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Add ZDDP to gearbox oil?

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The zinc helps prevent wear on cams and lifters in flat tappet engines, and isn't necessary for transmissions etc. We use Red Line's recommended MT-90-GL4 for both the standard 3000 transmission with over-drive, as well as the Toyota 5 speed we're running. I'd go with the recommendations of whichever oil manufacturer you prefer, and not mix your own. Check the witches scene in Macbeth for instructions on how to brew up something.... Doug
 
No. Not required. ZDDP is used in engines because the speed and pressure between the flat tappets and cam causes the oil film to to break down. Doesn't happen in the gearbox.
 
What is the recommended weight oil for the BJ8 tranny with overdrive?
Is it non detergent 30w or 20w-50 as the engine?
 
MTL/MT-90 or similar full synthetic. Just because something was recommended in 1950 doesn't mean it has to be used today. Put full synthetic in the gearbox and differential--different viscosities, of course--and don't worry about them for the miles you're likely to drive the car (just check the level and top up occasionally*). You might even get a smoother shifting gearbox (some newer cars come with a 'lifetime fill' of synthetic oil in the differential). One of the first things I did when I bought new Mustangs--in 2008 and 2018--was put full-synthetic oil in the gearboxes; the 2008 shifted better and the 2018, eh, not sure.

* I just learned from a respected Healey expert that the rash of spun rear wheel bearings might be due to owners not checking differential fluid levels (they can leak at the pinion seal and plug).
 
Years ago I tried MTL/MT-90. I didn't notice much change in ease of shifting, however the garage floor showed it leaked more. Bummer, I heard good thing about it, but it didn't work out with my tranny.
Unscrupulous car sales would put sawdust in.
 
Redline MTL is what I've been using Bob for 3 seasons now. It replaced 20w50 engine oil that had been previously used. I changed because I heard that it helps free sticky synchros and smoothes shifting - which it certainly did for me. I was warned it had a greater propensity to leak, but I've had virtually no loss of oil. No spots on the floor and the dipstick level remained constant over last years 2000 mile driving season.

My understanding of the use of ZDDP is that zinc has a solubility level in oil and unless it is present in oil, surface zinc will come out of the metal and into the oil in accordance with Le Chatelier's principle. Certain engine components are more susceptible to excessive wear arising from the loss of zinc and the weakening of metal, such as tappets and cam lobes. My question was essentially why would the same effect not be present in the metals in the gearbox - particularly as gear teeth and bearings can experience high shear from time to time.

Steve
 
Gear oils--e.g. MTL/MT90/GL-X--have 'EP' (Extreme Pressure) additives to mitigate the shear forces found in hypoid and helical gears. My understanding of ZDDP--not canonical by any means--is that the zinc/phosphorous bonds with the metal to form a sacrificial layer to protect the metal where, as noted, extreme pressure can shear the oil layer allowing metal-to-metal contact. EP gears oils contain a sulfur compound, hence the smell of gear oil. The sulfur compounds can allegedly 'attack' soft metals like brass and bronze, but I've never seen nor heard of any issues with it, besides possibly darkening the metal. I'm not sure mixing sulfur-based compounds with zinc/phosphorous-based compounds would be a good idea (but, it's your car, have at if you want). Two different compounds for two different usages.

I think the EP compounds are more useful in differentials. If you're running an engine oil--which I did for years before switching to synthetic--the ZDDP might do something useful, but why not use an oil with sufficient ZDDP for flat-tappet cam engines (e.g. Valvoline 20W-50). Not sure owners 'brewing their own' can do a better job of formulating oil than professional tribologists.
 
MT-90 for over 10 years. Sure it leaks but offers the best protection in my opinion. 20-50wt offers oil protection for hot or cold conditions. The gear box should not get hot enough for the need of the 50wt and cold enough to need thinner oil as the engine does for starting a cold engine. 30wt NON-DETERGENT is recommended if you don't use Redline. Detergent suspends metal particles in foaming and causes wear in the gears. Non-detergent lets those particles drop to the bottom of the gear box to attach to the magnet and get drained with changes in oil. You cannot find multi grade oils that are non-detergent.
 
Bentley, the shop manual, Sec. Q, says SAE 20W-50 in both the engine and transmission. Where did the SAE 30 non-detergent come from?
 
