| Author |
Message |
    
brian friend
| | Posted on Monday, July 22, 2002 - 10:53 am: | 
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Has anyone here geared down to 4.75? I have 265/75 on right now and I have broken my front ring gear and am trying to decide between 4.19 and 4.75 gears. My concearn with the 4.75 is highway driving---will I be able to go the speed limit with my little baby tyres?
brian friend |
hendrik
| | Posted on Monday, July 22, 2002 - 11:18 am: |
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@4000rpms you will be 140km/h fast (equalling 87mph - with 1mile=1.609km).
Or:
@100km/h (=62mph) you will have about 2900 rpm.
(provided you have a Disco I with auto)
FMO much too short geared. Take 255/85-16 tires giving you 146km/h @ 4000rpm. Still too short.
Go for the 4.11 ratio (Even that is a neglectable little lower geared than stock. And I don´t see there´s much wrong with the stock ratio). |
RVR OVR (Tom)
| | Posted on Monday, July 22, 2002 - 02:15 pm: |
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I agree. 4.75's are overkill unless you go with 35's or modify your transmission gearing. Even folks with 35's run 4.11's with success.
4.11's and 265/75's were very nice. A little high revving on the highway, but great added power around town.
Tom |
hendrik
| | Posted on Monday, July 22, 2002 - 03:23 pm: |
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Well, if thinking about transmission changes:
putting the 1.003:1 hig range gearset into the t-box (speaking of the LT230; Ashcroft say the gears [originally designed for the 3speed Chrysler automatic box Range Rovers - first Rover to have the LT230, with R suffix rather than the later T suffix] will fit and set you back 350$) together with the 4.75 diffs and the 265/75-16 will give you exactly the stock ratio in high range (while having a VERY low low range).
(If cost and effort is secondary) |
RVR OVR (Tom)
| | Posted on Monday, July 22, 2002 - 04:59 pm: |
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If you are going to mess with the trans, wouldn't you just do it all there? Not being argumentative, just discussing. 
Tom |
Sean Hanagan (Seanh)
| | Posted on Monday, July 22, 2002 - 11:25 pm: |
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Let me guess, IRON CHEST? Dude you realy need a more capable vehichle. I know how about a Defender!!HeHe. I would go with 4.10's if I were you. 4.75's would be like cruising up 24 at 65mph in 2nd gear. What's the plan for this Wed? |
Nathan Hindman
| | Posted on Monday, July 22, 2002 - 11:34 pm: |
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Brian,
I had 4.75s on my 90 and unless I was running 35s I thought the gearing was too tall. When I ran 33s the revs would be at about 3000 RPM at highway speeds. To pass another vehicle you're looking at extended revs to 4500+ IMO- that's a lot of stress to put on an engine.
I say stick with the 4.10s. They're much more liveable, and the ring gear is stronger to boot...
My 2¢
Nathan Hindman
http://www.PangaeaExpeditions.com |
CEJB
| | Posted on Tuesday, July 23, 2002 - 12:45 am: |
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4.75s also take perhaps too much metal out of the gears reducing strengyh. 4.1 is about as far as I'd be tempted to go |
nadim
| | Posted on Tuesday, July 23, 2002 - 08:58 am: |
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I have the 4.7 (47x10, where did we get the 4.75?). Anyways, with other stock gears, and 32"s, it is slow, and fuel economy somewhat suffered. The reason I went with 4.7s is because they are very abundant and cheap in Lebanon (75$ a set), and I plan on installing 35s.
Performance onthe street is very limited. Rock Crawling...(Y)...wow... |
Blue (Bluegill)
| | Posted on Tuesday, July 23, 2002 - 12:15 pm: |
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Nadim, it's a 38 X 8 ring & pinion setup
http://greatbasinrovers.com/rpgears.html#4.75 |
nadim
| | Posted on Wednesday, July 24, 2002 - 03:20 am: |
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Going less that 10 on the Pinion is not a good idea in my opinion. Having 10 is a wee bit edgy.
Ultimately, it depends on tire size, and where you are going to wheel: +33's, then 4.7; rocks, then 4.7... |
hendrik
| | Posted on Wednesday, July 24, 2002 - 10:49 am: |
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the 4.75 has 8x38 teeth.
the 3.54 has 13x46 teeth therefore a bigger and stronger pinion gear.
the 4.7 isn´t quite as strong as the 3.54
It seems contradictory that the 4.75 should be stronger that the 4.7 but the manufactureres (KAM or Ashcroft) say so. Maybe the pinion is larger in diameter and the teeth (and tooth contact area) ist better with it. |
brian friend
| | Posted on Wednesday, July 24, 2002 - 01:22 pm: |
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Has anyone here actually had a problem breaking 4.75 gears?
brian friend |
Nathan Hindman
| | Posted on Wednesday, July 24, 2002 - 06:29 pm: |
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I've sort of had a problem with the gears. Actually the guy that I sold my 90 to was going up Rocker Knocker locked F/R (with 35x12.50 SSRs). Stripped the front ring gear.
