'25 Transmission Gear Oil Foaming

[Guest oldodgeboys]

I've been using Shell 1500w gear oil from RSC for a few months now. The oil viscosity works nicely for slowing the gears during shifting.

I noticed that as I drive about 5 miles or further, the trans starts to warm up and shifting gets tougher without grinding the gears.

When I look into the gear box after a run I see the oil is frothy. It takes hours to settle the air bubbles back out of the oil.

I'm wondering if other DB's experience the same oil foaming, or is this an effect of the oil I'm using?

[Guest earliriser]

Thats some thick sounding oil your running there. I'm no expert on DB's for sure.

I have always replaced 600w with a 50/50 of 140w and stp or lucas additive.

If it heats up there's to much friction. That would scare me.

Just a noobie here but I have worked on a lot of oldies.

[Guest 1930]

My thoughts are if its frothy than its not properly lubricating your gears and you will burn the tranny up in short time. Air bubbles = poor lubrication. Thats why shifting becomes tougher, lack of lubrication.

[Guest oldodgeboys]

Your right about the foam causing poor lube and higher heat.

I put the same question to RSC. who in turn also put the question to Shell. Both agree that the viscosity may be too high which could cause foaming.

I'm draining the oil this weekend and refilling with 600w, as I (semi)successfully used before. I'll post the results here later.

The 1500 lube did help with the leaks and the gear crunching (under 5 miles anyway), so I'll miss those benefits. Ironically, and despite the high sounding viscosity, the 1500 is only slightly thicker than the 600.

[Guest oldodgeboys]

I drained the 1500 oil and refilled with 600 oil. After driving the same 5 miles, the amount of foam in the oil was only slightly less.

Both oils had significant air bubble entrapment in the oil itself. The 1500 had about 1/2" froth on top of the oil, while the 600 had about 1/4" froth. This stuff looks like a good beer!

The 600 started leaking from the trans immediately; you could see the flow path on the outside of the case. It resulted in more gear crunching too.

I drained off some of the 600 and added more 1500. Now the 2 quart ratio is 3:5 (600 to 1500). I used that ratio because it seemed like a reasonable compromise and, well, that's what I had available in the garage. Seems to work...I'll keep an eye on it.

Edited November 18, 2009 by oldodgeboys (see edit history)

[dwollam]

In past posts concerning tranny gear oil they reccomended 600w with medium grease added until it was thick enough to stand a screwdriver up for a few seconds. I don't remember the exact ratio.

I have tried several different lubes in my trannys to get them to shift, by quiet, etc. I built one beautiful tranny for my 22 screenside, was nice and quiet but you had to speedshift to get it in any gear but if you mised a shift you had to come to a complete stop to put it back in gear. After trying several high speed sliders, many different types and thicknesses of gear oil, I put together another tranny and it shifts great running with 90w gear oil and is the quietest tranny I have and the high speed slider gear had some serious pits in it! I run new sealed bearings in both ends of the tranny. My original plan was to run the 90w briefly to flush it out, then switch to 600w but it worked so well I left it. My theory is the 90w will not loose as much horsepower to drag as the 600w. It is also not the standard gear oil but is the stuff that is not harmful to bronze bushings. Sorry, don't remember the designation. I was able to order it through my local auto parts stores.

[RickBrinker]

I mix a qt of 600wt and 2 tubes on grease and that's what i run in my 25

[Guest oldodgeboys]

My trans is old, probably not rebuilt. When I rebuild it I'll use sealed bearings and new bushings; until then I'll have to play with the oil. The trans rebuild is officially on the (bottomless) 'to-do list'.

Edited November 19, 2009 by oldodgeboys (see edit history)