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Gear ratios?

TNR

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Assuming you really have 275/35r15 tires.. Which are actually 22.6" tall... 2900 rpms may be correct..

assuming .78:1 for top gear (.75 for a4ld, .78 for 5 speed manual)...

3000 rpms with a Rear Diff of 4.10 with a trans gear ratio of .78 and transfer case in high range (1:1) would be 63mph...
3000 rpms with a rear diff ratio of 3.73 and all else above being the same would be 69mph...

Now, if you really have 235x75r15 which is a 28" tall tire.....
3000 rpms with a rear diff of 4.10, trans gear ratio of .78 and transfer case in high range (1:1) would be 78.2mph...
the same with 3.73 would be 85.9mph..
the same with 4.56 woudl be 70.3mph

BUT, if your not going into OD (assuming an auto tranny).. you would have the following..
3000 rpms, 4.10 gears 28" tire-->61mph
3000 rpms, 3.73 gears 28" tire --> 67mph
3000 rpms 3.27 gears 28" tire --> 76.5mph
I did not figure it for 22" tires since I doubt thats what you really have (and the speed would be mucher lower than for the 28" tire)..

Soo, in short.. It looks like your are either not going into OD, or lockup is not working (with an auto tranny).. If your a manual tranny, You would have to have 4.56 gears (which is not an available stock gear ratio)

BTW.. to help figure the numbers I used http://www.4lo.com/calc/gearratio.htm I filled in the tire diameter, diff ratio, rpms, and set the transmission ratio to either .78 (for od) for 1 (for no od and the transfercase ratio to 1 (high range).

Sorry, yeah, Im sick with some flu type cold right now and not thinkin straight.

Let me turn my brain on..

yes, 235/75 R15, 5 Speed... I checked a few diff speeds on the highway this eve, at 65mph, it's around 2894rpm. But there seems to be very little difference between 60-65 when it comes to engine rpm (only about 150 -200 rpm or so.)

The reason I ask, is I'm *terrible* with numbers and ratios and such.

I guess Im looking for someone to say "thats normal, or your gears are spanked" :)

Im assuming when you say "no od" you mean the 5 speed?

When I put that all into the calc...

Tire:28
Diff: 3.73
RPM: 3000
TransRatio:1:1
TransferCase:1:1
I get 67mph

Thats about what my truck is doing.. 2900 rpm or so, at around 65mph.
One time I had to do about 85 for short period, and it sounded like the thing was about to blow up on me. Is there any way to regear for a better rpm range at highway speeds?
 


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TheFox88

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Which gear was this in? What is your rear axle ratio? We need a little more info to be able to tell.
 




TNR

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TheFox88 said:
Which gear was this in? What is your rear axle ratio? We need a little more info to be able to tell.

5th gear, and Im not sure what the ratio is, according to the calc http://www.4lo.com/calc/gearratio.htm it should be 3.73 (I think)

These things are what I am trying to determine. I didn't do anything with the case/tranny/rearend.. I'm trying to determine if I should :)
 




alexefron

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the m50d's 5th gear (od) is .79:1 i believe. 3.73 etc is your axle ratio. With my m5od and 3.27 rear end i do about 2100 rpms at 65mph.
 




TheFox88

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alexefron said:
the m50d's 5th gear (od) is .79:1 i believe. 3.73 etc is your axle ratio. With my m5od and 3.27 rear end i do about 2100 rpms at 65mph.
I'm also right around 2100 RPM's . Also, you can use the axle code on the door jam to find out what ratio rear end you have. Just take the number and plug it into the search here along with axle code.
 




hiridin

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is it 4x4 by chance? maybe someone lifted it... swapped gears to 4.56's and then took the lift and tires off. otherwise i don't see why the rpms would be soo high. i don't even run close to that high at 65mph and i'm geared pretty low. has it always been like this? ofcourse i don't know much about this stuff. so there could be a reasonable explanation other than that.
 




TNR

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TheFox88 said:
I'm also right around 2100 RPM's . Also, you can use the axle code on the door jam to find out what ratio rear end you have. Just take the number and plug it into the search here along with axle code.

Ok, the door says Axle code 45.

Forums say:
45 - 3.55 non-limited slip (Explorer/Mountaineer)

And yes, it is a 4x4.
Here's the rundown.
1991 XLT 4 door, 4L-6cyl, 4x4, Manual, 235/75/r15 tires

2900RPM at 65mph.

Any ideas? It's been like this since I've had it and I gotta say, you think gas prices are bad? Sheesh. Don't complain at 2100 rpm. :)

If you all think it would help, I'd be more than happy to make a video of what it does and up it to my server.... would that increase the odds someone could help me figure it out?
 




TheFox88

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The video might help. You are in fifth when its at 2900 rpm's right? If you were in fourth, it might be that high of rpms. I think that whoever said that you might have lower gears was probably right. But, you can look at this from the bright side, you can now lift and put bigger tires on without having to worry about regearing. :D We just have to figure out what gears they are and make sure you don;t have a problem with your tranny/t case that would be doing this. Keep us informed.
 








hiridin

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TheFox88 said:
, you can look at this from the bright side, you can now lift and put bigger tires on without having to worry about regearing.QUOTE]

:thumbsup: cuz if thats the case u could put a inexpensive lift (body lift or something)... 33's and right there u'd be lifted geared AND yer gas mileage would go up. and it could still be cheaper than paying someone to redo yer gears
 




Creager

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Check to see if the tag is still on the diff cover.