Thanks,
Nathan Hindman
http://www.PangaeaExpeditions.com |
Ho Chung (Ho)
| | Posted on Wednesday, July 24, 2002 - 06:34 pm: |
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nathan, were those the old series gears? |
Blue (Bluegill)
| | Posted on Wednesday, July 24, 2002 - 07:23 pm: |
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yeah, some vendors sell ancient 4.7 stock Series Rover gears as an "upgrade" to your Disco 3.54 gears. Great Basin's 4.75's are much different than salvaged Rover 4.7's. |
RVR OVR (Tom)
| | Posted on Wednesday, July 24, 2002 - 11:06 pm: |
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Ho - you thinking of 4.75's?
Tom |
\Mike... (Mpeters)
| | Posted on Thursday, July 25, 2002 - 01:13 am: |
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yeah, ho - and maybe some 35's to go with them?
/mp |
nadim
| | Posted on Thursday, July 25, 2002 - 03:47 am: |
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My 4.7s came out of Series Land Rovers, and they are very stout. I have broken alomst everything (before the ARB/HD axles) excpet these R&P. Stcok came with 13, I guess 10 is ok. You will need an ARB RD03A spacer for them tough! |
hendrik
| | Posted on Thursday, July 25, 2002 - 05:00 am: |
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usually the halfshafts go first.
But for someone after a bulletproof setup the 4.7 is not the right choice.
Take an old 109" LandRover and chase it up a hill. When the front axle "takes off" stay on the acc-pedal. When the tires come into contact with ground again chances are good the 4.7 teeth are being damaged.
But it might not only be the R/P that are guilty. The standard diff carrier is not very strong and flexes under above shock loads. As consequence the pinion pushes the ring gear away from itself -> the teeth contact is only at the tips that are easily broken then. Ashcroft once made a brass block that was screwed behind the ring gear (opposite side of the pinion) so this could not happen (maybe mor common in bigger truck-diffs).
All the diff locks like ARB are stronger and do not allow that much flex. Could be the 4.7 will not fail with them. |
Greg Davis
| | Posted on Thursday, July 25, 2002 - 09:22 am: |
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So Series R&P's will work w/ Disco carriers? Including the DSII's? Inquiring minds want to know. I just installed a Detroit and TT, and am always keeping my eyes out for a deal on R&P's. If this is true, with my upgraded diffs, would the R&P's hold up w/ 33's? |
hendrik
| | Posted on Thursday, July 25, 2002 - 09:48 am: |
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as said a distance ring is needed (the 3.54 ring gear is thicker than the 4.7.
Can´t give a guarantee, but maybe the following helps.
I once owned a LandRover with 4.7 diffs and 10spline standard Range Rover axles and 255/85 (in diameter equivalent to 33") tires. Haven´t been much offroad but had no problems with it (Tdi-powered). I chose to do like the Willys engineers, who in the early 40s put the GoDevil 2.2l engine on a bench and let it run at operating rpms. things that blew up were uprated and the test repeated, I think: certainly an option to start with cheap 4.7 second hand diffs and wait for them to break before spending more money. |
Kyle
| | Posted on Thursday, July 25, 2002 - 09:50 am: |
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THose R&Ps are pretty weak Greg. SKip it.....
Kyle |
Nathan Hindman
| | Posted on Thursday, July 25, 2002 - 12:32 pm: |
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Ho,
No, my gear problem wasn't with the series 4.7s. It was a set of 4.75s.(GBR HD R&Ps, 8 x 38 tooth count)
Nathan Hindman
http://www.PangaeaExpeditions.com |
brian friend
| | Posted on Thursday, July 25, 2002 - 01:26 pm: |
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gbr 4.75 will not fit in the carrier out of he box?
brian friend |
Ho Chung (Ho)
| | Posted on Thursday, July 25, 2002 - 01:58 pm: |
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nathan, now you got me scratching my head. |
Kyle
| | Posted on Thursday, July 25, 2002 - 02:05 pm: |
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Any of them can break. The series gears are just more prone... Like that throttle do ya Nathan ??
Kyle |
Nathan Hindman
| | Posted on Thursday, July 25, 2002 - 04:06 pm: |
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Kyle,
I'm actually pretty gentle with the throttle. Since swithing from the 90 to the Disco, I've taken taken a much more conservative approach to obstacles and offroad.
But you'll note that I said the guy who I sold the 90 to stripped the ring gear, not me.
Nathan Hindman
http://www.PangaeaExpeditions.com |
Nathan Hindman
| | Posted on Thursday, July 25, 2002 - 04:09 pm: |
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Ho,
No worries. The R&P that I put in was GBR part number: GBRCWP475
It's the "4.75 Heavy Duty Gears" about halfway down the page. Although I suspect the "heavy duty" designation was just to differentiate them from the 4.7 series gears...
Nathan Hindman
http://www.PangaeaExpeditions.com |
Nathan Hindman
| | Posted on Thursday, July 25, 2002 - 04:21 pm: |
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Whoops, forgot to add the page link:
http://www.greatbasinrovers.com/rpgears.html
Nathan Hindman
http://www.PangaeaExpeditions.com |
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