JD 1209 Mower Knife Drive Arm

philsmith

New User
I recently bought an older 1209 9ft MoCo. I have been trying to troubleshoot why the knife bar keeps breaking at the cup that holds the Pin. I just noticed that the Pitman arm (knife drive arm) doesn't match the serial number of the mower. Does anyone know if changing the arm and knife assembly to the newer model (higher serial number) would cause the knife to break.
I have replaced the wear plates and confirmed that the knife can move back and forth freely. When I look at the break it suggests that it was fatigued in the front to back direction, not up and down.
 
I also have an older 1209. A couple years ago I needed a new sickle and sicklehead. The only way the unit came was the newer style and you had to change pitman arm and all. I could still get the old style sickle head and the bare sickle bar(no sections)so I did that as I didn't want to spend big bucks to update. I don't see why it would cause a problem though. Does the pitman arm adjust up and down where it hooks to wobble box like on old style? The 2 bolts that hold pitman arm have to be kept really tight(torqued)
 
Thanks for the quick reply. The new pitman arm attaches to the yoke with a single nut - I think its the same for both styles of Pitman arms. It looks as though its possible to set the height based on how tight the nut is. Which two bolts are you referring to on the pitman arm?
 
(quoted from post at 11:31:41 07/23/13)
Which two bolts are you referring to on the pitman arm?

This is the old style knife drive arm that hayfarmer referred to. IS the knife drive TIGHT on the wobblebox shaft?? Also does the knife drive pin fit tight in wobblebox drive arm?
mvphoto19371.gif
 
The updated arm is not the cause of the knife bar breaking. The first 2 hold downs need to be the high arched ones to allow the knife bar to freely move back and forth. Your knife bar is binding in the hold down. I went down that road 3 years ago. It did not make a difference if it was a brand new bar or and old bar.
 
Hi Tx Jim. I now have the newer style pitman arm which does not have the bolts. Thanks for clarifying.
I noticed that the pin can sway a bit in the pitmam arm hole, so I have purchased a new arm, but I haven't installed it yet as I wanted to make sure that the new style was supported on the older mower.
The knife drive (pitman arm) does appear to be tight on the wobble box 'yoke'. I will have a closer look when i can get the bottom guard off.
 
The first 2 hold downs need to be the high arched ones
I bought 2 new hold downs from the JD dealer but they were the low cast-iron ones. They didn't give me an option. I will check with them again.
I also bought new wear plates. Do they need to be set all they way back near the knife head?
 
My dealer gave me the same low arched hold downs when I had the problem with the knife bar braking. You got to remember, sickle bar mowers are a thing of the past and not to many people are up on them, exspecially parts guys who don't have much experiance on them.
Before I realised that the hold down was the problem I chnaged the pitman arm because there was a little slop in the pin. This did not make a difference. I will try to remember to take a picture of my knife bar to show the difference and post it later tonigth or tomorrow.
 
Since it seems that the pitman arm and knife head have been changed from the < 285000 model to the > 285000 model, do the wear plates and hold downs need to be changed to match? I see in the JD parts list that there are 2 configurations (3 if you include the non-clog) for clips and plates.
Tim - I appreciate you taking a picture for me. It will be really helpful.
 
The new style pitman arm is an update on the older style. The newer 720 series haybines use the same setup. If you're certain the knife moves freely back and forth check your guards for excessive wear that will allow the knives to move up and down against the shearbar surfaces of the guard. Don't be afraid to spend the money on new knives and guards. Everything sharp and without excessive wear will make a big difference. No-clog guards work great plus there's the advantage that they are adjustable to take up slack as they wear.
 
The wear plates should be all the way back on all locations! There should not be any wear plates near the knife head area. The knife has to move fore and aft as it strokes.

The pin should not be loose in the arm. The bolt should be torqued to I believe 150 ft-lbs to retain the pin for the knife head. If it wiggles, it can break the knife head or arm. Tight, tight, tight!.
 
Thanks Tim. I received the pics and p/n's. I see you have the non-clog guards, but the shape and placement of the hold-downs should be the same for the original guards. I'll pull mine apart this weekend. At what location do the wear plates start? At the first guard from the head? (part 5B in your PDF). And where does wear plate 5A go?
On second thought, I'll have to buy a manual.
 
These are pics of the bolt that goes in the new style pitman arm to hold the Drive Pin. Has anyone experienced the wear shown? This is a grade 5 bolt. When I changed it to a grade 8, the knife head broke within an hour, rather than the 8 hours I usually get.

mvphoto19395.jpg


mvphoto19396.jpg
 
Thanks to everyone for their input. I think I finally have it licked. I bought new guards and a new pitman arm. As I was changing the guards I noticed that the older ones were not bent, but that the main frame where the guards are bolted was slightly bent up just in the middle, about a 2 foot section. I noticed this after I removed several bent-looking guards and moved the knife to and fro to check. I watched the sections getting pushed (tilted) upwards as they passed through the guards. When I put new guards on, it did the same. So the whole problem came down to the knife assembly twisting up then down as it passed through, causing the metal fatigue and eventually the wear in the pitman arm Pin hole. To correct it, I placed shims of various thicknesses just in front of the carriage bolt at the bottom of the guards that needed to be lowered. I also replaced the pitman arm. Now, after running it for a day I do not see any wear in the bolt that holds the pin in the pitman. I still have some chatter when its running so I'll adjust the guards to lessen the noise as it must still be catching a guard or two somewhere.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top