NG3 crown/pinion back lash adjustment

[BDA]

A little background:

The nut on the secondary shaft came loose at some point and I think that caused the destruction of my speedo gear and eventually keeping me from selecting 5th gear. A call to Richard at Banks yielded the advise to torque the nut 120 ft-lbs (IIRC) and button it back up. This seemed to work fine but I later noticed that when backing off the gas, there was a clatter coming from the rear. I actually thought I had heard it before but it didn't seem consistent and I figured it must have been something else. Now, it seems much more consistent. I figure the ring/pinion back lash needs to be adjusted.

A couple of questions:

Before I go to the trouble of taking the tranny out (again) does that sound like a reasonable diagnosis? If not, what would you suggest?

I have the pdf of the NG workshop manual from http://lotus-europa.com/manuals/ but there don't seem to be any torque values listed. Does anybody have a source for that?

[jbcollier]

Clatter on trailing throttle is a classic sign of worn u-joints.

[BDA]

They don't have that many files on them so I didn't suspect them, but I'll take a look.

Thanks, John!

[jbcollier]

Some u-joints come new with enough play to cause a slight off-throttle clatter: GMG for one have "loose' tolerances.

[EuropaTC]

I'll start off by saying I've virtually no experience in this area with the Renault boxes, so whatever I write must be taken with a very large pinch of salt.

Ok, firstly, what "sort" of sound are you getting ?  I only have experience of one differential problem and that was on a live axle car but in that case it went from a steady drone to someone hitting the underside of the car with a jack hammer almost overnight. In about 50 miles the car went from "noisy" to "undriveable" with massive vibration in the drivetrain and yet when I pulled it apart I was amazed at how little misalignment there was.  So is the noise screaming "STOP !!!" or is it just saying "I'd like some TLC please ?"

I hate working on gearboxes for some reason so I'd make sure pulling it apart was absolutely the last option.

I'd start from the back of the car and consider everything else that might move during weight transfer;  the engine and gearbox mounts, trailing arm mounts,  dampers top & bottom and probably even wheel bearings.  You've already got the UJ's on the list, do you have 4 UJs or 2UJ & 2CV joints on your conversion ? I've had CV joints sound awful before but I must admit I'd be surprised if they failed at low mileage on yours because they are probably under lower stress than a normal car with the twin link suspension ?

Brian

[BDA]

Thanks Brian! The noise is a bit like I have straight cut gears and as I say, only occurs when I let off the gas, not every time but most times. I haven't really sorted out any differences between when it happens and doesn't. So far, I wouldn't say that temperature has anything to do with it. It's not a "this is about to blow up" sound, but rather a "pay attention to me" sound. It reminds me of the sound a live axle car I had that I believed the rear end was going out on though I never took it apart to confirm that - there didn't seem to be any other explanation. So my first thought was this is happening again.

I have to estimate the mileage in the neighborhood of 10k miles on everything (could be less). Spax shocks, Banks twin link, U-joint and CV joins, adjustable lower links with rod ends. I don't remember the brand of U-joint I used nor do I remember if they can be greased. I haven't noticed that load plays a role as I generally don't push it hard.

As usual, I am trying to think about the situation before I get my hands dirty. I'll jack it up and see if I can find out more.

[EuropaTC]

I am trying to think about the situation before I get my hands dirty.

   I am 110% behind your way of working ! 

I used to dive in with hammers and spanners pulling everything apart until I found something to fix but these days I'm more of a "mull it over" sort of guy. I doubt it was any quicker diving in but probably just felt better to be doing something - even if it was wrong !

10k isn't a lot unless the UJ or CV was poor quality to start with.  One other thing for your checklist - the exhaust hangers allowing the silencer to rattle ?

[BDA]

I don't know if mulling is because it's smarter or because I'm lazy! Sometimes exploring can show you something you wouldn't have expected or even a problem that is unrelated!

10K miles on U-joints isn't much. I would think that there is even less stress on them since I have the twin link and CV-joints - all the stress is due to torque rather than axial forces.

Given the frequency of the clatter, I had discounted everything other than the ring/pinion lash, but it's good to check everything. The exhaust is mounted rigidly to the tranny and there is a slip joint between secondary tubes and the collector/exhaust pipe. It's possible that that joint is vibrating but I would expect a higher frequency.

There is another thing I didn't mention - some of the threads in the bell housing got stripped so the bolts in them are not tight (but they are safety wired so they won't come out but resist shear if any). There is no leaking from the bell housing/tranny joint and the tranny and engine mounts absorb most of the stress that might encourage the engine and bell housing to separate so I haven't worried too much about that. I was going to install helicoils the next time I took out the tranny so I was almost looking forward to taking it out (with emphasis on "almost"!).

[4129R]

In my experience, if a noise sounds suspect, I drive the car until the source of the noise become obvious.

The last time this happened to me was a back tyre on a Golf R32 had worn on the inside down to the metal bits, and I thought the noise/vibration at over 80 mph  was diff or driveshaft.

When I put the car over my pit, I was amazed at how bad the tyre had got, and I hadn't seen it.

[BDA]

Yeah, sometimes when I hear a noise I can't pinpoint, I almost wish something would break so it would be obvious what needed to be fixed. Of course if you wait too long and something actually does break, it might be something apocalyptic!