Womp / chug sound matching jumping speedo - help! (1 Viewer)

[Outono]

Alright guys, need some help here. Im getting a loud womp womp / chug chug sound as my tires rotate - the speedo jumps and matches the sound. Here's a video:

Untitled

When the video goes dark, I put the phone next to the transmission, which is where im hearing the noise emanate from. Its more pronounced as I slow down and tends to go away as soon as I hit around 60kph.

What do you think? Bad wheel bearings? Tires going bad? Im on 35" MTRs so I don't expect the speedo to be perfect, but i've had this sound since I bought the truck and would really like to know how to get rid of it.

The truck is a '91 HDJ81 w/ auto transmission.

 

[Tools R Us]

Speedo cable and or drive gear?

 

[LandCruisinMy93]

Does the rest of the vehicle shake? Does the steering wheel shake? Does it change when you're braking? Those are things I'd expect to see from a wheel bearing, bad spindle, bad tire etc... if you don't have these issues I'd think it is drivetrain related. But for fun check the steering control arms on the front and make sure theyr still bolted down and have their studs. Had a similar sound and had lost some studs after some heavy wheeling. I'm thinking just from sound and speedo that it's probably the drivetrain or as @Tools R Us said, speedo cable. It's really kind of difficult to tell.

 

[Michael Hanson]

Hi, If coming from transmission I'd say torque converter, transfer case. Mike

 

[Outono]

The rest of the vehicle vibrates, but only so much as an old diesel would. Its really not bad. Nothing changes when im braking, but interestingly if I let the car slow down by taking my foot off the pedal, the sound is more pronounced and the speedo bounces a lot more. If I brake, the noise and bouncing speedo is reduced quite a bit.

Did I mention the truck only has 81,000 miles on it and that it was never wheeled too hard?

The steering wheel does shake and this leads me to believe the tire balance is off. I checked the tires this morning and found out that the front two are 13 years old (back two are just 2 years old). The old tires still have a good amount of tread on them, but upon looking on the inside walls it seems there is quite a bit of wear. Tires are being replaced tomorrow. Wish I noticed this when I first picked up the truck...

Will take a look at the steering control arms, t-case, and torque converter, but would those 3 affect the speedo the way its shown in the video?

Thanks for the input guys.

 

[BlueCruiser84]

I'd be checking the rear of the transfer case. The speedo drive gear is there as well as a couple important bearings.

I would t drive it until you crawl underneath and confirm something isn't about to fly apart. That was a pretty loud noise.

 

[Sarmajor]

Hopefully you have a tyre delaminating and the new tyres make the sound go away. Were you actually travelling at the indicated speed?
Is your truck full time 4wd? It should ideally have all the tyres replaced at the same time. You say that the fronts are old and the rears are significantly newer. If they are at different wear levels then the Center diff is getting a real workout keeping things from binding all the time. I run 285/75R16 BFG MTR KM2's on my truck and from new to old the speedo changes about 3 mph.
I would also get under the truck (on a hoist is best) and check for loose anything. U joints, suspension bolts, gear box cross member are a few of the things to check.

 

[Outono]

Update time!

Swapped the old tires out for some new BFG KO2's (and damn do they look good). The chug noise has been significantly reduced, handling has improved, and the speedo doesnt bounce anywhere near as badly. I think those front tires were a big part of the issue (good call Sarmajor). The speedo itself is off by around 8 or 9mph at all times, but thats to be expected given the larger tires. And yea, the truck is full time 4wd (its an HDJ81).

A few weeks back Yotamasters reseated the front wheel bearings and mentioned that they may need to be replaced at some point in the near future. They didnt think it was critical and im still not convinced this is the issue. The noise doesnt change when I turn either way and as I mentioned above, its loudest when the truck slows down on its own (foot off the pedal).

If it was the drivetrain, you'd think the noise would always be there no matter what speed, but it begins to disappear around 60kph and totally gone by 80kph. In fact, the speedo barely bounces once you pass 60kph. Im out of town this weekend, but im hoping to hoist the truck and get a good look underneath next weekend.

 

[LandCruisinMy93]

Ok, listened again and read your updates. I'm going with question 1: is it part time? If the answer is yes, I'm going with rear output bearing and possibly damaged speedo gear. If it's AWD I'm going with the same thing if it's not Viscous coupled. The vibration could subside at higher speeds if it's a failing bearing, vibrations from imbalance of driveshafts and tires for instance, as long as they're not too far out smooth out with speed.

 

[Sarmajor]

Good luck with the hunting it down.
Do the 91 trucks have a cable drive speedo? My 92 has an electronic speedo although it uses the same drive gear system into the transfer case extension housing to drive the sensor. The speedo fluctuation could be a broken cable.
The speedo error seems about right for 315's on a truck that I think the factory recommends 275's for our trucks.
Wheel bearings are hard to detect due to the other noises competing for our attention.

I suspect the rear drive shaft universal joints or slip joint or the output shaft bearing for the noise.
Do you have a cdl switch?
You could drop the rear drive shaft and lock the cdl. Take the truck for a drive and see if the noise is still there.

Good to be talking with a fellow hdj81 owner.

 

[Outono]

Yes, my 91 has the cable drive speedo. The bouncing issue is the same problem I had with my 1992 FJ80 (US spec), except the 92 didnt have any noise with it. The speedo on that truck eventually just stopped working and I have yet to fix it (probably wont ever, whats the point...doesnt go very fast anyway ).

I drove the vehicle all over Joshua Tree this weekend and I almost completely forgot about the sound now that its so quiet with the new wheels/tires. This morning I took my time driving into the office, listening carefully for the chug/womp, but im only now hearing a light rubbing sound, as if a cable is brushing up against something beneath the transmission box. Maybe it really is just a bad speedo cable...

I do have the factory CDL switch - will take your suggestion Sarmajor and give it a shot later this week.

Thanks for all the help!