Setting Ring and Pinion lash

[BDA]

I thought I had been hearing my rear end "sing" a bit (a bit hard to hear, but since my car is pretty loud, I figured if I could hear anything, it was probably enough to investigate). I had always understood that that was a symptom of excessive lash (or backlash as it is called in the NG3 manual). The manual says it should be between .12 and .25 mm. I got the tranny out, took off the bell housing, and wiggled the crown gear. There SEEMED to be very LITTLE - almost no - lash at all! I hooked up a dial indicator and it didn't register anything. Sometimes, pushing on the crown gear, it would move several thousandths but I'm not sure if that is because I'm actually moving the pinion.


While the concepts and general idea of what I'm trying to do are not new to me, doing it is something new to me so I have some questions...



Q: Is there a good way to lock the pinion so I KNOW I'm only seeing lash. The manual doesn't suggest anything.
Q: Could it be that too little lash will cause it to "sing?"


I also noticed that the wear pattern on the crown covered most of the tooth. IIRC, manuals for other rear ends show a smaller oval wear pattern. I didn't try any blue yet.


Q: Does anybody have a comment on this?



Q: Are there other suggestions for things I should pay attention to?

[jbcollier]

Clean the gear teeth carefully.  The tooth faces must be clean and dry.  Thick oils will make it harder/impossible to get an accurate backlash measurement.  If the backlash is indeed too tight, make the adjustments required (READ THE MANUAL FOR DIFF CARRIER BEARING PRELOAD RECOMMENDATIONS) and then use bluing to do a pattern check.  I have never had to lock or hold the pinion.  Once you have some backlash, checking it becomes easy.

Gears that are set up incorrectly can quickly toast the gearset.  Set the backlash, check your patterns (drive and coast), and then you will know.

When I overhauled my 395, I set everything as per manual and the patterns were perfect.  Might even be nice and quiet though you can't tell with all the other noise..

[BDA]

Thanks, John. That's pretty much what I figured. I'll give that a try. I wonder if when they are too tight that it sings, too?! I can wiggle the crown gear (and I would assume that that would show the lash) and the dial indicator shows almost nothing. Then, I'm afraid that if I get it to read between .005 and .010 inches, (as the manual says) that it will be too loose... The anxiety of doing something for the first time (that is painful to do again)!

[jbcollier]

Supposedly if it is too tight it whines under load and, too loose, on coast.  I don't really buy that as there are other factors such as pinion depth.  The main thing is to set up correctly and then run a pattern check.  If the patterns look good, it will be quiet.  My concern with your gears is that it may be worn due to the lack of freeplay.  In which case you're looking for another gearset/transaxle.

[jbcollier]

PS:  It's not something you have to adjust very often, even in the trade.  In a bizarre sort of way I was "lucky" enough to work on Lada cars for a while.  Bearing quality was poor from new and having to strip, re-bearing and set the diff from scratch was not uncommon: great experience.

On another note, I have heard from several people, and experienced it myself, that the Renault diffs tend not to have the correct backlash on disassembly.  One theory is that they didn't do it correctly from the factory.  I don't buy it as the pinion depth is never off.  Good old Occam's Razor suggests to me that people changing axle seals screw it up.  After all, how many times have we read, I changed the axle seals and now the diff whines.

[BDA]

While you can see the wear pattern, the wear is not detectable by touch so I'm hopeful the hardening is not worn through. I wouldn't want to need to do it but I would prefer the lower ratio ring and pinion set that was (once) available.


I'm a bit confused by how this could happen. I bought the box from Richard. Presumably, if he did anything to it before he sold it, he would have set it up correctly. It was opened up one other time when it ate the speedo gears. I had a guy who knows transmissions look at it in case there was more to it than that. He said he took a look, cleaned it up, and put it back together. I don't think either of those guys would have screwed it up, but anything is possible, I suppose.

[SwiftDB4]

This may not be your problem, but check layshaft doesn't move back and forth at all. I had an NG3 that had a spring clip come loose and the rear layshaft bearing started to chew into the case. Gave a gear whine when the layshaft moved back and forth.

[BDA]

Interesting thought, Swift! About a year ago, I called Richard with some problem I was having with my tranny. I can't remember what the problem was but as I was talking to him about it I noticed that the nut on the secondary shaft was loose! I tightened it with red loctite and whatever problem I had then went away!


As for my progress so far: I managed to increase the increase the lash to a shade over .006 (a bit over 0.15 mm). The spec says between 0.12 and 0.25 mm). The bearing preload comes out to about 4 lbs. (almost 1.8 da N). The spec is between 1 and 3 da N. So far, the only thing I'm concerned about is that while the nut on the ring side of the tranny turned easily (loosen), the one on the other side was very hard to turn in. So far, the numbers seem good - I'd like a bit more lash - to .007 or .008 - given that I don't know that I can turn the pinion side nut in any more, I'm thinking that this may be as close as I'm going to get. updates to follow...

[BDA]

I was looking for something about adjusting the pinion depth but I don't see anything. I suppose that is because any lateral adjustment is constrained by the gears and synchros? Comments?

[jbcollier]

The pinion depth is set by shim.  You use a special tool to measure the current pinion's depth, add/subtract the correction factor etched on each pinion and you're good to go.  Naturally you do not have this special tool.  Once the backlash is to spec, you can check pinion depth by doing a tooth pattern check.  Different pattern combinations indicate the required corrections.  A gearset is considered worn/unuseable when the resulting tooth patterns indicate opposing corrections.  For example, the drive pattern might require the pinion moving in while the coast pattern requires the pinion moving out.  Gear patterns can be found in automotive text books and websites.

http://www.alloyusa.com/gear-patterns

http://www.alldatadiy.com/alldatadiy/DIY~G~C41407~R0~OD~N/0/80851247/83204708/83204719/110671822/34853741/34869949/124220653/145000890/145011224/145011277

https://performanceparts.ford.com/download/instructionsheets/FordInstShtM-4209-8.pdf

Real life example:

http://www.gearinstalls.com/kyron.htm

Some websites I found showed patterns as acceptable that I wouldn't accept.  YMMV

[jbcollier]

The factory method of setting the pinion protrusion is covered in the Renault manuals.  Here's the one for the R17 395 transaxle:

http://www.lotus-europa.com/manuals/misc/Renault%20Type%20395%20Transaxle%20Service%20Manual.pdf

Procedure is on pages E31 to E33.  Can't see it being useful with out the special tools though it is possible to make your own tool up.  Myself, I would just use the shim supplied and adjust based on tooth contact patterns.

[BDA]

Thanks John! I don't think I'll be making that tool! I looked in the NG manual again for similar instructions and didn't find anything, but I finally found where it said that pinion protrusion cannot be adjusted on NG gearboxes. I guess that's one thing I can't screw up!


Given that, it sounds like the only things that I need to worry about is the backlash and bearing preload. Am I missing something?

[jbcollier]

Sounds good but do a pattern check as the gearset may be toast.

[BDA]

Right. My fingers are crossed!

[FranV8]

I had a read through the manual, great link and thanks for posting it (this place really is a mine of information!)

As far as I could tell, the critical measurement was 58mm from the centerline of the differential, the tool shown was just a method of setting this, there must be a tonne of other ways of skinning this cat.