Pinion gear

[Rainman Advanced Member Find all posts View Profile Close Rainman]

This is probably a stupid question and indicative of my level of expertise in this area, but I've been thinking for a little while about changing my standard 3:9 gear ratio to either 4:1 or 4:3 on my RV diesel, but just wondering if the pinion gear also has to be changed to match the ring gear?

I've been running 265/75s for the past few years and hoping that changing the ratios will mean the beast doesnt run out of puff so early. Be kind with your replies.

[glen_ep Addicted PP Member Find all posts View Profile Close glen_ep]

Yes, you absolutely have to change both the ring (crown) and pinion gears, and it must be done to both diffs.

It's an expensive exercise though, gear sets are ~$200 from US (plus shipping) or ~$600 in AUS (per diff). Labour with diff removal/fitting is ~$400-$500 per diff. Then add new seals and potentially some bearings. Given the labour costs it makes sense to install lockers at the same time. All up with dual lockers you'd hit around $5,000.

However, if you don't have lockers and don't insist on new equipment, you could potentially just source some second hand diffs from a 3.4L model which has the 4.3 ratios. I've paid $400 for a complete front diff in the past, so that's a significant saving if you can fit the diffs yourself. NOTE: You'd have to ensure the prop shafts are the same between models, that they can still connect to the replaced diff.