just so I don't have to search...yes, it's Friday I'm lazy and curious...when I take my JDM tranny apart, how many teeth = .806 and how many = .762.

?uestion of the day

 

Just count the teeth on the gear and pinion and divide.

I'm going to guess:
.762: 45/59
.806: 50/62

Dave

 

where can I get the .806 5th gear? I know there was a chart I saw few years ago...

 

Silly me. I forgot that the ratio also depends on the gear from the input shaft to the countershaft. So you'd have to count the teeth on both that pinion/gear and the 5th pinion/gear and multiply it out to verify the ratio.

Dave

 

okay...I have 27 and 53 for fifth gear, now I need to count input shaft and countershaft but what will the equation look like? Thanks.

also anyone know where I can get a new blocker ring for whatever 5th I have?

 

The definitive answer:

55/25 = .719 (stock USDM)
54/26 = .762
53/27 = .806

 

thank you...do you know if the JDM 5ths had the same problem as USDM's?

 

better question, does the updated 5th gear blocker ring have all the teeth? and does it fit the JDM tranny.

The one I picked up in the FS section doesn't fit but is very different looking than the one in the tranny. I did notice REVERSE has all the teeth and 5th did not.

am I making sense?

 

I can tell you that the 5th gear syncro from my JDM tranny fit the USDM 5th gear perfectly. I don't remember anything unusual about it--I think it had all of its teeth. Having held a US and JDM 5th gear side by side, I didn't see or measure anything that was different other than the ratio, i.e., the gear tooth counts (not the dog teeth--they are the same). I do not know for fact that my JDM syncro is the updated part; however, given that it much newer--post 96 for sure--I assume that it would be.

 

Yes, you are.

I believe the old and new 5th synchro design have teeth going all the way around; the difference is the material.

There is no correlation between the number of dog teeth which engage the synchro and the number of gear teeth. So there would be no reason for a different synchro for the JDM and USDM ratios.

 

thanks for the help guys...I don't know the year or km's on the tranny, but everything looks good...5th synchro and 2nd synchro are the only things that looked like they should be replaced...to expect another 50k-75k miles (which would take another decade at this rate).

I ordered both synchro's, lock nuts, and seals from Ray...they will be here tomorrow, we'll see what the hell is going on here.

 

If you have any stuff you don't end up using, PM me.

Dave

 

I got the new synchro in today and it fits...missing dog teeth are at 12, 4, and 8 o'clock; just for ref.

 

bringing this bad boy back from the dead can anyone confirm

if i have a jdm post 99 model tranny

at 3500 rpms 5th gear i am at 80mph -18"wheels

any of you have the same

 

Also what are you referencing for "speed" source is important, or not. Swapping differential gear ratios and tires will not affect the Dash Speedometer reading, as this is based off what it thinks the rear end and tires sizes are. Without getting into absolute numbers and corrections for all these things, what you really are looking for is if the 5th gear is: 0.806 (JDM 1), 0.762 (JDM 2) or 0.719 (US). You can find this by ratioing percentage of RPM change between 4th 1.00 and 5th for a given constant speed.

 

Alex, we need to know your complete rear tire size to determine your overall diameter and match it against the OEM size.

 

3500 sounds about right. my car doesnt run right now to check. i had to change the speedo sensor when i went to 4.30 rear end so mine might have 1mph difference too

 

275-40-18 rich

 

yep. small synchro needs to stop giant gear. the delicate 5th gear synchro is just an R box thing.

 

I have a JDM tranny. I am at 3500RPM in 5th doing 80 MPH. Rear tires are 265/35 18

It also grinds going into fifth unless I rev match perfectly.

 

we'd also need the width of your wheel LOL since a narrower wheel will equate a taller tire , BUT . just to be clear .. YES you have a JDM trans , the difference between the USDM and JDM 5th is so large that you'd need some tiny tires in order to have to do 3500 on at 80 with US trans , even using an rx8 4.4 diff you wont be doing 3500 at 80 in a USDM trans


the JDM trans had this issue much less , since the 5th gear is much shorter so less work for hte syncro .. my trans currently has no syncro for 5th hah , double clutch rev match and you're set . I dont even grind anymore

my sources -->https://www.rx7club.com/3rd-generati...os-you-984896/ this thread would of probably given you your answer LOL

 

Jack the rear of the car off the ground, release the parking brake, pull a plug from each rotor, put the trans in 4th, hand crank the engine and measure rear wheel rotation for at lease 10 revs of the engine, do the same in 5th.

Thus you can calculate your diff gear ratio and 5th gear ratio.

Put the car back on the ground and measure the rear wheel/tire radius.
From all of this you can calculate theoretical rpms vs speed.

Find a stretch of road with mile markers, use that at a set speed to verify real speed vs speedometer speed. Or use GPS to measure speed vs speedometer.

It appears many are not good at math and problem solving. No wonder the forum and USA is falling apart.