Vibration at 45mph+

Torque Junkie · December 14, 2001

I'm crusing down the highway at 60 mph and I let up on the throttle about half way - not completely - and the whole truck shudders and vibrates. It does'nt do it at cruising RPMS, nor does it do it with the throttle fully lifted. I actually experienced it in Neutral the other day too, so I'm really thinking it's engine or tranny related - not tire or DS unballance.

I thought it was the U-joints but changing those did not help the problem. Granted, they still needed to be changed to keep my driveshaft from falling off.

Do any of you have any suggestions to what might be causing this vibration?

Thanks

-Mike

76BBSub · December 18, 2001

could it be a loose or worn tranny or motor mount? Those will sometimes induce some weird vibrations. Is your front suspension tight, maybe something a little loose? Or maybe wheel bearings, have they been repacked lately? I especially wonder about the bearings after your mud adventures...

Jeff

lowflyer · December 18, 2001

First off, try to isolate the problem.

When the shudder happens, shift it into Neutral and try changing the RPMs of the engine. If it only happens at a specific MPH and not a specific RPM, than its in the drive line. Only at RPM regardless of MPH, its an engine vibe.

If its an engine vibe, based on your observation, my first look would be at the exhaust system. Throttle off coast down with exsessive backpressure will cause some cylinders to drop and shake the motor.

If its a driveline vibe, try to see if you can feel it from a particular side (frt/back left/right) If it feels like its coming from the front, suspect tranny / torque converter or front drive axle. If its from the back, check your drive shaft, U-joints and rear axle. Good luck and keep us posted.

Torque Junkie · December 18, 2001

could it be a loose or worn tranny or motor mount? Those will sometimes induce some weird vibrations. Is your front suspension tight, maybe something a little loose? Or maybe wheel bearings, have they been repacked lately? I especially wonder about the bearings after your mud adventures...
Jeff

Jeff - Now that you mentioned it, this started right after my mud adventure, and I don't know when the last time the bearings were repacked, so it may be that. I also noticed it this morning going around a right-hand corner with the cruise set at 60 so it may be the left side.

If it is a tranny mount, however, i'll just deal with it until I do the swap.... like I said, if I have to spend a dime on that tranny, i'm just gonna hold off and save that dime towards the 700r4..

It definately feels like it's coming from the front of the truck, and it possibly could be the left (drivers) side.

I also notice it alot more with the hubs locked in, and it's even worse (almost at any rpm when the speed is above 35) with 4WD engaged.

With that said, I'm thinking it may in fact be the front end bearings. What do y'all think?

-Mike

Torque Junkie · December 19, 2001

OK, I did a little playing around on the drive home and discovered that it happens with the throttle open slightly at 2600 rpms and only 2600 rpms, with the exception of a mild one at 2200 rpms. It's most noticable when going down an incline and I let off of the gas slightly but not fully to maintain speed, and the engine hits 2600 rpms. It also only seems to happen in D; I havn't been able to duplicate it in 2 or 1 at all.

It's not backpressure, for sure. I've got headers and dual 2.5" exhuast with Flowmaster 40's and no cats, so backpressure is not an issue.

I wonder if this has anything to do with my tranny loosing all its fluid that night last month...?

The problem I mentioned about the shimmy in 4WD is separate from this, I think.

76BBSub · December 20, 2001

These are the tough ones to diagnose...I would check the front wheel bearings first, for two reasons.

First, you have to consider what has happened recently that could cause this, and the mud damaging the wheel bearings would have been pretty recent.

Second, it's relatively cheap and easy. The tranny situation also applies to rule #1, but it's alot more expensive and difficult to diagnose.

If you check the wheel bearings, the worst thing that can happen is that they are OK, and you repack them anyway and don't have to worry about it. But, you may save yourself alot of grief instead of delving into the tranny right away.

The fact that it comes from the front end, and is apparent at part throttle at more than one RPM makes me think wheel bearings. When you are not "on the gas" there's a light load on the front end, but not as light as when you are on the gas. This could cause a bad or dirty bearing to make alot of noise. What about under heavy braking, any new noise?

Regardless, after being hub-deep in wet mud I'd check and replace or repack the front bearings first.

Jeff

Torque Junkie · December 20, 2001

Is a hub repack something that can be done at home relatively easily with no garage and limited tools when it's 20 degrees outside? I'm gonna call around tomorow and find out what it would cost to have it done too..... I hate working on vehicles during winter time.

There's no abnormal vibrations or noises during braking of any sort.

If it is in fact the tranny, then I'm just gonna have to bear with it until I do the swap this coming year.

Thanks for all your help, Jeff!

-Mike

76BBSub · December 21, 2001

Hmmm....I haven't repacked 4WD hubs in about 4-5 years, memory is a little fuzzy.

I do remember that you need a special socket to get the hub nut off. It's about 2" in diameter and about 5" long. Should be available at any Pep Boys or other major auto parts stores, but they can be a little tricky to find. The other thing is the truck I had then had full-time 4WD and automatic hubs. I don't if there's a difference in the difficulty level of manual vs auto locking hubs. But, all that said, it should be pretty straightforward. Just remove the hub nut, pull the outer bearing out, then remove the hub/rotor assembly from the spindle (it just pulls off). Pry out the rear grease seal (be sure to buy a new one for each side before you start!) and the rear bearing comes right out. You can pack them by hand or use a double cone tool with your grease gun (also available at the parts store). When all the old grease has been pushed out by the new grease put the rear bearing back in the hub and tap in the new grease seal. I use a piece of wood to distribute the force along the seal to help it start in straight. Then put the hub back on the spindle and install the front bearing, follow up by tightening the hub nut. That's the quick instruction, you should read a Chilton/Haynes type manual to see if I skipped anything important.

It's not a bad job, but I hate working on cars in cold weather too. The only good news is that you will probably be done in an hour so.

Jeff

Torque Junkie · January 4, 2002

Well, I checked my Trany fluid yesterday, and it was about a pint low, so I added a pint, and sure enough, the vibration went almost completely away!?! It's still there at 2600 rpms, but it's MUCH fainter and less noticable than it was before.

Conclusion: The tranny is dying a slow, painful death. My hubs could still probably use a repack but I'm going to hold off until I can better afford it and have the time to do it when it's not 20 degrees with a foot of snow on the ground.

Time to start saving BIG TIME for the 700R4 swap.

-Mike

gslim · January 4, 2002

I would recomend this tranny swapThe Raptor I would also recomend packing your hubs with a good quality marine grease. Do you have full time or manual hubs? If your truck has lots of miles on it and the front end needs to be done you should also look at doing the ball joints and all bearings at the same time. Its expensive time consuming and a pain in the arse. but you have to tear everything apart to do each of those anyway. There is a couple of good posts about this on coloradoK5.com. Just do a search. If you want the tranny to last a little longer you may want to add a quart of transX. Also you could swap the fluid and change the filter. However this also has the nasty habit of causing the problem to expand and kill your tranny faster. Its a 50 50 chance. I would recomend looking for any leaks and just keeping it full till it dies.