Mysteries of the R154 R151 Gearbox.......

[Jon Wildsmith]

I think all the box's manufactured from August 92 to August 96 will have the asymmetrical dog teeth on 2nd gear Frank but they also changed the outer ring and synchro rings so between them they probably account for the stiff 2nd gear on yours compared to mine. Be interesting to hear if anyone has a box from between those dates (manufacture dates not registration) that doesn't have a stiff 2nd gear and also what they were like before August 92.

 

[Lorin]

I replaced my old box with what I was told was a low mileage one from a 96 truck. When the box was put in the oil was also replaced with fully synthetic. When cold, 2nd gear is always quite difficult to select on changing down from third. Changing up into second is fine. Once the box warms up it shifts perfectly.

 

[Jon Wildsmith]

what did your old box shift like Lorin? AFAIK there's no way to tell from the outside what is inside your 'new' box, but if more manual 80 owners post we might get a better idea what's the norm. What oil went in your new box?

 

[Cptsideways]

One thing I have noticed on these boxes is the selector forks become stiff where they slide through the main support plate. If you polish up the shaft & the sharp edges of the bearing notches it improves the shifting process no end.

 

[Chris]

Known good box Jon? Not sure what you are suggesting.

Cough




Wonder what this shiny thing might be?

Chris

 

[karl webster]

Lucky bugger Chris

 

[Jon Wildsmith]

Where's the rest of the truck to go with that then? Karl would have lent us a box but we needed to know it to be very close in manufacture date to Ian's because they changed several times over the years which is another complication if the bits have already been mixed up.

 

[Rob]

How do you find out the year of manufacture? Mines registered in 97 as an Amazon and shifts poorly into second and pops out of first on overrun.

Sent from my GT-I9100 using Tapatalk 2

 

[frank rabbets]

Hi Rob
I don't know about the year of manufacture but may be able to help on your problem. If you rest your hand on the gearknob when in 1st gear and move the throttle on and off, does the gearlever move much back and forth BEFORE it jumps out? Also is your gearoil dirty?

Frank

 

[Jon Wildsmith]

I'm not sure if putting your VIN into toyodiy gives you an accurate manufacture date but if not and you don't have the EPC if you give me your VIN number I can check manufacture date on the EPC.

 

[Rob]

Taking the LC for a drive up to Lincomb today so will let you know. This issues were present before and after I changed the oil, and the oil was clean when it came out. Have not checked the condition of the oil since (about 3 years worth of abuse).

One thing I have noticed is when I took it for a drive without the gear leaver rubber in place, I was surprised at how noisy the gearbox is. On closer inspection of the gearbox and TC it has been painted black including over the stickers and the wrong size bolts have been used on the bell housing so it definitely has been out. The black paint is making me think this is either a refurb original or refurb replacement.

Chris, what? When? How?

Edit: sent you a message Jon

 

[frank rabbets]

I judged my gearbox performance too quickly. I took it out for a longer run today and can now report that the 2nd and 3rd gearchanges are very much improved when the gearbox is up to working temperature. Also bone dry without the slightest sign of an oil leek.

Frank

 

[ajnabi]

I have a '98, manufactured in 03/97, with an H151F. I bought it at 72K miles, currently has 81k.

1st to 2nd was tough, especially when cold, but when I changed the oil the gear changes were a lot smoother, including 1st to 2nd.
I don't know when the oil was last changed though. I used Castrol Syntrans Multivehicle 75W-90 Fully Synthetic MTF.

But from all I've read, 1st to 2nd is always a bit difficult when these boxes are cold.
I try to pull of in 2nd mostly, when I can.

IQ

 

[Chris]

Well Rob it sort of dropped into my lap one day out of the blue "hey do you want a nearly new 80 manual box from a closing down main dealer?"

Hmmmm yes please. And suddenly there it was I'm the boot of my car

Chris

 

[Rob]

Sounds like you were in the right place at the right time Chris.

