T50 weird gear set What´s going on?

[fax0815]

Hello,

right I was driving a 20V AE86, with what I was told a "funny" gearbox. Pulls allright to 3rd gear, going all the through and to the top the rev range, but if you put in 4th it falls out of the power range, like shifting from 1 to third on a normal car.
4th to 5th works fine

I don´t know how trustworthy the aftermarket tacho was but it dropped from 8k to about 4,5k. Unfortunatly I have no clue what final drive it has got.

http://trdparts.jp/english/list_race-mis_ae86.html

Looking throught the avaliabe TRD gear sets, which all use standard 4th I can´t figure out why it does what it does...

Any ideas?

[Uzelac]

Drop of revs is up to gearbox ratio, final drive doesn't have anything with that.

Normal drop on T50 wouldbe 8000->5750 rpm.
Regular T50, 3rd->5th would make your engine 8000 to 4900 rpm

Drop from 8000 to 4500 sounds ... insane

[McKenney]

if it has a TRD quick ratio box, 1st, 2nd, and 3rd are much shorter ratios and 4th and 5th are stock. I drove an 86 with this gearbox and did the same thing. BTW thats an expensive gear set.

[fax0815]

Right had a chat with one of my mates, based on what I described and what we looked up in the gear charts it might me the 33030-AE851 gear set.
I´ll check the final drive, cause it will make it worse.

It is a weird non progressive gearset ( like a high torque band turbo diesel truck) and we couldnt figure out what it was ever made for, must be a very special aplication, probably be the reason why its discontinued...

[fax0815]

McKenney Wrote:if it has a TRD quick ratio box, 1st, 2nd, and 3rd are much shorter ratios and 4th and 5th are stock. I drove an 86 with this gearbox and did the same thing. BTW thats an expensive gear set.

That gotta be the 33030-AE851!

with 5,3:1



with 4,3:1
(look at the top speed )



stock gearbox with 4,3:1

[Bean]

I'm sorry to disappoint you but Uzelac is right. The TRD gear sets would make shifting from 3rd to 4th the same as stock (with the 3 gear set) or shorter (less drop, with the 5 gear set). The final drive ratio has no influence on the geardrop.
The only way I could explain such a behavior with a stock or TRD box is if your shifting really slow (i.e. loosing a fair amount of speed ~30kmh).
Or as he said shifting from 3rd into 5th (maybe someone fucked up on a rebuild but then I wonder what your 5th gear ratio is)

Can you tell us the speed you're doing in 3rd, 4th and 5th at the same revs (i.e. @ 4000rpm) - that way we can calculate the step ratio between them.

PS:

fax0815 Wrote:with 4,3:1
(look at the top speed )

I do the only difference to stock with same 4.3 is in 1st and 2nd gear. The drop line from top of 3rd to the intersection with the 4th gear line is the key and as Uzelac described

[Jan Pedersen]

It should drop to around 5.7k rpm when shifting from 3rd.

This is the main reason for my AZ6 swap

[fax0815]

Bean Bandit Wrote:I'm sorry to disappoint you but Uzelac is right. The TRD gear sets would make shifting from 3rd to 4th the same as stock (with the 3 gear set) or shorter (less drop, with the 5 gear set). The final drive ratio has no influence on the geardrop.
The only way I could explain such a behavior with a stock or TRD box is if your shifting really slow (i.e. loosing a fair amount of speed ~30kmh).
Or as he said shifting from 3rd into 5th (maybe someone fucked up on a rebuild but then I wonder what your 5th gear ratio is)

Can you tell us the speed you're doing in 3rd, 4th and 5th at the same revs (i.e. @ 4000rpm) - that way we can calculate the step ratio between them.

PS:

fax0815 Wrote:with 4,3:1
(look at the top speed )

I do the only difference to stock with same 4.3 is in 1st and 2nd gear. The drop line from top of 3rd to the intersection with the 4th gear line is the key and as Uzelac described

Still not convinced...
Definatly no granny shifting involved.

I understand what you are saying, 3-4th stays stock but due the dramatic changes to 1st and 2nd everthing gets messed up. Its a non progressive gear set, look at the rev drops on the TRD gear set, it gets bigger with shifting up, this is the kind of gearbox you find on big trucks.

The whole point in a close ratio gear box is to have a loong first gear and have all the others close together, with progressive layout i.e. Rev drops getting smaler the further you shift up, to make sure you hit the power band and the engine is able to pull away.

Thats exaclty what the other avaliabe TRD gear set looks like.

This is with 4,3 final drive, I recon first first gear will be tricky but the rest looks like what should be on a race car.

Call me fussy, but I think the final drive does have a big effect on what I described. Imagine this AE86 doesnt run the advised 5,3 ratio, for instance a 4,3 or a 4,7.

Now with the right final drive 3rd goes from 115kph to 160kph.
With the 4,3 3rd tries to pull from 155 to 210 which will take forever due all the occuring drag. Yes on the diagram it is the same but, revs will pick up even slower, making it fell bad.

I supose these diagrams were made with a 16v engine? This AE is running stock 20v without bottom end torque, compared to my 16V. I blame the missing airbox and short velocity stacks, which makes it worse cause unless you are past 5k 5.5k nothing is happening.

Does this make any sense to you?
my probelm its just as it goes nicely in the first gears and than you throw in 4th and think WTF is this sh**?

Well I understand its a bit too much "I feel" guesswork here, so I´ll gather more info of this, unfortunatly it runs a fancy instrument with no speedo and since I looked at the engine wireing, i don´t exactly trust the tacho either. but yeah I´ll try.

[Bean]

well feel wise it's true the gap from 3rd to 4th is bigger than the gap of the other shifts. BUT the gap itself is no different than stock. If you really have the TRD 3 kit and coming from a stock gearbox the main change, aside from the 1st and 2nd being higher than stock (therefor closer ratios) is the fact that in the stock gearbox the gaps between gears is getting smaller (1st->2nd biggest gap, 2nd->3rd a bit small, 3rd->4th smaller again, etc) - this is also the case with the TRD 5 kit. As this got a shorter gap between 3rd and 4th than stock, we can rule it out though.

the final drive changes NOTHING on the gap between gear. Fitting a shorter 5.3 will only yield less speed, for the same engine rpm, and hence more torque at the wheels, compared to the 4.3 (think of it like fitting really small (smaller overall diameter) wheels to the car)

I'll see if I can butcher together the gear graphs in PS to make it more visible what I described above.

As said going back to your initial statement IF your rpms drop the amount you mentioned AND are correct - something is off/strange.

[Bean]

OK here goes:
red lines are same rpm and show that the gap is the same between different final gears as well as Stock and TRD3
green lines show the gap change between gears.
As you can see the gap between 3rd and 4th on the TRD3 is the same as 1st to 2nd. 2nd to 3rd is marginally shorter.