Don't Get Shook Up

Let's face it; we make our living solving problems. Troubleshooting is the backbone of our business success. We are a typical shop that experiences problem vehicles almost weekly, just like many of you do. You know what I am talking about, the type of problems which already have been worked on and the original complaints still exist. Actually, sometimes previous work creates new, "friendly-fire" concerns. It seems I am amazed almost weekly with some incredible "new" solution that is found to a common type of problem or concern.

Here is a trouble vehicle suffering from a problem whose unique cause was difficult for us to find: a 1999 Chevrolet 4WD Silverado extended cab pickup. The customer's complaint was that thetransmissionto transfer case adaptor had repeatedly cracked. I don't know the exact count, but by the time we were blessed with this job, I think the count was three broken adaptors.Figure 1is an example of one of the broken adaptors that was cracked near the transfer case mounting bolts.

We all know this is common, and most of the time the cause is a bad U-joint, bent driveshaft, out-of-balance driveshaft or something that is inducing vibration into the adaptor. Because we could see the vehicle had a new U-joint, we immediately suspected a damaged driveshaft. Those aluminum shafts are fragile and easy to distort. There are a couple of quick techniques we use as a preliminary test to confirm a vibration and isolate its cause.

First, we use the vehicle for a lathe, start the truck up and put it in manual low. This allows the driveshaft to rotate slowly, and you can run an indicator up and down the shaft to see if it is bent. We lifted the Chevy up and went from the front of the shaft to the back; it was out less than .015".

我们的下一个测试是在升力上运行车辆，高达约70-80英里/小时，然后用手感受到转移壳体背壳中的振动，甚至适配器的感觉。我知道这需要一点经验或“感觉技巧”，但如果你得到一个已知的好运，并将它与反对糟糕的比较，你就不会需要很长时间，以知道驱动轴是否超出了足够的平衡来引起某些东西打破。我们测试了雪佛兰，感觉很棒。“哦，男孩，我们抓住了什么，”我在想。客户可以击中一些东西并物理损坏适配器吗？

I told the guys to go ahead and pull both driveshafts so we could take a closer look at them. This unit had a 246 (NP8) auto transfer case which spins the front shaft all the time, even in 2WD. That was why we needed to inspect both shafts on this unit. As the shafts were being removed, we got a break. The technician, Don Williams (with the keen hearing of a 25-year-old), thought he heard something moving inside the rear driveshaft. He said it sort of sounded like a liquid. We looked at the aluminum tube, and near the front U-joint we could see that the little black rubber plug usually found on the shaft was missing.Figure 2shows the shaft with the rubber plug missing, andFigure 3is a different shaft that has the rubber plug in place.

我们站起来，让它坐下来坐下来，洞穴左右。果然，里面的水耗尽，留在地板上的水坑。我们必须考虑轴是如何制造的。当运气有它时，我们仍然有另一个，类似的驱动轴从以前的工作手头拿走，所以我们拿了一个Sawzall®并将它打开，看看它是如何制作的。正如你可以看到的那样Figure 4, these driveshafts are foam filled.

The cause of the Chevy's problem was becoming clear. Water would soak into the driveshaft foam, settling in bottom of the shaft when the vehicle was sitting still. If the shaft was allowed to sit outside in 20-degree weather and freeze, the ice stuck in one side of the foam would create a terrible imbalance issue. To make the problem even more difficult to diagnose, the imbalance would solve itself as soon as the ice thawed. Running the Chevy in manual low at the beginning of our test distributed the water outward in the foam equally enough to correct any imbalance issue. I feel this is what allowed the driveshaft to pass our 80 mph test on the lift.

鉴于此信息，我们弄清楚了我们的客户正在发生的事情。这个家伙会在寒冷的早晨进入雪佛兰，并且在冰融化之前，他在高速公路上做了80英里/小时并摇晃车辆分开......字面意思。然后，当卡车到商店时，神秘的平衡条件本身就愈合了。我觉得自身浸泡的水泡沫的一侧可能导致足够的平衡问题，即使在经常看到冻结天气的区域也可能导致足够的平衡问题。

We considered drilling holes and trying to remove all the water, but because of the foam and with no way to know if all the water was out, we choose to replace the driveshaft. Once the shaft was replaced, it cured the repeat adaptor failures.

Sonnax最近发布了用于铝轴的替代焊接饼干，允许您切掉结尾并更换它们，而无需担心在轴上失去整体长度。虽然我相信这些焊接轭是在U形关节夹区域中修复损坏的轴，但我想它可能有helped get the water out. Here is a Sonnax weld yoke inFigure 5.

作为最终的说明，水是如何进入轴的？在2009年在阿肯色州的80多个“下雨”中，水似乎到处都是。当然，随着驱动器淹没的情况下，淹没就会填满这个插头缺失。让它难以诊断的事情不是考虑什么在轴上。我们幸运有一个驱动轴，我们可以做一个尸检并发现泡沫在里面。它让我惊讶了像橡胶插头一样的批判。应该在你的情况下不要损坏这些插头- 替换。

Dan Tucker is owner of Tucker's Transmission in Pine Bluff, Ark., and a member of theTASC Force®(Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Industries Inc. technicians.