SOS pressure testing

I'm currently working on a 5000 SOS with a slipping complaint in half the gears (R1,1,2,5,6,&9). A quick check of the troubleshooting chart shows the issue to be with the Direct Drive clutch (no surprise there).

Wanting to make this a teachable moment for my students, I recorded a unique pressure test sequence that some of you will likely find interesting. The video link below will show two different tests run through all of the gears: Test #1 shows pressures at all 3 bands. Test #2 shows pressures at band #1/DD clutch, the pump, and the lube circuit. A legend at the lower LH side shows what colors are for what circuits.

It was no surprise to me to see the major loss of pressures whenever band #1/DD clutch was engaged. What did surprise me was that the lube pressure dropped to pretty much zero whenever that same circuit was pressurized. This leads me to wonder why Ford ever abandoned the low lube pressure warning light, because if this tractor had a functioning lamp on it, the owner might have caught this problem earlier. Any thoughts on this? Do you think it was purely a cost saving measure?

Note how the pressures momentarily drop every time a gear change is made. This is because of the various "indirect circuit" clutch packs being engaged, which is completely normal. Since the pressures drop and then come right back up to where they were, that indicates no leakage in clutches 1, 2 or 3, which cannot be directly pressure tested.

Also note how the engine lugs way down from 8th going into 9th, but not from 10th to 9th. I have a theory on that, but I'll let some of you speculate on that one first - I'll let it be a brain teaser. Hint: study the clutch application chart on the RH side.

When viewing the video, click on the double arrow in the upper RH corner to maximize the screen for better clarity.
Pressure Test Video

I would guess with you, that Ford thought the lube pressure light meant little enough to its customers that the cost wasn't worth it. That's no more than a guess mind you.

As for the 8 - 9 shift pulling the engine more, it shifts two bands and a clutch rather than two clutches and band to enable the 8th/9th shift. The only other place that it does that is the 4th/5th shift. Of course that would happen on the downshifts in those ratios as well.

What a great demonstration! The students must be amazed that this technology existed in Grandpa's day.

Based on your clue, I notice that the 8 to 9 shift is the only one that triples the number of circuits pressurized.

Zeke B.

Bern,
As always, you are an amazing source of knowledge and wisdom. It is great that you share that with us.

THANK YOU!!!!

As for the 8-9 shift, looking at the chart, 9th is the only gear where there are 6 circuits pressurized. I would guess some of them are not pressurized well enough and some of the bands and clutches are not where they are supposed to be (not fully retracted or engaged). Almost like you are in 2 gears at once.
Most of the other gears have only 2 or 4 circuits pressurized at one time.

Keith

So to answer the "brain teaser" from my original post, my question was: Why does the engine lug from 8th to 9th, but not 10th to 9th? After all, the same elements are applied in 9th gear regardless of which direction you come from, correct?

If you look at the clutch application chart, when you go from 8th to 9th gear, you're moving from 2 hydraulically applied elements to 6, which is 4 additional elements that need to be filled. When you move from 10th gear to 9th, you're moving from 4 hydraulically applied elements to 6, which is only 2 more elements that need to be filled.

Because of the major internal leak in the DD clutch circuit, having another 4 extra elements on top of that needing to be filled is more than the pump can keep up with. The system pressure struggles to get up much over 100 PSI (and it's even less in the DD clutch circuit). Because the internal leak is so big, and consequently the pressure is so low, there's not enough pressure to fully release the #1 band. Since band #1 and the DD clutch cannot both be applied at the same time mechanically, you hear the engine loading down because of the internal "fighting" between the two (think tug-of-war). Of course, as the engine lugs down, the problem is only exacerbated because pump flow continues to drop, along with the pressure.

I hope that made sense. I thought it was an interesting anomaly - I suspect some of you did as well.

I forgot to add...Keith and Zeke, you guys both pretty much got the correct answer.

Very interesting thread. Thanks, Bern.

Relatedly, my retirement project (plan to retire again at the end of June) is to mechanically restore my 64, 4000 SOS. This will include installation of a very low hour 192 CI converted NG (high compression) engine. The engine should produce 60+ PTO HP so I plan to overhaul the SOS at the same time. Currently, the SOS operates well, but I believe that the tractor has lots of hours and was once used to pull a small square baler. I believe that it was not well maintained after it became older.

I've noticed that the SOS takes longer to shift when fully up to temperature (hot) especially at low engine RPM. I've not used this tractor much but am not sure if it will pull properly at 450 engine RPM. I've not done any pressure tests but symptoms indicate low pressures.

Correspondingly, I'm faced with a couple of dilemmas: 1.) condition of input shaft, which is unknown, and; 2.) condition of pump, also unknown.

I've overhauled automotive automatic transmissions before and am not hesitant to tackle overhaul of the SOS but am not certain if all needed replacement parts are available. I'm not worried much about clutches, seals, O-rings and gaskets or even bushings/thrust washers, etc., but am concerned about the input shaft and pump.

The input shaft issue is a well known problem but I hope that I may be able to find a replacement from one of you good folks on this board if I need one. If not, and if necessary, I may decide to have one made from scratch by a good machinist (this project is a labor of love, not a money making project).

The pump issue is another concern. Though I've not investigated, I suspect that pumps and pump parts are NLS.

Any advise as to what to do if my pump is worn out?

Dean

You have an engine that will operate at 450 RPM? If that's not a misprint, I don't think that will work, as I don't think you'll have enough pump flow at that low of RPM to generate sufficient pressure for your clutch packs. That said, with regards to the pump and input shaft, here are my thoughts:

Worn input shafts are common, but you don't need to make a complete new one from scratch. There are machine shops that could weld up and re-spline your existing shaft, or there's an option to mill the end of the existing shaft to a hex shape and weld an impact socket into the existing hub of the clutch disc. Instructions for doing this are somewhere in the archives here.

With regards to the pump, I doubt it's worn - I've never seen a worn SOS pump. More likely you have an accumulation of internal leaks that are causing the slow shift you describe. The last one I worked on with similar symptoms to yours ended up having a cracked pump pressure supply tube.

Thanks, Bern.

Yes, the engine will idle at 400-450 RPM.

I am aware of the hex socket repair procedure but do not want to go there, though welding/re-splining a worn shaft may be an option if needed.

Feel better about the pump now.

I hope to start work on it this sometime in the winter of 2018/9. I'll be certain to inspect the pump tubes.

Dean