help with wheel horse automatic

whats the trick to keep theese hydro's from taking off to full speed. i have tighten and bent around the clips on the plastic slider, and nothing seems to work. i even bought a nice used plastic slider and clips and those do the same thing. the only thing i can think is the aluminum houseing that it slides on must be wore out. i can control the speed with the foot pedal, but the forward/reverse handle will just drop to full speed. you'all have any idea's ?.....

thanks for the info. ill check it out this weekend. answer to bills question- this little machine is amazing. just last week it pulled my old simplicity out of a nasty mud hole with one try. i feel sorry for my tractors around here. they all get worked hard on my property. my 900ft driveway will put any garden tractor to the test when it comes to plowing snow. i have gone threw many cheaply built tractors in the past. i finaly have a well built fleet of 1960's & 70's wheel horse's, simplicty's , and a ford. but my sweet little 877 has to be my favorite. i use to have prombloms with the front end slideing all over the place when plowing snow. the chains on the front where a HUGE difference. now i can angle the plow and push snow where ever i need to. this thing will surprise ya for a little 8HP tractor.

Under that plate that covers the linkage, you'll find a "nut and bolt" assembly with a spring around it, running left-to-right, that's about 5/8" to 3/4" in diameter. You'll probably need some good penetrating oil, a couple of good wrenches, and a supply of profanity to get that nut loose on the assembly. The nut tightens a friction cone "thingy" that along with the spring, supplies the drag on the system to hold it in place. At the age that tractor is, you may well be missing one or two small springs in there that make the pedal return to a neutral position.