Greetings: I am still on the prowl for nice set of knockers aka front check breakers for a U series D4; preferably the spring loaded type. Safe to guess these were a West Coast item.
I need some bling to add to one of my D4 projects, any assistance is welcomed. Thank you in advance. JM

JM,
I do not have pictures of those items.
I think someone probably has photos that could be posted, help those that are not sure what you seek look like.

For all the people wondering what JM is talking about: an added on necessity to break the "check (levee)" you were crossing, easing the jolt to the machine and helping to keep the operator in the seat, especially tail seat orchard machines. They acted like mini-dozer blades directly in front of the tracks, busting the ridge. "Checks" pulled with a disc ridger were reqired in flood irrigation practices long before other methods came to common use.
CTS

A few pictures on D2 track frames. Spacers and width suggest may have been for D4

Thank you Brian: Are those yours, or are you teasing me? Hah! I would be interested in for D2 as well if available. Those look pretty nice from here. JM

Sorry but they are to go on one of my tractors. Pictures are from Florin tractor. I got the breakers, frames went to China.

Those do not look like they would be too difficult to fabricate. Perhaps someone has some drawings with more detail. Would be fun to try. I recall seeing a short video attached to a post some time back, showing these in use. 
Bruce

Nah, too much work to build a set of the spring loaded ones; not to mention the cast parts involved. Some around here fabricated ones from steel plate and set them up to hinge. Occasionally see a set of "roached out" ones that were home built. I have a very warm lead on a set from a gentleman winegrape grower and Cat guy, but those either fit a 6U or a D2, which I will likely gather up one day. They are out there, I will continue looking. Thanks everyone! JM