Excessive slow down

mbalbritton

mbalbritton

#@$%!
Joined
Mar 22, 2005
Location
Lakeland, FL
So, I went and test drove a ‘90 YJ today. Really clean nice YJ. But something had me concerned. The excessive deceleration when you left off the throttle. Even the slow to accelerate was a little concerning.

4.2l, A999 slush box, 4.88 gears and 35’s.

I know, not a real combo for speed, and I didn’t expect it. But I didn’t expect how sluggish and how much deceleration when I let off the throttle from 40 or 50 mph. I talking, I was looking for brake smoke.

The owner said he did the gears. And shared a picture of the pattern with me. Seems a bit deep to me. Just wondering what else it could be. I’ve already passed on the jeep, so this is just curious at this point.
 

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I’ve seen worse, but that ain’t right. Pinion too deep. But that shouldn’t be causing major decel.
 
Still thinking about this Jeep. It was in great condition for age and asking price. Just really curious about why it could be so slow and decelerate so quickly. What are some things I could look at?

Specs:
‘87 YJ
4.2l with Weber
Stock ignition, no nutter bypass
A999 auto
4.88 gears that the owner installed
35x12.5 Mickeys
3” BDS and I noticed the rear pinion is angled up at the tailshaft for a DoubleCV shaft, but it has a standard U joint shaft. I can feel the vibes too.

It’s slightly squirrelly in the steering and has two steering dampers “to try and calm that down”. That tells me both axles weren’t set up properly when they lifted it.

I’m tempted to go back and put the thing on stands and run it to see if I can find the issue. Could be a combo of the pinion angles, the tire size, the gear ratio, the gear set up, etc?

It doesn’t pull to one side or the other so I’m not thinking brakes.

Thoughts?
IMG_0031.jpeg
 
mbalbritton said:
Still thinking about this Jeep. It was in great condition for age and asking price. Just really curious about why it could be so slow and decelerate so quickly. What are some things I could look at?

Specs:
‘87 YJ
4.2l with Weber
Stock ignition, no nutter bypass
A999 auto
4.88 gears that the owner installed
35x12.5 Mickeys
3” BDS and I noticed the rear pinion is angled up at the tailshaft for a DoubleCV shaft, but it has a standard U joint shaft. I can feel the vibes too.

It’s slightly squirrelly in the steering and has two steering dampers “to try and calm that down”. That tells me both axles weren’t set up properly when they lifted it.

I’m tempted to go back and put the thing on stands and run it to see if I can find the issue. Could be a combo of the pinion angles, the tire size, the gear ratio, the gear set up, etc?

It doesn’t pull to one side or the other so I’m not thinking brakes.

Thoughts?
View attachment 413360
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Tires rubbing? :laughing:

How was the acceleration? Maybe some issue in the exhaust restricting flow that really slows it down when off throttle?
 
Acceleration is slow too. Interesting thought on exhaust restriction.

This Jeep was towed behind their motorhome mostly. So minimal miles actually driving.
 
braxton357 said:
All jeeps are turds and 35" mud tires kill momentum but that thing is sweet, buy it anyway.
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He’s right, and it needs sidepipes!
1709435818467.png
 
A 4.2 was a good engine, but it's a turd. I can only imagine it being worse with an auto. I agree that you should buy it and figure it out.
 
Maybe the calipers are just sticking. It doesn't have to be just one, maybe both fronts are old and stuck. Maybe the transfer case doesn't have lube and it's about to lock up. Since it was towed I wonder if it was ever left in gear or engaged improperly, each trans and transfer case has a sequence for flat towing. Could be the guy didn't know how to set bearing preload on wheel bearings when he did the gears.
Tell him your concerns and tell him you want to get an idea of the issue before buying it but beware, if you figure it out he may want to keep it lol
 
Thanks RQ. Definite good considerations. I’d definitely like to check the fluids for glitter and spin some pinions to see what sort of resistance I’m seeing.

I know the 4.2’s aren’t race engines by any means, and I’m not trying to even hit 0-60 in 10 sec. I’m just trying to make sure it can merge onto a country road without being rear ended by a tractor.
 
Have had a 4.2 with the 4 spd, the 5spd, and a triple 9. The Auto was the most gutless and it only had 31’s. The others were 33’s. All of them were stock gears
 
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