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TR6 72TR6: Why does it get hard to shift when warm?

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CuriousGeorge

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When I start out on a drive, she shifts fine, but after a while it gets more and more difficult to shift gears...?

Also, what rear end and tranny oil should I use, and what about additives? (I plan to drain and change these fluids)
 
Changing the oil can have nicely positive results.

Both the gearbox and rear end take Hypoy 90w gear oil GL4, not GL5. You need to look carefully as most will be GL5.

There are multiple suppliers, and some of the oil will be listed as Hypoy 80W-90.

Fill them, on a level surface, until just a little bit weeps out.
 
tdskip said:
Both the gearbox and rear end take Hypoy 90w gear oil GL4, not GL5. You need to look carefully as most will be GL5.
Click to expand...

Why not GL5? If it's because your worried about compatibility with yellow metals, GL5 is actually more friendly to yellow metals than GL4. If you don't feel comfortable with that statement, then make sure that the gear oil (GL4 or 5) says on the bottle that it is compatible with yellow metals.
 
Been running GL5 in my Triumph diffs for a long, long time. Works great. The secret is <span style="font-weight: bold">which</span> GL5. I use Valvoline full synthetic, but anything also rated MT-1 should work fine.
 
CuriousGeorge said:
When I start out on a drive, she shifts fine, but after a while it gets more and more difficult to shift gears...?
Click to expand...
Have you checked for clutch drag when it gets hot?
 
TR3driver said:
I use Valvoline full synthetic, but anything rated MT-1 should work fine.
Click to expand...

MT-1 designation denotes lubricants intended for non-synchronized manual transmissions in heavy-duty services. I wouldn't think that a MT-1 designation is necessary.
 
You're old. So's yer car.

Funny thing: same here... on both counts. But it's an MGB. :shocked:
 
"Lubricants meeting API MT-1 provide protection against the combination of thermal degradation, component wear, and oil seal deterioration which is not provided by lubricants meeting only the requirements of API GL-4 and API GL-5. "

The "problem" with some GL-5 oils is that at high temperatures and pressures, one of the EP additives breaks down and forms sulfuric acid; which can attack and shorten the life of "yellow metal" components like synchro rings and the thrust washers found in Triumph differentials. Although the GL-5 standard has tests for yellow metal compatibility, they are done with new oil rather than used. Meeting MT-1 ensures that the oil does not break down to form acid.
 
CuriousGeorge said:
When I start out on a drive, she shifts fine, but after a while it gets more and more difficult to shift gears...?
Click to expand...
I've also read that the plastic hose from clutch master to slave can become more pliable when warm allowing it to expand under pressure, thus sending less movement to the slave cylinder. I replaced mine with stainless steel and noticed improvement.
 
Actually part of the API definition of GL-5 is the protection of yellow metals.

"API GL-5 quality gear lubricants possess adequate extreme pressure characteristics for essentially all automotive gear applications to prevent wear, pitting, scoring and ultimate gear failure, along with protection against oxidation, thermal degradation, rust, copper corrosion, foaming and water emulsification."
 
I had that issue on my 71 TR6 back when I had one. It wasn't the tranny, just marginal clutch hydraulics that worked when cold but didn't release sufficiently when warmed up. In my case, I had to change out the throwout lever to finally get rid of the issue.

Randy
 
Mark Jones said:
Actually part of the API definition of GL-5 is the protection of yellow metals.

"API GL-5 quality gear lubricants possess adequate extreme pressure characteristics for essentially all automotive gear applications to prevent wear, pitting, scoring and ultimate gear failure, along with protection against oxidation, thermal degradation, rust, copper corrosion, foaming and water emulsification."
Click to expand...

Sorry if I led anyone astray - my research indicated that GL4 was safer.
 
tdskip said:
Mark Jones said:
Actually part of the API definition of GL-5 is the protection of yellow metals.

"API GL-5 quality gear lubricants possess adequate extreme pressure characteristics for essentially all automotive gear applications to prevent wear, pitting, scoring and ultimate gear failure, along with protection against oxidation, thermal degradation, rust, copper corrosion, foaming and water emulsification."
Click to expand...

Sorry if I led anyone astray - my research indicated that GL4 was safer.
Click to expand...
Call me stubborn or "old school" or whatever you like. I trust the opinion of a few folks with vast experience who recommend GL-4. Since it's still readily available, that's what I use. :smile:
 
CuriousGeorge said:
Thanks guys. Yes, much difficulty getting into reverse. What is 'clutch drag'?
Click to expand...
In a nutshell, the clutch is always letting the engine turn the transmission input shaft to some extent. That means the synchro rings have to fight the drag in order to shift, which can make shifting difficult.

Next question : Does your clutch engage very near the floor ? If so, the problem is likely lack of travel at the slave. As noted, travel lessens somewhat when things get hot, so if it's very marginal, the problem will get worse when hot.
 
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