satan
06-01-2001, 10:14 AM
I know Tiff had a thread on this going somewhere:
I just did the first fluid change on my new rear gears at 500 miles... The stuff that came out way MUCH heavier in phosphates than the stuff that went in. I'm asuming that the phosphate is from a coating material used when the gearset was heat treated or some other finishing step to pospone oxidation.
Having that in the gear oil and probably from the wear, made the drained oil about the consistancy of whole milk (from 80-90W to Milk -- very thin). I couldn't find my centipoise cup so we'll have to live with the "milk" analagy.
I was suprized to see very little metal in the draining oil -- a quick magnet sweep through the pan and the empty housing neted almost nothing. the magnetic fill plug was covered in fine particles, but nothing major and nothing 'sharp'.
As usual, I plotted case/carrier/bearing temperatures for these first few miles watching for any signs of excessive heat build-up (gear killer). Perhaps the most significant data from that effort was from the first 17 mile heat/cool cycle. Immediately following the first 15 miles the carrier cover temperature reached 175*F. the next morning the vehicle was driven at higher speeds (50mph) for 22 miles, and the cover only reached 151*F. The next run, after fully cooling, covered 14 miles at speeds over 60mph, and the cover only reached way up to 166*F. cover teperatures since that time have been slowly settling down and seem to have stabilized near 135*F for most types of driving regardless of distance.
I know that that's too much information, BUT I believe it to be of value indicating that all gearsets do need to be run-in, and have the lubricant changed on a short cycle one or more times.
If I had driven the first distance at any appreciable speed or for more distance, the oil would surely have broken down much more than it did; opening the door for catestrophic failures or untold premature wear. Allowing the oil to FULLY cool after that first few miles is (IMHO) absolutely vital - It may be possible to drain & refill after the first few miles, but I believe that the tempering effect of residual heat would be lost.
Taking the first few miles very slowly (OK, sub-light) appears to be equally vital. By stepping-up the speed driven in the 3rd jaunt, it's easy to see that the gears weren't quite ready for that (more heat developed over a shorter distance).
Based on the crap that I drained out of the case, I believe that changing the lube on a new gearset at 500 miles is mandatory; in the future I will most likely change at 250 AND 500 as I have in the past. The intent is to keep the gearset as well lubricated as is possible while the surfaces work harden and polish .
If I were asked to render an opinion on this whole practice, I would suggest:
that the initial 15-20 miles be covered at speeds below 45mph and that the fluid/case be allowed to fully cool before proceeding;
that the first 100 miles be covered in at least qty=2 steps (allowing for minor cooling - pee stop or Pepsi break) at speeds below higway speed
that all of the first 250 miles be driven at variable speeds (meaning no cruising at any one speed - kinda like the folks we all see everyday that can't get a single rate of travel) with some decelleration and some acceleration every few minutes; nothing abrupt at all
that the diff lube be changed after the first 250 miles if you have any conserns about anything (possibly got it too hot once or whatever);
that all driving up to 500 miles is silly-granma stuff (no wheelstands, no trailers, no trails);
that even if you changed the lube at 250miles, it absolutley gets changed at 500 miles;
after that change your lube at 2000 miles and get the best stuff you can afford;
that all fluid changes be "cover off" allowing the interior of the carrier to be wiped-down and inspected (no "JiffyLube" suction changes);
Lube for the first changes can be (probably should be) less than premium quality stuff - non-synth for sure.
I have repurchased a few of the rear-ends that I've built & broken in over the years - the last Chevy that I set up was scrapped (T-bone wreck) with more than 195Kmiles on the rear 3.73:1 posi I installed and broke in. The driver regularly demonstrated the posi action by powerbraking wicked-sick smokey burnouts.
Just for your info Tiff - hope it helps some.
I just did the first fluid change on my new rear gears at 500 miles... The stuff that came out way MUCH heavier in phosphates than the stuff that went in. I'm asuming that the phosphate is from a coating material used when the gearset was heat treated or some other finishing step to pospone oxidation.
Having that in the gear oil and probably from the wear, made the drained oil about the consistancy of whole milk (from 80-90W to Milk -- very thin). I couldn't find my centipoise cup so we'll have to live with the "milk" analagy.
I was suprized to see very little metal in the draining oil -- a quick magnet sweep through the pan and the empty housing neted almost nothing. the magnetic fill plug was covered in fine particles, but nothing major and nothing 'sharp'.
As usual, I plotted case/carrier/bearing temperatures for these first few miles watching for any signs of excessive heat build-up (gear killer). Perhaps the most significant data from that effort was from the first 17 mile heat/cool cycle. Immediately following the first 15 miles the carrier cover temperature reached 175*F. the next morning the vehicle was driven at higher speeds (50mph) for 22 miles, and the cover only reached 151*F. The next run, after fully cooling, covered 14 miles at speeds over 60mph, and the cover only reached way up to 166*F. cover teperatures since that time have been slowly settling down and seem to have stabilized near 135*F for most types of driving regardless of distance.
I know that that's too much information, BUT I believe it to be of value indicating that all gearsets do need to be run-in, and have the lubricant changed on a short cycle one or more times.
If I had driven the first distance at any appreciable speed or for more distance, the oil would surely have broken down much more than it did; opening the door for catestrophic failures or untold premature wear. Allowing the oil to FULLY cool after that first few miles is (IMHO) absolutely vital - It may be possible to drain & refill after the first few miles, but I believe that the tempering effect of residual heat would be lost.
Taking the first few miles very slowly (OK, sub-light) appears to be equally vital. By stepping-up the speed driven in the 3rd jaunt, it's easy to see that the gears weren't quite ready for that (more heat developed over a shorter distance).
Based on the crap that I drained out of the case, I believe that changing the lube on a new gearset at 500 miles is mandatory; in the future I will most likely change at 250 AND 500 as I have in the past. The intent is to keep the gearset as well lubricated as is possible while the surfaces work harden and polish .
If I were asked to render an opinion on this whole practice, I would suggest:
that the initial 15-20 miles be covered at speeds below 45mph and that the fluid/case be allowed to fully cool before proceeding;
that the first 100 miles be covered in at least qty=2 steps (allowing for minor cooling - pee stop or Pepsi break) at speeds below higway speed
that all of the first 250 miles be driven at variable speeds (meaning no cruising at any one speed - kinda like the folks we all see everyday that can't get a single rate of travel) with some decelleration and some acceleration every few minutes; nothing abrupt at all
that the diff lube be changed after the first 250 miles if you have any conserns about anything (possibly got it too hot once or whatever);
that all driving up to 500 miles is silly-granma stuff (no wheelstands, no trailers, no trails);
that even if you changed the lube at 250miles, it absolutley gets changed at 500 miles;
after that change your lube at 2000 miles and get the best stuff you can afford;
that all fluid changes be "cover off" allowing the interior of the carrier to be wiped-down and inspected (no "JiffyLube" suction changes);
Lube for the first changes can be (probably should be) less than premium quality stuff - non-synth for sure.
I have repurchased a few of the rear-ends that I've built & broken in over the years - the last Chevy that I set up was scrapped (T-bone wreck) with more than 195Kmiles on the rear 3.73:1 posi I installed and broke in. The driver regularly demonstrated the posi action by powerbraking wicked-sick smokey burnouts.
Just for your info Tiff - hope it helps some.