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Old 10-16-2018, 09:03 PM   #1
zac
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Did front axle swap--front end now bounces and wobbles under braking

'79 K20 Camper Special. Swapped to 3.42's years ago. Bought a 10 bolt that by all appearances is in much better condition than the one I was running. Put in new Spicer ball joints and new u joints in the knuckles. Was my first time putting in ball joints. Everything went surprisingly well. Installed them exactly per the manual. Lower nut 80 ft lbs, upper sleeve at 50 with the special socket, upper nut 100. Truck already had new drag link, steering box is good, new tie rod ends. Shocks are gas magnums a couple years old. Steering stabilizer is sketchy but new one on order. Rotors turned, new pads. I used the 8 lug hubs, spindles and ALL the outer stuff from the other axle that was working perfectly. None of that stuff was changed. The only issue with the old axle is that the lower ball joints were wearing out and I knew from looking the gears weren't great. Came off a full time truck. I get everything together and take a test drive but figure I'm done. So anytime I do moderate to heavy braking the front end bounces and wobbles uncontrollably, to the point it's terrifying. It sometimes gets into this sort of harmonic bounce that forces me to come to a complete stop. When the brakes aren't applied it drives perfectly. Or as well as one of these ever does.

Wheel bearings checked and adjusted 3 times. No detectable slop anywhere. Rotors turned again just for good measure. Dropped the axle again just to check for cracked leaves and to make sure it's tight and located properly. I'm running Ford 7" wide 8 lug steelies because the work well with my tires. Sometimes they don't seat perfectly true some I'm very careful about that. The truck is not lifted and is essentially completely stock. And it was driving perfectly well with the old axle. All of this is entirely new. I see no damage or anything bent. I'm out of ideas.

Thanks in advance. FYI I'm on the road til early AM Saturday so my internet access will be hit and miss and I won't be able to go out and look at anything.
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Old 10-17-2018, 08:22 AM   #2
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Re: Did front axle swap--front end now bounces and wobbles under braking

I had a 63 shortbed that did that and a steering stabilizer cured it. I don't know about the 4x4 tho. Are you running older shocks?
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Old 10-17-2018, 10:32 AM   #3
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Re: Did front axle swap--front end now bounces and wobbles under braking

You had your rotors turned...check them for runout....I had mine turned and I don't know what they did but one had .020 ,the other was .043 runout.....I trashed em and bought new ....problem solved...on mine anyway....
Also check to make sure the rotor is seated good when you press the studs in...
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Old 10-17-2018, 03:22 PM   #4
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Re: Did front axle swap--front end now bounces and wobbles under braking

Thanks guys....stabilizer should be at the house when I get back. Shocks are standard Monroe gas magnums 2-3 years old. But you mentioning that made me remember something. I will double check runout and rotor seating on the hub. Cheap and easy.

I’m going to spare you a bunch of unnecessary details of how this came up, but a bad tire/bent rim could cause this I assume. Don’t know why it would just start when I swapped on a better axle, but sometimes when you open a can of worms you get worms. When I was reinstalling the shocks the passenger side one had enough resistance that it was a real struggle to get it back in place. On the drivers side I just put my palm under it and pushed it into the mount. And now that I remember that I can remember a low stump I hit last winter with that tire. Had to replace the steering box as a result because it had internal damage.
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Old 10-18-2018, 12:13 PM   #5
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Re: Did front axle swap--front end now bounces and wobbles under braking

U-bolts torqued to at least 150lbs, alignment for proper toe-in
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Old 10-18-2018, 09:40 PM   #6
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Re: Did front axle swap--front end now bounces and wobbles under braking

The stabilizer is important but I'd bet you have another issue. Did the front drive axle ujoints move freely after you installed them?

Have you tried locking the hubs and driving the truck does it still shake? I had a frozen drive axle ujoint create the same issue.
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Old 10-18-2018, 10:04 PM   #7
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Re: Did front axle swap--front end now bounces and wobbles under braking

Subscribed. Afraid I'm not much help. Agree with the above post, a stabilizer might help but I have driven my K20 a lot without one, and no problems. I'm running one again now but it's more for looks than anything.

