Sucky, rattly noise, low RPM, under load?

[Hopkins]

I just remembered that I have not concluded this. (Actually, nor have I concluded the oil hose replacement video - this is still very much on my list. However, I've relocated to London and I've barely found time to do anything, even in this ridiculous covid situation.)

Anyway! I had a load of work done to the car at The Performance Shop - formerly LC Rotary. It's the first time I've used them, and I was impressed. That work was an annual service and MOT, but during this work I had a second hand PZ exhaust fitted, a replacement cat (after a failed emissions test) and a complete set of sparks, leads and coils. The noise has gone . However, so much has changed that a diagnosis is impossible :/

[Hopkins]

Sorry, I missed the last couple of replies here - thanks though! However, I think I finally have a diagnosis, courtesy of the recent rebuild! Pulling away the next morning from cold after the first long journey on the new engine produced a very horrible scraping sound which made me rather nervous. This has subsequently faded but still pops up in a quieter form between 2 and 3k rpm under load. (When the rebuilt engine was limited to 5k I found myself doing this way more frequently than usual.) TPS diagnosed it as the "thrust bearing" in the gearbox.

I have no idea how many miles my gearbox has done. I picked up my car just over 5 years ago when it had 42k on the clock. I've added another 43k. Synchromesh from first to second had never been perfect, but at about 50-something-k miles I destroyed what was left of it on the fantastic car limits day at North Weald. After that, I had to double de-clutch to go from first to second whenever the revs breached about 5k. Whoops. Later, Essex Rotary replaced the gearbox with a reclaimed replacement of unknown (to me) mileage. If we suppose that it was from a victim of engine failure then the gearbox could now have well over 100k on it.

In any case, TPS seemed to think that it is not an urgent problem to fix and that the best course of action is probably to find a specialist to rebuild the gearbox, rather than replace it with another second hand 'box of unknown origin. I will do some research and then pick the brains of you wonderful folk on this forum when my bank balance permits another investment!

[Ollie]

Having the gearbox rebuilt is a pricey endavour. You can only really order parts once the box is open and they have to be made to match up with everything else. The parts of the gearbox from Mazda are well over the thousands price range, before the person rebuilding the box does anything.

A second hand box will set you back up to £200-300~ (can't remember the last good box price so a bit of a high estimate on my end).

Just so you're aware most people tend to buy a second hand box over going rebuilt/new for the fact you can arguably buy up to 10~ second hand ones for the price of new/rebuilt and its likely you'll find a good one before you get anywhere near the cost of a rebuild/new gearbox.

[350matt]

I'd say to replace the gearbox oil the next course of action as the standard Mazda stuff can be improved on

I've had very good experiences with the latest Redline thin MTL 70W80

[Hopkins]

...you can arguably buy up to 10~ second hand ones for the price of new/rebuilt and its likely you'll find a good one before you get anywhere near the cost of a rebuild/new gearbox.

Thanks for the advice. I will keep my options open. I heard that "someone here" who also uses TPS recently had theirs rebuilt for "about £500", but I have yet to establish anything more concrete!

I'd say to replace the gearbox oil the next course of action as the standard Mazda stuff can be improved on

I've had very good experiences with the latest Redline thin MTL 70W80

Thanks - the gearbox oil was replaced 12k miles ago. I did suggest that as a possibility but was advised that it would not make any difference. I don't know which brand they use.

[350matt]

Well compared to the work required in swapping the gearbox surely a fluid swap is worth a go
if it doesn't work you can always re-use the new fluid in the replacement box?

[Hopkins]

Hello all, it's been a while, and my life has changed quite a lot recently so my membership lapsed and I've only just got around to renewing. Anyway, the saga continues...

Last year I had the gearbox changed for a second hand box which had been tested by TPS. The rattly noise when the engine is warm and it is under load at low revs persists. They clutch and release bearing were all changed during the engine build. Engine mounts changed to no avail. TPS have managed to recreate the effect on the ramp by applying the brakes to create a load, but the noise seems to resonate through the drive train so it appears to come from the back or the front depending on where you stand. They're out of ideas. Does anyone have any suggestions?

[warpc0il]

Is the exhaust system original or aftermarket?
Specifically, is the joint between the cat and the catback still a spring-clamped flexible joint with the original donut seal?
If this joint has been fitted such that it's solid, then the engine and transmission can't move on it's mounts independently to the catback exhaust, which can cause all sorts of noises and harshness.

Applying a load to the engine would change the stance of the powertrain (see above) and also increases the intake vacuum, so a leak on the intake is also a possibility, especially if it's more obvious when the engine is warm.

[Hopkins]

Hi Dave, thanks for the reply and sorry for the delay - I've been in holiday (lucky me!).

