What would cause "lunging"?
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Fleet Mechanic
Joined: Sep 2013
Posts: 1,504
Likes: 8
From: Indian Falls, New York
I've experienced this on multiple 80s trucks now, from bullnose and Bricknose trucks, half tons and 3/4 tons. I can only describe it as a lunging feeling that shakes the entire vehicle. It typically happens when costing between 45-55mph. Tapping the brakes usually solves it. It will immediately stop. Think of costing down the road nice and smooth and slowly you get a shake that's "forward and back" that's rather fast.
I've only ever noticed it on older Ford pickups. Never on new trucks, never on GM or Dodge trucks and I've been around them all.
The only things I can think of are out of balance tires and bad alignments which isn't uncommon on D44 TTB front ends. I always wonder what this was and what was causing this to seemingly be only on older Fords, specifically 80s trucks.
I've only ever noticed it on older Ford pickups. Never on new trucks, never on GM or Dodge trucks and I've been around them all.
The only things I can think of are out of balance tires and bad alignments which isn't uncommon on D44 TTB front ends. I always wonder what this was and what was causing this to seemingly be only on older Fords, specifically 80s trucks.
Posting Guru
Joined: Apr 2011
Posts: 1,636
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From: Orlando area
I had a truck once that would get up to 40ish mph and start to shake. It would shake real bad. Tapping the brakes would stop the shake - for a short while.
The problem was that one of the tie rod ends was bad causing the LF wheel shake/vibrate. Of course new tie rod ends fixed the problem.
However this is not a "Ford only" problem. Actually this instance was on a Toyota truck.
The problem was that one of the tie rod ends was bad causing the LF wheel shake/vibrate. Of course new tie rod ends fixed the problem.
However this is not a "Ford only" problem. Actually this instance was on a Toyota truck.
Postmaster
Joined: Jun 2014
Posts: 3,206
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From: Oakhust NJ Jersey Shore
Is the problem a shake in the steering wheel or a feeling like the truck is lunging. You can feel it in the seat, forward and backward? That could be TCC shutter, the torque converter locking and unlocking, very common on fords, next time it does it dont hit the brakes, down shift with the stick or take it out of overdrive, if it stops, you got TCC shutter, Add a can of anti shutter, they actually make it, it's in a red bottle and I have used it many times, it works. 
Moderator
Joined: Jan 2001
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From: Virginia
He is hinting in his post that it's not a problem with his truck, but a common symptom in a lot of trucks he has driven. I know what he is talking about, it's more like a bucking at certain speeds and throttle positions.
I think it's a action/reaction thing with either the rear leaf springs, or the whole frame is flexing in the middle. If you want to aggravate it, get a decent sized trailer and pull it with your truck. Certain speeds with certain loads, it will really buck up and down.
I think it's a action/reaction thing with either the rear leaf springs, or the whole frame is flexing in the middle. If you want to aggravate it, get a decent sized trailer and pull it with your truck. Certain speeds with certain loads, it will really buck up and down.
Thread Starter
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Fleet Mechanic
Joined: Sep 2013
Posts: 1,504
Likes: 8
From: Indian Falls, New York
He is hinting in his post that it's not a problem with his truck, but a common symptom in a lot of trucks he has driven. I know what he is talking about, it's more like a bucking at certain speeds and throttle positions.
I think it's a action/reaction thing with either the rear leaf springs, or the whole frame is flexing in the middle. If you want to aggravate it, get a decent sized trailer and pull it with your truck. Certain speeds with certain loads, it will really buck up and down.
I think it's a action/reaction thing with either the rear leaf springs, or the whole frame is flexing in the middle. If you want to aggravate it, get a decent sized trailer and pull it with your truck. Certain speeds with certain loads, it will really buck up and down.
I was always curious as to why some of these Fords have done it.
I've felt it in several vehicles, an 89 Bronco, a 92 Bronco and my dads 85 F250.
