Steering and brake booster pump should produce 350 psi.

Hi Team,
the material in the suction screen could be either from the trans clutches or the steering clutch packs as BOTH pump suction screens ultimately pull oil from the one pickup passage in the Transmission Transfer Case--this in turn connects to a bulged area at the drain plug on the bottom of the bevel gear area of the main rear housing, and so it is luck as to which screen gets the crud, unless only one screen has been checked and cleaned in the past.

Yes, Early machines had both a Trans Pump, mounted on the rear of the T/C housing, and a Steer Pump mounted on the front right side of the engine accessory drive housing--later units used a larger volume gear pump here to serve both the Trans. and Steering circuits.
In the first instance, the trans. pumps were a Vickers Vane pump and were soon upgraded to gear pumps after the vane pumps suffered from dirty oil wear and so early hour failures.

You could do a comparison of the radial line radius's on the lining material, these then can be compared to both a Trans lined disc and a Steer clutch lined disc, then you should be able to determine which clutch has failed--Trans. or Steer.
Trans discs are a larger diameter when compared to the Steer discs. and the REV Clutch Trans discs are largest of all.

Regards,
Eddie B.

Hi Eddie,
Flow schematic shows to be two separate circuits.

Hi OM,
the schematic you kindly posted above does show the Trans and Steer circuits, as apparently being separate, BUT which Siameses into one cast passage for both of the Trans and Steer pump oil pickup screens back inside the Trans. Transfer gear case which in turn pulls oil from under the bevel gear area sump via a single passage/tube/opening? in the bevel case and an external bolted on elbow between the Main case and the Trans Transfer gear case.
These items may show in a Trans rem/refit and overhaul series of pix in a Service Manual.

The screen each side of the Trans case combines into one inside the casting of the Trans Transf Gear case--believe me--you are looking at a schematic representation for the Trans and Steer circuits.
As shown, the return oil from the steer valve etc. dumps into the bevel case from where it comes back to the steer pump via the said elbow and Siamese passage and split to the dual screens--one for each circuit pump.

I will try and find some school note pictures from the school hand outs and from a 68A D8H Parts Book and label as needed to help explain the simple set up. As is often the case that if you could see the iron it is self evident.

Done in a rush and I am no ace with Paint--lol.

Respectfully,
Eddie B.

Hi OM,
just found a Parts Book as above.
Naturally the Scans show the layout for Trans and Steer systems better and I think now will make more sense than my last post.
It should be noted that the double section Steer system pump only has one inlet and one outlet connection.

Note position of Trans pump (5) on left rear upper half of T/C housing, and position of Steer system pump (15) om front of the Accessory drive right side engine rear.
Each pump connects to their respective suction screen ports on the front lower of the Trans Case.
Trans to the left and Steer to the right--both fed from one pick up in lower of the Trans Transfer gear case as depicted in the other pump lines scans.

The vane pump was soon phased out and a gear pump substituted and still later both systems ran of a larger output pump at the old Steer pump location on the engine rear accessory drive front face an used one pickup only from the right front lower of the Trans case--the other pick up port was blanked off.

It should also be noted that the captions say Lubrication system for each circuit--that actually means lube and pressure for each. It caused some confusion back in the day as it still does to us here now--from memory this machine was Cats first Powershift Model so terminology was still a bit loose and not refined.

Hope this helps.
Cheers,
Eddie B.

The discrepancy between the flow diagram and actual plumbing makes no sense to me. Why go to the trouble of having separate pumps, screens, filters and piping then combine into a single source sump?
Seems something went haywire between design and actual fabrication.

Hi Team,
I have no explanation for the discrepancy with the flow chart and original design used for the oil pumps etc. suffice to say that it was the first of Cats PS units out of the design shop and we all know that things need to be Field Tested beyond the proving grounds for the true deficiencies to show up--at least Cat made mods. in a timely manner as time went on--there were many updates to get these transmission innards and their circuits up to the reliable systems we see today--something we have seen from the Holt/Best days and again why a Serial Number is VITAL for correct data to be handed on to you all.
On the D8H in question it can be seen from the scans above that changes were made as early as 48A0333 and still more after that--Darwin's Theory of Evolution comes to mind.

Over the years at the Dealer I also saw the same design mistakes made thru the range of gear that had been made and rectified in the 1960's 70's and so on, only to re-appear as new Engineers came to design systems fresh with the same University taught mistakes repeated.
I often sent on unasked a report with a Service Magazine, or other publication, telling of the problem in a newly released unit having the same problem as one in the past and so how it was rectified then--the Engineers at Cat Australia I dealt with in later years as a Service Tech. were a great bunch of blokes and were always willing to listen and act as needed. They often came to me with queries about current issues that I/we had not encountered yet and ask if I had any ideas--two way street so to speak.

Cat has a great record of I reckon some 98% success rate these days with new designs and are quick to act to improve the product as needed to keep their well earned great name and product--yellow blood flows in my veins--lol.
It could be said of todays designs sometimes the computer design has helped and sometimes it has left metal a bit sparse in some areas too.
The old guys over built things somewhat and so we see these long lived units still doing useful work after 80-90 odd years.

I do not know if it was an old wives tale, but I was once told that the gent who designed the Cat PS Trans sadly came to a sad end later on--I sincerely hope that was not the case because they were one of the best in their day, once the small stuff like OM is referring to was sorted.

Sorry for waffling on!!

Cheers,
Eddie B.