Sounds like you might have damaged that pass. side shock when you hit the stump. I would consider replacing both front shocks. FWIW, I was disappointed in my Monroe Gas Magnums many years ago. They are huge and look plenty capable but they got mushy way too soon. I replaced them with KYB Gas-a-justs and they are still on the truck.

Good luck and I hope you find the problem. It sounds dangerous....
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Old 10-18-2018, 10:29 PM   #8
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Re: Did front axle swap--front end now bounces and wobbles under braking

Yeah, I’m not putting a lot of faith in the stabilizer but it was overdue for replacement.... now that I’ve had time to think and be away from it I’m leaning towards the shocks and maybe tire issues. Because of job loss related issues I have never had new tires on this truck and I think it may be a factor here as well. I was getting a little shake in the front end before the axle swap but figured it was rotors. My situation is much improved but ironically I was waiting to get the front end gone through before buying new tires. Weird that this wouldn’t have happened before, but I guess when you have a mishmash of various used parts mixed with new and maybe worn parts anything can happen. Thankful that I have a bunch of stuff to look at this weekend.
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Old 10-18-2018, 10:37 PM   #9
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Re: Did front axle swap--front end now bounces and wobbles under braking

Oh, and the u joints seemed fine. I was careful. They were free but not floppy like you see on used ones. I have used the 4wd but not on the road, so I haven’t had it going fast enough with the hubs locked to really know. The u bolts are probably torqued to about a quarter million ft lbs at this point which I’m sure I will regret at some point. I tweaked the toe a bit. I will get it checked before getting new tires but I’m confident it’s within service tolerances right now.
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Old 10-19-2018, 12:36 PM   #10
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Re: Did front axle swap--front end now bounces and wobbles under braking

Drag link, tie rod end, pitman are all good? Steering arm has the tapered shims and is torqued? Tires don't have a slipped belt? Rim not bent?
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Old 10-19-2018, 01:09 PM   #11
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Thumbs up Re: Did front axle swap--front end now bounces and wobbles under braking

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Drag link, tie rod end, pitman are all good? Steering arm has the tapered shims and is torqued? Tires don't have a slipped belt? Rim not bent?
Voice of experience right there....
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Old 10-20-2018, 10:38 PM   #12
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Re: Did front axle swap--front end now bounces and wobbles under braking

Think its a tire and/or wheel. No runout on the rotors. Checked the shocks, they are fine. Put on the new stabilizer, made me realize the old one was completely non functional. Seemed to have a little too much toe in so I adjusted it. Other than that everything seemed good. Since I thought the front left tire was the problem I swapped it with the left rear and took a test drive. I could tell right away there was still a tire shaking but the seat of the pants feel was different. When braking I got the bouncing again but not in the front and not as severe. After a couple tests I was sure it wasn't coming from the front. Whole truck shakes but controlability not an issue. Went home and for better or worse swapped my 9.50R16.5LT "Trailcat LT" spare for the one I think is bad which was now the left rear. On the test drive the tire shake was gone. Still some vibration from the back when heavy braking but much less. Known for a while I need to get the drums turned in back. Don't know if the bad tire also has a bent wheel, but when I bought the set of steelies I bought the whole set of five, so I have an extra. I have a spare set of drums I will get turned this week and tires are on order. Fairly confident that this is figured out, but you never really know.....

Still don't understand how I drove the truck home from work and into my shop with none of these issues. Two days later I have a new front axle and all kinds of problems. Thanks for all your input so far.
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Old 10-21-2018, 11:11 AM   #13
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Re: Did front axle swap--front end now bounces and wobbles under braking

I have chased that problem as well! Twice I had that issue, and each time I went crazy looking for something to blame. Last time I replaced most of the steering trying to fix it. Both times were with used tires, and both times it end d up being a bad tire (in my defense it was years between the two issues and I admittedly forgot to check tires)! Rotated them and the problem was fixed or moved to the corresponding tire location.

