Gearbox oil (a perennial question?) / reverse gear grinding

[Jules TR6]

I having trouble finding information I need through searches, so asking here...

Hard to push into gear - especially 1st and 2nd (they never grind though), reverse grinds.

> Reverse can be worked around by selecting 3rd (or sometimes 2nd), then reverse, but that's not ideal, and often it takes a few goes.

> Fresh oil helps to push into 1st and 2nd gear.

What I've tried...

GL4 EP80W90 mineral, reverse grinds, somewhat notchy gear changes.

GL4 EP75W90 synthetic, Redline MT90, reverse grinds, gear change very notchy, more vibration felt through footwell (not a lot but I'm sensitive to noticing these things), this oil seems too thin!

GL5 EP75W90 mineral, smooth gear changes as if nicely 'greased', reverse never grinds, great!! (this GL5 oil was only in a week to flush out an old oil full of metal from reverse grinding).

The best oil was the GL5 EP75W90, but yes I know it should not be used.

/

What oil would you recommend that's yellow-metal friendly? - also with a J-type OD.

The fact the GL5 oil was perfect, immediately incredibly good in fact (for a week), what would that suggest to you? Oh and I'm not intending to take the GB apart, just need an oil that makes the GB happy.

Edited August 9, 2025 by Jules TR6

[Tim T]

This is surely a clutch issue. Had all of these symptoms. Busted taper pin was the culprit. Not oil.

Tim

[Mike C]

Clutch or selector issue. GL5 causes my synchro rings to slip.

[Jules TR6]

9 hours ago, Tim T said:

This is surely a clutch issue. Had all of these symptoms. Busted taper pin was the culprit. Not oil.

Tim

ok, but the type of oil made all the difference... why would using GL5 cure the problem? - zero issues with GL5 75W90, but issues with GL4 75W90 - is this due to actual viscosity or slippy additives etc, must be one of the other?

Clutch doesn't feel odd to me, smooth no judder at all, doesn't grab. Will keep with the fresh EP80W90 and see how it goes (still has the reverse gear issue), just wondered how the GL5 could solve the reverse gear issue. If the issue gets worse quickly, spreading to other gears, I guess the finger really will be pointed at the taper pin.

Edited August 9, 2025 by Jules TR6

[Jules TR6]

8 hours ago, Mike C said:

Clutch or selector issue.

Relatively new clutch. New master and slave cylinders. Changing feels good, no judder or grab.

Main issue is reverse grinding, unless I re-engage the clutch in neutral, disengage, then select 3rd, then reverse.

GL5 no issues with reverse - slips right in immediately. Selecting all other gears felt sweeter also.

8 hours ago, Mike C said:

GL5 causes my synchro rings to slip.

- not sure what that means, it's bad? - like jumping out of gear? didn't have that issue at all, GL5 felt great, but I didn't want to leave it in.

[Mike C]

Slipping synchros cause  the gears to grind when engaging and  to jump out under high torque.. Generally the worst gear for this problem with a TR6 is second gear.

[Jules TR6]

3 minutes ago, Mike C said:

Slipping synchros cause  the gears to grind when engaging and  to jump out under high torque.. Generally the worst gear for this problem with a TR6 is second gear.

...ok I'll add that to my info file. For the past two years of ownership, all forward gears never grind nor slip out, so slipping synchros is not my current issue.

[Jules TR6]

I'm wondering about trying a thicker or thiner oil.

Castrol Classic EP90, GL4

monograde EP90, as would've been originally used in the car back in the day. Potential downside of this oil is hard shifts when cold - but actually my ol' box might like it.

/

GB40 (Penrite Gear Box Oil 40)

25W-70 oil designed for use where SAE 40 or 50 oils were originally specified.

Has no EP additives, maybe more greasy, less thin-slippy? Not having EP additives - is this wise for a TR6 driven spiritedly - or is it more intended for pootling cars?
RobH from another thread  >> Before the confusion starts, note that although they are gearbox oils, the Penrite GB40 and Dynolite 40 oils are rated using the engine oil number so are equivalent to approx 90 sae gear oil <<

/

RedLine MTL 75W80, GL4

MTL is a low 75W, almost a 70W, at very low temperatures and a high 80W, nearly an 85W, at elevated temperatures. The synthetic base oils used have a very high viscosity index which provides relatively constant viscosity as temperature changes. 

Problem is I tried MT-90 and it was the worst oil I've tried in the gearbox! felt too thin and notchy, and no help with reverse grinding.

/

Maybe worth starting with the monograde Castrol EP90? Oddity there is the GL5 oil which was in for a week - and did very well indeed, was 75W90.

Oh and anything I try needs to be compatible with a J-type overdrive - not sure GB40 is?

Edited August 9, 2025 by Jules TR6

[RobH]

 

I think Tim and Mike are probably correct and what you are experiencing is actually due to clutch 'drag'.  

