Front axle rebuild - howls at 1800-2000rpm

[Northwards]

Hi folks, 

I feel this is a 'long shot' but I'll try anyway. Car is a 1994 300Tdi 110SW, but possibly with a Td5 axle case fitted about 17 or 18 years ago. 

Over the last three months or so, between juggling other things, I've been rebuilding the ends of my front axle. Essentially almost everything from the end of the axle case outwards was replaced. The exceptions are the hubs, the calipers, and the half shafts/cv joints because they'd been done last summer. The diff and propshaft stayed connected and in the axle case as they had themselves only been fitted last summer.

So this was intended as a proper 'rebuild' - just to give you a quick idea, though many of you will have been here before:

^^^ new stub axle with new roller pin bearings, and a bronze bush pressed in.

I've certainly been in/around the front axle and hubs before, so nothing at all caused me any concern doing the work and I wasn't expecting any problems at all when I took it out for a test drive a few days ago. But when I get to about 1800 - 200rpm a "howling screech" kicks in. It goes away if I lift off; comes back when power is re-applied. It's 1800rpm rather than a specific road speed - i.e. it'll do it at 1800 rpm in 1st, then drop off when I go up to 2nd only to return once the revs build - and so on. 

Other stuff that's happened includes the Tbox coming out and going back to Ashcrofts, who gave it a clean bill of health; same with the rear diff, which is an Ashcroft ATB. But I don't think this is transfer box or rear diff related. I had also rebuilt my Roamerdrive and assumed that was the issue - pulled it off and put the Tbox back to standard - noise still there. I then thought it might be my X-eng handbrake, and have removed that - noise still there. If I put the transfer box in neutral and rev the engine, I don't get the noise, so it's 'drive' and transmission related.

So just before coming in tonight I put the front axle off the ground; transfer box in neutral and if I turn either wheel, in either direction at any kind of speed there's a notchy 'ribbed' feeling to the movement. It is an Ashcroft ATB in the front too, but it was new in from July to December last year and gave no issues. If I go to the back and try the same thing, then the wheels turn nice and smoothly. I can't say with 100% certainty it didn't do this before, but I don't think so. 

If I was turning a bearing and got that notchy feeling I would say it was too tight, but in reality I don't understand enough to see how I could have made the axle ends too tight? As the photo above shows, I still had end float once I'd built up the bearings and drive flange. I don't think there's an issue here with later vs older parts as the likes of stub axle are the same (??) and the cv joints were running in that diff and axle for the last 6 months without any issue.

Like I said at the start, a 'long shot'. I'm stumped, and to be honest I'm nearly at the point of taking my car to a garage for the first time in about 5 or 6 years. I just don't know where to go with this, and with work getting busier and busier I haven't really the energy left to start stripping it all down randomly without an idea what I'm looking for. 

Anyone come across anything like this before? I always say 'any help appreciated' and I always mean it, but this time I extra-mean it!

 

[Snagger]

1800 rpm wis where a turbo diesel starts ramping up its torque, so it is possible that something is skewing or a bearing having problems at that point.  It is also possible that the turbo is on the way out - while revving the engine with the transmission in neutral will spin the turbo, with the engine unloaded, it won’t generate the EGTs and pressures that it would when accelerating the car, so this could conceal a turbo fault.

I would try removing the front prop shaft and driving in diff lock to see if the noise persists.  If it does, I think it unlikely to be the front axle.

[Bowie69]

As above, given it is engine speed related, I can't see it being the axle, sounds more like a belt tensioner, heatshield resonance or turbo on the way out. 

I'd do Snagger's test and see what's going on. 

[Northwards]

Thanks Gents,

I hope it’s not the turbo, as it’s a VNT that’s only been on the car for a couple of years. On the other hand, as I still have the transmission tunnel out there is a distinct whistle to be heard even at low revs. It would be a shame to have to change/rebuild something like that as I wouldn’t say it had been heavily used. It’s a “big” noise though, the sort of thing you wouldn’t want to drive too far into for fear of causing real damage. Maybe too ‘big’ for the turbo?

