[Evan Purple240]

You guys helped alot with my differential swap, i was sent to the z gararge to check out the swap, now i have a question, How do i tell which 5sp i have???? The only thing i could distinguish as a characteristic was when it was mentioned that a hole had to be cut to fit the earlier transmission. The reason im asking is because my engine is not making enough power for off the line gentile starts and the tunnel wasnt cut to acomidate a 5sp trans. it almost seems as if its geared to high. I belive that i still have the stock diff, which i think is a 354 but if i have the zx trans i need a 390 right.? God someone please help me i need a new diff, but cant seem to figure out which ratio i need due to the year of the transmission.

Thanks all, evan

 

[Phantom]

> You guys helped alot with my differential
> swap, i was sent to the z gararge to check
> out the swap, now i have a question, How do
> i tell which 5sp i have???? The only thing i
> could distinguish as a characteristic was
> when it was mentioned that a hole had to be
> cut to fit the earlier transmission. The
> reason im asking is because my engine is not
> making enough power for off the line gentile
> starts and the tunnel wasnt cut to acomidate
> a 5sp trans. it almost seems as if its
> geared to high. I belive that i still have
> the stock diff, which i think is a 354 but
> if i have the zx trans i need a 390 right.?
> God someone please help me i need a new
> diff, but cant seem to figure out which
> ratio i need due to the year of the
> transmission.

> Thanks all, evan

Evan,
It appears that you in a Catch 22 situation. If they had to modify the car to put the 5-spd in then it sounds like you don't have a 79 or earlier Z transmission. I have heard that the '83ZX turbo transmission is a bit different in mounting and doesn't retrofit to the older Z's real well. You need to know the heritage of your parts. What was the donor vehicle? the 5-spds have a model number on them. Those numbers are identified in the Z & ZX Haynes manuals. That way you can tell which transmission, and which ratio, it is. There is also a way you can pull the cover plate off the differential, count the gear teeth and tell the differential ratio.
From what I do know though is that the US spec 240's came primarily with 3.70 rear ends. A 77-79 Z 5-spd will work fine with this but an 80-83 ZX 5-spd will be a bit sluggish. If your car is running now here's how you can tell. Take it to 50 MPH in 5th gear. If it is turnig 2,000 RPM or better you are probably geared OK and need to look for another problem as to why you're so sluggish coming off the line. If you're turning like 1,800 or less at 50 then you need to find a differential with a 3.90 gear set.
Phantom

 

[Mike kZ]

Re: Trans, and Diff info web page

> Evan,
> It appears that you in a Catch
> 22 situation. If they had to modify
> the car to put the 5-spd in then it sounds
> like you don't have a 79 or earlier Z
> transmission. I have heard that the '83ZX
> turbo transmission is a bit different in
> mounting and doesn't retrofit to the older
> Z's real well. You need to know the heritage
> of your parts. What was the donor vehicle?
> the 5-spds have a model number on them.
> Those numbers are identified in the Z &
> ZX Haynes manuals. That way you can tell
> which transmission, and which ratio, it is.
> There is also a way you can pull the cover
> plate off the differential, count the gear
> teeth and tell the differential ratio.
> From what I do know though is that the US
> spec 240's came primarily with 3.70 rear
> ends. A 77-79 Z 5-spd will work fine with
> this but an 80-83 ZX 5-spd will be a bit
> sluggish. If your car is running now here's
> how you can tell. Take it to 50 MPH in 5th
> gear. If it is turnig 2,000 RPM or better
> you are probably geared OK and need to look
> for another problem as to why you're so
> sluggish coming off the line. If you're
> turning like 1,800 or less at 50 then you
> need to find a differential with a 3.90 gear
> set.
> Phantom

This is a great web page on what your looking for, hope it helps
Mike

 

[240Dave]

We need an archive...more

Ok, so you've got a 240Z with a 280Z? 5spd and stock R180 diff.

Manual (77-79)280Z 5spd ratios
1st 3.321:1
2nd 2.077:1
3rd 1.308:1
4th 1.00 :1
5th .864:1 (anything less than 1:1 is overdrive)

Manual (79-81)280ZX 5spd ratios:
1st 3.062:1
2nd 1.858
3rd 1.308:1
4th 1.00:1
5th .745:1

So, with your 3.364:1 diff, 1st gear is as follows:
240Z 4spd 3.549x3.364 = 11.94:1 overall
280Z 5spd 3.321x3.364 = 11.17:1 overall
280ZX 5spd 3.062x3.364 = 10.3:1 overall

As you can see, the engine is turning much slower with the 280ZX, and this might be the transmission you have. There are casting numbers to help you identify this.

Or, you can do it scientifically, using the following method.
1. Drive with a friend, who has an accurate speedometer, and have them drive at exactly 50mph.
You stay right beside, and write down your rpm. (not while driving of course )
2. Now, knowing your rpm @50mph, you need to measure the OVERALL diameter of your rim and tire.
Measure from the ground, to the top of your tire. Record this number in inches as close as possible.
3. Use this formula, to determine which ratio diff you have.

