one4fun
Full Access Member
- Joined
- Jun 1, 2013
- Posts
- 175
- Reaction score
- 6
- Location
- Portland, oregon
- First Name
- chris
- Truck Year
- 1986
- Truck Model
- k10
- Engine Size
- 350
What happens when the "center has spun on the tubes"?
please help quickly
- Thread starter aGood'olBoy
- Start date
Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.
What happens when the "center has spun on the tubes"?
chengny
Full Access Member
- Joined
- Feb 22, 2012
- Posts
- 4,086
- Reaction score
- 1,008
- Location
- NH
- First Name
- Jerry
- Truck Year
- 1986
- Truck Model
- K3500
- Engine Size
- 350/5.7
But there is one thing I can't wrap my head around yet.
It's regarding the conclusion that the differential shift and the increased upward angle of the pinion shaft is the result of excessive torque applied to the rear end by the drive shaft.
Maybe someone can straighten me out on this:
When rotational force is applied to the road wheels via the axle shafts, those shafts are attempting to overcome the resistance to rotation due to inertia (the weight of the truck) and some rolling resistance (from bearing friction etc.).
To move the truck forward (we'll have to assume Jeremiah wasn't peeling out in reverse), the axle shafts would be trying to rotate in the CCW direction - as viewed from the LH tire.
My problem with this is; wouldn't the resistance to rotation on the axle shafts - as they tried to move the wheels in the forward direction - create a force within the differential that would tend to deflect the front end of the pinion shaft down towards the ground. In my head, it seems like the truck would have to be trying to move backwards in order to get a loose differential to shift so that the front of the pinion shaft moves upward.
I probably just have a mental block on this issue.
It's regarding the conclusion that the differential shift and the increased upward angle of the pinion shaft is the result of excessive torque applied to the rear end by the drive shaft.
Maybe someone can straighten me out on this:
When rotational force is applied to the road wheels via the axle shafts, those shafts are attempting to overcome the resistance to rotation due to inertia (the weight of the truck) and some rolling resistance (from bearing friction etc.).
To move the truck forward (we'll have to assume Jeremiah wasn't peeling out in reverse), the axle shafts would be trying to rotate in the CCW direction - as viewed from the LH tire.
My problem with this is; wouldn't the resistance to rotation on the axle shafts - as they tried to move the wheels in the forward direction - create a force within the differential that would tend to deflect the front end of the pinion shaft down towards the ground. In my head, it seems like the truck would have to be trying to move backwards in order to get a loose differential to shift so that the front of the pinion shaft moves upward.
I probably just have a mental block on this issue.
Last edited:
chengny
Full Access Member
- Joined
- Feb 22, 2012
- Posts
- 4,086
- Reaction score
- 1,008
- Location
- NH
- First Name
- Jerry
- Truck Year
- 1986
- Truck Model
- K3500
- Engine Size
- 350/5.7
What happens when the "center has spun on the tubes"?
IDK - I didn't write that. It was quoted from higher up on the page.
I don't mean to put words in his mouth but, I assume he means that if the ends of the axle tubes are free to articulate inside the differential case - the angle formed by the pinion shaft and the trucks's frame can be altered .
IDK - I didn't write that. It was quoted from higher up on the page.
I don't mean to put words in his mouth but, I assume he means that if the ends of the axle tubes are free to articulate inside the differential case - the angle formed by the pinion shaft and the trucks's frame can be altered .
aGood'olBoy
Full Access Member
- Joined
- Oct 8, 2013
- Posts
- 187
- Reaction score
- 3
- Location
- Waterford Pennsylvania
- First Name
- Jeremiah
- Truck Year
- 1985
- Truck Model
- k10
- Engine Size
- 350
I understand what your saying but the way I'm picturing it. The pinion would be deflected down and the tubes then spun inside the differential. As the axle wrap twisted the axle back up the pinion had shifted up. At least that's how I see it.
I would think if I broke the perch welds I would hear it every time the suspension cycled
I would think if I broke the perch welds I would hear it every time the suspension cycled
chengny
Full Access Member
- Joined
- Feb 22, 2012
- Posts
- 4,086
- Reaction score
- 1,008
- Location
- NH
- First Name
- Jerry
- Truck Year
- 1986
- Truck Model
- K3500
- Engine Size
- 350/5.7
I understand what your saying but the way I'm picturing it. The pinion would be deflected down and the tubes then spun inside the differential. As the axle wrap twisted the axle back up the pinion had shifted up.
You know, in the back of my mind I think you're right and want to agree with you. Except for the last sentence - I can't understand what you are saying there. I just haven't had a quiet few minutes to sit and think about the chain of events that occurs whenever a vehicle is accelerating from a dead stop.
I would think if I broke the perch welds I would hear it every time the suspension cycled
Keep in mind that the scenario I described was totally imaginary - and just meant to be an alternative to the "axle tubes are broken loose in the differential housing" theory.
But if that did happen - and the axle shift occurred - that would most likely be it for a long time. The u-bolts would still be tightly clamped down and they would most likely keep anything from moving until the next big shock event.
