I have 2 Volvo DPX drives that have 60 hrs on them. They shift very hard. Cables are fine very smooth. RPM at idle is 800. On a 2001 Formula 353 Volvos 502. Help. Also need the best spark for these engines.

Using the synthetic gear lube?

Your shift interrupters are bad, call Innovation and order new ones.

No

The synthetic makes a difference and is the recommended oil. Typically the Volvos shift beautifully.

Had a client that the previous marina was putting Merc HP into the drive and it was dragging severely when shifting - changed over to the recommended syn and it was a beautiful drive for shifting. They take just under 3 quarts and results were immediate

Merc gear oil glazes the cone clutch and causes the delay. Merc Hi perf gear oil is mineral oil and is a GL 4 rating spec ---- Volvos SX and DP and dpx require a GL 5 spec syn oil of 75 w 90.

Also Volvo nedox coating the cone clutch and when that gets glazed there will be a big delay shifting for when the props actually start spinning.

The hard shifting could also be caused by cable routing/securing in and around where the interrupt switches are located. If they are not straight and secure around the switch, it can have an affect.

As stated above also, ONLY use Volvo synthetic gear lube