Awesome. A new noise!

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thesameguy
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Awesome. A new noise!

Post by thesameguy »

Man, I had ten years of rock-solid motoring with this car but it seems I can't win over the last three or so... one mystery after another.

The current noise a clunking, but not a low-pitched one. It sounds sort of like someone tapping on a metal bucket, but I could also describe it as a grinding noise. It's rhythmic, and varies with road speed. It seems to only happen under load - taking my foot off the pedal or putting it in neutral and coasting and it seems to go away. I can't feel it anywhere, only hear it. With something on either side of me (car, wall, etc.) it's VERY load, but it's barely audible without something reflecting the sound. After about 15 or 20mph the rhythm is so fast I can't hear it no matter what.

Since it's tied to road speed and not engine speed, and it doesn't matter whether the clutch is in or out, I don't think it's the clutch.
Since it doesn't care whether I'm on or off or dragging the brakes, I don't think it's the brakes

I think I'm left with either the gearset, driveshaft u-joints, or the diff. I cannot see or feel anything with the car in the air, and since it only happens under load replicating it is tough.

I'm leaning towards the driveshaft, but it was a brand new FMS aluminum part and can't have 30k on it. Seems weird to kill u-joints that fast.

Anyone have any other ideas?
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R Code
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Re: Awesome. A new noise!

Post by R Code »

I'd suspect the center support bearing and/or guibo.
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Re: Awesome. A new noise!

Post by thesameguy »

It can't be that, because there isn't one. :)
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Re: Awesome. A new noise!

Post by R Code »

thesameguy wrote: Mon Nov 18, 2019 3:58 pm It can't be that, because there isn't one. :)
Sorry if I missed that part. U joints are cheap/easy, so you can check those easy enough.

What else aren't you telling us?
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Re: Awesome. A new noise!

Post by thesameguy »

I'm not sure what I'd be hiding - I thought the OP was pretty complete!
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Re: Awesome. A new noise!

Post by Ed Lijewski »

CV joint?

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Re: Awesome. A new noise!

Post by thesameguy »

On the table, but I think the sound is too far forward and too loud. But, the CVs are VERY old, so I couldn't rule them out. They aren't untouched originals, but they're at least 20 years in the car... though the boots are intact.

Here's The Sound, captured remarkably well!

https://youtu.be/sgo1JJrI4sc
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Re: Awesome. A new noise!

Post by john keefe »

Might be missing something, but is your DS a one-piece FMS Alu? In the "How To Prep the Sierra..." book, the factory tried and gave up on one-piece shafts due to vibration, and never ran them again. The Cosworth DS I've got on mine is very beefy, with a larger diameter front tube, double-walled tubing from center-joint to diff, and big u-joints. Very quiet.

I tried a one-piece DS with one of the first T5's I installed (fit from a 5.0L), and tossed it for custom 2-piece DS's ever since then. It's not like the rear diff is floating (as with a solid axle) and any vibration/movement can be countered at the other end. With the fixed diff, I think all the vibration goes right to the tail housing and transmission bushing, then resonates back again. Plus, the two u-joints are always working at much different ranges of motion, adding to the problem, unless you've got solid motor and transmission mounts... but that's a whole 'nuther bag of NVH to bug you.

Going to a harder durometer or PU transmission bushing would seem to exacerbate the issue, transmitting any/all NVH from the bushing forward. If you stick with the one-piece, you'll need a good (maybe TBird) transmission stock mount-bushing and updated engine mounts.

The Turbo TBird Coupe had a big, weighted damper which bolted onto the top of the tail housing. I don't recall if those had a one-piece DS or not, but Ford definitely thought it best to add it on for NVH in their Hi-Po "Luxury" vehicle. When you're next to another car/wall, etc., can you hear it under load and when coasting, or just under load? Coast with clutch depressed, vs. transmission in neutral? If it goes away with the clutch depressed, then perhaps you've got some wear and tear going on there that is transmitting to the DS. Without a guibo to help dampen, that's just resonating up and down the solid tube.

