Hey guys
I have an 89 f250 7.3 pre-powerstroke that shakes a ton when under load. It idles fine, but when driving between 1100-1600 ish rpms it shakes a ton and doesn't really want to accelerate too well. The R's don't really drop while shaking, it just takes a while for them to climb. I have done some poking around and realized all 3 of my U-joints need replacing, and I need a new throw-out bearing. Would these cause this problem? The shaking happens in every gear at about the same rpm's.
Also, I'm pretty sure I have some air intrusion, I ordered some Viton rings the other day to hopefully get that fixed too. But would that cause this problem as well as the hard starts?
It's gotten a new air filter and fuel filter recently, and it got an oil change in August, at that same time I drained the tranny and re-filled it.
Any help I can get would be greatly appreciated.
Brandon

 

Bad joints will def cause some vibrations, get them replaced before they go completely out.

 

I see.... The reason I was asking is because I heard that normally when U-joints go out, it shakes at the same speed, not so much the same rpm's. Is that different because I have 3 bad ones?

 

The joints will show up as a vibration at ground speed, depends what that speed is..

If the shake is at the same engine RPM every time then the problem is engine or accessory related.

I'm not saying to not fix the U-joints, if they are bad they need repaired. But your speed related shaking and lack of power are not caused by them. What you described sounds like a miss under load. You may be onto something with the air intrusion.

 

That's kind of what I was afraid of. What do you mean by accessory? Just some examples?
Could that throw-out bearing be a culprit? Sorry to bombard y'all but I'm not really a mechanic (at all). I'm learning, getting better, but I'm still pretty newb-tarded.

 

An accessory is anything on the belt usually. AC, PS, Smog....

A miss is def likely. Though joints are cheap and easy to replace. Itd at least be a good starting point before moving onto more serious and expensive repairs.

 

Replace your joints first off, cause if one breaks, down falls the driveshaft!


And what makes you say you need a new throw out bearing? It is making noise at idle in neutral with the clutch engaged?


As for the shaking, how does it shake? Like just a vibration, or a violent shake that rattles the dash??


And since you say it have trouble making rev when it starts doing that, gotta be something putting drag on the engine, could be something seizing, or binding.


I'd do the accessories test first, since that's the easiest. Just remove all your belts, and go for a quick drive, to see if it still shakes. Be aware though, with the vacuum pump belt removed, you will have no vacuum going to the brake booster, meaning you'll have very little, and very stiff brakes.

 

It's a violent rattle, it rattles the dash and everything inside the truck. It only does it between those certain rpm's though. As for the loss of power, it isn't falling on it's face or anything, it just slowly accelerates (very slowly), primarily during the rattling. After it smooths back out, it accelerates a little better. It never had a lot of get up and go, but now.... all of it's get up and go has got up and went.
I'm definitely going to change the u-joints as soon as possible though.
When I first noticed the truck driving differently I had just got off the freeway doing 75. When I got to the light and turned is when I noticed it starting to feel a little off, but not nearly like it is now. Starting be very annoying...
I've never done an accessory test before though, so that should be interesting, I'm glad you put up there what to do. That'll at least give me a starting point.
Thanks everyone for the help. I'll let you know what I figure out, and if anyone has other suggestions please let me know.