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Ok, time for another technical article, this one about Sure-Grip rebuilding. This is for cone-clutch 489 cases, not the earlier style Dana/Spicer 742 cases. I don't have the magazine articles here with me, so I'm doing this from memory. I'll reread them and post an update next week. High Performance Mopar had finally published a good tech article, I thought (genius level for them), until it became obvious they hadn't quite thought it through as much as possible. Shortly after the first article, the writer answered a question in a letter to the magazine about the side gears moving too far away from the spiders. His response was that "He works on big trucks during the day, and it doesn't hurt THEM!" Well, we're not talking about trucks here, are we? Alrighty then.
Mopar Action also wrote about this problem, but I was surprised that they didn't suggest the obvious fix. They were too busy talking about the new $300 or so 30% stronger differential which has a one piece case so you can't take it apart when it wears out, you have to buy another one. How did they machine and assemble it in a one piece case? I don't know, but I'd rebuild 10 old ones before I bought 1 new one like that. So what did I do to fix the side gear problem? Simple: Shim them back in! You just have to be darn careful with your measurements to get the right thickness shim. Too tight and it might mess up the gears and not let it unlock for turns. Too loose, and it won't do any good, either. Here's what I did. I know this one guy who is a machinist, he has a lot of machining tools at his home, too. Many different kinds of micrometers, which were useful. I took the Sure-Grip to him and showed him what I wanted to do and how to do it. After laying each case half on a flat surface and measuring the height of each cone clutch (inner flat surface next to side gear) and seeing that each had the 1/2" or so rub mark on the outer edges, we cut 0.060" off the outer edge of each cone. after carefully reseating them, we remeasured their new depth. We also now had 0.040" clearance between the case and cone (outer flat side). Each had dropped 0.020" down in the case, with the clutch surfaces now touching. To allow for wear (before and after I rebuilt it) I decided on a 0.035" shim thickness for each side. Went to a local metal place and got some 0.035" thick stainless steel. Went home and cut a donut shaped piece for each side. Donut piece goes between the cone clutch and side gear. Reassembled Sure-Grip, but without the springs and plates in the middle. If you reach your fingers in the middle, you can push up on the side gear and watch how far it falls back down to engage the spiders fully. I had about 0.020" or so clearance on each side gear. So, that part was done. The article said to add springs if you want more pressure. This would come in handy on snow and ice, where the wheels would spin before much torque was generated to push on the cone clutches. I added 4 high gear clutch pack springs from a 727 transmission someone else had taken apart. They fit inside the original springs just right. Reassembled Sure-Grip and put it in the car. Did it work? Yes! The old Sure-Grip, before it was rebuilt, would work, but it wasn't very sure. If both tires were on dirt, they were ok, but one tire in dirt and one on pavement, forget it. Now that it was rebuilt, it locks up VERY well! One tire on ice or mud, the other on pavement? Pavement tire spins immediately. Tried it on both tires. Many times. A successful operation. Now, with 0.040" clearance, I don't know how long it will last. One guy I talked to at Auburn Gear said they built them new with a tolerance of between 0.010" and 0.050" clearance. But I think I could have gotten more reliable information from a brick wall. I rebuilt it back in the spring and put it in my Valiant with 3.23 gears. Soon took it out. 3.23's were too much for my highway speeds with a /6, and I didn't really need a Sure-Grip in it for the summer. See my article 'My first torque converter failure' for more information on this. So I decided to 'save' it for this winter. Just put it back in on New Years' weekend, and so far so good. Have been giving it lots of excercise in icy parking lots. Well, I'll have to review the articles this weekend, and since I'm in a library typing this, some ugly retard is rushing me for his turn on this computer. So, I'll add more later, and I'll be looking forward to seeing your responses on this. |
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