High 3rd gear, low 4th gear vibration (2 Viewers)

[truckfighter]

1980 FJ40, 4 on the floor -

I get crazy high amounts of vibration at the high end of 3rd gear and into the start of the 4th - once I get wide open into 4th it clears out.

This has been an issue for a while but it seems like it's getting worse and shaking everything inside the truck really bad.

What am I looking at repair wise?

 

[charliemeyer007]

So what happens when disengage the clutch at speed. Maybe the balance weight(s) fell off the drive shaft. Perhaps someone pumped the drive shaft full of grease. You checked the u-joints, pinion bearing play. Fish a magnet into bottom of the tranny, transfer and differential - look for metal glitter. Tire pressure and balance are worth looking at.

With the hubs turned out, start out in 4, at speed put the transfer in N - what happens. This will isolate the tranny and maybe 1/2 the transfer from the drive shaft and rear end. - You will need to stop to go back to 4H.

 

[45Dougal]

Sounds like it's downstream of the gearbox and vehicle speed related rather than engine or gear speed.
Prop shaft or wheels not balanced?

Prop shaft reassembled out of sync?

 

[truckfighter]

So what happens when disengage the clutch at speed. Maybe the balance weight(s) fell off the drive shaft. Perhaps someone pumped the drive shaft full of grease. You checked the u-joints, pinion bearing play. Fish a magnet into bottom of the tranny, transfer and differential - look for metal glitter. Tire pressure and balance are worth looking at.

With the hubs turned out, start out in 4, at speed put the transfer in N - what happens. This will isolate the tranny and maybe 1/2 the transfer from the drive shaft and rear end. - You will need to stop to go back to 4H.

Thanks for the quick reply.

I'm woefully ignorant about any kind of auto work, so I'll have to research everything you said since I only recognize half of the words.

Are most of those things doable by a complete newbie or should I leave them in the hands of a professional?

In the meantime, do you think driving it would be harmful before it's sorted? Not that I have any real desire to drive it while it feels like it's going to come apart due to vibration...

 

[truckfighter]

Sounds like it's downstream of the gearbox and vehicle speed related rather than engine or gear speed.
Prop shaft or wheels not balanced?

Prop shaft reassembled out of sync?

What kind of auto shop would sort that out, am I looking for someone that does transmission work?

 

[45Dougal]

Yea maybe.
If you look under the truck, there's a big drive shaft in the middle heading backwards to drive the back wheels.
Does it move side to side if you jiggle it?
There should be a steel weight welded to one side to balance it.
You could photograph the front and back joints?

 

[truckfighter]

Yea maybe.
If you look under the truck, there's a big drive shaft in the middle heading backwards to drive the back wheels.
Does it move side to side if you jiggle it?
There should be a steel weight welded to one side to balance it.
You could photograph the front and back joints?

I'll do that shortly, thank you!!!

 

[charliemeyer007]

Do you know any "car people" that would go for a ride with you to help you figure out what is wrong. I'm not a fan of just take it to a shop and say fix it $$$$$ will leave your pocket.

Did it sit for years - tires could have flat spots even thought they "look" good. Elsie sat for perhaps 14 years, several tires are almost new but are now worthless except for moving her around in the yard.

At this point it could be anything. Your goal is to figure out what is wrong by systematically isolating stuff and see what happens.

I assume you are in 2H with the hubs turned out, you get up to speed in 3rd say 30 mph and vibrations happen, you shift to 4th and vibrations continue to happen until say 65 mph and things smooth out. So is the whole truck shaking, what do you feel on the stick shift for the tranny and transfer vs the steering wheel?

Make sure the tires have the same air pressure and look like they are in good shape. Rotate the front tires to back and the back to front on the same sides - go for a drive - see if anything is different. Yes start with the tire shop for inspection/ balance. No, well on to more testing such as my earlier suggestion.

 

[truckfighter]

Do you know any "car people" that would go for a ride with you to help you figure out what is wrong. I'm not a fan of just take it to a shop and say fix it $$$$$ will leave your pocket.

Did it sit for years - tires could have flat spots even thought they "look" good. Elsie sat for perhaps 14 years, several tires are almost new but are now worthless except for moving her around in the yard.

At this point it could be anything. Your goal is to figure out what is wrong by systematically isolating stuff and see what happens.

I assume you are in 2H with the hubs turned out, you get up to speed in 3rd say 30 mph and vibrations happen, you shift to 4th and vibrations continue to happen until say 65 mph and things smooth out. So is the whole truck shaking, what do you feel on the stick shift for the tranny and transfer vs the steering wheel?

Make sure the tires have the same air pressure and look like they are in good shape. Rotate the front tires to back and the back to front on the same sides - go for a drive - see if anything is different. Yes start with the tire shop for inspection/ balance. No, well on to more testing such as my earlier suggestion.

Unfortunately the backyard mechanics and car people I know are all pretty tied up with stuff, which makes this even more frustrating, but I'll see if I can get them to go for a simple ride with a beer for their time.

It hasn't really sat much since I bought it two years ago, but there are times it may sit a month without moving - could that do it?

I'll check the air, it's been crazy hot here lately, even though it lives in my garage. The tires are pretty big so I'll have to check around and see who can balance them - definitely wanna go after the easy and cheap stuff first so that's my first thing to tackle...

