Need help with front end head-scratcher (1 Viewer)

[JL2167]

Good evening: I'm trying to diagnose a front-end problem with my '78 FJ40 and am looking for some advice from those with more experience and know-how than I possess. i apologize in advance for the length of this post, but I figure the more information I give the better.

Was driving to work the other day, about 1/2 mile out of my driveway I started hearing a rattling and thumping sound from under the front end. Seemed to be coming from the passenger side. No vibration or pull on steering wheel, no loose steering, no strange smell. Just rattling and thumping. Then I started to get an intermittent high-pitched whining sound. My speed of travel at the time was between 20 and 30 mph. At that point I turned around and tried to limp back home. Made it about 1/2 mile when all of a sudden my front end locked up -- it was as if I had hit the brakes, but I hadn't. Called a tow, when he was winching my rig onto the flatbed the front wheels wouldn't turn at first, then they suddenly released and rolled. Same thing when we were unloading -- front wheels were locked at first, but after a couple of hard pushes the front wheels released and it rolled down the ramp and into the street. I jumped in and drove it into the garage, where it now sits. Rig was in 2WD the whole time and front hubs were not locked.

I jacked up each of the front wheels and checked for wobble, noise, or sticking. Passenger side makes a slight ticking noise when I spin it, other than that both wheels spin free with no noticeable wobble or noise.

Rig has original front brake rotors and calipers (I'm pretty sure brake lines are original too), so I was thinking it might be a stuck brake caliper. But there was no brake pad smell and the rig did not pull to one side when I was driving it. So not sure if that's it.

Wheel bearings are only three years old, and aside from the slight clicking sound on the passenger side the wheels seems solid. So that doesn't seem to be it either.

If anyone has advice as to what the problem might be, or anything I should do to try and better diagnose the problem, I'd greatly appreciate it.

Thanks for taking the time to read this post.

 

[Mr. Green]

I had a rubber brake line corrode internally on a 1969 z28 to the point that it exhibited exactly what you experienced. It slowly manifested over a 10 minute drive just out of the blue one day. When it sat unused, the brake pressure slowly bled back so that car could roll again but if you tapped brakes at all it would instantly try to lock up the front wheels. I’d check those rubber lines or any hard lines for debris. Bleed your system, likely not done in forever. Being back in your garage, see if you can replicate it on jack stands.

 

[JL2167]

I had a rubber brake line corrode internally on a 1969 z28 to the point that it exhibited exactly what you experienced. It slowly manifested over a 10 minute drive just out of the blue one day. When it sat unused, the brake pressure slowly bled back so that car could roll again but if you tapped brakes at all it would instantly try to lock up the front wheels. I’d check those rubber lines or any hard lines for debris. Bleed your system, likely not done in forever. Being back in your garage, see if you can replicate it on jack stands.

Great advice. Thanks so much!

 

[charliemeyer007]

Sounds like wheel bearing whine - ticking could be a cracked race. Pull the hubs and look.

+1 for internal brake hose damage acting like a diode. Had that happen on my F150 - hard to figure out if you aren't a where that could happen.

 

[JL2167]

Sounds like wheel bearing whine - ticking could be a cracked race. Pull the hubs and look.

+1 for internal brake hose damage acting like a diode. Had that happen on my F150 - hard to figure out if you aren't a where that could happen.

Thanks - I’ll do that!

 

[1969FJ]

Perhaps a something with the birfield ? Could be.

 

[JL2167]

Perhaps a something with the birfield ? Could be.

Had to look that one up

Could Birfield/CV joint be the cause even though I was in 2WD with hubs unlocked?

 

[Malleus]

The driveshafts rotate every time the transmission/transfer output shaft rotates. It makes no difference whether the driveshafts are conencted to the wheels or not. This is why, IMHO, lockout hubs are useless axle jewelry.

 

[pb4ugo]

It sounds like an issue with the brakes or hubs. It's all guesses until you start disassembly. When you take each item off inspect them carefully. Were the caliper bolts tight, are the pads loose or wearing unevenly, do the caliper pistons retract, are the lockouts working properly etc. If it was making noise, look for wear or loose fastners.

 

[45Dougal]

I note that the OP states both front wheels were locked up when putting on the ramp.

Maybe this was just an assumption because one of them was stuck?

