Technical Acceleration knock Fiat 500 TwinAir

[JasonPap]

Hello everyone

I just changed both wishbones on our twinair 500 (ball joints were dead)
And i was hoping that the knocking under hard low RPM acceleration would have gone away, but it seems not..

What do you think it is? Engine mount? The little dog bone one underneath?

DMF?

Has 68,000 km on it.. 2010 model...

 

[typecastboy]

I had a knock which was the dog bone.

 

[JasonPap]

I had a knock which was the dog bone.

Was it a sharp knocking or more of a loud rumble? I seem to have a loud rumble

Its worse with the wheels straight ahead that it is with them turned.. also it gets worse as i go up the gears..

 

[JasonPap]

Its actually more like a loud rumble in 5th when accelerating at 2000 rpm..

Engine mounts? Strut top mounts?
DMF?

 

[typecastboy]

Mine was at low revs and over bumps, a district bang.

 

[AndyRKett]

Its worse with the wheels straight ahead that it is with them turned.. also it gets worse as i go up the gears..

Sounds more like a wheel bearing or cv joint than DMF or mounts of any kind, probably more likely the bearing.

 

[p6baseunit]

Sounds more like a wheel bearing or cv joint than DMF or mounts of any kind, probably more likely the bearing.

Again, no DMF in that model year.
There is of course the most strain on the engine, accelerating in 5th at low revs, but I would kind of expect it in 4th also of it was an engine mount or wheel bearing/cv joint.
The gearbox isn’t leaking oil is it?

 

[p6baseunit]

I had a knock which was the dog bone.

You could get a rumble - basically vibration transmitted through the body if the mount is completely knackered and touch metal to metal.. but I would really expect it under the same conditions in 4th

 

[wardpaa]

Assume you have checked your exhaust brackets from manifold to down pipe ? That would cause a rumble....
Failing that engine mounts.

Suspension issues would usually be road surface related.

 

[JasonPap]

Again, no DMF in that model year.
There is of course the most strain on the engine, accelerating in 5th at low revs, but I would kind of expect it in 4th also of it was an engine mount or wheel bearing/cv joint.
The gearbox isn’t leaking oil is it?

Hi there,

No, no leaks, i just changed the transmission oil and it hadnt lost any, and i did fill it with the right stuff afterwards. The reverse moan went away but then came back about a week later but not as loud. i had probably overfilled it a bit..

Are you sure there is no DMF in that model year? I would much rather change drive shafts : p

I will crawl under in an hour or two and give the driveshafts and exhaust mounts a wiggle.. i will update you all later

 

[JasonPap]

So the driveshafts seem to have no excessive play in them, barely noticable play in the longer of the two shafts, so im a bit stumped as to where this loud rumble i can feel in the floor of the car is coming from..

I will either wait for it to get worse or start changing parts in the below order

Lower engine mount
Strut top mounts (since the noise is affected by turning)
Flux capacitor...

 

[Ralf S.]

If it rumbles more when you're going up a steep slope, or if the car is travelling quickly and you go through a "dip" in the road, then that's the driveshafts.

You could also try driving forward slowly on full lock, stopping the car, turning the wheels to the opposite lock and then reversing. If there's a knock as the drive engages, then again it's the driveshaft.

If it's just a rumble and not any kind of clonk at all, then it's probably not a mount. Mounts tend to make a clonk or bang when you accelerate but then if you're on a light throttle, they'll be silent. You can check the lower one, since 500 tends to beat them up but "rumble" and engine mounts don't usually to go together.

I would check the wheel bearings too. Jack each corner up and spin the wheel round. It should spin freely and silently +/- some light pad noise. Don't rule out the rear bearings just because the noise comes from the front.

If you have time/inclination, this may be a good time to pull the driveshaft inner CV joint out of the cup and check the spider and the inside of the cup for damage/wear (grooves, in the case of the cup).

The outer CV should have absolutely zero play in it.

If the wheels are off, move the rear wheels to the front and vv, to see if the noise changes. Knacked ball joints *migh* have caused some strange tyre wear pattern that could be making the noise.

I dunno if I'd worry about the top strut bearings as there's not much going on up there... but have a look at the front suspension springs, to be sure there's no broken spring or that it hasn't jumped out of the top mount (it would have a bowed appearance, even if you can't see all the way up there).

Ralf S.

 

[JasonPap]

If it rumbles more when you're going up a steep slope, or if the car is travelling quickly and you go through a "dip" in the road, then that's the driveshafts.

