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TK5 (used from 83-87) best oil?


Mike Tonon

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What is the best oil to use in the TK5 transmission? These, based on what I’ve read, all originally had 80w90 conventional gear oil from the factory. But mine used to be hard to shift when the transmission was cold and the temperature was below about 25 degrees Fahrenheit. So what about something that flowed better or something slightly thinner?

How about this Motorcraft full synthetic 75w90?
https://www.ebay.com/p/Genuine-Ford-Fluid-XT-M5-QS-Full-Synthetic-Manual-Transmission-Fluid-1-Quart/1466980446?iid=323546406068&chn=ps&ul_ref=https%3A%2F%2Frover.ebay.com%2Frover%2F1%2F711-117182-37290-0%2F2%3Fmpre%3Dhttps%253A%252F%252Fwww.ebay.com%252Fp%252FGenuine-Ford-Fluid-XT-M5-QS-Full-Synthetic-Manual-Transmission-Fluid-1-Quart%252F1466980446%253Fiid%253D323546406068%2526chn%253Dps%26itemid%3D323546406068%26targetid%3D483853014227%26device%3Dm%26adtype%3Dpla%26googleloc%3D9003173%26poi%3D%26campaignid%3D1698888467%26adgroupid%3D65736218829%26rlsatarget%3Daud-497631946031%3Apla-483853014227%26abcId%3D1139396%26merchantid%3D8588904%26gclid%3DCj0KCQiAkfriBRD1ARIsAASKsQLSCdnmk2VVuvzgJttDXTUMnE_wYdBoUWvZi1Xv8l9x6mnpcid1k0QaAvtjEALw_wcB%26srcrot%3D711-117182-37290-0%26rvr_id%3D1852582073104%26rvr_ts%3Dd5166f171680aad75e23a8cffff33622
 
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adsm08

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I'd say you could probably use 75W-90, but you need GL4 or it is gonna eat the syncros, and I have yet to run across a GL4 75W-90.
 

Mike Tonon

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adsm08 said:
I'd say you could probably use 75W-90, but you need GL4 or it is gonna eat the syncros, and I have yet to run across a GL4 75W-90.
Click to expand...
It says that it’s recommended for older transmissions, recommending GL3 and GL4. What is GL3/4?
 
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GL3 and GL4 are just standard fluid specs, they tell you things about what's in there, if you know how to interpret it.

I'm not surprised that an MTF would be OK, it would have been made with the brass syncro rings in mind.
 

Mike Tonon

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adsm08 said:
GL3 and GL4 are just standard fluid specs, they tell you things about what's in there, if you know how to interpret it.

I'm not surprised that an MTF would be OK, it would have been made with the brass syncro rings in mind.
Click to expand...
So this 75w90 mtf might be more than fine, then?
 

Mike Tonon

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Another thing I was thinking about... years back on here, someone claimed to be getting mid 20 something mpg, with a 2.9 Ranger 5-speed, that he did something like a dozen mods to. High quality fluids all around was one thing he did. I wonder if he used this mtf or something like it. I think he said that he also did an efan, port and polished the intakes, headers, flowmaster, cold air intake, high performance ignition system, tune and a maf conversion.
 
8thTon

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Consider Pennzoil Synchromesh. I have used it in several older gearboxes with great success, and much improved shift quality. Including my old ‘90 Ranger. You can get it at most auto stores (AZ and Advance).
 
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Mike Tonon

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Transman304 said:
This is what I use in all my builds of this type of transmission. Just what I prefer and have found to work best over the years. Price point is steep,but I wouldn’t use anything else at this point in time.

https://www.redlineoil.com/Content/files/tech/MTL_GO_PROD_INFO(1).pdf
Click to expand...
Very cool! How does it compare to Motorcraft 75w90 full synthetic? Also, how often should the fluid in these transmissions be changed? Some have said it’s lifetime. Others said 100,000 miles. I did mine in my old 87 Ranger at about 120,000 miles and the transmission was still ok at about 190,000 miles when I sold the truck and I used to beat on it too. I had the clutch changed also at about 120,000 miles and afterwards was able to chirp third gear. I also used to load this truck up to its weight limit and gun it! But as I said, the thing was crazy hard to shift when cold and also, the 2nd and 3rd gear synchros seemed a bit worn.
 
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