I have 5.5 MTD lawnmower with a Briggs engine and the mower runs and works great except the automatic drive is slow. I think the issue may be the belt, but it looks like you have to remove all the plastic from under the deck and the wheels to get to it. Is there a way to tighten the belt or does it have to be replaced? Anyone familiar with this machine. Anyone have a pdf for a manual. I can get you the model number on the next post if needed. Thanks for your help.

Also in the event that the belt needs to be replaced how much smaller should the new belt be from the original belt that is stretched?

Bob

The model number would be a big help.

Many MTD's have a tension adjustment on the lever that engages the drive, it's usually a little thumb wheel that is turned to add more tension to the idler pulley that tensions the belt. If the belt is worn and requires replacement, it should be replaced with the original size belt. Drive belts don't actually stretch, but they do wear down, which gives the appearance of stretching. The drive pulley's can also wear and require replacement.

Here is the model MTD # 12A-378N302, In case someone has access to a repair manual for this problem.

I took apart the mower and got access to the belt. The belt looks to be in excellent shape. The mower drives fine, but really slow. The mower has the tension adjustment on the handlebar which is set properly. The idler pulley can't move any further without hitting the other side of the belt, so I ordered a new belt. Do you think the new belt will fix my problem? Thanks Bob

I don't think a new belt with fix the problem, I suspect your engine may be running to slow.

Anyone know how to adjust the speed on the engine?

Do you think the new belt will fix my problem? Thanks Bob

I'm betting it will,
let us know,
thanks,

Last night in my cold shop, I installed the old belt without all the plastic guards. I adjusted the belt idle pully and the belt is tight. Now, I know that last spring I did the same adjustment (by tightening the cable on the handlebar) and it did not work. However, last night on my driveway the mower was moving at a fast speed which was a surprise. The engine speed is perfect. I am thinking that the belt was wet when cutting the grass and it was slipping, last year when the proble occured. Do they make any any products to stop a wet belt from slipping or give the pulleys more traction? Thanks Bob

no they do not, I cannot look up the model number, but if it is the model that I think it is it is going to happen due to MTDs design of the plastic shroud on the bottom having "breathers"

having those the grass packs up in there, and rusts everything because it is normally wet

best thing to do is make sure your blade is always nice and sharp, and clean underneath it after every cut