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Unread 08-14-2003, 01:04 PM   #1
jasinner
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Join Date: Jun 2003
Location: Hemet, CA
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What is wrong with my jeep?

I have an '85 CJ-7 (four cyclinder) and it has a four speed manual transmission.

In third gear, the beast will max out at around 55 mph.

Then I put it into fourth gear.

Immediately the speed drops down to about 50 mph and won't go back up.

I am assuming that this is not normal (I can't even go on the freeway). I took it to a shop and they are drawing blanks (I think that they are just going to give it back to me unfixed).

They replaced the cat, checked the vacuum lines, fixed the egr valve, fixed a butterfly on the air intake, checked the carb, and just about everything else.

I have never driven another jeep before but I notice that my jeep goes fast in the low gears which seems unusual. The gears seem "long" which seems strange for a 4x4. Could somebody have regeared it or something be otherwise malfunctioning?

Somebody also said that it might be the tires (It came with 31" tall tires on it).

I have no idea. If you do, I would be much obliged.

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Unread 08-14-2003, 01:39 PM   #2
MR.CJ-7
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Do you have a tachometer? If so what are your rpm's? You could have a terribly high(numerically low) axle ratio. With 31's you should be at 3.73's or numerically higher, in my opinion. My CJ came stock with 3.54's and they worked well for the 30" tires that were on it when I bought it. I swapped to 33"s and I could still drive it on the freeway but it seemed really weak even with a V-8 for the engine. I swapped my gears to 4.56 with 33"s now I run about 3200 rpm with my auto trans on the freeway(no overdrive).

Also any other info would be helpful. I am assuming you are running the d30 up front and M20 in the rear? and a D300 trans. case?

I am thinking either the engine isn't producing adequate power , or you are losing the power somewhere maybe a slipping clutch, maybe just poor axle gearing, if it is the M20 two piece rear axle you could have a spun axle hub and could be losing the power there.

Just my $0.02 worth if I can think of anything else I will repost.

Good luck!
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Unread 08-14-2003, 07:43 PM   #3
jadams68
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If the clutch was slipping I would think you'd have vibrations and clutch chatter shaking the jeep.

Did your mechanics ever think to replace the fuel pump and the fuel filter?

I think your motor might be having fuel starvation problems.
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I used to own two CJ's...Perhaps a 3rd is in the future?
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Unread 08-14-2003, 10:04 PM   #4
jasinner
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In response to the first reply, I don't have a tach.

There is no vibration or anything, it runs very smoothly.

Yeah, they checked the feul pump and filter because that occured to them too.

If I think it is the axle ratio, how can I test this? Should I put it in 4wd (low or high?) and see if it goes faster than 55? It never occured to me to try this. Also, why do they call 2wd High "high" if there is no 2wd low?

Thanks for all of the ideas, I can't wait to actually use my jeep.
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Unread 08-14-2003, 10:35 PM   #5
jddausch
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it could be any of the above, but don't forget to start with the basics. make sure your idle, mixture and timing are set right and use high detergent gas. all of this stuff is easy to check, and it don't cost nothin!

good luck
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Unread 08-14-2003, 11:10 PM   #6
Lightningdon
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Let's see.........heavy *** CJ7?,.....weak 4 cylinder engine?,....Can anyone say"engine swap"? You just don't have the power to pull that thing in the higher gears. Re-gearing may help.
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'75 CJ5 304cid, t18 tranny w/granny low, model 20 T Case, DANA 44 rear, 30 front, 4" suspension lift, 33" tires, in need of more work!

"The only thing necessary for the triumph of evil, is for good men to do nothing." (Edmund Burke)
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Unread 08-15-2003, 02:38 PM   #7
twmattox
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WOW!
I have an '84 with the AMC 150 4-cylinder, T-4 4-speed tranny, 3.54 axle ratio, and 31" BFG TA/KO's. I have no problem running at 65-70 on the interstate. I do, however, run into big problems when I am pulling my trailer uphill into a strong headwind...

The four cylinder should be more than enough engine to handle the lightweight CJ-7 (these are not tanks like the Grand Wagoneer). Alll four cylinders came with stock axle ratio of 3.54 (with the optional 4.1 on a few). I suspect one of two things. Either you haven't swapped your speedo gear (this would mean that your speedometer is out of synch and you are really moving much faster than the speedometer says), or that you have a swapped in tranny (largely because you can run around 55mph in third gear). Mine screams at anything over 45mph in third gear.

Check your speedo first. Find a vacant stretch of highway. Look at the mile markers, and see if your odometer is off over a 10 mile stretch (there are more scientific ways to do this, but it has worked fine for me)...If the speedo is off, go to your local Jeep dealer and order a new "pinion" gear (this is what my Jeep dealre refered to it as). Check the websites to get the tooth count (I believe that it is a 31 tooth). They run around $10 and are very easy to change...
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Unread 08-15-2003, 03:33 PM   #8
jadams68
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Dumb question, but are you in 4LO?
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Unread 08-15-2003, 11:10 PM   #9
jasinner
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Wow, thanks for all of the ideas guys!

I was thinking about it and I remembered that when I brought it from the dealer, they said that they had JUST put on new tires. I went to the shop, took the cover off my spare, and sure enough, the spare was only 27" high. The new tires they put on were 31" high. I might be wrong but I am pretty sure that all tires have to be the same height for four wheel drive vehicles.

What the dealer must of done is just slam on some huge wheels and didn't really test it on the freeway after that.

So I went out and bought the 27" 's.

Yeah, the 31's look way better but the problem is solved, I can go all the way to the end of the speedometer (85mph but I don't really plan on ever going that fast in the beast).

I have no idea what the axle ratio is and if the speedo is reading low now, well, I'm afraid of how fast the thing might go!

I'm going to have to check the parts anyways because the gearing still seems strange. I guess that its time to get "friendly" with my jeep!

Thanks again all!
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Unread 08-16-2003, 10:41 AM   #10
wm69
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Your jeep probably came with 215 75R15, (what came on my dad's jeep) or 235 75r15's. The 27" is way small, but if you're happy with them..... When they wear out try the 235 75R15's. they are a little under 30" around, and were more than likely what came on your jeep. There should be someway to check to see what tires yours came with, but unless you have the sticker on the inside of the glove box (which is usually gone) you'll have to try and get the info from the vin # (and I don't know if that included the tire size)
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85 CJ7 258, A/C, T176, MC2100, Team Rush, Warn XD8000i, superwinch hubs, 3in lift 31" BFG AT/KO
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Unread 08-16-2003, 10:23 PM   #11
jasinner
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I was talking to a friend today and he told me that somebody may of put "highway" gears on the jeep before I bought it to make it a better daily driver, hence the inability to pull the big tires.

I would check in the glove box but it was locked when I bought and came with no key for it. I will, however keep the 235 75R15's in mind as the friend I mentioned recommended those exact tires to me earlier today.

Thanks!
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