RPM = mph x overall gear ratio x 336/tire diameter

So, for example:

280Z 5spd overall 5th gear w/ 3.36 R180 = 2.91:1
280Zx 5spd overall 5th gear w/ 3.36 R180 = 2.51:1
Tire diameter of 23.2 (this is what mine is)

RPM @50mph with 280Z 5spd=

50 x 2.91 x 336/23.2 = 2107rpm

RPM @50mph with 280ZX 5spd=

50 x 2.51 x 336/23.2 = 1818rpm

Obviously, you can notice a large difference with the rpm. This way you know what 5spd you have. If the numbers don't come out correctly, just swap in the different overall ratios for the rear ends, until the numbers match. Since everything else is a constant(or pretty close), the only part of the problem that can change is the overall ratios. You should be able to get a correct answer by swapping one of the ratios. Then you will know what type of transmission and what ratio rear end you have. Swapping a R200 into a 240Z, is a whole other story.

You can check if you have a R180 just by visually looking at the rear end, and compare it to the diff from the 280Z. The R200 280Z should be physically much larger. I would assume the 3.364:1 ratio for the R180, since that is what most of them are, unless someone planted a R180 from a mid 80's 4wheel drive into your car, which is in my opinion, highly unlikely.

If you do have the 280Z 5spd, then you need a 3.545 R200 or higher.
If you have the 280ZX 5spd, then you need a 3.9 R200 or higher.

The higher above the base figure will give you higher overall ratios, which will help in acceleration, but will raise your rpm while cruising on the highway. It's up to you to decide which way you want to go.

By the way, I've noticed the manuals, even Haynes are somewhat vague in this area, and are not entirely accurate. Afterall, these manuals are British publications, and Europe spec cars often have different parts and requirements than US cars.

 

[Phantom]

Re: We need an archive...more

> Ok, so you've got a 240Z with a 280Z? 5spd
> and stock R180 diff.

> Manual (77-79)280Z 5spd ratios
> 1st 3.321:1
> 2nd 2.077:1
> 3rd 1.308:1
> 4th 1.00 :1
> 5th .864:1 (anything less than 1:1 is
> overdrive)

> Manual (79-81)280ZX 5spd ratios:
> 1st 3.062:1
> 2nd 1.858
> 3rd 1.308:1
> 4th 1.00:1
> 5th .745:1

> So, with your 3.364:1 diff, 1st gear is as
> follows:
> 240Z 4spd 3.549x3.364 = 11.94:1 overall
> 280Z 5spd 3.321x3.364 = 11.17:1 overall
> 280ZX 5spd 3.062x3.364 = 10.3:1 overall

> As you can see, the engine is turning much
> slower with the 280ZX, and this might be the
> transmission you have. There are casting
> numbers to help you identify this.

> Or, you can do it scientifically, using the
> following method.
> 1. Drive with a friend, who has an accurate
> speedometer, and have them drive at exactly
> 50mph.
> You stay right beside, and write down your
> rpm. (not while driving of course )
> 2. Now, knowing your rpm @50mph, you need to
> measure the OVERALL diameter of your rim and
> tire.
> Measure from the ground, to the top of your
> tire. Record this number in inches as close
> as possible.
> 3. Use this formula, to determine which
> ratio diff you have.

> RPM = mph x overall gear ratio x 336/tire
> diameter

> So, for example:

> 280Z 5spd overall 5th gear w/ 3.36 R180 =
> 2.91:1
> 280Zx 5spd overall 5th gear w/ 3.36 R180 =
> 2.51:1
> Tire diameter of 23.2 (this is what
> mine is)

> RPM @50mph with 280Z 5spd=

> 50 x 2.91 x 336/23.2 = 2107rpm

> RPM @50mph with 280ZX 5spd=

> 50 x 2.51 x 336/23.2 = 1818rpm

> Obviously, you can notice a large difference
> with the rpm. This way you know what 5spd
> you have. If the numbers don't come out
> correctly, just swap in the different
> overall ratios for the rear ends, until the
> numbers match. Since everything else is a
> constant(or pretty close), the only part of
> the problem that can change is the overall
> ratios. You should be able to get a correct
> answer by swapping one of the ratios. Then
> you will know what type of transmission and
> what ratio rear end you have. Swapping a
> R200 into a 240Z, is a whole other story.

> You can check if you have a R180 just by
> visually looking at the rear end, and
> compare it to the diff from the 280Z. The
> R200 280Z should be physically much larger.
> I would assume the 3.364:1 ratio for the
> R180, since that is what most of them are,
> unless someone planted a R180 from a mid
> 80's 4wheel drive into your car, which is in
> my opinion, highly unlikely.

> If you do have the 280Z 5spd, then you need
> a 3.545 R200 or higher.
> If you have the 280ZX 5spd, then you need a
> 3.9 R200 or higher.

> The higher above the base figure will give
> you higher overall ratios, which will help
> in acceleration, but will raise your rpm
> while cruising on the highway. It's up to
> you to decide which way you want to go.

> By the way, I've noticed the manuals, even
> Haynes are somewhat vague in this area, and
> are not entirely accurate. Afterall, these
> manuals are British publications, and Europe
> spec cars often have different parts and
> requirements than US cars.

Dave,
The 77-79 5-spd's had the .864 OD you described. The '80 model had the newer 5-spd 1st & 2nd gearing but had a .777 OD. The 81-83's had the .745 OD.
Just to add a little more confusion to the equation.
Phantom