You want to discern whether what you've discovered is the way it is from the manufacturer, is the result of an accident, is the result of an improper repair or a repair using the wrong part, or is the result of human intervention.

What brand and model of rider and what size deck?

Did you buy it new or used?

Do the quills mount from the bottom of the deck or the top?

grass how did you go about measuring? Usually the primary datum plane of the deck is determined by the underside of the cutting edge area of the three blades; eveything else is a function of that datum plane.
The one main exception would be a bent or tilted quill assembly in relation to the other two.... a somewhat tricky measurement to make...?

Thanks for the replies.
LOYC :), It's a used Steiner MD60. No descernable damage to deck or sign of improper assemly or other stupid human intervention..Quills are undermount.
Rcbe, 1/4" difference was determined by measuring blade tip to blade tip with middle blade. Level as measure on blade tip with a blade hight guage on a level concrete floor. I guess I could have confirmed height of offending blade by using height measurement guage on other outboard blade.
I actually never noticed the difference in cut until I lowered the deck to cut under 2". There just isn't any noticeable quality{{gwi:807}} of cut at 3" or more.
I suppose I could have a piece of 1/4" plate machined to put between the Quill and the deck, but that's a route I'd rather not take if there is a simpler avenue.
Dealer had no suggestions. Well, other than maybe a total rebuild.

This post was edited by grass1950 on Mon, Apr 22, 13 at 17:16

grass - if the blade running/cutting low at 2" or less is on the deck exhaust side, may be a question of extra weight toward that end combined with some slop/wear in the deck hanger sys at those height positions giving you the different results. To that end, are you getting a sawtooth cut or just one blade path by itself cutting low?

This is a front mounted floating deck. The offending blade is i/4" high, not low so it is cutting 1/4" longer.
I won't bore you with all the specifics, but I nurmally mow with a Honda walk behind HRR. I cut at 2" in the Early Spring but I wanted to take it down just a little more so I got out the Steiner and set it for 1 and 3/4". I did a test cut and when I checked it, I noticed that 2/3 of the cut was starting to scalp, but the right hand 1/3 was fine. That's what led me to find that one blade was higher than the other two. Does that help{{gwi:807}} rcbe?

I hope my teasing hasn't ticked off JL. I question his bias, not his knowledge.

This post was edited by grass1950 on Mon, Apr 22, 13 at 19:42

grass - might it be possible to first level that deck side to side to get blades one and three on the same cutting plane and then level the deck front to back to bring the middle blade to the same cutting plane?

Thanks rcbe. I'll look into that tomorrow and see if its feasable.

Check the air pressure in your tires BEFORE you level the deck.

Good advice JL. Except in this case the MD60 is totaly independently suspended on two front caster wheels and a full length roller in the rear. The tractor just pushes it around. Although I got a manual for the tractor and snow blade, I didn't get one for the mower. So tomorrow I'll see if I can find one and try rcbe's leveling suggestion--or at least see if it's possible.
Thanks again to you both.

Located an owners manual for the MD60 on line. Read the "leveling" instructions and find that the previous owner had taught me how to do that correctly.
Now when I previously called the dealer about this issue, I may have gotten a new employee or a sub covering the service department or maybe the dept employee was too busy that day to give me his full attention. Whatever.
The owner's manual has a parts list and drawings. Lo and behold it lists 3 (count them, THREE) different thickness shims for placement between the deck and the quill to adjust the final blade height- 20, 16 and 12 guage. I would be surprised if the blades weren't adjusted by the manufacturer originally, so as JL sugested, a previous owner must have removed the quill and not reinstalled the shims. I'll see if I can order the shims I need. Thanks guys and sorry for taking your time. I should have found the manual before posting.

Would those "shims" be anything akin to "washers"?

Lol. No, they are shaped like the bottom of the quill Each shim is 1/2, so one shim for each side of the quill and each 1/2 has two holes for the quill bolts (2 of 4) to pass through.

grass, this whole episode is shaping up to being a classical case of thinking outside the box, as it were... :)

It's always better to RTFM than guess...

This post was edited by justalurker on Tue, Apr 23, 13 at 21:30