You could also try driving forward slowly on full lock, stopping the car, turning the wheels to the opposite lock and then reversing. If there's a knock as the drive engages, then again it's the driveshaft.

If it's just a rumble and not any kind of clonk at all, then it's probably not a mount. Mounts tend to make a clonk or bang when you accelerate but then if you're on a light throttle, they'll be silent. You can check the lower one, since 500 tends to beat them up but "rumble" and engine mounts don't usually to go together.

Ralf S.

Thanks for all that info,

I have to give you a bit more info on the rumble, it feels like something big is shaking back and forth..

It is load related, worse in higher gears, and it changes when you steer a little bit. ie say it is rumbling in 5th under acceleration at 2000 rpm and i turn to the side a bit, it goes quiet. Turn back straight and it starts again.

I just put the winter tyres on and the noise is the same (only a tiny bit different)

Actually since i just changed both lower wishbones 2 days ago it seems to have gotten a bit worse!..

There is no distinct clonking except sometimes when i start to release the clutch in first gear starting from traffic lights..

I did grab the driveshafts and pull them around and i didnt detect any play but i know under acceleration it is different when the shafts are loaded. It seems to have the original driveshafts and cv boots (we bought it with 10,000km on the clock)

So i will try the reversing test tomorrow or thursday and post back.. but im running out of ideas..

 

[Ralf S.]

It's interesting that it goes quiet when you turn the wheel and the noise only started to get worse when you changed the wishbones but there would have been some movement in the mount at the back of the engine, so it's possible that lifting the car to change the wishbones strained the mount and made it worse, if it was already failing.

If the wheels spin freely and without noise when you jack it up (to check the wheel bearings) and the driveshafts don't clonk or feel notchy then it's worth changing the mount to be sure it's not the problem.

The mount lives outside whereas the bearings and driveshafts are all inside rubber boots. At your mileage I wouldn't expect the bearings and driveshafts to have any problems.

Ralf S.

 

[JasonPap]

The mount lives outside whereas the bearings and driveshafts are all inside rubber boots. At your mileage I wouldn't expect the bearings and driveshafts to have any problems.

Ralf S.

It now has 68,000 km on the odometer so it might be driveshafts...

It is strange that it is steering related.. I will feed back as soon as i get a chance to do the reverse test..

 

[JasonPap]

Hi All,

Thanks for all your responses so far

The reverse test i did, gave no noises.. i reversed on full lock, stopped, went to opposite full lock and drove forwards.. several times in both directions..

I also got a chance to crawl under again and the driveshafts are 100% tight on the Cv side, and the tripod joint side has the smallest amount of play between the gearbox and the joing, but none in the joint itself. When i say small, i say so small and stiff i could not feel it by hand, i could barely see the tripod cup move a fraction of a mm.. ive seen that a lot before so the driveshafts seems fine..

Dogbone engine mount ordered from fiat.. changing that first mid next week!..

 

[Ralf S.]

Yes, the driveshafts sound okay, especiallyafter your last couple of posts.

Gearbox or engine mounts would seem to be the most likely thing now.


Ralf S.

 

[rallycinq]

How corroded are the top mounts?

D

 

[Twinkletwinklelittlestar]

Sounds crazy but had a nasty knocking and rumbling noise that turned out to be the front most mounting on the air intake. Alan key bolt through the front of the engine bay which holds the fresh air intake pipe. I couldn’t believe all this noise came from a simple lose mounting bolt allowing pipe to vibrate and rattle against things. Worth checking as you never know.

 

[JasonPap]

Sounds crazy but had a nasty knocking and rumbling noise that turned out to be the front most mounting on the air intake. Alan key bolt through the front of the engine bay which holds the fresh air intake pipe. I couldn’t believe all this noise came from a simple lose mounting bolt allowing pipe to vibrate and rattle against things. Worth checking as you never know.

Hello,

Thanks for the info, ive had a rummage around the engine bay and everything is tight, this is a rumble i can feel in the floor!..

And, i had an NVH specialist where i work drive around with me, and he just casually looked at me and said “torque strut is toast”

I did get it half way out, and the non round side is quite loose compared to the new part..

How does one get that mount out?

Remove the 2 bolts on the mount and also remove the two bolts on the curvy steel bar that goes from the mount to the gearbox?

I need a bugger breaker bar.. the two bolts on the curvy steel bar were so tight i couldnt get them loose..

Someone has had it apart before from the looks of it and made it all impossibly tight..

Or do you drop the exhaust out to get the long bolt on the round side of the mount out?

Is there a writeup of this change? If not maybe i should make one..