I had planned to try removing the front prop, though I was going to check the half-shaft end float first as it’s done a (very) few miles now, just in case that’s too tight and possibly binding. I was also going to do the same with the wheel bearings given they’ve at least rolled a little under load.

I’d agree that there’s a ‘resonance’ element to the noise (fan shroud, heat shield type of thing) and there’s a couple of things I’ve seen which are worth attention even if they might not be the cause of this noise.

It’s just disappointing/annoying because there was zero sign or sound of this when the car went into the garage and it hadn’t turned a wheel until last week.

Loathe to start unbolting the turbo, or anything else to major just on a ‘might be’ basis, so front prop off and see what happens will be the priority.

1 hour ago, Snagger said:

I would try removing the front prop shaft and driving in diff lock to see if the noise persists.  If it does, I think it unlikely to be the front axle.

Just on this though, if the noise appears under drive; eases when you lift off; returns when the power is reapplied - isn’t there a chance that removing the prop will just mimic rolling along with no load? I haven’t really needed to try a ‘prop off’ test before so I’m not that familiar with it.

[steve b]

the dimpled and grooved disc is handed ....and that is on the wrong side. 

As for the noise, from your description it appears more engine related than transmission.

How are the viscous fan hub / drive belt and tensioner / water pump etc?

Steve

[Bowie69]

Assuming it is manual, a seized clutch release bearing can do this sort of thing.

[Northwards]

Thanks again guys - I do appreciate it. 👍

Steve b -thanks for looking closely at the pics. I'll admit you had me worried for a bit, as the discs came in handed packaging and I was sure I'd have at least tried to follow that, but I could have been distracted or called away. Anyway I contacted Luke at LOF who's confirmed that they're OK, and that his discs are not directionally-vented anyway, but that other manufacturers (he mentioned Brembo) have them the other way round. 

"How are the viscous fan hub / drive belt and tensioner / water pump etc?" ; "Assuming it is manual, a seized clutch release bearing can do this sort of thing."

To the best of my knowledge these things will be OK. The engine was down to Turners for a rebuild in early 2020 and on the refit we'd have put in a new belt, water pump, probably tensioner. The viscous coupling was a 2018 job. As the engine went back in it also had a LOF clutch and their nice release bearing so probably not that. 

In general the car is well enough (possibly over) maintained. Obviously even new stuff can fail, especially depending on the colour of box it might have come in and I tend to avoid blue ones, but it's annoying that it was working more or less OK when it went into the garage, and now has this new noise as it comes out. 

I'll need to see if I can figure out how to record and post sound clips. Meantime, front prop-shaft out and we'll see what that might tell us. 

[steve b]

The whole point of putting spiral grooves in the disc face is to throw water/mud out to the edge of the disc and off, just like a tractor tyre's directional tread blades.

Of course the brakes still function whichever way the discs are fitted but my point is still correct and I stand by it. 

Steve

[FridgeFreezer]

1 hour ago, steve b said:

As for the noise, from your description it appears more engine related than transmission.

I thought this too - if it happens at a specific engine RPM regardless of road speed it's unlikely to be downstream of the main gearbox.

[Paul C]

My disc's are the same as yours,  the vents are scavenging air from the centre as they should, even though the grooving goes against what would appear to be the correct way.

[Northwards]

1 hour ago, steve b said:

The whole point of putting spiral grooves in the disc face is to throw water/mud out to the edge of the disc and off, just like a tractor tyre's directional tread blades.

Of course the brakes still function whichever way the discs are fitted but my point is still correct and I stand by it. 

Steve

I hope it didn't come across that I was 'challenging' this in any way. I've never had brake discs like this before, so could quite easily have been wrong. My apologies if I phrased my reply badly - categorically not my intention. 

Meanwhile back to the noisy grindstone. I had half an hour there so whipped off the front prop and....... the noise is still there. Not sure if I think that's good or bad. 🤔 Starts as a whine about 1500/1600rpm and then builds to a screech/howl about 2000rpm. Definitely not there when the car was reversed into the garage at Xmas. This suggests to me that it's related to stuff I've done, but I understand it doesn't have to be like that. It could be some new, random thing that's happened as the car's sat still for 4 months. 

