I have an '85-'86 non world class T-5 in my roadster. I'm replacing it this week with a rebuilt one of the same year and numbers 1352-145. What I understand is that the early ones like mine use 70 weight gear oil while the later World Class used ATF. Is that correct?
Dexron II/III for S10 T5s. Gear oil was used in the early 80's Mustang T5s, but it was 50wt. Find out what synchros were used, brass use gear oil, fiber use Dexron. If the gears were upgraded to 'WC' type then they use caged needle bearings which need Dexron.
That is correct according to my Lube recommendation guide. The correct ATF would be Dexron III, which is obsolete now but still widely available.
"3542 post's and you mentioned 1987 on HAMB?" And you just joined last year and you think you're the Hamb police? Sometimes we have to mention the year of an old part you know.[/QUOTE]
A little more of what I found: The Dexron II is no longer availabe. A new recommendation is Valvoline Synchromesh Manual Transmission Fluid MTF. I think I'll go with that.
That's what I used in mine with no issues. I no longer own it, but I do know it's still going strong behind the old Flathead.
Thanks, that's good to hear. When I built the car I used 70 weight gear oil based on the information I found back then.
NO! Dexron is for World Class T5s, with needle bearings! A Non-World Class T5 takes 50W gear oil! If yous use ATF in a NWC T5, it will be short-lived.
I know you ain't supposed to do this, but I use SUPER-SYN, Heavy Duty, Extended Drain, NON-EP, API MT-1, Manual Trans Fluid, 50 wt. in my 1988 WC T-5. It's the same thing they use in Heavy Duty semi trucks... and it works very well, thank you!
If it neither eats the syncros, nor causes the shifts to get clunky, it should do no harm. It's going the other way that is a problem. Thinner lubricants are a friction/drag reducing strategy. If you can find 30 places to recover 0.25MPG, you have +7.5MPG.
gimpyshotrods, That's what's so confusing about this, there are so many varying opinions with no agreement. I've read S-10 forums etc, they can't agree either. The shop where I had this one rebuilt told me to use ATF. A product that's name says "Synchromesh Manual Transmission Fluid" on it really appeals to me.
How do I know what lubricant takes, with authority? I am an engineer at General Motors, and have access to the complete archive of technical data. SAE 50. Trust me. I am not interested in walking you through rebuilding your transmission. This is the current recommendation for dealer service: https://www.mobil.com/en/mobil-delv...n-fluids/mobil-delvac-1-transmission-fluid-50 Note, this is an API GL-4 grade oil, not GL-5.
With ATF it was very noisy. Plus, my motor has almost 600 lbs. of torque and I thought the 50 wt. would help save the gears and bearings. Been using it for about 6 years now. Works fine.
Well Gimpy, you may be a engineer at GM, I'm an engineer at the 3rd largest lubricants company in the world, though to be open I work with Commercial lubricants, or Heavy Duty lubes; not Passenger car lubes, which are light duty. T5's are not my specialty; Allison's, Macks/Volvo's & Road Rangers are. However, I do have access to the OEM recommendations, and for S10/S15 pickups, w/ manual shift transmission the recommendations are: model years 70 - 87 - 80W or 80W-90 GL-5; Post 87 the recommendation is Dexron III spec ATF (which as I posted above is an obsolete specification, but still widely available), with some exceptions (82 - 83 model years within a specific serial number range, the recommendation is GM part #1052951, which appears to be an obsolete part # and I haven't found a cross reference to it yet. Though I did find some for sale on eBay, cheep too: https://www.ebay.com/itm/ORIGINAL-G...ART-1052951-6X-1-Liter-CASE-NOS-/183265190353 But that's neither here nor there. Re the OP's trans, the recommendation is GL-5 spec oil, in 80W, or 80W-90 viscosity grade. Now, straight grade SAE 50 oils have been used in manual shift transmissions for many years, heavy duty trucks made that change many years ago, and the viscosity for the newer automated manual shift transmissions is even lower at SAE 40. But now we're talking 2 different ways of grading oil viscosity. The SAE is the body that sets the official grades for viscosity of automotive lubricants (The ISO sets the viscosity standards for Industrial lubricants). You can see a comparison of Engine Oil to Gear Oil viscosity grades here: https://www.bobistheoilguy.com/viscosity-charts/ So from that you can see that a 50 grade engine oil falls within the viscosity range of a 90 gear oil. So a 80W-90 gear oil is pretty much the same as an SAE 50 motor oil. The big difference is in the additive's used, with GL-5 gear oil having EP or "extreme pressure" additives not present in the 50 grade trans fluids like the Mobil product you linked to. What the heavy duty market found was that the heavy EP additives were not necessary in manual shift transmissions, and that they actually can cause some damage to any yellow metals present, which many (most?) manual shift transmissions have, such as the synchros. Which makes me wonder why GM recommends GL-5 for that transmission. Like I said, those are not my area of specialty, anyone who has experience with the T5 trans may be able to answer it, but I would assume the transmission is under a heavy load that they want the EP additives to protect the gears, and that it doesn't use much in the way of yellow metals. With @Montana1 talking abut putting the trans behind a 600 horse power plant, well, some EP additives may be called for. What's the typical failure mode in a T5 transmission? Is it gear failure?