It’s easy to dismiss the simplest solutions looking for a bigger one (I have been there).
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Old 10-21-2018, 02:36 PM   #14
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Re: Did front axle swap--front end now bounces and wobbles under braking

Glad you're seeing some progress. Fairly easy to look for a bent wheel -- install it on the rear (either side), chock the front tires (on level ground), jack up the rear and put jackstands under it (I would also leave the jack in place). Start the engine, put the trans in low gear at idle, and eyeball the suspect wheel. If you don't see obvious runout, try holding a crayon against a brace and use that to mark any 'high' spots on the wheel.
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Old 10-21-2018, 04:57 PM   #15
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Re: Did front axle swap--front end now bounces and wobbles under braking

I was thinking the same a stocker to check wheels and tires....thats easy enough to do...
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Old 10-29-2018, 08:14 AM   #16
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Re: Did front axle swap--front end now bounces and wobbles under braking

Update: Work schedule hasn’t allowed me to do much. Tires never showed up because I ordered them online from Pep Boys. They are so terrible, don’t know why I keep dealing with them. Canceled the order and have some coming from somewhere else. Using the suggested technique it appears the front drivers wheel is bent. But yesterday I installed the turned drums, new shoes and hardware kit on the rear. So with totally redone brake system I still get this wobble or vibration under medium to heavy braking. I’m using 3 crap tires and an old spare, so there is no way to really troubleshoot this until the new tires are on, hopefully next week. But there’s still a “that ain’t right” feel to this, although it’s an understatement to say I’m pretty paranoid at this point. And during normal driving the problem isn’t noticeable with the very light braking I normally do with an empty truck and the big full floater brakes.

I hate the idea I may have to swap the other axle back on, at least temporarily. The new one seems to be in great condition. I was told it came off a ‘90 Suburban—still a square body. If it had been subjected to any Fall Guy treatment I think it would have been evident.
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Old 10-31-2018, 12:23 AM   #17
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Re: Did front axle swap--front end now bounces and wobbles under braking

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U-bolts torqued to at least 150lbs, alignment for proper toe-in
This ^^^ the basics.

Alignment is often overlooked, cheap to have done on these trucks and really often overlooked. Bad alignment will trash a new set of tires in short order as well.

If all shocks, bushings and joints are in good shape and alignment is in spec, a stabilizer is seldom needed. Every truck that Ive ever had that needed one usually had a different underlying problem that the stabilizer masked a little.

I haven't had to run one on the last 4 straight axles that Ive owned.
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Old 11-10-2018, 07:03 PM   #18
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Re: Did front axle swap--front end now bounces and wobbles under braking

So after a week, Pep Boys couldn't even confirm they had my tires anywhere in their system. Canceled the order and ordered from Discount Tire Online on a Sunday evening, tires came about noon the next Tuesday. Take that fwiw.

Take the tires in to get them mounted at my usual tire place. New people, don't recognize anybody. Take them home and two weights fall off while I'm mounting them. That was the reason I quit going to my last tire place. Amazing. So I mount those wheels on the back and go out for a drive. It's better, but vibration when braking is still there. Figure I'll drive it to work in the morning anyway, so I check the oil in my rebuilt engine--less than 1000 miles. Dipstick tube comes off in my hand. Tube broke off flush with the block. It gets worse. Locate another dipstick and tube in the pile, grab a tool with a hook on it I use for snap rings, seals, etc. I get it in the tube stump and it starts to turn, I think it's coming out. Then the little hook on the end breaks off and falls in the oil pan.

Have to move the truck because its getting dark and it's stuck blocking my wife's car in the garage. Engine runs for maybe 20 seconds as I pull it in my shop. When I get a chance to look at it a couple days later I drain the oil and fish around with magnets trying to get the hook out the drain hole. Pointless. Dropped the pan, pulled off the oil pump and knocked the hook out of the pickup where it was up against the screen.