If indeed they were both locked then that indicates a common problem - maybe a dirty master cylinder? Take off the lid and check if the fluid flows back when you release the pedal? Otherwise, one brake binds up and then gets warm, and the pressure increase suddenly locks both fronts.

 

[JL2167]

The driveshafts rotate every time the transmission/transfer output shaft rotates. It makes no difference whether the driveshafts are conencted to the wheels or not. This is why, IMHO, lockout hubs are useless axle jewelry.

Got it -- thanks!

 

[JL2167]

I note that the OP states both front wheels were locked up when putting on the ramp.

Maybe this was just an assumption because one of them was stuck?

If indeed they were both locked then that indicates a common problem - maybe a dirty master cylinder? Take off the lid and check if the fluid flows back when you release the pedal? Otherwise, one brake binds up and then gets warm, and the pressure increase suddenly locks both fronts.

It sounds like an issue with the brakes or hubs. It's all guesses until you start disassembly. When you take each item off inspect them carefully. Were the caliper bolts tight, are the pads loose or wearing unevenly, do the caliper pistons retract, are the lockouts working properly etc. If it was making noise, look for wear or loose fastners.

Roger that. Thanks for your help!

 

[JL2167]

I note that the OP states both front wheels were locked up when putting on the ramp.

Maybe this was just an assumption because one of them was stuck?

If indeed they were both locked then that indicates a common problem - maybe a dirty master cylinder? Take off the lid and check if the fluid flows back when you release the pedal? Otherwise, one brake binds up and then gets warm, and the pressure increase suddenly locks both fronts.

I guess it could have been only one that was locked up. I'll definitely check the master cylinder. Thanks!

 

[charliemeyer007]

When I'm in 2H and the hubs are turned out, the front axles don't move and neither does the front drive line. If I try and put in 4H while moving I can feel the drive line try to catch. If the hubs are turned in, I can shift from 2H to 4H with no effort or clutch action - that's because the wheels are turning the axle and the drive line at the same speed as the rear stuff. That's why I like and have hubs.

 

[cruiseroutfit]

The driveshafts rotate every time the transmission/transfer output shaft rotates. It makes no difference whether the driveshafts are conencted to the wheels or not. This is why, IMHO, lockout hubs are useless axle jewelry.

What? How does the front driveshaft spin if the free-wheel hubs are un-locked and the transfer case is in 2WD.

In fact it sits perfectly stationary and doesn’t rotate under those conditions. Nor does the Tcase front output flange, ring & pinion, carrier, inner axles or birf… they are all static.

 

[jim land]

Maybe just a small rock between the backing plate and disc

 

[jim land]

The driveshafts rotate every time the transmission/transfer output shaft rotates. It makes no difference whether the driveshafts are conencted to the wheels or not. This is why, IMHO, lockout hubs are useless axle jewelry.

Fj40 are not full time 4wd , the locking hubs are usefull for less wear on parts and better mpg

 

[Malleus]

Normally, I just ignore comments like these, but you're wrong. The FJ40 is fulltime four wheel drive. The transfer case only has a high/low selector lever, meaning both axles drive the vehicle. Always.

The only way an FJ40 is not fulltime four wheel drive is when the front axles are fitted with locking hubs, removing the left and right driveshafts from engagement. To my knowledge, North American FJ40 front axles were fitted with lockout hubs as a dealer installed option.

You can argue, as many people have over the last several decades since locking hubs became commercially available, that they have benefits. The only real benefit locking hubs have is profit for the manufacturers supplying them. The ring and pinion in the front axle turn regardless of whether the driveshafts in the axles are connected to the wheels or not. The argument that there is no load on them since they are not connected to the wheels, and therefore do not wear, is wrong. The ring and pinion gearset is hardened to prevent wear and strengthen the overall gearset. Normal driving loads present no more wear on the front gearset than on the rear gearset.

As to increased mileage, I've never seen proof of that.

 

[Malleus]

What? How does the front driveshaft spin if the free-wheel hubs are un-locked and the transfer case is in 2WD.

In fact it sits perfectly stationary and doesn’t rotate under those conditions. Nor does the Tcase front output flange, ring & pinion, carrier, inner axles or birf… they are all static.

Kurt, maybe you have a different transfer case in mind than mine. My '77 only has high and low, not front and rear. My '76 and '80 also only had Hi/Lo, IIRC.

 

[middlecalf]

There’s no FD engagement lever on the later 40’s?