When the clutch is operated the gearbox input shaft is not driven, allowing the speed of the gearbox internals to be matched  by friction from the synchromesh for easy gear selection.   If the clutch does not disengage properly there is still some drive to the gearbox and the synchro has a harder job in matching the gear speeds, and so 'baulks' initially, preventing engagement until it has managed to sync the speeds. That could be what you are experiencing in 1st and 2nd. 

Reverse gear has no synchro and a 'crunch' on engagement is common; however prolonged grinding must  be because the input gear is still being driven and can only be slowed down when hitting the reverse gear. Your double-declutching  could somehow be helping to disengage the clutch properly.

Why different oils should change the behaviour is odd.  Maybe higher viscosity from a thicker oil manages to slow the input gears so lessening the effect of the drag. 

 

[Andy Moltu]

GB 40 works ok with overdrives A or J type.

Your clutch may “feel” ok but your symptoms are of a dragging clutch - one that isn’t disengaging fully. This fits with your difficulty engaging gears and reverse grinding. AFIK reverse in TR gearboxes is non-synchro so oil being too slippery for the synchro is not a factor. 
 

Causes of this are:

Hydraulic air in the system not giving adequate movement at the slave end to disengage the clutch. (Rarely the wrong master or slave bore)

Mechanical with wear in the pedal, push rods and pins meaning that the movement is excessive before the hydraulics get to disengage the clutch.

Broken clutch fork pin. The pin shears but continues to operate the clutch until the ends get fully rounded of and you progress from reduced clutch disengagement to none!

Badly worn or crankshaft thrust washers giving excessive end float, Usually for this to affect the clutch function it has to be bad enough for the thrust washers to have been displaced.

A defective clutch cover.

2 simple checks to do. Bleed the clutch and check end float. If these don’t help you probably need to take the box out.  If these clutch fork pin is broken, replace it along with the clutch (too much work to recycle a part worn clutch only to replace it in a few thousand miles later)

If everything checks out you might need to get your box/selectors checked over.

[Tim T]

I drove my car for 2 years with this 1/2/reverse issue trying everything to avoid taking the box out. Clutch was heavy and engaging gears was possible but not as it should be. My clutch/ gearbox/ od were all newish and original spec. Finally bit the bullet in May this year and everything now works a dream. I also run with GB40. 
Cheers,

Tim

Edited August 9, 2025 by Tim T

[Jules TR6]

12 minutes ago, Tim T said:

I drove my car for 2 years with this 1/2/reverse issue trying everything to avoid taking the box out. Clutch was heavy and engaging gears was possible but not as it should be. My clutch/ gearbox/ od were all newish and original spec. Finally bit the bullet in May this year and everything now works a dream. I also run with GB40. 
Cheers,

Tim

...the culprit was a broken taper pin?

[Tim T]

4 minutes ago, Jules TR6 said:

...the culprit was a broken taper pin?

Yes, on an original box that had been reconditioned by a very much respected company. It is a pain to do but the result brought a huge smile to my face and driving through the Alps in July was wonderful!

Good luck.

Tim

[Jules TR6]

22 minutes ago, Andy Moltu said:

GB 40 works ok with overdrives A or J type.

Your clutch may “feel” ok but your symptoms are of a dragging clutch - one that isn’t disengaging fully. This fits with your difficulty engaging gears and reverse grinding. AFIK reverse in TR gearboxes is non-synchro so oil being too slippery for the synchro is not a factor. 
 

Causes of this are:

Hydraulic air in the system not giving adequate movement at the slave end to disengage the clutch. (Rarely the wrong master or slave bore)

Mechanical with wear in the pedal, push rods and pins meaning that the movement is excessive before the hydraulics get to disengage the clutch.

Broken clutch fork pin. The pin shears but continues to operate the clutch until the ends get fully rounded of and you progress from reduced clutch disengagement to none!

Badly worn or crankshaft thrust washers giving excessive end float, Usually for this to affect the clutch function it has to be bad enough for the thrust washers to have been displaced.

A defective clutch cover.

2 simple checks to do. Bleed the clutch and check end float. If these don’t help you probably need to take the box out.  If these clutch fork pin is broken, replace it along with the clutch (too much work to recycle a part worn clutch only to replace it in a few thousand miles later)

If everything checks out you might need to get your box/selectors checked over.

...many thanks for such a clear explanation and list of what might be the issue. I'll go forward on this ...perhaps toward the winter.

Immediately though, I do know the clutch pedal bush is absent (probably was plastic) and the pedal does rock about a tad. Thing is, the the clutch does feel like it disengages and engages positively, I'm not pressing into the floor.

[wheeler]

Good clutch info and advice here

https://www.buckeyetriumphs.org/clutch

Bill

[PodOne]

 

35 minutes ago, Jules TR6 said:

...many thanks for such a clear explanation and list of what might be the issue. I'll go forward on this ...perhaps toward the winter.

