1ton87 Posted February 16, 2014 Share Posted February 16, 2014 Alright guys, I'm at a loss again. I have an '87 MJ 4x4 with the 4.0l, AW4, metric ton. Everything was fine, I could easily go 80+ mph on the highway. Then one day I took an hour drive, didn't notice any problems, but when I got back in the truck to go home it would only go 65 tops (70 downhill) with my foot to the floor. I made it home, but this concerns me of course. I started tinkering with the rear end. Replaced the pinion bearings, wheel bearings and all seals, but it's no better. When I have the rear end in the air, I can spin one wheel and the other spins easily (in the opposite direction of course), but when I stop one wheel and turn the other it becomes alot more difficult to spin. What am I overlooking? Link to comment Share on other sites More sharing options...
Eagle Posted February 16, 2014 Share Posted February 16, 2014 1. Brakes. The drum brakes are a type called "servo assist." When the brakes are applied in the forward direction, the rotation helps to force the shoes against the drums for better stopping with less peddle pressure. Doesn't work that way in reverse, which is why the parking brake always holds better when the vehicle is pointed downhill rather than uphill. So check to see if a wheel cylinder is hanging up and not allowing the brake shoes to retract. Or possibly the parking brake cable is rusted and won't let the shoes retract on one side. 2. A clogged catalytic converter reduces power at higher RPMs. Link to comment Share on other sites More sharing options...
1ton87 Posted February 16, 2014 Author Share Posted February 16, 2014 The brakes were the first thing I checked, no dragging on the rears or fronts. I'm gonna try disconnecting the cat., the exhaust is getting old, probably 6 - 8 years. Won't be too surprised if it needs replaced. I'll post my findings. Thanks. Link to comment Share on other sites More sharing options...
1ton87 Posted February 16, 2014 Author Share Posted February 16, 2014 You were dead on, Eagle. I pulled the exhaust off and sure enough a 2" chunk of catalyst had broken free and was blocking things up between the cat. & muffler. Cruised right up to 85 mph with no hesitation on a test ride. Also, my rear end work did get rid of the howling she was making when decelerating. Double plus. Thank you! Link to comment Share on other sites More sharing options...
Eagle Posted February 16, 2014 Share Posted February 16, 2014 Glad you got that solved. For posterity, I just went back and fixed my post. I referred to brake shoes in three places, and I managed to type it wrong in all three. Gotta be a defective keyboard. Link to comment Share on other sites More sharing options...
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