Author Topic: Diff Gear Ratios  (Read 111 times)

KChromick

  • Newbie
  • *
  • Posts: 7
  • Vehicle: 1995 Land Rover Discovery 1 1997 Land Rover Discovery XD
Diff Gear Ratios
« on: December 06, 2018, 11:06 AM »
Installing a set of air lockers with new gears on my 97 Discovery 1, Anyone have any experiance with 4.75:1 ratios on their diffs? Im running a 305/70/16 which is a 33". If it revs out on the highway i guess i just have to do 35's..
Was mainly wondering if anyone had run KAM products.. wanted to get a review.

Trevor

  • Club Member
  • *****
  • Posts: 934
    • Boogie baby
  • Club Membership: Yes
  • Vehicle: 1998 Defender 110 Camel Trophy; 2004 Disco 2 G4
Re: Diff Gear Ratios
« Reply #1 on: December 06, 2018, 03:51 PM »
I've not run KAM products before, so I cannot offer any insight there. Ashcroft and GBR throughout my drive train.

Regarding gearing I was running 4.11's in my D2 w/ 33's. It was ok, not great, not problematic per se on the highway. But the D2 will likely have a slightly higher geared t-case in high range as well than your D1.

I've since moved to a set of 35" tires and went with GBR's 5 to 1 low range t-case gear set. I'm REALLY happy with this configuration. It runs really well on the highway with the 4.11's and 35" tires with the revs sitting in a reasonable range and lots of power available. With the 5-1 ratio in low range its right where I want it for rock crawling down in Moab as well. I'm quite happy with setup as it gives me the best of both worlds. 
“Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe.”

― Frank Zappa

brendan leier

  • Club Member
  • *****
  • Posts: 33
  • Club Membership: Yes
  • Vehicle: 92 Disco tdi
Re: Diff Gear Ratios
« Reply #2 on: December 06, 2018, 03:57 PM »
Your truck looks great! I just put tall tires on my disco 1 and a trutrac in the rear. I don't feel like I need a lower ratio but my truck is a manual TDI. In my own research  however I didn't find that lower ratio sets were a popular upgrade for daily drivers, more for comp vehicles.  Prairie offroading typically requires many miles of highway before playtime.  It might actually be simpler to put a defender transfer case on your truck as they are lower ratio.  I know it was common to put disco transfer cases on defenders to make them a little better on the highway.

Red90

  • Administrator
  • *****
  • Posts: 1295
  • Club Membership: Yes
  • Vehicle: 1991 D90
Re: Diff Gear Ratios
« Reply #3 on: December 06, 2018, 04:12 PM »
35s won’t help. It is only a few percent. They also require lot of body removal.

Going to. 1:1 transfer ratio is the easiest path.

Don’t do KAM. They went under a couple of years ago. What was left was bought by Terrafirma and it is garbage.

Trevor

  • Club Member
  • *****
  • Posts: 934
    • Boogie baby
  • Club Membership: Yes
  • Vehicle: 1998 Defender 110 Camel Trophy; 2004 Disco 2 G4
Re: Diff Gear Ratios
« Reply #4 on: December 06, 2018, 07:20 PM »
They also require lot of body removal.



I'll second that. If you don't want to do a lot of cutting, 35's aren't for you. I have a 3" Rovertym lift (which is actually a 4") and I still had to cut a lot. Could still cut some more actually, but my snorkle is in the way.
“Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe.”

― Frank Zappa

binch

  • Club Admin
  • ******
  • Posts: 1714
  • Club Membership: Yes
  • Vehicle: 110, RRC, D11
Re: Diff Gear Ratios
« Reply #5 on: December 06, 2018, 08:05 PM »
Sounds like fun!

But I'll be the voice of experience on the KAM products.....I bought a set of rear axle shafts a few years back, to go in when I put the Detroit in the Salisbury diff.   When I did my research at that time KAM had just been through a spout of bad products and their reputation was damaged.   However, they were taken over by a new group when I bought my axles shafts and they had done a complete reversal of the quality control in an effort to land a MOD contract.    They testing done at that time of their new management showed the KAM shafts to be every bit as good as the Ashcrofts.   But the damage to their reputation was done already.   They did get the contract in the end and I didn't really follow them too long after I got my stuff.   Now that was a good 6 or 7 years ago now....but the axle shafts are still on my truck and I've had no issues with them.  I'm happy with what I got.

I had a truetrac installed in the front this fall and had strengthened shafts install this time too.  But since Britpart was carrying Ashcroft stuff at the time I bought a set of theirs front axles, for no other reason then they were more convenient for me to get this time around.