Mechanically the job list since Xmas was:

• Remove/Refit transfer box (declared OK by Ashcrofts);
• Rebuild/refit Roamerdrive (and now removed again in an attempt to trace this fault);
• New half-shafts on rear axle, fitted with Ashcroft HD drive members, X-eng deflex ARB; replace rear ATB diff (declared OK by Ashcroft);  
• Rebuild ends of front axle with nearly all new components, replace anti-roll bar links;
• Fit gearbox cooler to R380;

Along the way I had the fan off and radiator top hose to try and improve routing of the lower intercooler/turbo pipe, and a bunch of electric work. 

Does anyone know if there's guidance on the 'forum matters' section about posting sound clips? 

 

[Northwards]

1 hour ago, FridgeFreezer said:

I thought this too - if it happens at a specific engine RPM regardless of road speed it's unlikely to be downstream of the main gearbox.

Definitely this - engine RPM rather than roadspeed. So it comes on pretty instantly in first; drops away and returns into 2nd etc.  If I was trundling along at 40mph or so in 5th I'd barely get it at all.

And to follow your last point, because the Tbox is downstream of the main gearbox, and because the Tbox rotation will be linked to roadspeed, it does suggest that Tbox isn't the problem?

 

[Junglie]

If it needs load to get things happening, could you stick it in gear, stand on the brakes and gradually let the clutch out while maintaining revs? Then you're not just revving on no load. It may get a bit smelly quite quickly, but you're only going to do it for a few seconds...

[steve b]

Not taken the wrong way at all , just trying to explain my point, keyboards aren't the easiest way of conversing! 

The set up Paul C posted is a further level of upgrade to your discs so not really comparable- @Paul C , is that a full LOF performance kit? 

I don't recall ever seeing vented rears before on a Defender.

Re: the noise, I'd be looking at the engine - maybe run it up the road with the turbo disconnected first to see what difference there is, then a very short run with the drive belt off to eliminate belt or any of the items. With no waterpump running it would need to be done with care. From cold would help. 

Steve

[muddy]

It sounds like a boost leak or exhaust manifold leak to me. I have a rubber cap that fits over the turbo inlet with an air fitting so you can use a compressor to pressurise the inlet system and check for air leaks, very useful on Mercedes sprinters as they have all many of air issues.

[FridgeFreezer]

27 minutes ago, Northwards said:

And to follow your last point, because the Tbox is downstream of the main gearbox, and because the Tbox rotation will be linked to roadspeed, it does suggest that Tbox isn't the problem?

That's what I'm suggesting, yes - if it's across a specific engine RPM then you would usually look at whatever is fixed to the engine RPM - so everything downstream of the clutch really although there are of course bearings in the gearbox / mainshaft.

I'm not guaranteeing it won't be something else, but you've got to start with the obvious.

[reb78]

1 hour ago, muddy said:

It sounds like a boost leak or exhaust manifold leak to me. I have a rubber cap that fits over the turbo inlet with an air fitting so you can use a compressor to pressurise the inlet system and check for air leaks, very useful on Mercedes sprinters as they have all many of air issues.

I was about to say manifold gasket too. My manifold is warped again on the D2 TD5 and that means the gasket will whistle and screech under load at about the same revs as yours and slighty higher if I push it (its as the turbo kicks in which ties in somewhat with what Nick said above). I know what it is, so am not worried in my case and will fix it at some point but worth looking at the manifolds on yours.

[Snagger]

5 hours ago, Northwards said:

 

Just on this though, if the noise appears under drive; eases when you lift off; returns when the power is reapplied - isn’t there a chance that removing the prop will just mimic rolling along with no load? I haven’t really needed to try a ‘prop off’ test before so I’m not that familiar with it.

That’s the point - if the noise no longer appears, you know it has something to do with the forward transmission, from transfer box front output and forward.  The idea of the propless test drive is to eliminate or isolate this as a source of the problem, since it is an area you mentioned as a possible source.  I think the source of the noise is more likely to be engine related too, but this is a quick and free test you can do since you seemed concerned about the work you had done on the axle.

