Noctivagans

Hey all,

I'm a long time reader, first time poster. Can't quite figure this one out on my own...

I have a 2003 Taco 4X4 DoubleCab with 135000kms on it. It's been under extended warranty (and still is) and dealer maintained up until I bought it in November. My problem is that when I come to a complete stop (or shortly before, if I let up on the brake a bit) I hear and feel a slight thump in the drivetrain (somewhere... I'm not sure where exactly). I also notice the shifter (it's a automatic) jumps forward a bit. The thump only happens in 2WD and usually gets worse as the truck warms up. I've lubed the drivetrain, and the fluid is full and looks to be in good shape. I'm sure it hasn't done any heavy hauling and know it hasn't done any towing (didn't come with a hitch... I just put one on). I'll be towing a light (1200lbs) trailer around all summer and don't want it to crap out on me. I'll be installing an AT oil cooler soon, but I'm sure that won't solve the thump issue. What the heck is going on? Any help would be greatly appreciated. Being a student, I usually do all my own maintenance to save a few bucks... but trannys aren't my thing.

Cheers!

Kiroshu

Try simple replace tranny filter and put new fluid in it. Check your UV joints. If theres play in them they are bad and need replacing. Mounts?

Noctivagans

Thanks for the advice, Kiroshu. I just installed a Hayden transmission cooler so the AT fluid has been replaced. The thumping seems to be a bit better, but is still there off and on. I'll look into u-joints and mounts soon.

99sr5runner

Make sure that the slip yoke on the driveshaft is greased up to full capacity.

jdsdj98

Ditto. That's all it is.

How exactly does one know when "full capacity" is reached? I fixed this in my '01 with a little grease, then it started again shortly afterward. After lubing it a couple of times since that first time (January'ish, shortly after buying it), it stops thumping for a couple hundred miles, then starts again. It's expelling grease at the joint (that's just excess grease, right?), so I'm fairly confident I reached "full capacity," but I'm wondering if there's now a slightly bigger issue. I wouldn't expect needing to grease it practically every time I fill up with gas.

97ltd4x4

How exactly does one know when "full capacity" is reached?

When I grease the driveshaft,The slip yoke can take a lot of grease...

I watch the two pieces that telescope as soon as the outside piece starts to move every time pump the grease gun..I stop,its full at that point.

Noctivagans

This sounds exactly like my situation. The slip yolk was my original guess. But like jdsdj98, I've greased the slip yolk a number of times now and each time the thumping stops for a few days but then slowly returns. The fact that it does stop after greasing probably means I was originally on the right track. I'll go and give her another lubing and see what happens. Maybe it takes a few time for the grease to work its way through?

jdsdj98, does it stop thumping when it's in 4WD? I find that's the case with mine. I'm not about to drive around in 4WD full time, but I was trying to think of what it meant in terms of what's going on under there. Led me to think it was something with the front driveline...

jdsdj98

I haven't tried that, as I reserve 4WD only for ice/snow/gravel/dirt conditions, which we haven't seen much of here this winter. I've pumped a load of grease into the slip yoke and still get the thump every couple hundred miles. Like you, I guess I'll just keep pumping it in there until I can get it to stop. I'm aware that it can be pumped until the joint visibly expands, and while I haven't actually seen that when lubing, it is now expelling grease and making a nice gunk ring under my truck. For this reason, I feel like full capacity has been reached. That gunk ring wasn't there when I bought the truck, and the joint was bone dry, leading me to believe the PO didn't pay attention to the driveline. Hopefully I can get it lubed up and keep that thump at bay.

Good luck with yours. Sounds like we're experiencing the same thing. If you're able to permanently fix it, please post back. I'll do the same.

Noctivagans

Yeah, I've pumped it full of grease until it starts coming out... but to no avail for a permanent fix. It was bone dry when I bought mine (as was the rest of the driveline), so I'm wondering if there's any permanent damage that can be done if it's neglected for a long time. If so, would a guy have to end up replacing the slip yolk? And how big of a job would that be?

