Description
Two part numbers, one machine, no published supersession. That is the honest summary of 708-1T-00420 and 708-1T-00421, and it is the kind of situation where a confident catalogue is more dangerous than a cautious one.
What the sources show
EPC-derived parts data lists a fan pump assembly for the Komatsu D275A-5D under both numbers, with one source recording the applicability as D275A-5D from serial 25001 upward against a specific build specification. Komatsu’s own online parts catalogue does not return an entry we can cite for either number, so the item name could not be confirmed first-party, and no source we found states that one replaces the other. What we can say: both sit in Komatsu’s 708-1T pump group, and the rest of that group is published as Pump Assembly.
How we handle it
We publish one page rather than two competing ones, because two pages claiming the same machine would split the ranking signal and, worse, invite the wrong order. When an enquiry arrives we ask for two things: a photograph of the number cast on the old pump, and the machine serial number. If the parts record for that serial gives 00420, we quote 00420. If it gives 00421, we quote 00421. We do not treat them as interchangeable, and we do not let a customer order on the assumption that they are.
Diagnosis on a D275A-class dozer
- Clean the core pack first and re-measure temperatures under load.
- Measure fan pump output pressure and flow with the oil hot.
- Check the fan motor case drain volume before condemning either unit.
- Confirm the control signal reaches the pump; a pump never commanded to full stroke mimics wear exactly.
Notre guide de diagnostic des pompes de ventilateur hydrauliques sets out the tests, and the fan motor guide covers the other half of the circuit.
Montage
Match shaft spline, pilot, flange, port positions and control orientation against the removed pump. Prime the casing with clean oil before cranking. Change the return filter element and clear the suction strainer, targeting ISO 4406 18/16/13. Keep the case drain unrestricted to tank. Prove full fan speed under load and record both temperatures.
Commande
Minimum order one piece. Three to six month warranty on new aftermarket units as stated on your proforma invoice. Bench checked and photographed against your order before the wooden case closes, delivery 5 to 8 working days from payment subject to stock. The D155-6 fan pump is 708-1T-00472; la gamme se trouve sous Moteur de ventilateur hydraulique Komatsu.