The mud shields on the back of drive flanges in the diff and transfer box can make horrendous squats and scrapes if they are slightly misaligned and contact the housing. They might be coming into contact when the diff pinion or transfer box output shaft move a bit more under high torque.  Worth a look.  Have a feel for any play on those bearings while you’re at it.  They should be under a preload, so the slightest hint of play would make them well off spec.

As for the brake discs, I did remember that Paul C’s were the same way around and that they were the same brand.  I have EBC dimpled and grooved discs, and like Brembo, Wilwood and every other brand I know of, they have the spiral sweep the dirt and water outward with the forward motion of the vehicle,  not inward like LOF.  Personally, I think they have had some good products made up for them but mislabelled their whole stock, or perhaps they don’t understand what is going on dynamically.  They are on the wrong side.

[Northwards]

4 hours ago, muddy said:

It sounds like a boost leak or exhaust manifold leak to me. I have a rubber cap that fits over the turbo inlet with an air fitting so you can use a compressor to pressurise the inlet system and check for air leaks, very useful on Mercedes sprinters as they have all many of air issues.

 

2 hours ago, reb78 said:

I was about to say manifold gasket too. My manifold is warped again on the D2 TD5 and that means the gasket will whistle and screech under load at about the same revs as yours and slighty higher if I push it (its as the turbo kicks in which ties in somewhat with what Nick said above). I know what it is, so am not worried in my case and will fix it at some point but worth looking at the manifolds on yours.

Someone else mentioned 'manifold screech' to me, and I had to say I'd never heard of it. Are we talking something like a mechanical version of the 'blade of grass whistle', where the gasket, or parts of it are whistling/vibrating? That would certainly tie in with what sounds like a turbo whistle.

Gasket was new on when I did the VNT in 2020 and has given no issues. It's not been disturbed in this latest bout of work, but it's been inactive for 4 months so.. maybe. I guess they can just go. As I said above it feels like a "big" noise, that I wouldn't want to go too far into.

On the idea of a pressure test, would one of those coolant system testers work here? 

2 hours ago, Snagger said:

 but this is a quick and free test you can do since you seemed concerned about the work you had done on the axle.

Just to confirm in case I buried it in the post above, but I did take the prop off, and the noise is still there exactly as before so sounding very much as if it is something in the engine bay. (Fairly sure all the dust shields - pinions, discs etc are clear).

[reb78]

4 hours ago, Northwards said:

 

Are we talking something like a mechanical version of the 'blade of grass whistle'

 

Yup. Common on the td5 if the manifold warps (which they love to do)

Whats your engine? I may have missed it. Be less common on a tdi i would think as the gasket is different IIRC. But still worth a look for soot marks around the exhaust gaskets or boost leaks elsewhere as Muddy says. 

[reb78]

Sorry. You do say its a 300tdi. Still check though. 

[landroversforever]

21 hours ago, steve b said:

The whole point of putting spiral grooves in the disc face is to throw water/mud out to the edge of the disc and off, just like a tractor tyre's directional tread blades.

Of course the brakes still function whichever way the discs are fitted but my point is still correct and I stand by it. 

Steve

The grooves are there to break up the layer of hot gasses trapped between disc and pad, Nothing to do with mud/water, and with the former, only allow it to get trapped and grind your pads away faster.

[Snagger]

2 hours ago, landroversforever said:

The grooves are there to break up the layer of hot gasses trapped between disc and pad, Nothing to do with mud/water, and with the former, only allow it to get trapped and grind your pads away faster.

That’s what the dimples do.

I have heard plenty of comments that grooved and dimpled or cross-drilled discs erode pads faster.  I haven’t experienced it myself, but I can see why it could happen, especially on cars where the brakes are used hard.

[landroversforever]

18 minutes ago, Snagger said:

That’s what the dimples do.

I have heard plenty of comments that grooved and dimpled or cross-drilled discs erode pads faster.  I haven’t experienced it myself, but I can see why it could happen, especially on cars where the brakes are used hard.

The dimples and grooves do the same thing. The drilled holes are there to give the gasses somewhere to go. Look at the funky patterns on some discs!

[steve b]

The main thing is, whether drilled/dimpled/grooved or slotted they only really work fully when the callipers are painted the right colour....

Steve