I'm installing an Eaton posi with new bearings into my '66 401 4 speed GS. Using the original 0.26" pinion shim, I got this pattern. I deemed it unacceptable, due to insufficient gear mesh.
Installed a 0.022" shim... So I installed a 0.022" pinion shim to increase the gear mesh. I think this looks pretty good.....
Coast side... Until I looked at the coast side... Backlash is set at 0.010", the same as the original setting. (these are the same 3.36 gears). Does this look acceptable???? And will a different backlash setting affect the contact pattern? Thanks!
I would decrease the backlash to .007-.008.Back lash with change the pattern slighly.The last patern you have bothers me .It should cover more of the tooth.You may not be applying enough pressure on the ring when you rotate the pinion.I would also like to see the results on a few more teeth I usually try to apply the compound to the same #of pinion teeeth you have aka if you have 10 teeth on the pinion then mark 10 on the ring then I rotate the gear set a couple revolutions.Make sure you apply pressure the the ring gear when you rotate the gear set to check the pattern.
Thanks Kevin! Here it is with backlash at 0.008". I did preload the ring gear by using a wooden wedge between the housing and ring gear. It took 10-15 ft lbs to turn the pinion. I'm thinking the drive side (top pic) looks pretty good. Or do you think it's too high on the tooth? I don't like the coast side pattern...but if I go to a thinner pinion shim to correct that, I'm afraid I'll make the coast side worse... o No: Note the grease smudge on the coast side is larger than the spot where the grease was totally squeezed out...does that mean under more of a load, it'll be better? I don't want to change out the pinion shim (again) unless I have to! BTW, this is a used gear set (70k miles), car will be street driven... Thanks!
That looks better.I have a couple ? though are those the old gears or new.If it is the old gear set I wonder why the pattern changed.I have done plenty of bearing changes and never had a pattern problem even when I changed the posi unit.I wonder if you don't have the rear race seated all the way in the housing. It still looks a little deap I might try a .020 shim.It looks like it's driving a little to far inboard you may take the tips off the tooth.Most of the time I don't check the coast pattern unless I have a noise problem.When I set a gear set up I use a T&D depth checker so 95% of the time everything goes good.I know this tool is expensive for the average guy if I was in the area I would gladly swing by and help.
gear pattern in the late 80's we were having problems with getting a good pattern reading on replacement gm gear sets (i work at a chev dealer).here is what we were told to do to get a good load on gear set. install axle shafts,drums,wheels,& connect driveshaft.leave cover off,apply marking compound (does not need to be a thick coat).have someone get into vehicle,apply brrakes,start vehicle & put in drive,slowly release brakes just enough for ring gear to turn,allow ring gear one complete revolution,stop,put in reverse & onr complete revolution.now check your pattern.you won't believe the difference this method makes. one more thing....don't stand in front of open housing,or you may end up with yellow freckles. good luck
pattern a LOAD IS A GOOD IDEA But you only need to put a drag load. Like let the yoke rub against the side of you knee as you spin the ring gear round by pulling it or pushing it. (gloves work good here or you end up with ripped up hands...lol). The last pattern compared to the rest is the best. I would like a better more center tooth contact on the coast side. Looks to be too deep in the root. What was the back lash at on the last one? Your getting close. It does take some paitents to do what your doing. I really would have thought the original shim would have done you right and the back lash would have been the only thing to deal with. If the gears were original to the housing. (Were they?) The first picture looks like you did not give the marking compound a chance to do its job. Remember everytime you change the pinion depth the backlash will need correcting also. ALWAYS. Good luck keep the pictures coming...lol. Jim
Not right? As a builder I've not had to change out the original pinion shim because of doing a full bearing change or swapping carriers. Unless the inner pinion bearing race had "spun" on the pinion wearing the pinion shim down a few thousandths. It happens. To me the BL should be kept the same as when removed (.010). Now if the inner pinion race did not seat correctly or had even a small partical of metal behind it when installed, this could cause an improper root/crown pattern. The BL mostly controls the heel/toe pattern on the ring gear. Going from .026 to .022 shim Decreases the gear mesh. Personally I take my reading off the next few teeth after running it through the compound for better accuracy. To me (from just your last pic) I'd increase the BL and re-up the pinion shim. Thats just my .02 (Roger) OPH you're next rebuilder up...
Would agree with Jim. Some serious drag has to be applied to the gearset to get the gearset to pattern out. Not enough drag, pattern will be off & can be misread. Respect to Tims response, I agree, if the gears are original to the housing, it just does not make sense to have to go to a thinner pinion shim. The only cases I've seen a "need" for a thinner pinion shim was when a burr (or two) was raised on mating surface where the large pinion bearing race sits. This often will happen when one does not use the correct driver to knock the large pinion bearing race out. Using a large picklefork, due to design, will often cause this problem. Installing a new race on such a flawed mating surface will create an error when setting pinion depth. Usually such burrs will throw off pinion depth more than .020 With a difference closer to .004, there is probably some grit or a small metal particle under the race. If rear was on my bench, I'd disassemble, remove the race, & see what was up. If there are burrs, they can be carefully bumped down with diegrinder bit. Changing pinion shim in rearend with original matching hsg & pinion... On original gear rearends where the gearset showed wear & pinion drag was rel tight but backlash was somewhat loose, I have had good luck going back with a .001 thicker pinion shim. This often helped recenter the pattern, & by bringing the pinion head slightly closer to the centerline of the rear, allowed backlash to be tighenened up slightly. As an example... merely swapping in a posi carrier in a pegleg rear, tightening up back lash to .007-.008 on a gearset that has run for a long time at .015 backlash, is not recomended. Hope this helps. :3gears: Roger
Thanks for the advise guys! :TU: I tried an 0.020 shim....drive side looks great, coast side is still off to the inside. I had to get away from this ordeal for a few weeks. I needed a break! Roger, yes, I did raise some burrs when I removed the old bearing race. I did clean them up tho. I guess it is possible something is between the new race and housing...there's only one way to know for sure...take it all apart AGAIN ou: I did check backlash before disassembly... I did measure pinion depth using a home-made setup (not perfect, but repeatable to within 0.001"). I'm within 0.002" of the original now. But... I wish I had checked the pattern before I took the rear apart.... I wish I had set the pinion depth and checked pattern before I installed new crush collars and pinion nuts.....I've used 3 pair$ so far. Next time I'll know better! I still don't understand why my drive side pattern is good, but the coast side looks to be too shallow. How can I improve the coast side, without making the drive side worse?
rearend Do not worry so much about the coast side unless you do reverse burnouts alot...lol. Get the drive side in right and the coast side will follow. As for the nuts and crush sleeve. I never put them in till I get the pattern correct then I disassemble and put all the good stuff in. I use the same nut on assemble over and over. Does not take much to put it on and off anymore...lol. Good job hope everything runs well for you on the street/track. Take care, Jim
