Outer Limits 4x4 Board

After towing the caravan away again for the weekend I was thinking about this 5th gear problem we have.

First up, what normally goes wrong with the gear itself? We've all heard not to tow in 5th in just about any Toyota 5 speed, mine is the R150f.

Anyways, assuming it's teeth breakages I had a thought. I wanted to change out my 5th for a Dyna overdrive to get the taller ratio. Was wondering if a solution would be as simple as getting the 5th gear treated some how, like modified CV's. Would this solve our problems?

I ask because in it's current guise, my 4Runner is happy to chug up just about any freeway hill in 5th gear with the 1.6t caravan behind, apart from my paranoya. In fact almost every hill the guage was still showing vacuum, so I barely went past 1/2 throttle. I wish I could confidently leave it in 5th and save fuel seeing as I have the power to do it.

Nem they are a strong gearbox for sure, I tow a trailer for work every day of the week (sometimes it has had 2 tonne in it).
Been doing it for 10 years and the V8's been in for 6years and I cruise in 5th all the time up and down hills.
The Dyna overdrive is a great idea too.
I think paranoia has set in man

I've heard of many failing though, well I guess more in the 80's and Hilux boxes.

That's good to know though, I guess I'll hunt down a Dyna 5th.

Any idea where to find one? Big job to fit?

I have to pull the box soon as my rear main is so bad it even sprayed the van

Try a truck parts place theres one on the central coast tho what part of the dyna do ya need and from whet model i have a dyna here an 85 mod with the 13b and 5 speed ive got to part it out as its badly rusted in the body and its only done 130K

the R150 is a much beefier box than the explod-o-matic R150F's and G52's. Its based more on the H150 box behind the big turbo trucks than the Supra gearbox the 151 is based on.

The main issue with 5th is its an unsupported gear.


Thats 5th gear in an R151F i blew up (with 10mm socket for scale)

While the gears itself arent small, its the way they are fitted thats the issue- that nut is the end of the counter shaft. Now first->3rd are on the countershaft between a bearing in the front housing and one in the intermediate plate, but 5ths hangs out behind the intermediate- its only supported at one of that shaft, and under sufficient loads, can flex the counter shaft, move the teeth out of full mesh and shatter the tips off them, causing a big mess very fast.

Its a design problem with 99% of light truck boxes, and i dont think the Dyna is any different. I dont think a bigger gear from a dyna will help either- you still will get that flex problem no matter how hardened or tough the gears are.

What about getting the shaft itself hardened? or is there enough meat on the alloy housing to add a retainer to hold a bearing then add a bearing to the end of the shaft,replacing where the nut is?

cheers mark.

Top info Ferrit, apart from that confusing first sentence lol....

So changing the 5th gear is as simple as undoing that nut and fitting a new one? (never opened a g-box yet)

Actually, I've got a spare R150f in the shed from Nemesis 1, might pull it down and get to know it.

lokka wrote:Try a truck parts place theres one on the central coast tho what part of the dyna do ya need and from whet model i have a dyna here an 85 mod with the 13b and 5 speed ive got to part it out as its badly rusted in the body and its only done 130K

I'm not sure mate, will try and find out. The gearbox is the R452 though I know that much.

-Nemesis- wrote:Top info Ferrit, apart from that confusing first sentence lol....

So changing the 5th gear is as simple as undoing that nut and fitting a new one? (never opened a g-box yet)

Actually, I've got a spare R150f in the shed from Nemesis 1, might pull it down and get to know it.

im good at that- makes sure the important info only gets to people determined enough to read further!

I never stripped mine down that far, but 5th gear is a combo of both the counter and mainshaft gear, so you'd have to strip and swap the mainshaft gear too, and i dont know how well that would work.

i though the R151F were supposed to be one of the strongest. 2nd in line was the R150 and then lastly the G52

or have i got it wrong??

Outer Limits Hilux wrote:i though the R151F were supposed to be one of the strongest. 2nd in line was the R150 and then lastly the G52

or have i got it wrong??

I was under the impression all the R series are of the same strength, G52 is not even in the same league as the R150f. Mine has been behind a V8 for years and is now seeing serious numbers with the blower, still no problems touch wood...

80 series box is by far the strongest. R151F is a pile of turd as are most of the other toyota boxs. 75 series box has had the same issues for 200 years and toyota in there wisdom have never fixed it.

from about 2000-2003/4 the R151F ran a two piece main shaft with a coarse spline joining collar on it.

the collar eventually chewed the splines off the shafts and the whole mess stopped transmitting power to the transfer case.

After 2004 toyota went to a 1 piece shaft :roll

the R151 in the prado TD, Surf TD, 78/9 1HZ and 105's all shared a similar problem. my old 2001 work truck (79) chewed its apart, old mans 3.0TD prado chewed its apart and about 40 trucks from WMC did too- the gearboxes were sitting in my diff/gearbox guys shop waiting for new one piece shafts to be installed.