mm (1/2 in.)
- Single belt new tension 578-622 N (130-140 lb force); used 378-423 N (85-94 lb force)
- Dual belt new tension 423-467 N (95-104 lb force); used 378-423 N (85-94 lb force)
Full service-parts list: John Deere 4039 →, John Deere 4045 →, John Deere 6068 →
Source: John Deere operator's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.