Well that explains something I have been wondering about. An old CAT operator told me he thought the spring bolt should always be slack on the D6. Now I know he's right on the late ones.

I have one the bolt is REALLY slack on. The adjuster is pushing against the guide because the bolt is broken. That is something that needs taking care of.

Another area to check carefully when fixing the recoil spring/adjuster setup .. is the idler recoil rod, that fits into the idler yoke.
Most of the Cats in the 50's and 60's suffered from bent recoil rods and/or yokes after some heavy duty work .. and many modifications and strengthening Bulletins were put out for them.

There's a Product Bulletin dated Oct 6, 1960 (page 3) which outlines reinforcing procedures to prevent bending of the idler recoil rod on the 8U and 9U D6.
This involves cutting the attaching plate, and its gusset, off the recoil rod .. drilling two extra holes in the plate, to increase the number of retaining bolts to 6 .. then welding a short length of heavy wall tube to the attaching plate, and machining the end of the recoil rod to slide into the tube, thus making a less rigid, but better supported assembly, overall.

A second suggestion involved welding U-shaped flanges to the recoil rod guide assembly, to assist with support of the rod against bending.

After much thrashing about in parts and service manuals and specs. it appears that the long springs w/long ears are in fact 9U units. They were used on the 7-roller optional track frame attachment. These use a different spring and pilot but are still of the old double spring and pilot type even though the application was very late serial number at 29,219.
7-roller track frames get their parts from the 977 loaders which are standard with 7-roller units. A check of the 977 20A series prior to sr. #2508 confirms the use of the #6F1523 spring and 8F4880 pilot, same as the 9U attachment option. (after 2508 a D7 undercarriage was used)
What I can't tell is what the installed length dimension is for these units as I don't have the specs. Can somebody out there help us out???
As to fitting these to standard 9U tractors, I have my doubts but maybe it can be done if there is enough length available after accommodating the required installed spring length.

Hi Team,
S/M Feb 25 1949 tells of heavier recoil springs fitted to D6 8U4406--up and 9U1956-- up.
It says:- "To install the heavier recoil springs on tractors in the field the following parts are required: 2--6F1523 spring (Replace the outer spring)
The assembled length of the spring is 24 3/8 inches.

Just for the record and Not to confuse things the article also covers same for D4 6U2215-up & 7U4045--up , Ass. length 18 1/4".

S/M March 01 1954 page 23 & titled "A Field Expedient-- Recoil Springs".
Covers D6 & D7 and covers welding in stop blocks to arrest the recoil spring if the bolt has broken. If the bolt has broken then the tension is applied to the track and must be relieved. Compress the spring with a block between the track and sprocket to compress the spring on:-- D6 to 24 3/8" & D7 to 26 1/4".
Hope this helps
Regards
Eddie B.

Hi edb,
Thanks for the info, I didn't expect the replacement springs to have the same installed length as the regular springs on the 9U as there seems to be more coils to the 7-roller frame units.
I checked the ones I have on a 10,xxx 8U and a 24,xxx 9u and they have about thirteen coils and I can fit a piece of 1/4 in. plate between most coils and a tight fit 3/8 in in a couple of center gaps. I have no idea what is expected for recoil allowance movement but maybe it's not that much. What Yellercat has must be from the 9U/20A combination as all my research shows later models trending towards shorter springs. Still some what of a mystery. Think we scared ole Yellercat into hiding:D

Hi OM,
may be I have a hazy recollection that the Spring Length means Spring Length ONLY measurement, ie, in the compressed state with the end plates etc. on, you only measure the length of the spring in the calculation not the length over all of the group?
To be sure of this, one would have to check the distance between the stops and the bolster--fixed bit welded to the frame.
I stand to be corrected on this! Yes M8 its too far in the past to be 100%.
Regards
Eddie B.

Hi edb,
Think we're in agreement here. Installed length spec is actual spring length only with spring in its compressed state. Yes, it would also have to fit between the stops (if used) and the bolster. On the earlier set up with no stops the length would be limited to where the adjusting nut would run into the guide assembly and/or the adjusting screw bottomed out in the adjusting nut without sufficient travel for the front idler.

Hi again OM,
I too believe we have it sorted now due to good Team Effort, I was pretty sure I remembered it was a trap for young and old players alike. Some more of Yellow Father's way of expressing things in obscure terms, happens quite often with new Engineers coming through. Over the years I saw the same University taught mistakes come around 2 or 3 times, so it was up to us lowly mechanics to sort it out. Several times I respectly sent copies of old S/M's etc. along with my Report to highlite a previous fix for same symptom, saved lots of explaining. Did have a good rapour with CofOz Engineers and most of your fellow country men as they rotated through CofOz. Enough waffle for now.
Regards
Eddie B.

Hi edb,
Guilty as charged;) There was more the the occasional time in my engineering career that I (usually had to) released stuff to the shop floor knowing full well there would be problems...........but also knew that was the best place to sort it out with those that are closest to it. There comes a point when you can only do so much on paper and computer. Thanks to all you fabricators and mechanics that came to the rescue.

Got stalled at the ranch with other work , and there ain't no puter' there.
Sorta' embarrassed with the pics below, but the tracks are on 'run-out', but still very dirty. My memory did not serve me correctly as the stops are bolted on. Look like the pics that OM put up from the D-5. Check it out and see what you guys think.