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2000 jimmy 4x4, brakes dragging/bad mpg

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Old 06-18-2008, 08:58 PM   #1
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2000 jimmy 4x4, brakes dragging/bad mpg

Welp i was checking everything over today and noticed that my brakes drag, mostly my front from what i could tell with it jacked up in park, rears seem to have resistance also.

but the front you can hear drag the rotor which is warped. you can feel that when stopping most of the time, it will have a spot that just catches and makes it stop harder on that spot everytime the brake pad hits it.


would this be a major cause of my mpg issue?

ive gotten mostly 15mpg averages, one was 13.5 and one mixed highway was 16.5

sounds like the numbers are way lower than everyone else is saying 22mpg highway blah blah.

i have 235/75/15? stockers that i beleive are 29" tall, 3.73 gears and auto, i accelerate slow and slow down ahead of time for stop lights so im not abruptly slamming on brakes.

its got 89,000 miles on it and it idles at about 600rpm in drive, in park it idles at i beleive 1000 and will slowly drop to about 800.

i took the roofrack off, antanae, 4wd towhooks and a few other small things along with uncranking the torsion bars to lower it 1" up front.

check engine light isnt on and it drives fine, but the mpg says it needs some love.

i dont have a job at the moment (suicide attempt from work stress) so i dont want to spend $700 on o2 sensors to find it makes no diffrence

my dad is going to get me new brake pads and help me change those/check brakes to see what the deal is.

what else is there to do to improve mpg? i cut the bottom of the airbox off for some better airflow, and its got a k&n drop in filter that was clean, but i gave it a bath with a k&n filter recharge kit.
Old 06-19-2008, 09:03 AM   #2
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Unless the pads are completely worn, how are new pads going to help with a sticking caliper(s)?

The back brakes should rotate freely when off the brakes but if you have rear disk, you need to see if it's the parking brakes causing the rub, or if it's a sticking caliper. I have gotten a caliper unstuck by pushing the piston back in and out a few times, but you never know. Other things that could cause your problem would be collapsed brake lines (unlikely) or a lot of dirt in your brake fluid.
Old 06-19-2008, 11:40 AM   #3
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

u can try to clean the calipers up but i had to repalce mine they are not that much what year and modle are you taling about i dont see it

14 or 17 maybe 25 depending on what you get each
just replace them
Old 06-19-2008, 04:28 PM   #4
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

its a 2000 gmc jimmy SLE 4x4 with 89,XXX miles, bought it a month and a half ago and im just making sure everythings all good and maitnenced up.

the spark plug wires have cylinder numbers on them near the cap, makes me think their stock, the plugs look ok, a little brown near the electrode but gapped fine. cap and rotor dont look horrible or bad at all.

the front brakes you can hear them dragging when you spin the hubs, krrrrrrrrrr and you cant spin the hubs 100% freely, probably about 60% free, has enough resistance to know its there, beleive the front rotors are warped also.

my dads going to help me pull a caliper off and check the pads and so on, never worked on disc brakes.

im tihnking the brakes dragging is sucking the mpg out i should be getting, maybe an o2 sensor is bad too? dont think they did any or many tuneups on this, but its very clean, college girl was driving it, mustve been a good driver theres not many scratches or dings! woot
Old 06-19-2008, 06:19 PM   #5
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Front brakes will normally drag a touch and you'll be able to hear the pads rubbing the rotor. It will be a bit harder to turn the front because it's 4wd and you have the cv shaft in there. These vehicles are also known for having the bearings go bad. Check for odd tire wear and a grumbling/grinding type sound coming from the front as you are driving. The rears should spin freely with both tires off the ground. The pads may also barely touch or rub, but the tire should spin without much trouble. If you try to turn one rear tire with both of them off the ground you should be able to do it pretty easily. It will be a lot harder if you try to turn it by the studs or rotor. I do know one dragging rear caliper can make it seem like the truck doesn't want to go anywhere when you step on the gas.

PM me if you need anything. I just changed front and rears in a 2001 and found that I had one caliper pin sticking in the rear and also had to remove the pad shims to get everything free spinning. Drives much better now.
Old 06-20-2008, 11:58 PM   #6
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

just got 15.8mpg with 50/50 city and highway, babying it and doing 55 for half the highway and 65 for the rest.

what shall i tune up to get my mpg higher, mind you i dont have a job at the moment and i have a $30,000 hospital bill brewing above my head.
Old 06-21-2008, 11:46 AM   #7
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Mike is right. All disks drag some because they operate with zero clearance. You have the surging when stopping diagnosed properly. You need to turn the rotors to fix it.