This is a manual tranny right? The 1:1 gear is 4th.

I have 4.56 on 32"s, which is equivalent (pretty close, .03 off) to 4.10's on 29" (~235/75 R15) tires.

4th gear i hit around 3400~3500RPM @ 65 MPH

5th gear i hit around 2700-2800RPM @ 65 MPH

5th gear i hit around 3000~3100RPM @ 70 MPH

Maybe someone did swap in 4.10's before? Count the teeth on the gears.
 




CodePoet

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If you want to be sure, open the rear diff cover, count the number of teeth on the ring gear, then the pinion. Divide the two and you have your ratio ;)

Not too hard, and you could probably stand to change the diff fluid anyway :D
 




TNR

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CodePoet said:
If you want to be sure, open the rear diff cover, count the number of teeth on the ring gear, then the pinion. Divide the two and you have your ratio ;)

Not too hard, and you could probably stand to change the diff fluid anyway :D

Easier said than done.
My truck gets parked on hill covered in mud and gravel. I have to drive it down to the street to jack it up, and the icing on the cake.. its illegal to jack up a car on the street except to change a flat tire. (Im still cooling from the argument I had to with the officer the other day when I was trying to figure out what went wrong with the manual hubs. However, Im not a person to bitch and not try suggestions, but it might take a few, so hang in there, I'll let you know when I do this. Oh and when I do, what is a good way to mark my starting tooth? Will chalk mark it good enough?

Thanks :)
 




TNR

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hiridin said:
TheFox88 said:
, you can look at this from the bright side, you can now lift and put bigger tires on without having to worry about regearing.QUOTE]

:thumbsup: cuz if thats the case u could put a inexpensive lift (body lift or something)... 33's and right there u'd be lifted geared AND yer gas mileage would go up. and it could still be cheaper than paying someone to redo yer gears

On that line of thinking, got any ideas for inexpensive body lifts for it?
 




hiridin

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any body lift is only going to be like $100 for a 3" for your year truck. if u do it yourself... otherwise yer looking at like probably $500 for everything. which makes it alot more expensive
 




TNR

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hiridin said:
any body lift is only going to be like $100 for a 3" for your year truck. if u do it yourself... otherwise yer looking at like probably $500 for everything. which makes it alot more expensive

Are you serious? I was thinking like 500 dollars DIY.
100 I can live with!

Any specifics?
 




Creager

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TNR said:
Are you serious? I was thinking like 500 dollars DIY.
100 I can live with!

Any specifics?

are you 5-speed? auto tranny?

do you like your bumpers? i say this because it will be a chore to make them look 'right' again, since the body lift uses brackets to raise the bumpers up level with the body. a Sawzall and a die-grinder will do the job of making them right... (a torch and a drill press would be better)

then you gotta add in wheels and tires

Rockcrawlers = $50 bucks a wheel
32x11.50 Kumho MTs = $115 bucks a tire

and since you practically already have gears installed, i'd say you would be a happy camper at this point... but dont forget a locker!

Aussie locker = $229 for the rear + 2.5 quarts of gear oil and some silicone.
 




hiridin

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Creager said:
are you 5-speed? auto tranny?

do you like your bumpers? i say this because it will be a chore to make them look 'right' again, since the body lift uses brackets to raise the bumpers up level with the body. a Sawzall and a die-grinder will do the job of making them right... (a torch and a drill press would be better)

then you gotta add in wheels and tires

Rockcrawlers = $50 bucks a wheel
32x11.50 Kumho MTs = $115 bucks a tire

and since you practically already have gears installed, i'd say you would be a happy camper at this point... but dont forget a locker!

Aussie locker = $229 for the rear + 2.5 quarts of gear oil and some silicone.

i believe he's got the 5 speed in there. so ya with the body lift... wheels/tires and even the locker yer looking at about how much a gear swap would cost. only you'll end up with a lifted much more capable truck. the install on the locker... well thats going to cost you extra$$$ or maybe u could do it yourself (maybe) but i considere it well worth it since its night and day difference what u can do offroad with it. on a side note, still need to figure out exactly what gears are in that thing. make sure it has different gears installed and not something serious.
 




TNR

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TNR said:
Ok, the door says Axle code 45.

Forums say:
45 - 3.55 non-limited slip (Explorer/Mountaineer)

And yes, it is a 4x4.
Here's the rundown.
1991 XLT 4 door, 4L-6cyl, 4x4, Manual, 235/75/r15 tires

2900RPM at 65mph.

Any ideas? It's been like this since I've had it and I gotta say, you think gas prices are bad? Sheesh. Don't complain at 2100 rpm. :)

If you all think it would help, I'd be more than happy to make a video of what it does and up it to my server.... would that increase the odds someone could help me figure it out?

Sorry, this morning all I had was my camera phone. I'll get more detailed stuff later..

Here's speedo/tach at the speeds in question:

http://explorer.oscllc.com

under the "gearing" directory.
 


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hiridin

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the way its reading its like u have 4.56 gears on yer 29" tires... from i can figure out. out of overdrive going 65mph yer at like 3400 rpm's u put it in overdrive and it should drop atleast 15%. which will put u at yer 2900 rpm's. so thats how it appears to me. jus seems kinda weird it would be like that :confused: lucky in a way if thats the case but strange no one let u know about it when u bought it...
 




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