would look in the cavity under the tilting seat, find ID tag with full model and serial number: go to website http://manuals.mtdproducts.com/mtd/Public.do  ; download free pdf copy of parts list which will show exploded view of deck assy - letting you know whether spring is involved with arm for tensioning purposes..

I have the manual but what I'm wanting to know is , before I put the spring back on , how loose should the arm should be.Is it tight with some resistance or so loose it swings freely (with no spring or belt).Don't want to put it back together if the idler arm is still not working right.Txs

if the arm is spring loaded by design, then it only makes sense for the arm to swing freely. BUT, that should not be accomplished by leaving hardware loose - something seems out of whack at the arm pivot point..?

Agree with rexlex. Suggest you loosen to the point that you can get some grease into the joint. Remember, WD-40 is for Water Dispersal and disappears in a few weeks so rust, etc. can return. IMHO, it's lubrication properties are kind of a "oh by the way" type of thing.

Grease is good :) The WD40 is just to try a loosen it up so I can loosen it up and be able to undo the bolts etc. I couldn't even get the belt off to take the deck out before I started the WD40 treatment it was so frozen.

Forget WD40, use penetrating oil, let it soak and tap occasionally to add penetration. JMHO

The WD40 did do the job but now I've run into another problem. The pin in the idler arm is frozen(rusted) in and I need to pound it out (if I can). To do this I need to remove it from the deck , meaning I have to take the belt off. Unfortunately , Cadet (MTD) decided to add a wire retainer and it's bolts are also frozen (or torqued too tight) and I can't get leverage to break it loose on the deck. It doesn't appear in the parts manual nor on the Cadet video so it's more like an engineering after thought. Tempted to just take a grinder to it and cut it off as I can't remove/change belts with this wire retainer on. Anyone else have one of these on their 54" deck?

would try some good rust peretrant mebbe with a bit of heat first - that retainer is most likely there for a good reason - like a belt keeper/guide?

Thanks for the comments but I've come to the conclusion it's beyond repair. The pin is frozen in so hard I can't budge it with a hammer and the bolt that attaches the pulley to the idler is frozen as well. I don;t have the luxury of a torch to heat it up. I think the cheapest and easiest thing I can do is order all the parts and build a new one vs taking it to the dealer 30 miles away and paying $120+/hr labor + parts.

dooley - if that deck idler arm assy was so frozen up with rust/corrosion that you are jumping thru hoops now, got to wonder about balance of deck assy condition - spindles, brgs, blades, shell, etc. ..... OK?

Everything else seems OK but I'll give it all a good going over. I put the idler assembly back on and left it loose enough to work as the mowing situation is getting desperate and it's either mow now or get someone in with a mower/baler to take it off. BTW - the area isn't a Kentucky Blue Grass manicured lawn but an old horse pasture and exercise arena that's come back to quack grass/dandelions and poplar shoots.:D

That's what I've decided to do. I printed off the deck schematic and parts list , highlited what I need and am just waiting to hear.

good luck, dooley and let us know along and along..