Tahoe is correct about the two oils Detergent oil are used where filters are used as in motors. Non Detergent as in gear boxes is for settling to the bottom to drain out. I knew an old guy that never changed the oil in his cars just changed the oil filters and added as needed every so many miles and they all went 100,000 miles. Oil in motors is for lube and cooling and is pumped all over the motor. Where gear boxes by weight 90/100 plus are for load on gears and lube same that run much cooler so straight weight. Dry sump aircraft motors use Detergent oils only. Madflyer
 
John, it appears you are correct. The info I had must have been from my Jag or MGB. It must have come from the mechanic who worked with me on my 140. I just checked my original owner's manual and it does recommends using the same oil as the engine. (20-40wt, 20-50wt or 40wt) Still, I stand by Redline in the gear box. The problem had been getting straight 30wt non-detergent those days. I will search the source of my information about non-detergent oils.
 
TH,
You're not the only one who says SAE 30, non-detergent. I'm wondering where that started. I can see using the Redline, though, as it seems to be better for most people.

My gearbox already leaks too much with 20W-50, so I don't want to hire an environmental remediation company to follow me around - I know how much those guys cost!

I agree with the hard-to-find SAE 30 non-detergent. The ones I've seen, I wouldn't put them in anything I cared about.
 
I'm going to go against 'common wisdom' here on the 'non-detergent lets the crud sink to the bottom, which is a great thing' theory*. The last couple times I changed-out gearbox oil in my BJ8 I drained it into a clean pan, and looked at it in bright sunlight. The oil did have an extremely fine brass 'shake,' that was only visible in the bright sunlight; it looked like a really fine metal-flake paint job (kinda pretty, actually). I rubbed some of this oil between my fingers and could feel absolutely ... well, nothing but oil. No grit or anything potentially abrasive. The brass particles--likely from the shift forks wearing down--were so tiny I can't imagine them plugging any passages in the gearbox or OD. Brass is a soft metal, and would be ground to virtually nothing in a gearbox; note many greases are made with finely-ground metal (lithium, moly, etc.). When I rebuilt the box a couple years ago the inside of the box was spotless, but there was a few small grains of silver metal on the magnet in the OD strainer. I've never had any OD issues--that weren't electrical--whatsoever (I rebuilt the box because is was jumping out of fourth). The gearbox had no appreciable wear at 200K miles, but I replaced the fourth gear cluster to remedy the jumping-out issue.

Anybody ever have a failure of a gearbox or OD that can be definitively attributed to using detergent or synthetic oil? If not, I'm putting this one in the "old wives tale" category.


* Note 'detergents' were added to oil to do what detergents do; i.e. clean things out. In engines, it's used to clean lead--when autogas was still lousy with the toxin--and other deposits in the engine; I believe ZDDP--'P' is for phosphate, which is a key ingredient in many detergents--was first added as a detergent, then the anti-wear properties were discovered. 'Dispersants' are what's added to oil--as the name applies--to keep particles in suspension. A non-detergent oil will not necessary be non-dispersant, but I do think they usually are.
 
John Turney said:
TH,
You're not the only one who says SAE 30, non-detergent. I'm wondering where that started.
Click to expand...
Straight 30wt was the oil requirement for the 100 engine(under normal temperatures) and transmission. I don't find anything regarding non-detergent requirement. Perhaps all oils in the 50's were non-detergent?
For a while I couldn't find 30wt non-detergent here in the East Bay, and could not order it online for shipment to any California address, but have since found a source not far from me that does(or did a couple years ago) carry it in Valvoline.
 
After opening the link Bob gave us (https://www.machinerylubrication.com/Read/31107/oil-lubricant-additives) I looked at some of the courses offered and found the array thought provoking. For example I thought I knew all that is needed in order to load, handle and use a grease gun but never considered lubricating the gun itself! I guess I do not know what I do not know.
 
I have heard a few times that non-detergent oil in the gearbox is good because it won't foam like a detergent oil.

Except modern multi-weight oils have very good anti-foaming agents, and I believe non-detergent oils have none.
 
In the 60's the Shell station I worked at sold non detergent oils in bulk that we put into a glass filler bottle for those old 40's and 50's cars that need oil. The new Detergent oil came in cans ready to fill. How old are we now to talk about the old days and oil. I guess it is because we have old LBC's Madflyer
 
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