Noise, Vibration and Harshness.

[paul_adamson]

HELP!!

I've been running the engine in on my Elan and now have just about 1000
miles on the clock.
In recent days, I've done some miles on Motorways and I can't help noticing
that there is some "Boom" and vibration. (Alright - dammit. Noise!)
The noise gets worse when the throttle is lifted.
Last week I spent some time checking the differential bushes and the torque
rods to make sure that the bottom of the unit wasn't sat on the chassis.
I've replaced all the bushes and the situation did improve a little.
So, I'm trying to decided what the cause could be.
My list is:
Worn/damaged diff. unit
Worn/damaged Propshaft U/J's
Out of Balance prop shaft?

When I encounter problems of this type, my mind turns to other aspects of
the car that have raised "question marks" in the past.

My thoughts turned to the gearbox mount. On my car, the crossmember has
reinforcements to each side. These stop the mounting sitting flush with the
underside of the chassis. I'd always wondered about this but could see no
alternative but to shim the crossmember down.... (About 3/8"?)
Perhaps, this is causing some misalignment with the propshaft and causing
the vibration?
Casting my mind back, I also remember that the engine mountings and gearbox
mountings where - tight - and stressed more than I would have expected.
I few nights ago, I woke up in the middle of the night and had to check that
the propshaft for 3.77 and 3.55 diff's where the same! I had had an idea
that maybe, the propshaft was not the right length and was somehow bottomed
out and causing the vibration! (This situation is not healthy)

If it is the diff. what should I do? Can they be rebuilt easily?

PS. In a little over 6 weeks, I'm getting married and going on Honeymoon
from the UK in the Elan and doing some touring in Italy! (That's 2020 miles
according to AutoRoute). I'd rather have this problem fixed before the trip
than have it manifest itself during the Honeymoon (I'm sure that would not
be a good start!)

Paul (NVH) Adamson

[elansprint71]

Paul,
Every time I drive the ?lan I hear a different noise(s), this is normal,
however........ changes to marital advice counsellor/Dutch Uncle mode......
do not go on honeymoon in the ?lan, hire a Subaru Impreza turbo, enjoy
trouble free trip and take her in the ?lan next year. By this time she will
be used to the Lotus way of life, i.e. breakdowns at the most inopportune
moment, arriving late at weddings (as best man)/funerals/bar mitzvahs, etc.
covered in oil/blood/sweat etc.and trying to explain to a group of Volvo
owners that "the car let me down".
See you at Swettenham,

Pete
----- Original Message -----
From: "Paul Adamson" <***@***.***>
To: "Lotuselan" <***@***.***>
Sent: Thursday, April 26, 2001 10:02 PM
Subject: [LotusElan.net] Noise, Vibration and Harshness.


HELP!!

I've been running the engine in on my Elan and now have just about 1000
miles on the clock.
In recent days, I've done some miles on Motorways and I can't help noticing
that there is some "Boom" and vibration. (Alright - dammit. Noise!)
The noise gets worse when the throttle is lifted.
Last week I spent some time checking the differential bushes and the torque
rods to make sure that the bottom of the unit wasn't sat on the chassis.
I've replaced all the bushes and the situation did improve a little.
So, I'm trying to decided what the cause could be.
My list is:
Worn/damaged diff. unit
Worn/damaged Propshaft U/J's
Out of Balance prop shaft?

When I encounter problems of this type, my mind turns to other aspects of
the car that have raised "question marks" in the past.

My thoughts turned to the gearbox mount. On my car, the crossmember has
reinforcements to each side. These stop the mounting sitting flush with the
underside of the chassis. I'd always wondered about this but could see no
alternative but to shim the crossmember down.... (About 3/8"?)
Perhaps, this is causing some misalignment with the propshaft and causing
the vibration?
Casting my mind back, I also remember that the engine mountings and gearbox
mountings where - tight - and stressed more than I would have expected.
I few nights ago, I woke up in the middle of the night and had to check that
the propshaft for 3.77 and 3.55 diff's where the same! I had had an idea
that maybe, the propshaft was not the right length and was somehow bottomed
out and causing the vibration! (This situation is not healthy)

If it is the diff. what should I do? Can they be rebuilt easily?

PS. In a little over 6 weeks, I'm getting married and going on Honeymoon
from the UK in the Elan and doing some touring in Italy! (That's 2020 miles
according to AutoRoute). I'd rather have this problem fixed before the trip
than have it manifest itself during the Honeymoon (I'm sure that would not
be a good start!)

Paul (NVH) Adamson








reserved.

[gobw2]

Paul - I don't have fancy equipment, so do it with labor. 1st thing I
would do - jack car up, supporting on rear lower arms so suspension is in
normal position. make sure it is solid. get under it, rotate diff rock
back and forth - watching u joints - if you see movement - suspect. try
to move prop shaft radially at pinion bearing - any radial movement -
suspect bearing. try same with axle shafts. In doubt - Remove wheels
- have friend run car up, look it over - should be easy to tell where
culprit lies. If I think in diff - remove donuts from output shafts and
try it again - You should be able to see prop end vibrating if bearing/u
joint is shot. In doubt - take a pencil and gradually bring in contact
with shaft while rotating. When engine is off - should see a mark all
around. If just on a small part of shaft - you should have seen
vibration,and felt it when using pencil- then components at that end of
shaft are suspect. One last thought - did you have diff or shaft out? If
so - did you mark flanges and get them back in same rotational alignment?

