BajaTaco

EDIT: Mar. 7, 2005 - Problem seems to be fixed! Scroll down to 5th post for info.

OK, I have been trying to figure this one out and have come up empty handed so far. Grab yourself a beer and have a seat... this is going to take a while

Here are the specs on the truck:

1998 Toyota Tacoma 4wd xcab w/115,000 miles
GVW = 5,000 lbs. + (might be a factor? don't know)
V6 - 5 speed manual/original clutch
ADD (automatic disconnecting differential) with shift-on-fly 4wd (but not push-button)
Rear factory elec. diff lock
Front ARB air locker
Stock gear ratio 4:10
Alcan 8 leaf packs w/Downey shackles and worn out Rancho RSX9000's

I first noticed it I believe about 5 months ago. It's fairly hard to describe, and seems to be more likely to happen after the truck has been sitting parked and the ambient temp. is cool or cold, and also during use of 4wd. But, it has happened many times in 2wd as well, and also when it is warm. Sometimes it feels like axle wrap. But the thing that makes me think it is not axle wrap is because there seems to be a "dead spot" or some kind of binding that happens at one spot in the revolution of the drivetrain. When the "high spot" or "dead spot" comes around, it binds up against something else, and provides a lot of resistance. It's not enough to keep the vehicle from driving (like having the parking brake engaged) but when coasting to a very slow stop, you can feel it just as the truck is about to come to a final stop - it's as though I suddenly mashed the brake pedal, and an abrupt halt occurs. Also, there is no wheel-hop or clunking when I take off from a stop (like axle wrap). Several weeks ago, I was following my friend Mark to his house, and when I was stopped somewhere along the way (traffic light I guess), I depressed the clutch pedal, and put it in nuetral, and then released the clutch pedal, and felt a prounounced "clunk". Another night, I was leaving a parking lot, and I got some symptoms - this time very pronounced, and repetitive. I was able to play with it a bit in the parking lot and get a better feel for it. I was feeling more now like the rear-end might be going bad. Let me describe what happened that night...

I got in the truck and started it. I released the parking brake and depressed the clutch pedal, put it in 1st gear. As I began to release the clutch pedal, I could tell it wasn't starting to move the truck - something felt like it was binding up. So I quit the release of the clutch pedal well before the pedal was fully up. I put it in reverse, and slowly engaged the clutch. It felt like there was more travel in the clutch pedal than there normally is for the gear to engage, but nowhere near as much resistance as I had in 1st gear.

After backing up a bit, I depressed the clutch pedal, put it in nuetral, and let it slowly roll forward (I was on a very slight grade). As it started to roll fwd, I get a "BANG" like the back of the truck got hit by something, and then it continues to slowly roll forward.

I tried it again, and backed up the truck once more. This time, I put it in nuetral and released the clutch (took my foot off of the pedal). And then I took my foot off of the brake. I was on a slight grade, and the truck should have rolled forward, but it didn't. I swung my left leg and hip outside and planted my foot on the ground and used my leg to leverage a push while my other foot remained above the brake pedal (didn't want to hit a passerby). The truck was definitely binding up. Then it slowly seemed to get past the "dead spot" and rolled freely forward.

I played with it some more in a different area of the parking lot (with some downhill grade), and got the truck slowly rolling - as I applied the brakes very slowly, and just as it was about to come to a complete stop - I got the abrupt "Bang" and felt like I got hit again. I am hanging out the driver side door, and trying to watch the driveline and rear diff, but it is difficult to do while still operating the clutch and brake. At one point I can see the whole assembly lurch when the bang happens, but couldn't really tell if the axle tubes were rotating or the springs were flexing (axle wrap). As I left the parking lot, it proceeded to do the banging thing whenever I pushed the clutch in and came to a stop (stop sign, traffic light, etc).

Fast forward a bit:

** I took the truck to my friend Mark's place on Feb. 5. **

I thought for sure when I got in the truck that morning, and it was cold, and I hadn't driven it for about 19 days, that it would be doing that "binding up" and "clunking" thing really bad. Well, guess what? It drove as smooth as could be from my house all the way to Mark's place (about a 20 minute drive with plenty of traffic stops). Geez! As a side note - a friend had suggested that I take a look at the carrier bearing on the 2-pc. rear d-shaft. I never thought of that, but it made good sense to me. I was hoping that that would be the culprit (easy fix!).

So, we put it up on jackstands. Spun everything and looked at everything, and couldn't feel that binding, or see anything that seemed wrong. I would have followed another friend's suggested method of isolation, but we couldn't get it to bind up. One thing we discovered, is that the front d-shaft does not spin when you rotate the rear d-shaft with the transmission in nuetral, and the t-case in the 2-HI position (guess I was never sure on that).

Here is how the t-case operates:

2-HI - front d-shaft does not spin, 4-HI - front d-shaft spins, Nuetral - front d-shaft spins.

Because this problem occurs with the t-case in the 2-HI position (normal driving, with the d-shaft not spinning) we pretty much ruled out the front end. But as I write this, I am having second thoughts, since the front axles do turn when the truck is rolling on the ground. (But the clunk does seem to come from the rear, so I dunno.)

