Convert SunStrand from ATF to Oil

[Redav72 227]

I recently acquired a 1970 Charger 12 and observed that after the transmission warms it seems to lose some of the power especially under load; it's not horrible but not terrific either.  I've been wondering to myself if it's possible to find a higher viscosity ATF when I ran accross this in the transmission manual.  

 

Quote

Oil The recommended transmission oil is SAE 1OW-30 or SAE 1OW40 engine oil. IMPORTANT: All 1972 and prior, and some 1973 models use automatic transmission fluid (Dexron 11). Determine type of oil in these units Do Not Mix engine oil and automatic transmission fluid. Units may have been changed to engine oil ,during prior overhauls. To convert to engine oil, the entire system transmission, transaxle, hoses, hydraulic lift valve must be totally cleaned Of transmission fluid.

 

Will the higher viscosity 10W provide a better response from the hydro than the thinner ATF?  I'm presuming that the issue is fluid seeping around the pistons and reducing the pressure to the drive-train and that perhaps Wheelhorse made the change to standard engine oil for precisely this reason.  Thoughts?

[daveoman1966 3,752]

What you've described...loss of power at operating temp...is typical of pump internal parts wear.  I don't know that the fluid change you allude to will resolve that issue and I'd expect the 'sluggish' condition to only worsen.  After all, the Chg 12 is now 51 years old and parts just plain wear out...eventually.  To overhaul the pump is not a difficult task...if you can manage a wrench, you can manage the overhaul.  Your unit, if original, has the Sundstrand HydroGear power unit model 90-2046.  I've prepared a .pdf file with narrative and pics of what to do...free for download at your leisure.  The file name is SUNDSTRAND HYDROGEAR refurb.pdf. Another file from Sundstrand is : Transmission_Sundstrand_Hydrogear_Piston-Piston_1965-1982.  Both of these are in the TRANSMISSION section for download.   Here are a couple pics of what you'll find inside the Pump...

Edited December 9, 2021 by daveoman1966

[953 nut 55,299]

Dave has you covered on the Sundstrand issue. If there is anything else we can help with please feel free to ask.

[pfrederi 17,741]

I run ATF in 6 Charger Electros and Motor oil in the D200 sunstrand.  Only difference i can see is the motor oil in the D200 has a slower response on the hydro lift when it is cold.

 

Dave is spot on  your unit is getting older.  A switch to thicker oil may mask the problem for a bit but if you use it in the winter may bring on new issues

[clueless 3,002]

My '77 C160 auto has ATF, I bought it from the original owner he always had it serviced at the dealer, so I assume the ATF came in it from the factory.

[squonk 41,150]

22 minutes ago, clueless said:

My '77 C160 auto has ATF, I bought it from the original owner he always had it serviced at the dealer, so I assume the ATF came in it from the factory.

That should have had engine oil. I think around 74 it changed. My 76 has eng oil.

[kpinnc 12,085]

I'd stay with ATF. Of the ones I've seen inside, ATF is superior for anti wear and keeping out moisture. 

 

If the tranny is weakening after some run time, it's time to start prepping for a rebuild. 

 

As has been said already, higher viscosity oil is a short term fix. It may help, but I think the earlier you fix it, the less damage you will have.

[ebinmaine 67,594]

4 hours ago, squonk said:

That should have had engine oil. I think around 74 it changed. My 76 has eng oil.

 

My '75 C160 Automatic was long-term dealer owned and dealer serviced. Started life with engine oil. 

 

 

 

[pfrederi 17,741]

My 1974 D200 has Motor OIl and the original decal specifies that. 

[953 nut 55,299]

I changed from ATF to 10 W 30  Universal Trans-hydraulic fluid while I had the Sundstrand apart for an axle replacement. Everything was drained except the little bit in the lift cylinder and associated valve/hoses. The filter drained for a few days while the work was being done. I filled the transmission with 10 W 30, used the old drained filter and ran it around the yard for a while  as well as exercising the lift several times to flush the whole system. I then jacked up the front, drained the fluid and replaced the filter with a new NAPA  1410, filled the transaxle with fresh Trans-hydraulic fluid and have been pleased with the outcome. It seems to run a bit quieter when going up steep slopes. This was a strong Sundstrand to begin with but I went the 10 W 30 route because I always have it on hand and have heard others on here post good results. A five gallon bucket at tractor supply was less than $50.00 and with Dexron running nearly $6.00 a quart it was a no-brainer for me.