Mentally recovered from that and took the truck to a different shop. Told them to rebalance all the tires and align it. They are truck people. They said the "AW" on the weights the other place used were for aluminum wheels. Go figure. All the wheels were out of balance. They aligned the truck using the new tie rod ends and adjuster sleeve I brought in. Heading home I'm freaked out by the fact that in the 9+ yrs I've had this truck, this is the first time I'd seen the steering wheel straight when I'm going straight. But the brake vibe is still there. Otherwise, drives and handles great. Figure I've eliminated all the other problems, it's just a brake system issue.

I had left my phone on the counter at the shop so I went back to get it. Owner asked me how the truck drove, I told him great except for the braking thing which wasn't on them, something I had to figure out. He wanted to drive it to see for himself, so we test drove it all around town. He quizzed me about my wheel bearing adjustment technique and made a few suggestions. Said if I can't get it sorted out to bring it back. He did mention that sometimes bigger trucks don't do well with turned rotors, that they have to be replaced. I ran into this a few years ago when I had a mid-70's 472-500 Cadillac thing going on. Those cars were so heavy that turned rotors warped pretty much after my first exit ramp off the interstate. They had to be replaced. Problem is, I have no faith in the quality of new rotors available for sale now.

Hopefully at some point this thread will be of some use other than just me venting.
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Old 11-10-2018, 08:49 PM   #19
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Re: Did front axle swap--front end now bounces and wobbles under braking

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Hopefully at some point this thread will be of some use other than just me venting.
Other than your truck driving better now (except for braking), you have seen improvement, so that's a positive for you.

For me, your thread has helped me feel just a little better about all the problems my truck has had lately!
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Old 11-10-2018, 09:50 PM   #20
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Re: Did front axle swap--front end now bounces and wobbles under braking

way back in post #3 I pointed out my issue with turned rotors...new ones from oreillys fixed my problems....vibration under braking usually points at some issue with the brakes...glad the other stuff worked out...as for your lost hook that's why its best to run a magnet attached to the oil pan..
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Old 11-13-2018, 06:04 PM   #21
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Re: Did front axle swap--front end now bounces and wobbles under braking

Noticed after the wheels were actually balanced and front end aligned, truck pulls left when braking. That was new. Lots of brake dust on the left front wheel, way too much considering that was the new, unbent one that had been on for less than 100 miles. Put new pads on. Checked for runout on both rotors, on more than one spot. None.

Still the wobble, but stopped straight ahead. Driveable now, just not much fun. Put about 120 miles on it over a couple days in normal, mixed driving--the first time I'd really been able to do it since this all started. Every time I came to a stop, "that's rotors" is all I could think. Finally found an O'Reillys that had two in stock, put them on, problem solved. Not just better, day and night difference. Smooth, straight stops.

Not sure how I could have done this differently. 40 years of abuse and neglect, and then I decided to make it a daily driver. Where are you supposed to start? I worked my ass off this year welding, engine building, wiring, fixing gauges, lights, etc. etc. etc. All the problems I had at the end here popped up when I did the axle swap. Obviously there were a lot of things going on other that just the rotors. Bad tires, bent wheel, bad alignment. I guess you just plow through it. Mixing new, good used and repro parts. Bound to be issues, I guess.

Thanks for everyone's input and help. So my truck had problems when braking, and it turned out to be rotors. Go figure. This truck was the warmup/guinea pig for what I really want to work on, a '70 K10 Suburban, so I will be back with more stupid problems I suppose. I've got a disc brake D44 for it that I pulled off a '72. I'll probably get new rotors....
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Old 11-13-2018, 09:05 PM   #22
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Re: Did front axle swap--front end now bounces and wobbles under braking

Glad you got a handle on it....
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Old 11-18-2018, 06:15 AM   #23
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Re: Did front axle swap--front end now bounces and wobbles under braking

Great thread! Sounds like you haven't made an offering to the Square gods lately! ��

Before you have more issues when you do the D44 swap - get the BOM number off the axle tube to see whether it's the older version or newer version.
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