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transmission/OD oil question

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nevets

nevets

Jedi Knight
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The oil that is in my transmission was not put in by me so I don't know exactly what it is but I may need to add more. My question is what brand/weight oil should I add? Yes, I know I could (should) drain the oil and replace with fresh. I may do this, but if I don't, what should I add? Many thanks.
 
If its unknown it will be best to drain it completely. I beleive Castrol GTX 20w50 is the brand and weight to use.
 
[ QUOTE ]
Yes, I know I could (should) drain the oil and replace with fresh. I may do this, but if I don't, what should I add? Many thanks.

[/ QUOTE ]
Yes, you really should drain & refill. There is no sure way of knowing if the new & old are compatible or if the old oil is even good. I certainly wouldn't take a chance. Overdrives cost big bucks to repair, taking a chance on the old oil could be a mistake.

Original factory specs called for 30 wt motor oil. Triumph specs called for 90 wt GL3 gear oil in the same overdrive. Folks have successfully used 20W50 motor oil, Redline MT-90, & many other things. My personal choice is RL MT-90. Before that, 20W50 motor oil worked ok. This is a topic that has been argued endlessly with no single conclusion.
D
 
ok I'm convinced...I'll drain and replace. Will the RL MT-90, which I assume is a synthetic, collide with the residual oil?
 
RL MT-90 is a GL4 synthetic gear oil, SAE 75W90. It is equivalent in viscosity to a SAE 40, 10W40, or 15W40, engine oil. It has been known to improve shift quality by prompting more positive synchro engagement. This is due to it having a higher friction coefficient than standard oils. To my knowledge they won't collide. Be sure to drain the transmission, forward plug, AND the OD, big plug at the rear. When you take the rear plug out, also remove the screen & clean it.
D
 
thanks Dave - presumably both the trans and the OD oil are filled from the common fill-port accessable from the cockpit? And since I would like to order the RL-90 right away but don't have ready access to my AH documentation, can you please tell me how much oil is required? thanks
 
OH Nevets,4 quarts will do it and you only need to put in 3.75 Qts.---Keoke
 
Nevets,
You might just drive to your nearest auto parts store. I have purchased gallon jugs of 75w90 gear oil to refil the rear axles of several jeeps that I have owned. I don't know if they will carry the brand that Dave suggests but it may be worth a look.
 
Question for the experts:I have 20w50 motor oil in my BJ8 tranny and am thinking about switching to the Redline. What will the synthetic stuff do to the rubber seals in the system?
I have visions of seals dissolving as they did in the brake booster and master cylinder when I replaced old brake fluid with the correct Castrol fluid.
 
To my knowledge, RL does not harm the seals in the transmission/OD. I can't tell yet from personal experience as I have only been using RL for four years. Another subject for lengthy research?
D
 
I noticed a slight increase in oil leaking from the gearbox after switching to Redline MTL from whatever motor oil was in the gearbox originally. I called them and spoke to someone in their tech dept. He said their oil will not harm any seals but it might be able to slip through spaces that other oils will not (depends on viscosity). He recommended that I switch to MT-90 and if seals/gaskets are leaking they are probably due to be replaced. Before I made the switch I started a restoration on the car so seals, gaskets and MT90 should take care of the problem.

BTW, the change to the Redline oil gave a dramatic improvement in shifting feel (much smoother shifting .. less notchy feel) and the worn first gear was much quieter.

Cheers,
John
 
I believe MT is preferable over MTL. Something to do with saving synchros. The RL rep I spoke to said use MT not L
 
MTL is just slightly lighter (70W-80 GL-4 Gear oil) than MT-90 (75W-90 GL-4 Gear oil). The "L" is for light or lite or low fat /ubbthreads/images/graemlins/grin.gif

Cheers,
John
 
I tried the Red Line and could not tell the diference. I have heard the red line causes more leaks - mine never seemed to leak though. I recently had a tranny rebuild and went back to non detergent 30 weight and have no complaints
Bill
 
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