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AVO Dampers for B, C, & D Series Vincents

Expansion and revision of AVO suspension units range for Vincents.

As of July 2016, AVO have now extensively revised their range of products for Vincents.


New Coil-over.

coil_over

A coil-over rear suspension unit for B and C series bikes is now available based on the well proven rear damper.

It is available either with a 275 lb/inch spring or a 350 lb/inch spring.

The 275 lb/inch spring was primarily chosen to give the maximum comfort when the bike is ridden solo. However, testing has shown that the facility to quickly adjust both spring preload and damper stiffness allows the unit to cope remarkably well with two-up use. This testing was done with a 14st Rider and a 10st passenger.

The 350 lb/inch spring was chosen for predominantly two-up use.

For reference, the standard springs have a combined spring rate of 378 lb/inch.

 

Revised Dampers

new_damper

The damper range has also been revised.

Front and rear dampers are now supplied complete with shroud and ready to fit.

Prices are as follows:

All dampers £140 + vat

Coil-over units £200 + vat

Damping adjustment of all units is by an Allen key.

The following technical information will be revised at a later date to reflect these changes.


The Case For AVO - A Quick Summary

In my view, the AVO rear damper is the best at any price.
It allows the greatest amount of useable suspension travel and can be quickly adjusted to give a balance between comfort and control that best suits the rider and the circumstances.
Combined with a change of springs, it can give a ride that is close to modern standards.

The AVO front damper is superior to the older alternatives and is likely at least the equal of more expensive modern replacements.
Unlike the rear suspension, a change of damper and springs cannot dramatically transform Girdraulics, but they can be made much better by attention to detail, and this includes the choice of damper.

The Rear Suspension: Damper Bump Travel is the Key

My involvement with AVO began when I tried to choose a replacement for the original rear damper.
All of the available choices seemed badly mismatched with the springs.

This mismatch has arisen because the original friction damped “B” series rear suspension design required the springs to also limit the suspension travel. They are very short and stiff so that they go into tension as the suspension extends. When the new Girdraulic hydraulic damper was fitted to the rear suspension it took over the task of limiting suspension travel as well as providing improved damping, but the specifications of the damper and the springs were not changed, in spite of the altered requirements. In fact, depending on how the spring eyes are adjusted, the Vincent damper can bottom out more than 0.5” before the springs are solid, so there is a loss of travel compared to the previous friction damped only arrangement. So in my view, the original damper, having been designed for the front was a bit on the long side for the back. Then the replacements copied this, and added thicker bump stops! The popular change to a fully sprung seat makes matters worse by increasing the spring loading and hence lowering the ride height.

The table below shows the available “bump travel” in inches for a variety of spring/damper combinations. By “bump travel” I mean the available suspension compression measured at the damper from the normal ride height to the point where the bump stop comes into play.

This is for a fully sprung seat, a solo 11 stone rider and with the eye bolts set 1” out.

Travel at the wheel is about 1.5 times greater of course.

I have assumed the AVO dampers are fitted with a 0.5” thick bump stop.

 

Damper

Closed length

Bump travel in inches.

 

of damper

Standard

Petteford

 

inc. bump stop

Springs

Springs

 

 

 

 

Vincent

7.188

0.41

1.54

Armstrong

7.3

0.3

1.43

Koni

7.625

0.0

1.11

Thornton

7.5

0.1

1.23

AVO TA1445

7.15

0.45

1.58

AVO TA1446

7.38

0.22

1.35

This is not quite the whole picture, because of the variation in bump stops.

The Vincent damper bottoms out quite sharply because of the short travel of the hydraulic bump stop, so at the point where the Vincent damper stops with a thump, the TA1445 still has 0.5” of quite soft bump rubber compression available.

 I have not shown rebound travel, as all of these spring/dampers combinations have more than is needed, bearing in mind that it is widely accepted that vehicle suspensions only need about half as much rebound travel as bump travel.

In fact, for some of these spring/damper combinations, most of the extended part of the dampers travel only ever gets used when the bike leaves the ground over a hump back bridge.

Long damper travel in itself is no advantage if very little of it can be used!

 

The AVO Solution.

 avo front damper

 The AVO rear dampers have an offset rear mounting, allowing room for an adjustable damper with full travel but a shorter closed length. This offers the greatest usable suspension travel without excessive saddle height.

These dampers are much more than a modified standard item; they are designed and built from scratch exclusively for Vincents. They can be rebuilt, but is not a diy job. I think it would take a lot of miles to wear one out, as they are solidly made.

They are supplied bare, without a bump stop, shroud, or top mounting.

 The damper rod is threaded to accept the standard Vincent D8 top mounting.

More details about bump stops, tops and shrouds later.

 

Which AVO Rear Damper?

 

The AVO rear damper is available in two lengths.

 TA1446

If you just want to replace your rear damper with minimal fuss, choose the TA1446.

It will give you much better damping than the original and more bump travel than the other replacement choices.

TA1445

If you want the best possible combination of maximum bump travel without a high seat, and are prepared to do some checking and adjusting, choose the TA1445.

If you have retained the original springs and semi-sprung seat, this should fit without problems.

In a bit more detail: -

TA1445 has a closed length of 6.65”, an open length of 9.65” and a stroke of 3”.

TA1446 has a closed length of 6.88”, an open length of 10.12” and a stroke of 3.24”.

The shorter TA1445 can provide the most bump travel, but there are two considerations if this damper is chosen:

  • Petteford springs will probably require some compression when fitting, depending on their free length.
  • With a fully sprung seat, there may be insufficient clearance between the mudguard and the seat at full damper compression. Please note, there are NO clearance issues around the damper itself.