Frank, after paying attention to the gearbox yesterday, it shifts fine when warm although a bit clunky into second when cold. The gear leaver does not move much in first so I compared it with other gears. In first the gear leaver seems to move diagonally whilst all the other gears it just moves forwards and backwards. The leaver never seems to move more than 5mm at the end, difficult to work out how much as its not easy to find a reference point whilst driving.

Jon mentioned yesterday the reason first could be popping out is due to axial play in the first gear caused by the thrust load from the helical gears, seems to only pop out under really heavy load and only in overrun. This usually only happens in low but has occasionally happens in high. From what I understand, if there is enough axial play and the thrust load is high enough it can disengage the dog clutch on the synchromesh. And the fact that it only happens on overrun makes this theory more plausible, as under acceleration the thrust load would be in the opposite direction potentially pushing the synchromesh together. What do you think Frank?

Also it turns out my truck was made in 02/97, however I have no idea if my gearbox is the original one.

 

[Jon Wildsmith]

I used Castrol Syntrans Multivehicle 75W-90 Fully Synthetic MTF

That's what I'm using as well, seems to work well.

But from all I've read, 1st to 2nd is always a bit difficult when these boxes are cold.

I think 3rd to 2nd is more usually stiff when cold on the later boxes, I don't know if 1st to 2nd usually is on these later boxes? Mine isn't.

 

[Lorin]

what did your old box shift like Lorin? AFAIK there's no way to tell from the outside what is inside your 'new' box, but if more manual 80 owners post we might get a better idea what's the norm. What oil went in your new box?

From what I remember the original box had a very difficult shift from 1st to 2nd when cold and was almost impossible to select 2nd from 3rd when cold. This was somewhat improved with the addition of Toyota fully synthetic 75w-90 gearbox oil but by no means cured. The reason I changed the original gearbox was because it used to jump out of 2nd and reverse gears.

The oil I put in the new box was Castrol fully synthetic 75w-90 gearbox oil. Big improvement in shifts when warm but it remains especially unwilling to down shift from 3rd to 2nd when cold and is also a little 'tight' shifting from 1st to 2nd when cold.

One observation I do have is that the (earlier) original box was generally a nicer shift when warm than the new box in that the throw was a fair bit lighter and the gate felt more precise/crisp. No idea if true or not but I recall being told this was something to do with a different number of synchros in the later box - 3 as opposed to 2 or something similar.....

 

[frank rabbets]

Rob, I think Jon has described well what might be happening but I do not know why your lever is going diagonally into first unless accompanied by play which could then be a worn or loose fork or worn needle rollers on the first gearwheel, all unlikely. Regarding jumping out of gear one of the thrust washers on the first motion shaft may have broken up causing the shaft to move back and forth compared with the gear lever and selector mechanism. If this is happening it could come out of gear especially under load due to the spiral cut gears acting like a thread. I think the most important thing to do is to drain the oil when hot and see if there are metal grindings in the oil. If there are not any you could well live with the problem but should avoid jumping out of gear under load because every time this happens it wears the engagement dogs at an angle and this makes it even easier to jump out and eventually it jumps out too easily. If there are a lot metal grindings in the oil, especially coarse ones or obvious pices of metal, then even though you put clean oil back more grindings are likely to be created as there is obviously something wearing rapidly in the box. There is an oil pump in the box and this pumps the grindings around the internals. Just a few fine grindings looking a bit like coarse metallic paint could well be just from wear on the dogs caused by jumping out. If a dog tooth comes out don't panic this is quite common. It will have a diameter of 5mm.

So lots of coarse grindings or worse means the box needs to come out and the damaged bits replaced as grindings being pumped around means all the lubricated surfaces are being worn away. If you are a bit uncertain as to whether or not you can do this yourself p.m. me and I'll send you my phone number but heres hopeing your oil is cleanish.

Frank

 

[frank rabbets]

There are 2 magnets in the box which catch some of the metal fragments. One low down on the sandwich plate and the other in the bottom of the pickup strainer.

Frank

 

[Jon Wildsmith]

I judged my gearbox performance too quickly. I took it out for a longer run today and can now report that the 2nd and 3rd gearchanges are very much improved when the gearbox is up to working temperature. Also bone dry without the slightest sign of an oil leek.

That's good news Frank