973 hydrostat relief valve

[farmer bob]

does anyone have pictures of where the main hydrostat relief valve is located? 86G serial number

 

[Nige]

Curious minds are asking what you plan on doing with them and if you have the a copy of the Test & Adjust procedure.?

 

[farmer bob]

the problem started a few years ago when i blew a hose and needed to replace oil and new filter. when the machine was cold, it would travel fast. but after up to temp, it would slow to a crawl. i had put too high of viscosity fluid in along with a napa trans filter. ive since replaced fluid with 10w and with a Cat filter. its still performing the same way. my thoughts are that the pressure relief is possibly stuck open or the spring is broke? my service manual doesnt go into any detail as where its located. if i can remove it and see the issue, i can take it to the Cat dealer and get it repaired. it never slowed in travel speed until the oil change and filter replacement. thanks.

 

[Nige]

its still performing the same way. my thoughts are that the pressure relief is possibly stuck open or the spring is broke?

Unlikely I would think. Much more likely to be internal leaks that worsen as the oil gets hot. They are not exactly unknown in the hystat track loaders.

The lines you need to be looking at are the small ones in the top RH corner. To confirm Part Numbers would require the full machine S/N in order to identify the exact transmission arrangement that it has installed. The illustration may not be 100% correct, it needs to be based on S/N, but you get the idea.

 

[farmer bob]

serial number is 86G00173

 

[Nige]

See the illustration below. You're going to have to get into the hydrostatic power case and carefully start removing tubes one at a time to inspect the condition of the hardware at the end.

If you find any damaged big black seals (RH side of the photo) the Part Number for a replacement is 8T-9502. If any of the other three items in the photo are damaged then you need to order a 5P-8752 Nut Assembly which also contains the 8T-9502 Seal.

If when you disassemble you find end fittings that look different to what's illustrated below, please post photos.

There is a specific torque for these particular fittings - 14.8±2 lb ft. Don't over-tighten.

 

[Nige]

Can you please double-check the Serial Number on the transmission data plate (on the transmission itself, not the plate in the cab) and confrm whether or not it is 7ZA00312.

 

[farmer bob]

i think we are talking about 2 different things. the relief valve im referring to is the RV that lifts if the filter get too high of pressure differential and sends fluid right back into the oil pan. i found a 70 page suppliment to the 943-973 transmission tips and helpful information, in this group. it talked about the importance of using the correct filter and viscosity oil or it will slow down travel due to lifting the rv. the issue im having started immediately after using higher viscosity oil and a napa brand filter.

 

[Nige]

the issue im having started immediately after using higher viscosity oil and a napa brand filter.

So you're talking about the bypass valve to which oil filter exactly.?
What viscosity of oil did you put in and what was in there before.?

 

[farmer bob]

i mistakenly put in sae68 and thats when i started getting the slowing down after warm up. i have sae32 in it now along with a new cat filter and it still behaves the same after warming up. it has full power pushing and steering. it just slows to a creep when doing it after 15-20 minutes. the hydrostat filter that is under the cab, it has a flat top with six bolts holding lid on.

 

[Nige]

Losing drive speed/power is a classic symptom of internal pipe seal leakage, especially if the seals are original. I mentioned this already with photos in Post #6 above. Your problem is unlikely to be in the filter bypass valve, much more likely to be one or more of the big black donut seals shown on the right of the 2nd image.

 

[farmer bob]

ok thank you. ill look into that when i get a chance

 

[farmer bob]

how many of those lines are there to remove and check? ive never been inside this machine so its all new to me.

 

[cat951b]

If I remember correctly, there are 12 such seals inside and outside the 973 hydrostat. Nige provided the part number above.