Rubber donuts

[Brian Walton]

and I bet that after 500k he still has a silly smile on his face.

Now 500k is a lot of miles. Let say the average MPH was 35mph....that's 14,000 odd hours or he has been sitting in his
car for a total of nearly 5 years solid at 8 hours a day. Forget about the donuts........how many times has the
drivers seat been changed?

["William \" Ski]

Better than a silly smile ..... more like a sh*t eating grin. With the
exception of being parked for a couple of oversea tours and a restoration
it's been my daily driver since '69. For eight years that was 140 miles a
day, five days a week. By the way, I know I have slowed down a lot in the
past few years, BUT 35mph average, I would hope I've done better than that.
After all it is a Lotus. Seats have been redone three times and usually get
swap side to side every year or so.

Skip King

'69 Elan S4SE
'61 Seven S2

Measure it with a micrometer
Mark it with a grease pencil
Cut it with an ax

[gobw2]

Dag -not that bad. I did them with diff in car.A lot easier than on a
conventional rear axle, where you have to remove brake system and reach
inside tube with special tool. If yours is like on my '67 - just remove
bearing retainer and tap stub shaft out. The bearing dust seals are used
to retain the oil, no separate seal.

Remove inner retaining ring and replace bearing. Clean out snap ring
grooves, check condition of snap rings - they are cheap, and I would
replace if new available. While out, check stub shaft splines - if they
show twist, have stub shaft magnafluxed. Original shafts are very soft -
methinks mild steel and fail at spline. Lightly lube outer race,
reinstall.
On Wed, 22 Nov 2000 09:14:19 +0100 "Dag Henning Nielsen"
<***@***.***> writes:

[gobw2]

I believe any grade 5 bolt of same diameter will exceed shear of
originals. George
On Wed, 22 Nov 2000 17:59:27 -0500 ElanS4 <***@***.***> writes:

[Rob_LaMoreaux]

Well yes and no to their being "special". What is special about the bolts
is that they are AN7-31A and AN7-25A Aircraft grade bolts, not SAE grade
bolts. Being AN bolts they have shorter threaded portions so the threaded
portion is not in shear. Any mechanic working on Lotus cars or rac cars
should have a selction of AN bolts, especially these two sizes.

When I removed the original bolts from my Elan I looked at the ones that
were "special", and recognized them to be AN, upon which I measured and
checked, and sure enough they were the same exact dimensions, so I placed
an order to Aircraft Spruce and Specialty for those and other bolts to
upgrade all the critical bolts to AN quality.

Rob LaMoreaux
Ann Arbor, MI USA
(734)-971-5583
***@***.***
Too many Hobbies.... Too Little Time
1969 Lotus Elan....It's not a restoration, it's a never-ending
adventure.

[Rob_LaMoreaux]

Well yes and no to their being "special". What is special about the bolts
is that they are AN7-31A and AN7-25A Aircraft grade bolts, not SAE grade
bolts. Being AN bolts they have shorter threaded portions so the threaded
portion is not in shear. Any mechanic working on Lotus cars or rac cars
should have a selction of AN bolts, especially these two sizes.

When I removed the original bolts from my Elan I looked at the ones that
were "special", and recognized them to be AN, upon which I measured and
checked, and sure enough they were the same exact dimensions, so I placed
an order to Aircraft Spruce and Specialty for those and other bolts to
upgrade all the critical bolts to AN quality.

Rob LaMoreaux
Ann Arbor, MI USA
(734)-971-5583
***@***.***
Too many Hobbies.... Too Little Time
1969 Lotus Elan....It's not a restoration, it's a never-ending
adventure.

[Brian Walton]

I can't help feeling that if the chassis of the Elan was designed to have rubber donuts..then rubber donuts it should
be. Without them the acceleration forces get transferred back into the chassis through all manner of solid UJ's. The
chassis maybe strong but not that strong.

For those who can remember the BMW Isetta/ Hilman Imp had similar rubber donuts. Not the same size, but they did the
same thing. Look after them and they looked after you. Treat them asthough it is a solid UJ and you are forever
changing the @$#% things. I believe they were also on the GT40's.....but then again 24 hours would have been an
acceptable life for them......and not a minute more.

["Richard Hinds"]

Dag,
It is advisable to warm the alloy diff housing, before driving the
shaft bearings out. These bearings are an interference fit only, and simply
driving them out will remove some of the alloy casing. I used an electric
hot-air gun, intended for paint-stripping. The alloy casing only has to be
warmed up to "hand warm" temp. around the bearing area, and the fractional
expansion means the shaft+bearing will come out easily. Same procedure when
replacing. It worked for me on my +2!
Good luck, Richard Hinds, England.

As I am without a shop-manual, can anyone that has got one tell me if you
are adviced to pre-heat the aluminium before extracting the shaft/bearings
and seals ? - like with the waterpump bearing ?
Thanks,
Dag

[Dag-Henning]

Thank you george, we'll see.........
Dag
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Kopi: ***@***.*** <***@***.***>
Dato: 23. november 2000 16:31
Emne: Re: SV: [LotusElan.net] Rubber donuts

[Dag-Henning]

Thanks Richard, that was just what I had in mind.
Dag
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Dato: 23. november 2000 23:13
Emne: Re: [LotusElan.net] Rubber donuts/bearing replacement.