The one thing that we were skeptical about, was that carrier bearing. It has a rubber donut that the bearing sits inside of, and it sure seemed to have a lot of play in it. We marked the flanges at the front and back of the d-shaft, and then removed it. We laid it up on my tailgate and inspected and greased it. The u-joints all seem just fine. The carrier bearing spun freely and didn't bind at all, or make any funny noises (dang!). So everything with the driveshaft seems fine. With the driveshaft disconnected, we spun stuff again. No binding. We noticed that there is a slight bit of play in both rear axles, when you grab the tires and push/pull really hard. The passenger side seems to have a little more play than the drivers side. The play is not really up/down or side-to-side, but in-out. The axle tube flanges are tight against the backing plates for the wheels, so no problem there. We took a sample of oil from the rear diff. and it seemed just fine. We changed the oil in the transmission, and the t-case. It was fine. No play in the pinion flange on the rear diff. No play in the output flange on the t-case. All of the rear axle u-bolts were tight.

So, we put it all back together and I backed out into the street, and proceded to put it in first and drive a little. The clunk came back! Mark heard it. He got close and tried to see what was happening, but there was really nothing to see. He also seemed to think it was coming from the rear.


We pulled it back into the garage and checked the rear brakes. They look great. Spun the wheels some more, and couldn't get any binding. Put the wheels back on, and I drove it home - never felt the clunk again. What the hell??!!!

Fast forward a bit:

** I pulled the 3rd member on Feb. 26 and inspected it. **

The 3rd member looked to be in excellent condition. And spinning the pinion by hand, everything looked great. The diff housing and oil were clean (no shavings, metal chunks). I tried to remove the actuator, so I could release the locker and spin the side gears, but the actuator didn't want to budge. I decided after talking to my friend Brian, that side gear damage was unlikely (with no evidence found in the oil or diff housing) and what was visible looked good. So I never did turn the side gears. But I am pretty confident in saying that the 3rd is just fine.

My next steps are to probably inspect the rear spring hanger bolts (found an old post on a forum where someone had a problem with those) and then maybe have a clutch job done (and consider it preventative maintenance) since I am still on the original clutch and the bearing seems to whine a little louder than it used to (it has whined since day one).

I also should mention something that has happened a handful of times (probably 4) - both before and after I have experienced the above problem. And that is that when engaging 1st gear, it does not engage at first, and then engages very violently with a "bang!". Very isolated and cannot duplicate the problem.

OK - get out your crystal ball and tell me what's wrong! Somebody out there must have gone through the same thing by now. Maybe?

Thanks!

jimbo74

whats the wear on your tires? my truck is very small and light but has pretty beat up mud terrains on it, and coming to a stop it feelis liek the suspension is loose and about to fall off, but its the tires giving that feeling

Rick F.

Wow, that sounds like a problem I recently had starting last November when it started getting cold. It seemed to occur mostly (correction: nearly always) when the truck had sat overnite and hardly repeated itself after it had warmed up but would sometimes occur while crawling to a stop in traffic. I posted and had a few suggestions and everything I saw pointed to the brakes, but a trip to the Stealership found nothing unusual. Someone said it sounded like it had to do with a rear axle seal leak. Strangely enough, after driving me nutz for about 2 months, it went away after I pressure washed the truck (I had concentrated on the wheel wells to get rid of salt and other non-skid crap) which makes me believe it may have been some kind of contamination that I STILL think caused the brakes to bind/grab. I've been under the truck and haven't been able to find any evidence of oil or whatever, but it hasn't happened since. Good luck!

BajaTaco

Great input guys! The tires - yea, it wouldn't surprise me - I have MTR's that have been "bouncing" since they were put on the truck. Either not balanced or out of round. They probably have about 11,000 miles on them now, and I have never been back to get them balanced or rotated (shame on me!). Maybe that has something to do with it?? Never thought of it. Maybe I should try to swap another set of tires onto the truck. I really doubt the tires could cause these sort of symptoms though - but you may be on to something.

As far as what Rick said - sounds like you have a mystery too! I actually have tightened the u-bolts on the leaf packs a couple of times, and that seemed to make it go away - sort of. But I think maybe that was coincidence. I think I will get a brake service done though - just to make sure they are to specs. The shoes and drums looked good though when we had the drums off. You mentioned axles seals - I have had 3 blow-outs on axle seals since the truck was new. And one of them was recently (within the time frame of this problem) but I was experiencing this before the seal blew. The brake shoes don't show any signs of oil saturation.

BajaTaco

Well guys, long story short - it looks like the rear brakes were the culprit. I took the truck in to have the rear brakes replaced and the drums turned, and the guy said both were fine - no need to do it. BUT, I had him do them anyway. Since replacing the rear brakes, I have driven the truck at least 350+ miles, with a bunch of 4wd and locker use at AZRocks. No symptoms at all!! So far so good Only some more time/driving will tell for sure, but I think this probably cured it. I ended up going through my records, and even though I thought the rear shoes had been replaced once before the last time the axle seal blew, I guess they had not. So, even though I went for a long, long time with no symptoms, somehow that contamination reared its ugly head - and only at certain times. Weird! Anyway, Rick - I highly recommend that you get those brakes done. Even if you aren't getting the symptoms now, if they come back, at least you have a good idea of what to blame.

For more details on how I came to resolve this - you can read this thread at the TTORA forum...

http://www.tacomaterritory.com/forum...ead.php?t=5752

Thanks to Dan and Shane from AZTTORA for their insight on this.