If I come up with anything, I'll let you know.

KBToys

I have the same issue, depending how fast I stop will determine how big of a thump I feel. Also I am pretty sure it is the tranny because I put it in netural and I don't get the thump.

jdsdj98

No - that's your slip yoke. Get some grease in it and you'll notice it stops. Putting the truck in neutral removes most of the torque in the driveline, making the slip yoke much less susceptible to the binding that produces the thump. That's the conclusion at which I've arrived, although someone here may have a better explanation. Start with the yoke, though. Your transmission's fine.

mt_goat

I have a different opinion about the common thumping problem the Tacos always get. I think the problem is really axle wrap from those crappy Dana leaf springs. And the reason packing the slip yoke with grease helps is because it basicly turns the drive shaft into a form of a traction bar, at least until the grease works its way out and relieves the hydraulic forces helping to hold the axle from rotating when you come to a sudden stop.

I think the hydraulic force put on the drive line by packing the slip yoke with grease could do far worse damage than the axle wrap will. I wouldn't do it. Think of the pressure it puts on both ends of the drive shaft and input/output flanges. You'll realize how much force there is the first time you go to remove your driveshaft and its locked in place by the hydraulic forces.

The real solution IMHO would be to get a good set of leaf springs (like Alcans) and or install a traction bar (like a Budbuild bar).

http://www.budbuilt.com/new/traction_bars.html

http://www.alcanspring.com/

I have done both, no more clunking.

jdsdj98

Thanks, Dale. What you're saying makes perfect sense. Do leaf springs soften over time, thus allowing more axle wrap? I never had this issue with my 95, but maybe it's a difference between a 5 speed and an automatic and the different forces they each put on a driveline when coming to a complete stop. Regardless, thanks for giving us a different angle from which to approach this issue. I'll be looking to eventually put a traction bar under there.

In the meantime, is there any reason to be concerned with any potential damage being done by allowing the wrap/thump to continue?

mt_goat

Yes the springs wear out and get softer or weaker. The Taco springs will often get so soft they will have little arch or even a reverse arch. The pre-Tacos (95 and earlier) had better springs for sure. The axle wrap could cause some problems, but I'd be more worried about stressing the driveline with excess hydraulic forces on the drive shaft. Just take it easy on the starting and stopping until you get some better support for the axle.

Noctivagans

Thanks Dale! This gives me a few options to try to fix the problem. Much appreciated!

Cheers,
Brandon

mt_goat

Oh yeah, another thing that may help if you're just getting this when stopping is to try adjusting your rear proportioning valve so that you have more of the braking load on the front brakes. I have adjusted mine so that the front brakes lock up before rear brakes. There is a rod going from the bed to the rear axle that adjusts it automaticly when the bed is loaded down. As the rear leaf springs sag over time the rear PV could start to apply too much braking force to the rear brakes. The more braking force on the rear axle the more axle wrap you'll get when you apply the brakes.

AverysDad

I get that it's most likely axle wrap. My Tacoma has the "bump" that everyone else has, and my wife's 01 4Runner has the same "bump". However, since that truck has coil springs and control bars on it why would there be any axle wrap? I was under the impression that the control bars would keep the axle from turning and wrapping under stress.

jdsdj98

I do indeed have reverse arch in mine. They're shot. I'm instead going to start there before a traction bar. Any quick recommendations on aftermarket non-lift leaf springs? My quick searches only turned up springs for lifting the truck, something I really have no need or desire to do. Being that these OEM springs are done, I'd rather put a more durable aftermarket spring in without altering the truck's appearance or configuration.

eddieleephd

the previous post would answer that question weak coils increase the pressure applied by the brakes and thus forth more stress on the DriveShaft!
This makes perfect sense to me. The control bar lessens/aleviates this it does not eliminate it!

mt_goat

Alcan (link in earlier post) will do custom springs, just tell them what you want. They ask me how much weight I carry, how much lift I wanted. year make and model.