 

[truckfighter]

Yea maybe.
If you look under the truck, there's a big drive shaft in the middle heading backwards to drive the back wheels.
Does it move side to side if you jiggle it?
There should be a steel weight welded to one side to balance it.
You could photograph the front and back joints?

I tried moving it, and it feels very solid and immobile - I couldn't spot anything that looked like a steel weight, but you're talking to someone who just learned how to change oil last year so if it's hidden or obscure I may have missed it thinking it was something else....

 

[pb4ugo]

You need to note when it does it. Like What speed does the noise start and go away. Does it still make noise if you let off the gas or push in the clutch. Like when you accelerate, deaccelerate coast and does it clank or clunk between the transition. I agree with @45Dougal, it's probably not the trans, because it happens in 2 gears. It's probably downstream. Like in T/case, d/s, ujoints, tire balance, etc.

 

[Casey E]

when did you grease it last ? looks bone dry. What rims you running ? If you have old style drums in back with the Philips heads protruding from the drum it can be an uneven mounting surface in back , stock rims have a bump to acomadate this screw head.

 

[truckfighter]

when did you grease it last ? looks bone dry. What rims you running ? If you have old style drums in back with the Philips heads protruding from the drum it can be an uneven mounting surface in back , stock rims have a bump to acomadate this screw head.

I've never greased it - tell me what to do and I'll get right on it!

 

[truckfighter]

You need to note when it does it. Like What speed does the noise start and go away. Does it still make noise if you let off the gas or push in the clutch. Like when you accelerate, deaccelerate coast and does it clank or clunk between the transition. I agree with @45Dougal, it's probably not the trans, because it happens in 2 gears. It's probably downstream. Like in T/case, d/s, ujoints, tire balance, etc.

I'd say the noise starts around 35-40mph and stops around 45 and is clear higher than that (honestly too scared to take it over 55mph). Didn't think about the clutch disengaging and correlating to tires versus mechanical - the vibration goes away when the clutch is engaged for sure, so I'd say it's likely not the tires. I don't remember any clanking or clunking going into or out of gear, it seems to shift very smoothly...

 

[pb4ugo]

Any noise changing when and off the gas at that speed? Is it maybe a gear or bearing whine? Is there a vibration?

 

[truckfighter]

Any noise changing when and off the gas at that speed? Is it maybe a gear or bearing whine? Is there a vibration?

I just know that when it's vibrating, goosing it or flooring it doesn't really change the behavior or make any other sounds (that I can tell) - I wouldn't be able to speak intelligently on what a gear or bearing whine would sound like - I have a buddy that's going to come over and he might be able to translate better what I'm experiencing. I hate that I am working from zero knowledge on this, I really appreciate everyone's patience with me.

 

[pb4ugo]

It's a good learning curve. Tire balance usually shows itself at that speed.

 

[45Dougal]

Ok so as far as I can see from the photos, your drive shaft looks out of sync - I'm not an expert so please anyone else weigh in here!
This could be the whole problem, or just a part of it.

See photos below.
Firstly, I've circled the grease nipples. Buy a grease gun and lithium grease. You'll also need moly grease for the steering joints - look at the front of your rig - anything that moves has a nipple on it.
Pump clean grease in until it comes out of the joint.

Secondly the green lines should be oriented the same (if the prop shaft is sync'd).
You'll see that your front joint is vertical, while the back joint is at 45 degrees. (I assume that you didn't move the truck in between photos).

You'll need to remove the 4 front bolts, pull the shaft backwards off the handbrake, and then slip the front half of the shaft forwards until it separates from the rear half.
You then need to turn it until both ends are aligned. Turn the hand brake drum to match, and reassemble.

Then pump the slip joint and universal joint with grease.

 

[truckfighter]

Ok so as far as I can see from the photos, your drive shaft looks out of sync - I'm not an expert so please anyone else weigh in here!
This could be the whole problem, or just a part of it.

See photos below.
Firstly, I've circled the grease nipples. Buy a grease gun and lithium grease. You'll also need moly grease for the steering joints - look at the front of your rig - anything that moves has a nipple on it.
Pump clean grease in until it comes out of the joint.

Secondly the green lines should be oriented the same (if the prop shaft is sync'd).
You'll see that your front joint is vertical, while the back joint is at 45 degrees. (I assume that you didn't move the truck in between photos).

You'll need to remove the 4 front bolts, pull the shaft backwards off the handbrake, and then slip the front half of the shaft forwards until it separates from the rear half.
You then need to turn it until both ends are aligned. Turn the hand brake drum to match, and reassemble.

Then pump the slip joint and universal joint with grease.

View attachment 3417946

View attachment 3417948

I have a grease gun from doing the "zerk" fittings up front so I'm ahead of the game there, I'll get right on that, much thanks!

I didn't move the truck so what you see is what you get. I hope it's as simple to fix as you make it sound, I'll give that a shot...

 

[charliemeyer007]

You should invest in a book/manual. Chilton isn't all that great - they will tell you for example 10 times that anti-freeze will poison your pet and brake fluid will eat your paint but they don't tell you that the transmission needs to seat fully on the bell housing - if you draw up that last 1/8" with the bolts on Pinto with a C6, you will crush/ruin the torque converter - lesson for back in the 70's.