On Thu, 26 Apr 2001 22:02:05 +0100 "Paul Adamson"
<***@***.***> writes:

[Stephen Whitesell]

on 4/26/01 11:02 AM, Paul Adamson at ***@***.***e:


I have about 1500 miles on my new motor and had exactly the same problem as
you have. I just finished an hour ago changing the motor mounts even though
they were only a year old or so. The left side mount had collapsed enough
where the middle part of the bracket touched the top of the mount (barely,
and looked fine at a glance) transferring all the vibration into the body.
It was smooth on exceleration but vibrated on deceleration and idle. What a
difference, Smooth now. I also ordered a trans mount but haven't put it in
yet.

Good luck, I hope it's as easy as my car was.

Aloha,

Stephen

[Harald S. Feeß]

Paul,

after finishing a chassis replacement in 2000 I had a similar problem that vanished before I could find the reason.
I think it was a forgotten tool beneath the carbs/airbox (does anybody knowwhere my 13 mm wrench is ?).
Maybe your engine gets contact with the body or the chassis when throttle is lifted.
Check everything you can but don?t think too complicated.

If you need help during your honeymoon trip and you are near Munich just call.
Maybe I can help (I mean if you have problems with your Elan, nothing else ).

Good luck

Harry
Munich, Germany
71 Elan Sprint

[kstrutt1]

As previously mentioned I would check the mounts are not
pre-loaded(Also double check they are the right ones I believe there
are two types of front mount and check the engine is not contacting
the underside of the bonnet lid).
Also check the exhaust, this will twist one side to the other under
accel/decel and the effect can be amplified at the rear as the motion
is greater, the entire system can resonate, and the flat panels
amplify the noise.
As the Elan propshaft is very small it shouldn't be a problem unless
the joints are worn or it is very out of balance, check the front UJ
and the rear gearbox bearing by feel through the access hole in the
transmission tunnel.
Also a more detailed descrption may help, is it worse at specific
vehicle speeds or engine rpm?, does it get worse in lower gears etc.

regards
Kevin.

[TimMullen]

Harald S. Fee? wrote:

I once had a noise that turned out to be the bottom of a carb hitting the body
below them. Turned out that I had a weak engine mount, and the engine was
sagging a bit...

New mounts and the problem was fixed...

Tim Mullen

Chantilly, VA
72 Elan Sprint

[cusword]

Hi Paul, have you found the fault yet?

The clue is probably that it happens when you 'lift off'. As you
know when you 'put the boot in', the engine tilts to the right, and
when you lift off it tilts to the left. The diff does the same thing
to a lesser degree. Most of the time they sit in the middle. Have
you tried rocking the engine by hand, when stationary, with the
engine off? As you probably know the two engine mounts are
different, and it's important they go on the correct sides.

Good luck.

David



--- In lotuselan@y..., "Paul Adamson" <paul@a...> wrote:

[paul_adamson]

I've been away over the weekend and haven't been able to look at the Elan.
Now suitably refreshed, I intend to have a fresh look at the car tomorrow.
The current crop of suspects are:
Engine Mounts
Gearbox Mount?
Prop Shaft
Diff.

(The Engine and gearbox mounts are new - but that's not always a guarantee
that all will be well)
I got the car as a collection of Elan shaped parts - so the prop shaft was
already removed. So, I don't know how it had been aligned. I suppose I can
always rotate it through 180 degrees and test it...

I'll check everything and let you know what I find.
One thing that I did wonder about was the Pinion Flange and nut.
Maybe this has been over tightened? What effect would this have? Could it
affect the meshing of the diff?

As I've already mentioned, the Vibration occurs when the throttle is lifted,
I would have through an over tightened pinion would howl?

Paul Adamson

[paul_adamson]

I've been examining the Vibration problem on the Elan this evening.
I don't see anything wrong with the engine mounts (See for yourself in the
Files section - if you can get to it! Try the folder Adamson -NVH)

That gearbox mount looks badly wrong though. You may be able to see in the
photo, the reinforcements to the cross member would foul the chassis sides
if there where no spacers. How can this be? Maybe the cross member is from a
Plus 2 (assuming they're different?)

I removed the rear wheels and suspended the car on wooden blocks.
Everything looked fine with the engine running at 1500rpm in high gear.
I half expected to see the diff bouncing around. But - no, it was solid as a
rock.
I stuck some masking tape on the pinion and marked it with a pencil as the
prop turned. I got a nice continuous pencil line. (Worth a try I suppose)
There is a definite unpleasant sound coming from around the diff. But I'm
unable to determine if it's the diff. or maybe the rear of the prop shaft.
I wanted to run the engine up and down and listen - but the exhaust drowns
out the offending sound.
(This doesn't happen on the road unfortunately)

So, now I'm pondering my next move.... watch this space.

[gjz30075]

--- In lotuselan@y..., "Paul Adamson" <paul@a...> wrote:












Paul, I compared your gearbox mounting to mine. It looks like you
have spacers between the frame and cross member trans mount. I have
no spacers. The rest of the mounting, up to the bottom of the trans
looks exactly like mine.

Greg Zelazek
Sprint without Paul's problems.....other problems, certainly.