Never mind if you're got a 2-piece shaft. :)
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Re: Awesome. A new noise!

Post by R Code »

john keefe wrote: Tue Nov 19, 2019 1:58 pm ..The Turbo TBird Coupe had a big, weighted damper which bolted onto the top of the tail housing.
Some FMXs had those as well.

Not sure what setup the OP has either, and he didn't say. I assumed it was some sort of tribal knowledge that I should have known & he wasn't interested in sharing. ::shrugs::
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Re: Awesome. A new noise!

Post by John Brennan »

Random thought: how's the clearance for the shaft at the rear brake line mounting tabs? Understand those need to be trimmed to allow the DS to clear.
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Re: Awesome. A new noise!

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John Brennan wrote: Tue Nov 19, 2019 3:04 pm Random thought: how's the clearance for the shaft at the rear brake line mounting tabs? Understand those need to be trimmed to allow the DS to clear.
I think you may be onto something - I wonder if that little horseshoe guide is bouncing around off the driveshaft. I inherited another XR where the PO did a half-assed rear disk conversion and never fixed the cable so it bounces around on the stock driveshaft. I haven't driven that car in two years, but I think the noise is similar. The only thing that doesn't add up is why it goes away in neutral... but maybe something about subtle movement of the transmission when it's under load?
Last edited by thesameguy on Tue Nov 19, 2019 3:18 pm, edited 1 time in total.
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Re: Awesome. A new noise!

Post by thesameguy »

The car has a T5 gearbox and a one piece FMS driveshaft. The gearbox was old when I installed it, the driveshaft was new. Diff is the original one (auto ratios) but has routine service and at last oil change looked great. Diff has an original style MC2 poly mount, engine & trans are on stock Ford parts. It's been that way for twelve years and has been 100% problem free. The noise is new.
Last edited by thesameguy on Tue Nov 19, 2019 3:19 pm, edited 1 time in total.
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Re: Awesome. A new noise!

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john keefe wrote: Tue Nov 19, 2019 1:58 pm The Turbo TBird Coupe had a big, weighted damper which bolted onto the top of the tail housing.
The geabox is from a TC, and I'm pretty sure that weight is there still... it's been ten years since I looked though!
When you're next to another car/wall, etc., can you hear it under load and when coasting, or just under load?
Until yesterday afternoon, the noise was only audible under load. Yesterday when taking that video the noise started happening while coasting. BUT, only in gear. Second the clutch is in or the trans in neutral, the noise stops.
If it goes away with the clutch depressed, then perhaps you've got some wear and tear going on there that is transmitting to the DS. Without a guibo to help dampen, that's just resonating up and down the solid tube.
The transmission or clutch is definitely on the table, the only thing that strikes me is that I would expect to feel something that originated from the transmission or clutch in the shifter or pedal, and they're as stone-cold silent as they've ever been. Even when I'm really flogging it, none of that sound comes through as feeling to the cabin. It's just really loud and obnoxious!
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Re: Awesome. A new noise!

Post by john keefe »

I've got a built-up T5 behind my 5.0L, with the 5th gear reinforcement (Hanson? long time ago). Trans is solid, no clunks, shakes, etc. at any time. But, I get a really annoying rattle from the clutch when I'm at a stop, trans in neutral. Depress the clutch and it goes away, nice & quiet. But, can't feel anything in the clutch pedal, or the shifter. Been a few years, but not that many miles on it since the 5.0L swap; haven't driven it all that much. Annoying, but until it blows up, I just make it go away with high RPMs. :)

So, my opinion only, lack of feedback in the pedal, or lack of shaking/vibration in the shifter doesn't mean its NOT the clutch. OK, might have something to do with gutting most of the floor's sound deadening, too.
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Re: Awesome. A new noise!

Post by thesameguy »

I could definitely live with a rattle, but this sound is very loud. Loud enough to get the attention of other drivers and make them want to not drive near me, In a way, that's kind of a nice thing, but I've been reppin' the XR in NorCal for 15 years and I demand RESPECT!
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