Senior User
Joined: Jul 2014
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been there, seen that, same about speed very very annoying and terrifying
two things i've found as the cause
an egg outside the tire caused by the steel belt separating leaving 1/2 or so bulge in the tire which amplifies at certain speeds. take feel each tire and make sure no deformations exist
the most rare:
water inside the tire that throws the balance off horribly. this was caused because i used cheap worthless gas station "free" air which contained water. this accumulated inside the tire and would throw the car into "really bad jumpy mode" at certain fast speeds. this could also be caused by "fix a flat" or "goop or any of that slime"
lastly.....do you have a vacuum gauge when this is happening? because you could have some sort of brake booster leak or lastly...extremely rare could one of your brake drum rotors be catching?
maybe even suspension problems or loose steering tie rods, jack up car, and carefully shake wheels right and left to see if anything is clearly wrong. there should be very very little if any "movement" when you try to move the tire when jacked up.
two things i've found as the cause
an egg outside the tire caused by the steel belt separating leaving 1/2 or so bulge in the tire which amplifies at certain speeds. take feel each tire and make sure no deformations exist
the most rare:
water inside the tire that throws the balance off horribly. this was caused because i used cheap worthless gas station "free" air which contained water. this accumulated inside the tire and would throw the car into "really bad jumpy mode" at certain fast speeds. this could also be caused by "fix a flat" or "goop or any of that slime"
lastly.....do you have a vacuum gauge when this is happening? because you could have some sort of brake booster leak or lastly...extremely rare could one of your brake drum rotors be catching?
maybe even suspension problems or loose steering tie rods, jack up car, and carefully shake wheels right and left to see if anything is clearly wrong. there should be very very little if any "movement" when you try to move the tire when jacked up.
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Cargo Master
Joined: Mar 2007
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From: Arcadia, Fla
Its probably drive line back lash causing the bucking/surging . My 89 F250 does it around 40 to 50 MPH. I have a AOD so there's no TCC issues to cause it. Some days it's very noticeable, but mostly not.
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What does the vacuum gauge say?
Thread Starter
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Fleet Mechanic
Joined: Sep 2013
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From: Indian Falls, New York
I've felt it with in spec alignments and tires and that balanced at 0/0 myself. I have also felt it with various tire sizes. 215/85, 235/85, 265/75, and 33x12.5. No change.
Clearly it's not an uncommon problem if you all have felt it. I am extremely curious. It just doesn't make sense.
Clearly it's not an uncommon problem if you all have felt it. I am extremely curious. It just doesn't make sense.
Logistics Pro
Joined: Sep 2011
Posts: 4,491
Likes: 26
From: Algona,WA
Stiff suspension, stiff 10 ply tires, stiff shocks, all of those rebound very quickly to the mildest of bumps. Which is probably causing what most of us feel at certain speeds. My truck rides smoother at higher speeds and it smooths out allowing the mild bumps to barely be rebounded, and it works the suspension back and forth. Especially if the road isn't 100% perfect.
Thread Starter
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Fleet Mechanic
Joined: Sep 2013
Posts: 1,504
Likes: 8
From: Indian Falls, New York
Stiff suspension, stiff 10 ply tires, stiff shocks, all of those rebound very quickly to the mildest of bumps. Which is probably causing what most of us feel at certain speeds. My truck rides smoother at higher speeds and it smooths out allowing the mild bumps to barely be rebounded, and it works the suspension back and forth. Especially if the road isn't 100% perfect.
Senior User
Joined: Jul 2014
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I've felt it with in spec alignments and tires and that balanced at 0/0 myself. I have also felt it with various tire sizes. 215/85, 235/85, 265/75, and 33x12.5. No change.
Clearly it's not an uncommon problem if you all have felt it. I am extremely curious. It just doesn't make sense.
Clearly it's not an uncommon problem if you all have felt it. I am extremely curious. It just doesn't make sense.
Balancing doesn't work if there is water inside the tire. balancing also can't fix a slightly bulging tire.
What we need, is someone to test this with and without a heavy load in their trucks. same road, same speed, different amount in the truck bed. See if the problem gets better or worse. Also video!