Manual gearbox oil discussion.

[Dave2000]

Finally got around to draining both the GB and TB and putting in a 75/90W GL4 synthetic gear oil, the oil is designed for:

'manual gearboxes and transmissions and for use in mid severity conditions in light commercials and some cars, not for use in differentials using hypoid gears'.

First impressions...............not happy! Might be too early to tell at the moment but, I got the feeling that the gearbox internals were still spinning when trying to change 1 -2 and 2-3, something the synchromesh should have coped with...unless they (the synchromesh) do not work well with such a slippery oil that is also light enough allowing the internals to spin so freely when cold? To add credence to that 'feeling' is that from cold I had to select reverse and it 'crunched' as it went in, something it has never done before. Where I park in the underground garage I always have to reverse out of the parking space, so this is something I would have noticed before, I accept there may be no synchromesh on reverse but this is a new thing. I will leave it for a couple of weeks but the 80/90 dino oil was better......definitely. So depending on a few miles down the road I may go back to a typical 80/90 mineral GL4 which should be easy to obtain, I bet my gearbox insides are cleaner than yours!!

regards

Dave

 

[frank rabbets]

Stick that mineral oil in. Wish I had some. Can't seem to get it here. There IS synchro on reverse and if your changes are a bit more difficult I wonder if the clutch might have a little drag all of a sudden.

 

[Towpack]

Dave,

I think I too would find that worrying. For changes up the box to suddenly become 'sticky' along with a crunch into reverse, right after an oil change is a big coincidence to ignore IMO. Myself and others on this forum have found the opposite and synth 75w/90 has actually improved things so I've no idea what's going on with your gearbox.

 

[Dave2000]

@Frank, no clutch drag Frank, EVERYTHING in that area was renewed except the master cylinder, even the flywheel face checked for true. It would be very coincidental that I change the oil and then the clutch dragged.

@Towpack Is it possible that your self and others had problems and the change of oil improved it due to masking the problem? I am at this moment not sure what is happening, to get a sudden change in the change (no pun intended) seems very strange.

I was the designated driver tonight to one of the many Xmas dinners that you get involved in and we took my car, cold changes still not great and the usual roads between one venue and anther are steady 90km's punctuated with roundabouts so very little use of the lower gears. So a drive of about 15 minutes and then parked for about 5 hours, came out and forgot about the reverse grind until I had actually shifted the lever...no grind. 1-2 and 2-3 whilst not grinding you could feel through the gearstick what can only be described as if you were running a stick along a set of railings close to each other, you could feel the cogs engaging if that makes sense?

Car will see a good clean tomorrow and then not get used until Thursday for the Madrid airport run, see how it goes>

regards

Dave

 

[frank rabbets]

The railings thing you describe is the dogs running over each other until they pop in and engage the gear. The cause is as follows :-

1. Poor synchro :- a. Incorrect oil
b. Poor rings
OR

2. Clutch drag.

 

[frank rabbets]

I guess you ought to put the old oil back in to find out one way or another. Hope you are sorted soon.

 

[Dave2000]

I would like to discount the rings and clutch drag, I do like my thought of too thin an oil in a gearbox not designed for it, and the 75 being too thin for a warm climate, because it is the only option I like!

I will do the 1000 km's round trip on Thursday, after that I have some time over a few days to potter around the village in 1st and 2nd (narrow streets/cyclists/donkeys and so forth) to see if I can find a common denominator. Of note is it takes a fair push to move from centre to the 1 -2 slot and to move from centre to 5 - reverse slot is almost devoid of any effort, I am thinking that the top plate where the gearstick enters has the bias springs and that perhaps the springs were inserted on the wrong sides during the rebuild?

I cannot remember if it was this way on my old gearbox, common sense says it is wrong on this one, 5th and reverse should be harder to get to....I will wait for someone to check and get back to me........please?

My thoughts here are that I am artificially applying left pressure when moving from 1st to 2nd and of course 3rd to 2nd, this may be altering the way I am shifting the gears? Grasping at straws here but am looking at any and all options at the moment.

regards

Dave

 

[clivehorridge]

Don't believe you Dave, you forgot the photos

 

[frank rabbets]

The springs are the same.
The effort to move the lever into 1/2 is the same as that required to move the lever into 5/R.
Other things being equal the synchro will work better the thinner the oil. That's because the teeth on rings have to bite through the oil and touch the cones.
Other things being equal the more slippery the oil is the worse the change for the same reason.
I changed from multi purpose gear oil to semi synthetic and my change is worse. I would go back to the multi purpose if I could get it.

 

[Dave2000]

Don't believe you Dave, you forgot the photos

No honest it's true guv, stand on me!

regards

Dave

 

[Dave2000]

The springs are the same.
The effort to move the lever into 1/2 is the same as that required to move the lever into 5/R.
Other things being equal the synchro will work better the thinner the oil. That's because the teeth on rings have to bite through the oil and touch the cones.
Other things being equal the more slippery the oil is the worse the change for the same reason.
I changed from multi purpose gear oil to semi synthetic and my change is worse. I would go back to the multi purpose if I could get it.

I may have not explained myself very well there Frank, I am talking about swinging the gearstick from left to right and back again across the neutral gate between the 1-2 and 5-R, not the resistance of the detent springs. For whatever reason I missed throwing out the top cap where the gearstick enters the gearbox, found it in the garage earlier, there are two sprung plungers inside, they sit either side of the gearstick, and they appear identical but one is considerably stronger than the other, I believe this is what controls the bias of the gearstick?

