Why So Weak??

qwert98 · 05-09-2006, 08:55 AM

I bought an 86 Cj7 with:

32" wheels
3 speed auto (1 yr old)
Straight 6 (4.2L)
195K, but runs well - no sputtering or hesitating
Weber carb (1 yr old)
Headers

and the timing, plugs (didn't check gap) and wires look good.

The problem is the jeep has no power. It top's out about 60 MPH, but even low end seems extremely sluggish.

Any ideas? I know the gearing could be off, but then I would sacrafice top end speed for low end power - and I don't even have that.

I need to drive on the highway to get to the trails!!!

**jeepskate** · 05-09-2006, 09:01 AM

It's the gearing. You likely have the base stock gears which are 2.73's...barely adequate for moving the stock tires. With the towing package you get 3.31's which mine has/had (rear has been regeared, haven't had time to do the front yet) which are just barely adequate to handle 32's. I went to 35's and it could barely get out of it's own way which is probably about the performance that you're seeing. Prior to the 80's, stock was 3.54. You need to regear.

MR.CJ-7 · 05-09-2006, 09:41 AM

I'll second that!

I had 3.54's stock in mine. They were fine with 30" tires and marginal with 33"s. That was with the V8 with headers, 2bbl motorcraft carb and a 3spd auto trans. I regeared to 4.56 and love it. I just made the switch from headers to manifolds for IM reasons and despite what everyone says about minimal losses between headers and manifolds, I lost a lot of power. Now I'm kind of wishing I would have gone to 4.88's.

Good luck to you!

qwert98 · 05-10-2006, 08:43 AM

Thanks for the replies.

I marked the drive shaft and tires, lifted up the rear end, and spun the tire tire one revolution. That turned the shaft ~4.5 times. That means my gears are near 4.5's.
If that's the case, does that mean that my gears are good for the 32" wheels?

I am going to hook up a tach to check the RPM's at 60mph - but is sounds like it's screaming.

Any other ideas???

MR.CJ-7 · 05-10-2006, 02:32 PM

I tach about 3300 at highway speed. It hasn't hurt anything yet

CJ5_Fan · 05-10-2006, 03:02 PM

Quote:

Originally Posted by qwert98

Thanks for the replies.

I marked the drive shaft and tires, lifted up the rear end, and spun the tire tire one revolution. That turned the shaft ~4.5 times. That means my gears are near 4.5's.
If that's the case, does that mean that my gears are good for the 32" wheels?

I am going to hook up a tach to check the RPM's at 60mph - but is sounds like it's screaming.

Any other ideas???

I would be surprised if you came stock with that gearing. You would be better off taking the code off the axel and looking it up to be sure of the gear ratio.

MR.CJ-7 · 05-10-2006, 04:44 PM

Quote:

Originally Posted by CJ5_Fan

I would be surprised if you came stock with that gearing. You would be better off taking the code off the axel and looking it up to be sure of the gear ratio.

Maybe a previous owner swapped in 4.56s?

jakemary · 05-10-2006, 08:40 PM

pull the diff cover off. count the gears. its messy but it works no more wondering.

mr_frenchy · 05-10-2006, 09:04 PM

Have you done a compression test on the engine?

cage013 · 05-10-2006, 09:23 PM

well with 2.73s and open diffs i could turn 4+times with onw tire rotation so
pull the cover and check

famicom21 · 05-11-2006, 07:17 AM

i have an 86 cj7 w/ a manual 4 speed that had no low end torque whatsoever(and high end), for me it was the carb (a carter BDD - aka p.o.s.), i put a manual choke on to recover some low end torque back, but ultimately ended up switching to a motorcraft.
i would check and make sure your choke isnt sticking closed, that would make the engine sound gurgilie (???)

qwert98 · 05-16-2006, 02:27 PM

The rear end has limited slip (or a locker). When I jack it up and spin one wheel, the other spins.

I am thinking htat it is 4.56 gears, since the engine screams at 60mph. I have not checked the compression, but the engine does smoke a litte and it eats a little oil esp. at high speeds.

I think I may regear it with 3.54 a little higher to get more high end. Anyone want to trade a Dana 30 front end with 4.56 gears for Dana 30 with 3.54's or close?

Hibbitz · 05-16-2006, 02:36 PM

If you have 4.56 gears and there isn't anything really wrong with your engine, you should have No problem getting right up to 60 mph.... you just won't go much faster than that. The best way to know what you dealing with is to count the teeth. This will save you from ordering parts/changing things based on what you think the gearing is.

KLH

thenubsterman · 05-16-2006, 06:31 PM

or he could just read the 2 numbers on the ring gear divided them out and it will give your the gear ratio