The exhaust system is a second hand PZ, and looking at the time I had it installed it was about two weeks after my original post! I'll suggest checking the seal as you suggest. Re-reading the thread, I'll also suggest checking that the heat shield is secure.

Since first identifying the noise, here is a summary of work which has had no effect (not in chronological order):

Complete engine rebuild
New engine mounts
Replacement second hand gearbox
Replacement clutch
Replacement second hand PZ exhaust
Aftermarket catalytic converters (two)

[Hopkins]

Possible diagnosis: problem with the diff. One of the chaps at TPS recently came across a car with an even worse case of the same noise, to the extent that it was easier to pinpoint the source. He's trying a replacement diff. I'll report back!

[Mcgoo]

I have a 5 speed with the exact same problem! Sounds like pushing a shopping trolley in a rough carpark or like rattling a chain link fence. It happens in 2nd 3rd 4th under load but not in 1st or 5th. I can hear it between 3krpm and a little under 4k. Its pretty loud. I can record the noise if anyone's interested. This is a real head scratcher. Could it be e-shaft related?

[Hopkins]

I have a 5 speed with the exact same problem! Sounds like pushing a shopping trolley in a rough carpark or like rattling a chain link fence. It happens in 2nd 3rd 4th under load but not in 1st or 5th. I can hear it between 3krpm and a little under 4k. Its pretty loud. I can record the noise if anyone's interested. This is a real head scratcher. Could it be e-shaft related?

Ah, fantastic! Well, not fantastic, but you know what I mean .

A gent on this forum is helping me out with a spare diff, but I've yet to collect/install it. Perhaps wait until I've confirmed a resolution before sinking your cash into it. Your shopping trolley analogy is good.

On a related note, I'm disappointed with my new engine mounts which didn't need replacing (because they weren't the source of this problem). I half expected as much, given some of the discussions I've read on here. It's all fine except for a rough idle, which makes me sad in traffic. I may get the idle speed pushed up from the current 950 to perhaps 1100 as a work-around.

[warpc0il]

On a related note, I was just reading about a guy that's had an annoying vibration/noise for the last two years, after his Honda went in to a dealer for an airbag recall. The vibration was worse at particular road speeds and engine revs/load.

It's had multiple visits back to the same dealer, who confirmed the issue but were unable to fix.

It's also had checks done by a Honda specialist, plus the owner is quite handy and has been checking/replacing stuff following advice on their FB group, including the exhaust catback and mounts.

Last week the cause was discovered and the problem was resolved.

Spoiler:

It was the head of a vacuum cleaner left under the driver's seat, as the car had been valeted following the recall work

They didn't say who finally fixed it, but there's has been relief and embarrassment all round

[Mcgoo]

I found what it is! And I fixed the problem with a single zip-tie
It is the ssv

[Hopkins]

Thanks for the reply. I had dropped my car in for a service just after reading this but the garage is convinced that the SSV isn't the culprit in my case. It makes sense since the noise was present before and after an engine rebuild, and they specifically cleaned the SSV afterwards because it wasn't functioning smoothly.

However, in total now I have changed the diff, the diff mounts, the prop shaft, the gearbox, the pilot bearing, the release bearing, the engine mounts and the noise is reduced but it is still there! I suspect the reduction in noise is because everything else is so tight that the resonance has reduced, but the underlying cause hasn't been fixed.

The only idea they have left is that it is the springs in the stage one clutch (Competition brand). However, the noise has already survived a clutch change from an Exedy stage one, but perhaps these two clutches both have those weird loose extra springs? In any case, it seems like a daft design floor and something that would be widely recognised by all those who have installed stage one clutches.

[warpc0il]

I've just re-read this thread and I think I can see why others haven't had this issue....

The clue is in the Subject "...low RPM, under load"

The Renesis engine doesn't like load at low rpm, ever.

If you want to add load, then drop a gear and increase revs first.

Okay, this response may sound a little flippant and I don't mean to belittle the issue, though it seems that it could/should be avoided by a change in driving style.

[Hopkins]

I should probably contextualise this a bit better. This issue is at its most prominent about town in traffic where one is frequently and gradually increasing and decreasing speed between about 15 and 30 mph, usually in second gear. So the load is low, the throttle is opened gently and partially and nothing is being stressed.

One of the reasons I love this car is for its versatility and I am most at home keeping the revs above 5k on country lanes. However, I would prefer to use more than just first gear about town .

[warpc0il]

In that case I wonder if one (or more) fuel injectors isn't shutting off properly, causing it be over-fuelling under those conditions, which might be less obvious as the revs increase.

[Hopkins]

Thanks. Funnily enough, Essex Rotary have just started offering a fuel injector cleaning service which I was thinking of taking them up on... Although, I have to say, since this problem has developed I don't think that the title of this thread is the best description. It is not really "sucky". The description a few posts above - although apparently fixed by securing the SSV - is best: like a shopping trolley over rough ground!