I do not have the time at the moment but will look at it later in the week. As these plungers were not disturbed in my original strip down I have to assume they are in the correct position, I will compare them to the ones fitted in my replacement gearbox.

Re the oil Frank, I think there are two different forces at work here, I agree with you about the rings needing to grip the synchromesh which obviously allows the dog teeth to align and the gear to engage but, if my cones are nicely coated with nice slippery GL5 and the 75 weight synthetic oil is allowing the gears to spin more freely, then the mismatch of oils might be the answer why my shift quality has gone bad? It does feel as if the synchromesh is working but having trouble bringing the dogs up to speed. Lets face it there is a conflict here, we want super slippery to prevent/delay wear and yet we want traction with minimum wear for the synchromesh to work. It is too late now to do anything as I am set for the Madrid and back run Thursday, I simply do not have the time and if the truth be known inclination to change the oil again this week.

Get back to you all and give you and update.

regards

Dave

 

[Towpack]

Mine requires quite a bit more effort to move across the neutral gate to 5/R than it does 1/2. Moving the lever left for 1/2 is so light it's barely noticeable while driving. Many gearboxes are like this in my experience. I reckon it's to avoid accidentally going from 3rd into reverse?

 

[Dave2000]

Mine requires quite a bit more effort to move across the neutral gate to 5/R than it does 1/2. Moving the lever left for 1/2 is so light it's barely noticeable while driving. Many gearboxes are like this in my experience. I reckon it's to avoid accidentally going from 3rd into reverse?

Spot on Towpack! I think my original post was a tad ambiguous? It makes sense that it is harder to 'get to' 5th and reverse, my present shift allows the stick to almost fall into the 5th - revers gate. But moving back across to 1 - 2 is not difficult but significantly harder. I think once Frank reads this he will concur, and of course tell me off for not making my 'thoughts clear'.

regards

Dave

 

[frank rabbets]

Dave I knew you were talking about the gear lever centralising springs. My car gear lever is stiff to the left and right in equal measure and it's the original 'box.

 

[Dave2000]

Dave I knew you were talking about the gear lever centralising springs. My car gear lever is stiff to the left and right in equal measure and it's the original 'box.

Thanks Frank, I thought my explanation was a bit vague. So the centralising springs are definitely different in strength and gauge, I looked at them a few mins ago, I thought perhaps the guys who had assembled mine had them back to front? As above I will pull and compare and see what that nets. Of course it will not make it shift any better inside but might be easier to shift not having to apply such a hard bias trying to avoid a 1-4 shift.

regards

Dave

 

[womble_]

@Dave
Which oil did you end up putting in (i can't quite tell reading the thread back)


I have some Morris Lodexol FS 75W-90 Fully Synthetic at home waiting to go in the gear box. 2nd (!) is impossible when cold. Is the consensus that is or isn't the right way to go?


P.S. Do i need a crush washer or similar if i'm draining the GB?

 

[Dave2000]

Hi womble, I did eventually use the Cepsa gear oil, apart from being GL4 it is also recommended for off road gearboxes and is also accredited by Toyota. Sodding expensive as I had to purchase in individual litres as there is no 5 litre option. This oil is still under evaluation at the moment, if I had to make a choice right this minute I would drain and put dino 80/90 GL4 in.

Today covered over a 1000 km's, gearbox is silent in use, so I will try some local running around later in the week as I - 2 and 2 - 3 shifts have been......'obstructive', this is the only way I can describe it at the moment. Earlier in the week the first actual gear selected in the morning was reverse and this crunched, it did this for a day or two and then it has not done it since. Difficult one to call at the moment, I had the right weight mineral oil but the wrong additive and this shifted great, now have the above oil and shift is poor. In reality I have not had the same oil in there that was originally specified by Toyota due to it not being available at the moment. I will do dome very local village runs later to see how the shift is when hot, at the moment it has been all motorways or fast carriageways.


http://www.cepsa.com/cepsa/Products...PSA_Lubricants/CEPSA_Transmisiones_75W90_MV_S

regards

Dave

EDIT: I re-used the alloy washers over many times and no problems.

 

[Cptsideways]

I have a lot experience with R154 gearboxes, the 2WD version of the LC box as found in Supra's etc. Usually running with 500-600hp.

What I use to use was a mix of MT75 & Autobox lube, massively improved the shifting qualities. Now my new LC80 which is a manual is suffering from appalling cold shifting issues so bad I think it must have EP Tractor spec treacle oil in it. So I shall be draining it down if that's even possible & sticking my magimix in there to see if that improves things.

 

[frank rabbets]

I'm wondering if engine oil would be the way forward. In the 60's 70's the BMC mini had the gearbox in the sump and one just put engine oil in the unit. The gears were very small c/w the LC ones and the mini Coopers and GT's were quite powerful. The LC gearbox components design are no different to the 60's gearboxes. Mini gearboxes didn't seem to suffer from being run in engine oil.

 

[Towpack]

I read an article about engine oil in a motorcycle magazine years ago which said that car engine oil was unsuitable for use in motorcycles for 2 reasons:

1. The engine and gearbox are unitary.
2. Most motorcycles have wet clutches which are cooled by the engine oil.

Motorcycle specific engine oils contain different 'friction modifier' additives to those present in many car oils that could lead to clutch slip and they are also formulated to cope with the shear forces of meshing gears in a gearbox. Don't know wether the latter is true or not but present day motorcycle engine oils have a specific classification of JASO MA to address the clutch problem.