[Elan45]

On the Elan diff, there is a separate seal, 36R6007, which is inboard of the bearing. It is true that earlier Lotus models used the stub axle double sealed bearings as the only seal, but not the Elan. I have written in my desk copy of the parts book that it's generic number is 30 x 40 x 7, which should be available at most bearing supply houses. I'd still replace it in the car.

Roger


conventional rear axle, where you have to remove brake system and reach
inside tube with special tool. If yours is like on my '67 - just remove
bearing retainer and tap stub shaft out. The bearing dust seals are used
to retain the oil, no separate seal.

Remove inner retaining ring and replace bearing. Clean out snap ring
grooves, check condition of snap rings - they are cheap, and I would
replace if new available. While out, check stub shaft splines - if they
show twist, have stub shaft magnafluxed. Original shafts are very soft -
methinks mild steel and fail at spline. Lightly lube outer race,
reinstall.
On Wed, 22 Nov 2000 09:14:19 +0100 "Dag Henning Nielsen"
<***@***.***> writes:

[gobw2]

Roger - My 67 Elan unit 6078 with 3.7 rear never had separate seal! I am
original owner. Now I am curious - wonder if there is a way to fit seals
to mine. George

On Mon, 27 Nov 2000 08:33:03 -0500 "Roger Sieling"
<***@***.***> writes:
On the Elan diff, there is a separate seal, 36R6007, which is inboard of
the bearing. It is true that earlier Lotus models used the stub axle
double sealed bearings as the only seal, but not the Elan. I have written
in my desk copy of the parts book that it's generic number is 30 x 40 x
7, which should be available at most bearing supply houses. I'd still
replace it in the car.

Roger


conventional rear axle, where you have to remove brake system and reach
inside tube with special tool. If yours is like on my '67 - just remove
bearing retainer and tap stub shaft out. The bearing dust seals are used
to retain the oil, no separate seal.

Remove inner retaining ring and replace bearing. Clean out snap ring
grooves, check condition of snap rings - they are cheap, and I would
replace if new available. While out, check stub shaft splines - if they
show twist, have stub shaft magnafluxed. Original shafts are very soft -
methinks mild steel and fail at spline. Lightly lube outer race,
reinstall.
On Wed, 22 Nov 2000 09:14:19 +0100 "Dag Henning Nielsen"
<***@***.***> writes:

[Brian Walton]

Gee we have certainly had a discussion on the subject of rubber donuts. Many thanks to all who have placed their
comments.

I'm still worried about the vehicles originality and strain on the drive line if you go the CV way. Concerning the
strain I will tell you why.

Many years ago I was the proud owner of a BMW Isetta. Don't laugh, it did me well in the early 70's and I thought I
was the bees knees with the keyring. Anyway the Isetta had/has rubber donuts of the same design but smaller in size to
the Elan's. These @@@^&^ donuts would always break at the worst time. Like rush hour traffic....you know the thing.
Well I looked around and found Hillman Imp donuts that were a little bigger. I put them in (and believe me being under
a bubble car for three hours is not fun) and thought I had solved the problem. A week later the gearbox gave out and
the case broke. Too much strength in one area had killed another!

Sods law. Keep a spare donut set in the car's boot and the donuts you have on the Elan will last for decades. You see
'they know'!

[type26owner]

Can I point out most of the attenuation (dissipation of sharp spikes) of
the driveline is done with the engine and transmission elastomer mounts.
Gearbox and Diff are quite efficient attenuators too as long as the
lubricant is present. All forces are transmitted to the chassis or
driveline but the frequency and amplitude can be is changed by the
interplay of elastomer mounts. The tires can also serve as a dampeners.
It's very likely that the rubber donuts don't contribute much other then
torsional compliance. I'd say other then the expense the cv's are the
way to go. Best way to analyze is to attach the appropriate sensors with
telemetry.

It's bad to be leaving bits and pieces on the roadbed like the SSC
Thrust did when it punched through the sound barrier. No donuts just a
joke!

Brian, I never speak disparagingly of a car that I own because they
develop an attitude to bad vibes everytime.
--

Keith Franck

LBNL Engineering

http://www.lbl.gov/

http://www-eng.lbl.gov/

http://www-als.lbl.gov/

http://xraysweb.lbl.gov/esg/

[type26owner]

Kevin,
We are in agreement if I understand your point. The highest probability
of twisting a differential drive axle is in a lower gear with full
torque applied through the driveline and the tires at maximum grip.
Therefore, the grip of the tires can be and should be used as a torque
limiting mechanism to help prevent damage. In my case it's probably good
I'm to cheap to pay for the highest performance tires or I'd be
repairing the diff continuously even running donuts.

Obviously the engine and gearbox mounts are the connected to chassis in
a way that mostly the high frequency vibrations generated by that
assembly are attenuated. Their range of motion and compliance was never
intended to compensate for the windup of the donuts. The donuts could
possibly dampen some high frequency torsional vibration from the tires
reacting with the road. I can't image a vibration of that sort being
high enough frequency that the donuts' compliance can react in real time
at high speed and with the halfshaft assemblies' inertia though. I could
be wrong. Some data would be interesting!
--

Keith Franck

LBNL Engineering

http://www.lbl.gov/

http://www-eng.lbl.gov/

http://www-als.lbl.gov/

http://xraysweb.lbl.gov/esg/