The Wizzard (@Pist-n-Broke) and I were just talking about this very subject over the weekend. My 34 has a T-5 (non WC) behind the blown flatty, with only 350 miles on it I told him I was having trouble downshifting without double clutching. He asked about the trans fluid right off. I used synthetic ATF. The Wizzard (a well earned title and nothing to do with hoods other than welding hood) suspected that ATF. Reading your well informed comments @gimpyshotrods I am inclined even further to agree that I used the wrong lubricant.
We've sold 100's of rebuilt T-5s over the years and we have always recommended Dexron III. Many years ago some very low mileage S10 T-5's became available from some industrious GM parts men. Seems these trans were filled with 90 weight fluid at the factory and in cold climates these trans became very hard to shift and were replaced by warranty. The old trans were supposed to be destroyed but many of them made it out the back door. I was buying these 5-6 at a time and washing out the inside with diesel fuel and reselling them with my T-5 conversion kits. The supply of these finally dried up. Several of them I got had 1 ear broken off the trans that had to re-welded on.
Wow. I am not sure where you got the GM info, but it is wrong. I literally JUST looked it up in our database. You need to be a GM employee to do that. I am not talking about 3rd-party information. I am talking about FIRST-party information. You might work for a lubrication company, but you do not work for an automaker. By your own admission, you are out of your lane. That is, and will remain SAE 50, API GL-4, not 5, for a NWC T5. Why 4, and not 5: See for yourself. Ignore the API GL number, at your peril. Mobil Delvac 1 is not API GL-5: "Mobil Delvac 1 Transmission Fluid 50 meets or exceeds the requirements of the API service MT-1 EP gear oil service classification and is recommended by ExxonMobil for use in transmissions and gear cases where API Service GL-1 through GL-4 gear protection is required." "NOT suitable for hypoid gear applications in differentials and final drives, either for topping off or refills, where API service GL-5, MIL-PRF-2105E or SAE J2360 lubricants are specified" I have extensive experience with both WC and NWC T5s. Typical failures for non-drag-race applications are worn/damaged synchronizers. Hard-launch drag race applications have a host of other failure modes, the most significant one is the failure to understand that no T5 should be used for drag racing. I am not going to argue this with you. You cannot afford my consultation fees. Maybe you want to share with the rest of the class what API GL-5 does to yellow metal, and why it is contraindicated for any transmission that contains it. No NWC T5 ever had a GL-5 recommendation, because that would lead to an instant class-action lawsuit. No WC T5 ever had GL-anything. Now, explain why your company is making recommendations based the information you both claim is correct, and know cannot be.
Yes Blues4U, I highly respect your experience and wisdom in the Commercial Lubricants field. Personally, I'm an old farm boy and just barely made it through high school and I couldn't wait to get out and off the farm. Went dragbike racing back in the mid-80's and set 15 national records in the low 9's (H-2 Kawasaki) and was #7 in the nation in "DRAGBIKE". That's all I got to say about that. My experience with T-5's is they don't like a lot of torque, but can be made to work in a light car if you're careful. I have an Astro Performance 8620 gear set and all the goodies in my A-5. It's capable of holding about 500 lbs. of torque. My motor makes about 590 lbs. of torque. It's a little more than you want to drop the clutch on with slicks, but it works in a 2600# car on street tires. <This is my daily driver... The weak parts in a factory T-5 are yellow parts, third gear, cluster gear, counter shaft retainer and tail shaft. They can all be fixed. I also use a stock 11" Z-28 clutch disc for the fuseable link in the system. You can't power shift or it will never hook up again, but it don't break parts. I know I break all the rules, but it works. Rules are made to be broken, not parts! https://astroperformance.com/ (I know this doesn't answer the OP's question, but you asked.)
So based on this chart 50 weight engine oils the same viscosity as as 90 w gear oil. So far the recommendations have been all over the map from many sources. MTF Synchromesh from various manufactures, ATF, 50 w Modil, 70 w gear oil, 90 w gear oil, and some other fancy stuff. I appreciate all the help just the same. Looks like they'll work with anything so I'm going with Olive Oil.
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