Immediately though, I do know the clutch pedal bush is absent (probably was plastic) and the pedal does rock about a tad. Thing is, the the clutch does feel like it disengages and engages positively, I'm not pressing into the floor.

Think you have found the issue fix the bush and report back. 

[Andy Moltu]

The clutch pedal s bushed where it sits on the shaft. 
if the hole where the pin that links it with the master cylinder is worn just drilled and no bush originally you can drill oversize and use a bronze bush - can be done in situ or remove and weld the hole and re drill.

[Jules TR6]

Going back to an oil recommendation, I'm getting kinda concerned. While GL4 has less additives than GL5 (and maybe less additives that may be of harm to bronze components),

I thought I'd look at what Morris offers (as they offer good quality traditional oils, and are British). There's this...

Golden Film 80W-90 is a mineral oil based gear lubricant designed for use in a variety of automotive gearboxes and axles, where an extreme pressure (EP) product is required. It is ideal for gearboxes and axles fitted to vehicles built in the 1960s, 1970s, 1980s and 1990s, where an API GL4, API GL5, SAE 80W-90 or SAE 90 is specified. Note: This product should not be used in earlier designs where there may be phosphor-bronze components present, in this case you should use Golden Film AG90

https://www.morrislubricantsonline.co.uk/golden-film-80w-90-classic-gear-oil.html

So how can a GL4 oil be warned against with phosphor-bronze components - are they just being overly super-careful?

The oil they recommend with phosphor-bronze components is this, which has no EP additives, and so is GL1 !...

https://www.morrislubricantsonline.co.uk/golden-film-ag-90-gear-oil.html

Is this why GB40 (Penrite Gear Box Oil 40) is often recommended here, as it has no EP additives? - and it actually what we should be using, and avoiding EP90 GL4 oils at all costs?

[RobH]

Don't worry about it Jules, I don't believe it really is a problem for TRs.  

 If you look back at the loads of threads that have been on here over the years on the subject of gearbox oil, it is evident that people have their own favourites and that a whole range of different oils are in use from engine oil to EP.   I don't recall any instance where anyone has complained of damage to the yellow-metal components as a result. 

[Steve 286]

I use gb40 Penrite recommended  by peter cox when he rebuilt my gearbox. the overdrive and gearbox work as they should with no crunching and instant in and out overdrive with no slipping 

[Andy Moltu]

Triumph recommended EP90 back in the day.

The concern with GL5 EP 90 is/was some contain additives that were not safe for yellow metals. 

These days rather than straight monograde 90 80/90 multi grade is preferred as it gives a better gear change when cold.( I can recall struggling to go into 2nd on winter mornings until the box had warmed up a little.)

GL4 is fine as are some GL 5s. It's a case of checking. 

To further complicate things some companies,  use engine oil viscosity figures. Millers GB40 is a multi grade of roughly 25/60 equivalent which again is roughly 80/90 using gear oil ratings.

[Chris Hubball]

Does anyone know why Penrite GB40 is not available and has been for the last 12 months ?

Cheers Chris

[Mike C]

Available to special order in my local parts supplier.  Seems to be still available in the UK:    https://www.ebay.com.au/itm/254202882886?srsltid=AfmBOoqydobN6Hf8Wl6afkBAsaRyaBbsxSHoMog1t4r16ibAezx_F_VK

Edited August 10, 2025 by Mike C

[RogerH]

Some suppliers are charging a fortune for this oil.

TRy these  https://eshop.richard-shrive-cars.com/p/penrite-classic-oils-gearbox-gear-box-oil-gb40-non-ep-1-litre

 

Roger

[Jules TR6]

Ok well having flushed out the old oil with some GL5 and now using 80W90 GL4, no issues with reverse until hot, then a minor grate on reverse. Generally gear selection still feels a little notchy - not into the actually gears but more around the 'gates'. So while it's ok at the moment, I'd like to try a thicker more 'sticky' oil.

I guess GB40, without EP additives may be a little more sticky than EP90?

I note looking at the usual charts, SAE40 engine, in terms of viscosity, comes in on low side of 90 gearbox oils, overlapping into next down 85W. 90 gearbox oils covering quite a wide range, next up being 140 (so what might be sold as 90 could be 100 or 110 etc).

/

I note Penrite also makes Penrite Mild EP, GL4, SAE 110. May be used where SAE 90 grades were originally specified (especially if the gearbox or diff is slightly worn) or SAE 140 oils were originally specified and the equipment is in good condition.

Oil replaces viscosity:    
SAE 90
SAE 140

Anyone ever thought of using this oil? ...or you'd advise against for an OD (J-type) - I read that something can clog in them?

/

Otherwise maybe multigrade is what's unnecessary for my box, and Castrol EP90 might work well (which as a 'classic' oil may indeed be actually a tad thicker than 90).

/

Anyway I might try one of the above while I'm on this mission, then a winter job is to get the pedal box out and replace the pedal bushes.

Edited August 11, 2025 by Jules TR6