In the end...I'm happy with my KAM axles just as much as my Ashcrofts...but give me a few years and we'll see how things play out ;-)
Cheers, Bill

Red90

  • Administrator
  • *****
  • Posts: 1295
  • Club Membership: Yes
  • Vehicle: 1991 D90
Diff Gear Ratios
« Reply #6 on: December 06, 2018, 08:09 PM »
Yes but KAM was then bought by Allmakes and stripped.  They basically folded last year and are being strung along with none of the people that did the design work.
« Last Edit: December 06, 2018, 08:16 PM by Red90 »

binch

  • Club Admin
  • ******
  • Posts: 1714
  • Club Membership: Yes
  • Vehicle: 110, RRC, D11
Re: Diff Gear Ratios
« Reply #7 on: December 06, 2018, 08:16 PM »
yup, you are correct...they are no more :D
Cheers, Bill

KChromick

  • Newbie
  • *
  • Posts: 7
  • Vehicle: 1995 Land Rover Discovery 1 1997 Land Rover Discovery XD
Re: Diff Gear Ratios
« Reply #8 on: December 06, 2018, 10:11 PM »
Ive had nothing but good luck with terrafirma. I would  not recommend their springs but everything else ive installed on customer cars have been great. As far as gearing you get about the same from doing the diffs as you would doing the tcase,  my tcase is quite so ill leave it the way it is, where as my diffs have some slop. The KAM product from what ive heard from some rover guys in the UK have been great. I guess ill be the judge of that when i throw them in. The lift im doing is a 4 inch spring lift with a 2 inch body lift, ive got some old QT services stock that are adjustable front and rear trailing arms so i plan on pushing the axles apart abit to re-centre them in the wheel arches. As well i also have an Adjustable upper link for the rear diff which will help keep the pinion angle in its spot. Ill do a good write up once everything is installed and proper and aligned.

Red90

  • Administrator
  • *****
  • Posts: 1295
  • Club Membership: Yes
  • Vehicle: 1991 D90
Re: Diff Gear Ratios
« Reply #9 on: December 07, 2018, 07:28 AM »
As far as gearing you get about the same from doing the diffs as you would doing the tcase...

The diff affect both high and low range.  Changing the transfer case ratio only affects the high range.  It is also a much easy job.

I'm serious about not using KAM.  I know people that were involved in the company.  It used to be great.  It was then bought and stripped and all the knowledgeable people were fired.  The parts quality is very suspect now and there will be no future support.  You want to avoid them like the plague.  GBR or Ashcroft are the easiest quality options for people in Canada.  There are other options, but they are not convenient.

KChromick

  • Newbie
  • *
  • Posts: 7
  • Vehicle: 1995 Land Rover Discovery 1 1997 Land Rover Discovery XD
Re: Diff Gear Ratios
« Reply #10 on: December 07, 2018, 09:15 AM »


"The diff affect both high and low range.  Changing the transfer case ratio only affects the high range.  It is also a much easy job.

Having a lower low gear really is not a bad thing at all. The setup im going with now will return the gearing pretty much back to stock which is what i want.  Ive been in alot situations on steep slopes where the low gear in the tcase with the bigger tires still isnt low enough, or ive been in situatuons where crawling just isnt an option and you need some throttle with RPM and as youre going your watching you RPM bog out. where as if i had stock 29" tires i would be able to get by easily and drag my diffs across everything. By the time the truck is fully loaded, with that size of tire, that poor 4.0L v8 barely does it. As i said, ill let you guys know how the KAM gears go, for the price i get i can afford to experiment.

Red90

  • Administrator
  • *****
  • Posts: 1295
  • Club Membership: Yes
  • Vehicle: 1991 D90
Re: Diff Gear Ratios
« Reply #11 on: December 07, 2018, 01:12 PM »
Okay, I'm confused.  I thought that you currently have 4.75 diff ratios and you run out of revs on the highway and are looking for a way to lower the revs on the road.

My suggestion (1:1) high range gears with the 4.75 diff gears and 33" tire would put you geared exactly the same as stock in high range.  Low range gearing would stay exactly as it is now (15% lower than stock).

What exactly are you planning to do?

KChromick

  • Newbie
  • *
  • Posts: 7
  • Vehicle: 1995 Land Rover Discovery 1 1997 Land Rover Discovery XD
Re: Diff Gear Ratios
« Reply #12 on: December 07, 2018, 01:54 PM »
Im installing front and rear lockers and installong new gears thats are 4.75:1,  next season im installing 35s. My original post was asking if anyone was running the 4.75:1

Red90

  • Administrator
  • *****
  • Posts: 1295
  • Club Membership: Yes
  • Vehicle: 1991 D90
Re: Diff Gear Ratios
« Reply #13 on: December 07, 2018, 02:00 PM »
The better option is to change the low range gearing.  You keep the highway gearing and don't end up with weak ring and pinions.  I assume you are planning for chrome-moly halfshafts and CV joints.

KChromick

  • Newbie
  • *
  • Posts: 7
  • Vehicle: 1995 Land Rover Discovery 1 1997 Land Rover Discovery XD
Re: Diff Gear Ratios
« Reply #14 on: December 07, 2018, 05:01 PM »
On the highway as it sits, the rpms at 110km/h the revs sit to low, down shift and the sit to high. Your not in a good comfort band for highway cruising. The diff ratios will fix both the high, and low gear issues. Strength wise for the pinion though, a smaller gear ratio wont effect the strength. It will effect the wear though. The pinion shaft on a 3.54:1 and 4.75:1 are the same thickness, just one has less teeth.