Whats with the different ratios?

Northern Irelander · Apr 23, 2008

Been looking at an IRD overhaul,

The IRD ratios changed in 2001-02,

Old IRD ratio - 1.458:1
New IRD ratio- 1.467:1 *(every Freelander from VIN YA999999)

Some of the early FL have different final drive ratios as well:

Petrol engine - 4.200:1
L-series eng - 3.647:1
Td4 engine - (manual) 3.182:1, (auto) 2.910:1

Howcome the different ratios between the petrol and L-series???, both have PG1 gearboxes, same IRD unit etc

Some new ratios >2001:

IRD input shaft to IRD countershaft - 0.828:1
IRD countershaft to front driveshaft - 1.762:1
IRD countershaft to prop shaft - 0.553:1

IRD ratio > 2001

Td4 - 1.467:1
1.8 - 1.467:1
KV6 - 1.359:1

Can anybody explain these differences between models?

mackd0001 · Apr 23, 2008

I would think the different ratios are because of the different torque outputs of the engine

JonS · Apr 24, 2008

The Ashcroft transmissions site suggests that the reason for VCU seizure is down to an excessive difference in ratios between the ird and the rear diff. And that later models improved matters. In fact I was about to ask when exactly this happened. Maybe thats what we are seeing here?

Jon

Northern Irelander · Apr 24, 2008

JonS said:
The Ashcroft transmissions site suggests that the reason for VCU seizure is down to an excessive difference in ratios between the ird and the rear diff. And that later models improved matters. In fact I was about to ask when exactly this happened. Maybe thats what we are seeing here?

Jon

Yeah thanks, we have known about the VCU locking and constant slippage for sometime on LZ. It was a fudged job by LR, hence the new IRD ratio to solve the problem.

However the differences between the engine models I dont get?

You would think that you could swap the second hand diff/IRD between models, obviously not.

Although they dont state these ratios on the Ashcroft site or anyone else selling them for that matter

G13SJC · Apr 24, 2008

I understood Final drive to be calculated from the differential inside the PG1 gearbox.

I would guess that they fit a different diff - like they do in the 21 combinations of PG1 for Rover models.

The rear diff (TVK100380) is the same for both petrol and diesel models.

Regards,

Steve

Northern Irelander · Apr 25, 2008

G13SJC said:
I understood Final drive to be calculated from the differential inside the PG1 gearbox.

I would guess that they fit a different diff - like they do in the 21 combinations of PG1 for Rover models.

The rear diff (TVK100380) is the same for both petrol and diesel models.

Regards,

Steve

Cheers, some of that info in the OP was from an article you sent me last year.

Yeah too right about the Rover ratios, hard to believe that the MGF has a higher top speed than the Lotus Elise all down to gear ratios , yet the Lotus gets to 60 in Much quicker time and it goes round corners

Im thinking............ light bulb fizzles out, how interchangeable are the gearboxes, diff and other components between the early disesels and the 1.8

Surely it shouldnt have an adverse effect on the driving ability of the FL

G13SJC · Apr 25, 2008

Should be able to swap components about between petrol PG1 freelanders and Diesel PG1 freelanders.

Rover diffs wont fit due to the IRD splined drive being larger than the standard driveshaft spline size.

I think mine is way too low - im in third at 30 and fourth / fifth at 40. First is a waste of time - but could be useful if towing / pulling heavy objects.

I guess a 3.9:1 gearbox diff would be a good compromise, but unsure of availability.

Did i send you a whole list (word doc) of gearbox data?? If not PM your email address again matey.

Regards,

Steve

Northern Irelander · Apr 28, 2008

Was doing an inspection on the IRD at the weekend, the pinion looks fine, no obvious wear.

I changed the IRD oil around 8k miles ago, when I drained the oil it was as good as the day it went in. No swarf on the magnetic plug, a little bit of metal dust but thats about it.

Sort of puts my mind at rest that its just a bit of slack in the bearings.

Pics below.

Northern Irelander · Apr 28, 2008

Sorry to save you tilting your head to the left lol

Note the ratio numbers stamped on the pinion:

21/38 - 90

tank93 · Dec 7, 2009

Northern Irelander said:
Sorry to save you tilting your head to the left lol

Note the ratio numbers stamped on the pinion:

21/38 - 90

What exactly is ratio 21/38 - 90? What does it mean or relate to?

Hear a lot of talk on here about the IRD ratio's changing on later models. What exactly changed internallly to the ird to make it different from early models? For instance is it the diff inside the IRD that changed?

edge · Dec 7, 2009

Dont know much about ratios but my old 98 Freelander seemed slightly higher geared than my current 53 plate.
first is only good to get you rolling on the road pulls well on lanes though

Northern Irelander · Dec 7, 2009

tank93 said:
What exactly is ratio 21/38 - 90? What does it mean or relate to?

Hear a lot of talk on here about the IRD ratio's changing on later models. What exactly changed internallly to the ird to make it different from early models? For instance is it the diff inside the IRD that changed?

Well excuse me Tank!

I aint a gearbox specialist, that's why I asked the question.

like many enthusiasts on here.......on a fookin steep learning curve and probably give the professional garages a run for their money when we get to grips with the task in hand.

If you're not happy with the content, or don't have anything good to say.......then say nowt!

Is the search facility still down?

It is written on here, what IRD ratios changed > 2001
Might even be on the Ashcroft site and Bells.

I don't have a new IRD, so have listed the ratio 21 teeth on the older pinion, hoping that someone will do the same for the newer type. hint hint

tank93 · Dec 7, 2009

I was merely asking a question not criticising so I dont know what you are getting so upset about.

Anyway your post is making me.... :yawn:

freelance · Dec 10, 2009

1.8 fairly locally has had a mgf box fitted by way of replacement, driveshafts were changed so its 2wd only, says that 70mph at 1000 less engine revs and at least 25% better on fuel consumption, some of it must be down to final drive ratio being different.

Northern Irelander · Dec 10, 2009

freelance said:
1.8 fairly locally has had a mgf box fitted by way of replacement, driveshafts were changed so its 2wd only, says that 70mph at 1000 less engine revs and at least 25% better on fuel consumption, some of it must be down to final drive ratio being different.

Thanks Freelance, whats the speedo like?

I have all the ratios from the PG1 box, courtesy of G13SJC, they are listed all over the MG-Rover site, plus Powertrain Ltd (RIP) who made the PG1 have the figures listed in their brochure (their website is now obsolete since 2005, I have a pdf copy)

The MGF box and FL1 1.8i box have the same final drive ratio of 4.2 (15/63)

The ratios are the same in 1st and 2nd, it is 3rd 4th and 5th with different ratios.

MGF
1st 3.250 (12/39)
2nd 1.894 (19/36)
3rd 1.307 (26/34)
4th 1.033 (30/31)
5th 0.848 (33/28)

FL1 1.8i

1st, 2nd as above
3rd 1.222 (27/33)
4th 0.848 (33/28)
5th 0.648 (37/24)

PG1 box codes

FL1 = S4EM

MGF 1.8 VVC = G4BSV

MGF 1.6, 1.8i = G4BPF

G13SJC is familiar with splitting the box down, he says the differential between a Rover box and FL1 won't allow for a straight swap of the IRD/ standard driveshaft

freelance · Dec 13, 2009

looks to me like mgf ratios are actually slower than freelander, therefore would expect revs to be higher at any given speed, especially as mgf wheels smaller in dia, it points to speedo being way out after box change,

Whats with the different ratios?

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