Your mileage sounds about right for a 4x4 with a 3.73 axle. Those guys getting 22 mpg have 2wd 5 speeds turning 3.08 axles. Even a regular 2wd auto has 3.42 axle.

For a tune-up on a budget, I'd recommend plugs, cap & rotor. You prolly should do the wires too, but I'd make those optional if your short on cash.

Good luck!
Old 06-21-2008, 12:24 PM   #8
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

would the 02 sensors help more? and how many does it need.

i pulled 2 passenger plugs and they were gapped right, there was some black carbon around the white insulator, which had some browning on it.

the cap and rotor dont even look to be worn very much at all, but the numbers on the spark plugs make me think its stock plugs and all that, 89,000 miles

it was a teenage girl driver, who had a local muffler shop change the oil everytime so i dont think shes ever checked anything.

the city mileage isnt bugging me all that bad, its 4mpg lower than my old s10, but its 13-14mpg lower than my old s10 on the highway which is where its hurting the most
Old 06-21-2008, 01:01 PM   #9
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Quote: Originally Posted by beaniebmx
would the 02 sensors help more? and how many does it need.

i pulled 2 passenger plugs and they were gapped right, there was some black carbon around the white insulator, which had some browning on it.

the cap and rotor dont even look to be worn very much at all, but the numbers on the spark plugs make me think its stock plugs and all that, 89,000 miles

it was a teenage girl driver, who had a local muffler shop change the oil everytime so i dont think shes ever checked anything.

the city mileage isnt bugging me all that bad, its 4mpg lower than my old s10, but its 13-14mpg lower than my old s10 on the highway which is where its hurting the most
O2 sensors are good for at least 100k mi., and they are expensive, so I wouldn't replace those yet. You should have 2 or 3 O2s before the cat and 1 after the cat. When it comes time, only replace the ones b4 the cat as they are the ones that affect engine performance. The one after the cat is only there to monitor cat performance, so don't worry about it.

Original plugs are platinum which are also good for 100k mi., so if they are looking good and gapped right you can wait a while longer on those too. Take a wire brush and clean the insulator on the center electrodes.

Pay close attention to the posts inside of the cap. That is where the wear and corrosion is. If they aren't worn badly, sand off the corrosion with some sandpaper or emery cloth and reuse it for a while.

Wear on the rotor is hard to judge, unless you have a new one to make a side by side comparison. And that tip on the rotor gets zapped 6 times on each revolution, so it sees a lot of wear. You can get a Delco rotor for about $10, so I'd go ahead and just replace that.

I'm sorry about the highway mileage but there is no way that you can improve it by 13-14 mpg.

Last edited by Yogi; 06-21-2008 at 01:08 PM.
Old 06-21-2008, 03:18 PM   #10
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

i know im not gonna get 29mpg highway from my 1st gen 2.5l 5 speed i had.

im just wanting to see the 20mpg everyone talks about.

sucks about the price of o2 sensors, my old 91 costed $15 for the one sensor.

the jimmy runs great and ive had no problems with it other than mpg numbers not being as high as i wanted.
Old 06-21-2008, 03:28 PM   #11
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

I'm afraid that your just not going to see 20 mpg with the extra weight of the 4X4 and the 3.73 gears. It just won't happen.

The reason that the O2 for the '91 was so cheap is that it did not have a heater. The newer probes are heated.

You could pick up 1-2 mpg by having your PCM reprogrammed. Costs $75 at wait4meperformance.com

Last edited by Yogi; 06-21-2008 at 03:29 PM.
Old 06-22-2008, 01:21 AM   #12
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

if i HAD $75....
Old 06-22-2008, 08:50 AM   #13
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Quote: Originally Posted by beaniebmx
if i HAD $75....
I hear ya LOL!

Just trying to put some options out there for ya!
Old 06-23-2008, 03:22 AM   #14
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

sorry for off topic post but, how can you tell if your brakes are binding or dragging for that matter?
Old 06-23-2008, 10:21 AM   #15
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Quote: Originally Posted by 4UH8Rs
sorry for off topic post but, how can you tell if your brakes are binding or dragging for that matter?
Jack it up and spin the tire. A wheel with dragging brakes will be hard to spin and stop suddenly. Normal brakes spin for 1-2 turns and stop slowly. Note that you can hear the brakes touching, but not dragging, on a normal wheel.
Old 06-23-2008, 10:38 AM   #16
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

