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Old 12-21-2003, 09:27   #1 (permalink)
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diff run in period

I heard someone say that there was no run in period for a diff which uses second hand gears,but then they said the diff was noisy while cruising on the highway until a fair bit of thrashing.
I have just lapped a diff in myself (i.e. book in one hand and spanner in the other),it is a VL Commodore rear drum diff which I have converted to rear disc and LSD using a centre out of a 75 series diff from a ZL Fairlaine (2 pinion),I had to get a spacer made up for the crownwheel (i.e. 6mm) and then I had to cut out my own shims to get the tooth contact to an acceptable pattern (mine is acceptable,not ideal due to limited shimming sizes ,i.e. 0.1 & 0.2mm).
What I want to know is there a run in schedule which needs to be followed on a diff with second hand gears but has had its gears lapped in and new bearings fitted?
Is it like running a motor in which has just had new rings fitted?
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Old 12-21-2003, 14:39   #2 (permalink)
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Re: diff run in period

Quote:
Originally Posted by RB30DEVL
I heard someone say that there was no run in period for a diff which uses second hand gears,but then they said the diff was noisy while cruising on the highway until a fair bit of thrashing.
I have just lapped a diff in myself (i.e. book in one hand and spanner in the other),it is a VL Commodore rear drum diff which I have converted to rear disc and LSD using a centre out of a 75 series diff from a ZL Fairlaine (2 pinion),I had to get a spacer made up for the crownwheel (i.e. 6mm) and then I had to cut out my own shims to get the tooth contact to an acceptable pattern (mine is acceptable,not ideal due to limited shimming sizes ,i.e. 0.1 & 0.2mm).
What I want to know is there a run in schedule which needs to be followed on a diff with second hand gears but has had its gears lapped in and new bearings fitted?
Is it like running a motor in which has just had new rings fitted?
No. If it whines, either the gearset is no good, or the setup is incorrect.
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Old 12-21-2003, 20:50   #3 (permalink)
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Re: diff run in period

This other bloke didn't say it was so much of a whine,it was a slight noise like a hum coming from the diff at highway speed which totally went away after giving the car a thrashing.
I know of someone who has a VL turbo who uses it for circuit racing and he has changed the ratio 15 times since he has owned the car,he said it has always had a metal deposit in the oil whether he or a pro has fitted the diff together,I don't think he lapped the gears in when doing it by himself but I would imagine a pro would.
I couldn't imagine that everything is going to be perfect so to speak,that's why with a new car they tell you not to do any heavy towing so you can run the gearbox engine & diff in,same goes for fitting new gears I am told.
I would imagine with new gears you'd need to run it in because it is the final machining procedure like running in a new motor.

Last edited by RB30DEVL; 12-21-2003 at 20:53.
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Old 12-22-2003, 00:43   #4 (permalink)
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Re: diff run in period

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Originally Posted by RB30DEVL
I know of someone who has a VL turbo who uses it for circuit racing and he has changed the ratio 15 times since he has owned the car,he said it has always had a metal deposit in the oil whether he or a pro has fitted the diff together,I don't think he lapped the gears in when doing it by himself but I would imagine a pro would.
Was it a limited slip? I changed the gears in my car 5 times over a couple of hundred thousand kay period and had no significant metal deposit.
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Old 12-23-2003, 01:09   #5 (permalink)
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Re: diff run in period

The car had an LSD,the trouble I am having with mine now since it has been assembled is it makes a howling sound when decelerating or when you take your foot off the accelerator slightly,when under load the noise goes away,the tooth contact pattern seems fine so it is making me think it is something to do with the gearset.
I don't know if anything happened to it while it was out of the diff but what I noticed on the heel of the crownwheel on the coast side is that there was a small spot which looked to have some interference,it's definitely making me think it has something to do with the gearset.
I don't know if the problem will go away if say the end of the pinion is slightly burred or whether I should just get the gears lapped as it is making me think now that the gears originally came from the VL diff and after fitting new bearings,etc there is a slight possibility that I am trying to run gears out of their wear pattern,I mean the fact now is the pinion is in a different position due to the fact I had to shim it up because of too much end float in the pinion assy with the new bearings fitted.
I am also using a spaced out ZL Fairlaine LSD centre which will also throw things out.
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Old 12-23-2003, 01:44   #6 (permalink)
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Re: diff run in period

WBT56... that sound like incorrect backlash to you??
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Old 12-23-2003, 03:53   #7 (permalink)
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Re: diff run in period

Quote:
Originally Posted by Bass Crazy
WBT56... that sound like incorrect backlash to you??
Since this is my first diff rebuild I have being trying different things,I was trying out a gearset tonight just playing around with it to see what is going on,there is definitely a clearance problem,the tooth contact pattern I couldn't get very accurate and thought that it was close enough (really needs like shims going up in 0.05mm increments to get it spot on),my father actually convinced me it was o.k. him being a fitter with over 30 years of experience I took his word for it when the diff was grating whilst being turned over by hand in the forwards direction at the axle (was fine when tured at the pinion) (reverse is as quiet as a mouse),I wasn't happy with it but fitted it anyway to see how it will go,went o.k. in reverse and when pulling up a steep hill but coast with no load in the forwards gears is very different.
I think the pinion is either burred or the crownwheel may need a very minute amount of shimming to take away the noise,I should've gone with my own intuition and pulled the plug on it and do it right,I will fit the old diff with all of the new brake parts on it tomorrow which are on the new unit (diff has VN Commodore rear brake mechanisms on it which are different to the VL rear disc setup),then I can spend time on shimming it which is what I wished I could've done 2 months ago only that the firm who made the crownwheel spacer took nearly 3 months to make it when I thought a week as a realistic timeframe.
I was kind of in a hurry to get it in because the RB30 Nissan motor which I am putting into my VL is a twin cam high compression setup ready to put out around 190 FWKW of power and I wasn't going to fit it while I had a drum diff in my car,the LSD would've been ideal for that power output as it made the car corner like it was on rails.

Last edited by RB30DEVL; 12-23-2003 at 05:47.
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