You know, in the back of my mind I think you're right and want to agree with you. Except for the last sentence - I can't understand what you are saying there. I just haven't had a quiet few minutes to sit and think about the chain of events that occurs whenever a vehicle is accelerating from a dead stop.
I would think if I broke the perch welds I would hear it every time the suspension cycled
Keep in mind that the scenario I described was totally imaginary - and just meant to be an alternative to the "axle tubes are broken loose in the differential housing" theory.
But if that did happen - and the axle shift occurred - that would most likely be it for a long time. The u-bolts would still be tightly clamped down and they would most likely keep anything from moving until the next big shock event.
- Joined
- Aug 3, 2010
- Posts
- 29,114
- Reaction score
- 23,991
- Location
- Usually not in Ohio
- First Name
- Andy
- Truck Year
- '77, '78, '79, '84, '88
- Truck Model
- K5 thru K30
- Engine Size
- 350-454
1. I have never seen or heard of a perch weld failing.
2. When driving forward, the pinion tries to climb UP the ring gear. That's why the shock of the wheel hop caused the housing to rotate up.
3. The housing plug welds are a known weak point. It's recommended to fully weld the tubes to the housing for performance use.
4. You would not hear it. Even with broken plug welds, the tubes are still somewhat press-fit into the housing.
5. As much as the pinion angle is off, it will be pretty easy to see the pinion pointing up way more than the spring perches. Just go take another look or take a pic for the rest of us to see. Confirm with an angle finder, you can get one for less than 10 bucks.
2. When driving forward, the pinion tries to climb UP the ring gear. That's why the shock of the wheel hop caused the housing to rotate up.
3. The housing plug welds are a known weak point. It's recommended to fully weld the tubes to the housing for performance use.
4. You would not hear it. Even with broken plug welds, the tubes are still somewhat press-fit into the housing.
5. As much as the pinion angle is off, it will be pretty easy to see the pinion pointing up way more than the spring perches. Just go take another look or take a pic for the rest of us to see. Confirm with an angle finder, you can get one for less than 10 bucks.
aGood'olBoy
Full Access Member
- Joined
- Oct 8, 2013
- Posts
- 187
- Reaction score
- 3
- Location
- Waterford Pennsylvania
- First Name
- Jeremiah
- Truck Year
- 1985
- Truck Model
- k10
- Engine Size
- 350
The pinion is point up roughly 15 degrees give or take a degree. Or two.. But I don't know how well you can tell but the perches are rounded fairly significantly actually. Don't think this would cause the pinion angle to still be so severe. Probably doesn't help either
Attachments
- Joined
- Aug 3, 2010
- Posts
- 29,114
- Reaction score
- 23,991
- Location
- Usually not in Ohio
- First Name
- Andy
- Truck Year
- '77, '78, '79, '84, '88
- Truck Model
- K5 thru K30
- Engine Size
- 350-454
Wow, that perch is shot. It could be hurting the pinion angle slightly, but not that much. I'm surprised you were able to keep the u-bolts tight with perches like that.
aGood'olBoy
Full Access Member
- Joined
- Oct 8, 2013
- Posts
- 187
- Reaction score
- 3
- Location
- Waterford Pennsylvania
- First Name
- Jeremiah
- Truck Year
- 1985
- Truck Model
- k10
- Engine Size
- 350
I'm trying to sell my truck so I'd rather not put any money into it. But do you think I could weld new perches on at the correct angle and not abuse it till I sell this pig? That would make more sense than getting a new axle. I tried to spin the pinion back with a chain wrapped around the bottom of my jack and pinion. That way the more I pushed up on the diff the pinion would spin. But all it did was load the axle. So I think in my head welding the perches would fix my problem. What do you guys think?
Skweegle89
Full Access Member
- Joined
- May 21, 2014
- Posts
- 2,347
- Reaction score
- 25
- Location
- Oklahoma
- First Name
- Zach
- Truck Year
- 1985
- Truck Model
- K10
- Engine Size
- 350
All that would accomplish is fooling the person your selling it to. That's if he doesn't know any better and can't tell what you have done. Definitely not a solution to the problem at hand. Fix it right and sell it and keep a clear conscience. I have been on the receiving end of sales like that and I assure you the automotive world has enough of those people without adding your name to the hat. Just my .02.
Sent from my iPhone using Tapatalk
- Joined
- Aug 3, 2010
- Posts
- 29,114
- Reaction score
- 23,991
- Location
- Usually not in Ohio
- First Name
- Andy
- Truck Year
- '77, '78, '79, '84, '88
- Truck Model
- K5 thru K30
- Engine Size
- 350-454
Here's what I would do if I had no money to spend on it.
Cut the perches off and weld on good ones at the correct angle. Weld the tubes to the center section. It will probably be OK after that, but you never really know. Let any potential buyer know what you have done and that it should be ok, but if they don't want to take the chance, a replacement housing should be swapped in.
Cut the perches off and weld on good ones at the correct angle. Weld the tubes to the center section. It will probably be OK after that, but you never really know. Let any potential buyer know what you have done and that it should be ok, but if they don't want to take the chance, a replacement housing should be swapped in.