I average 20 mpg in a Jimmy identical to yours, 4x4, same year and even near identical mileage. So yeah I would be peeved too.
Old 06-23-2008, 10:48 AM   #17
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Quote: Originally Posted by benjamin86
I average 20 mpg in a Jimmy identical to yours, 4x4, same year and even near identical mileage. So yeah I would be peeved too.
With 3.73 gears it would be a minor miracle to see 20mpg. I'm about done working on my 2001 Jimmy 4x4 and during test drives I notice it turns some pretty low RPMs so i'm hoping the RPO code shows I don't have 3.73 gears. At least it will be used mostly by the wife and by me when it's snowing, so usage will probably be limited to far less than 10k a year. (I'm hoping)
Old 06-23-2008, 12:39 PM   #18
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

at 65mph im turning right around 1900rpms
at 55 im doing about 1600rpms.

dunno if thats high or not
Old 06-23-2008, 12:56 PM   #19
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Quote: Originally Posted by beaniebmx
at 65mph im turning right around 1900rpms
at 55 im doing about 1600rpms.

dunno if thats high or not
With a 3.42 you'd be doing approx. 1740 @ 65 and 1470 @ 55.
Old 06-23-2008, 10:26 PM   #20
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Quote: Originally Posted by Yogi
With a 3.42 you'd be doing approx. 1740 @ 65 and 1470 @ 55.
Are you sure that's correct? I have 3.42 gears in my extended cab IIRC and I turn nearly 2 grand at 65. I know in my old truck with 3.0 rears I would do 70 at 2k.

What sucks on my truck is that stock is 205/70 and i have 225 on the front and 235 on the rear right now as the fuel mileage is much better for the driving we do. I can get a set of 215s for $100 out the door from the local boneyard and they are near new. The dilemma....

Quick question: my 4wd is stock with 235/70. If I slap on 235/75 I should be OK, correct?
Old 06-24-2008, 10:43 AM   #21
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Quote: Originally Posted by MikeInCtown
Are you sure that's correct? I have 3.42 gears in my extended cab IIRC and I turn nearly 2 grand at 65. I know in my old truck with 3.0 rears I would do 70 at 2k.

What sucks on my truck is that stock is 205/70 and i have 225 on the front and 235 on the rear right now as the fuel mileage is much better for the driving we do. I can get a set of 215s for $100 out the door from the local boneyard and they are near new. The dilemma....

Quick question: my 4wd is stock with 235/70. If I slap on 235/75 I should be OK, correct?
No, I'm not sure that those speeds and rpms are correct. I just did a ratio calculation based on his rpms and 3.73 vs. 3.42 ratios. It should be correct for his set-up but not necessarily true for all.

235/75's will work. I put 120k on a set of Michelins that size. There was a slight rub when backing at full lock, but it was never of any consequence. Do it!
Old 06-24-2008, 12:42 PM   #22
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

so what your saying is once i get money, i should put a 3.0 gear in the rear end and while im at it get a 2wd frame and a 5 speed manuel transmission
Old 06-24-2008, 01:49 PM   #23
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Quote: Originally Posted by beaniebmx
so what your saying is once i get money, i should put a 3.0 gear in the rear end and while im at it get a 2wd frame and a 5 speed manuel transmission
Right! And then wait about 20 years for the better gas mileage to pay it off!
Old 06-27-2008, 06:10 PM   #24
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

one thing i noticed that im not sure on, is the cooling fan.

sometimes when i start up in the morning and take off, you can hear the cooling fan really loudly untill it shifts and gets a certain rpm or so long of time and then you dont hear it.

popped the hood and noticed that i can spin the fan in either direction as many revolutions as i want with no resistance.

i overheard that its not supposed to move more than 1/2inch?

correct me if im wrong, that makes me think this could be one thing to look at replacing
Old 06-27-2008, 06:31 PM   #25
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Re: 2000 jimmy 4x4, brakes dragging/bad mpg

Quote: Originally Posted by beaniebmx
one thing i noticed that im not sure on, is the cooling fan.

sometimes when i start up in the morning and take off, you can hear the cooling fan really loudly untill it shifts and gets a certain rpm or so long of time and then you dont hear it.

popped the hood and noticed that i can spin the fan in either direction as many revolutions as i want with no resistance.

i overheard that its not supposed to move more than 1/2inch?

correct me if im wrong, that makes me think this could be one thing to look at replacing
No, it's not 1/2", it's 1/2 of a revolution before it stops spinning. So there should be some resistance to spinning but the fan is free to spin as long as you push it. There is no mechanism that lets it spin 1/2 rev. and then locks it up. It's just a resistance that stops the fan from spinning freely. If it spins more than about 1/2 of a rev., then the clutch is bad and needs to be replaced. But note: a bad clutch will help gas mileage, not hurt it!
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