The issue of seat/mudguard clearance is complicated because there is so much variation between bikes. Mudguards fitted heights vary and the length of the front seat bracket can also vary.  These problems can occur when any bike is converted to fully sprung, this is not solely a problem with AVO dampers.

Seat/mudguard clearance issues can be overcome with a mixture of seat height adjustment, a thicker bump stop, and possibly adjustment of the mudguard position.

For my own bike, to create extra clearance I bought a reject rear lifting handle, which I shortened and fitted reversed. I also made shorter mudguard stays (FT22/4) and made two spacers, one to go between the mudguard and the upper RFM fixing point and the other between the mudguard and the rear stand. This allowed me to lower the mudguard without having to drill new holes in it.
The overall result is well worth the effort and modest cost, as the now very comfortable ride has allowed me to travel greater distances with less fatigue.

TA1445 Damper Fitted to my Rapide

rear damper fitted

  

Rear Damper Top Mounting D8 and Special Bush.

Please note that it is essential that the original bush pressed into D8 is replaced with a slightly longer steel bush that is a sliding fit.

AVO have agreed to supply this bush at no extra charge.

Excessive friction may occur in the spring boxes if this bush is not fitted, and the nuts securing the front eye bolts will probably work loose.

The need for this change is a consequence of the axis of the springs being slightly offset from the axis of the damper. As the suspension moves, the angle between the damper and the spring boxes varies slightly. The use of the longer steel bush in D8 prevents it being clamped by spacers F57/3. The upper spring boxes can now self align independent of the damper, in the same way as the lower spring boxes already do as standard. If anything, I think this is an improvement on the original arrangement.

To assemble, place the greased steel bush and one spacer F57/3 on stud F28/1, and then thread though the UFM and the damper top mounting D8.

Rear Damper Adjustment Range.

This is quite wide, so everyone should be able to find their ideal setting.

I found it was very handy being able to quickly change the setting when riding a heavily loaded bike on a hot day on some fast but undulating Welsh roads.

Fitting Petteford and Other Longer Springs.

 If required, a DIY spring compressor design is described here:  Spring Compressor

See also the discussion of fitting Girling springs for greater comfort:   Girling Springs and Seats

 

The AVO Front Damper

avo front damper

The part number for the front damper is TA1447.

The AVO front damper has open and closed dimensions that are nearly identical to the original Vincent damper, so it should be a straightforward fit.
The bottom mounting is not offset. If the allen key adjustment option is chosen and a black painted shroud is fitted, the appearance is quite similar to the original Koni dampers.

Front Damper Oil Weight.

I have previously discussed using lighter weight oil in the front damper, but after customer feedback and further testing, I have now concluded that the 5-wt oil originally chosen is still the best option.

Eye Bolt Length.

The VOC Spares Company website has the following advice with respect to choice of Eye Bolt FF57:
“Long damper eye bolt …..should not be used with the standard Vincent damper as the forks can over extend.”
As the AVO front damper is nearly identical in length to the original Vincent damper, the same advice applies.
If you do have a preference for the long Eye Bolts, the mudguard stay to magneto cover clearance must be checked carefully after fitting the damper.

Important Precautions When Fitting Any New Damper.

When fitting a new damper that has tighter clearances, any misalignment of the mountings that was compensated for by the sloppy fit of the old damper can become a problem.

To minimise friction and the possibility of a bent damper, the alignment of the new damper should be carefully checked. The front eyebolts need to be checked with particular care. I found mine were of slightly different lengths, but a much worse problem was that both were drilled offset and the holes in the bottom link were not in line. Depending on how these parts were assembled, a large misalignment of the damper was possible. My eyebolts are now stamped to ensure they are always assembled such that these errors cancel each other out.

Note also that a damper can be perfectly aligned at one point in its travel yet well out at another point. So to be really sure, damper alignment should be checked through its full range with the springs removed.

The following is a quote taken from: “Ex-Works Info Instruction Sheet No. 10A September, 1953”

“SERVICING HYDRAULIC DAMPERS VINCENT SERIES "C" MODELS”
When refitting:
"-it is good practice to verify that the assembly is not pulled out of line. On the front forks this may occur due to slight variations in the eye bolts FF57. A shim washer can be inserted under one of these eye bolts if necessary, and the lower mounting should be fitted first allowing the unit to be offered to the slot of the head clip FFl without strain.”

Front and Rear Damper Adjustment, Top Mountings, Bump Stops, Shrouds and Fitting

 Adjustment

When ordering, either allen screw or thumbwheel adjustment can be specified.

The thumbwheel is the most convenient and can be adjusted with gloves on. The allen screw adjustment is more discreet if you want a damper that looks as if it could be a period modification.

Top Mounting.

 The original Vincent D8 top mounting fits straight on to the damper rod. The rod needs to be gripped in a soft jawed vice, and I suggest a small amount of a medium or low strength locking compound.

I have not seen any tendency for the damper rod to come loose, so don’t overdo locking or tightening or you may find it difficult to unscrew the top mounting if required.

If this is a problem, a split collet made of aluminium gripped in a vice will provide more grip than the fibre jaws of a vice.

Bump Stops

For my rear damper, I used a Nissan Exhaust Rubber (DNR38 from Ebay). Probably a better choice is a BSA/Triumph fuel tank centre mounting rubber part numbers 40-8085 or 82-9064.

Both will require cutting to length with the objective of creating a conical bump stop that will act progressively.

For the rear where forces are high, I suggest a bump stop 0.5” to 0.625” thick.

For the front, I suggest a thinner bump stop 0.375” to 0.5” thick.

Make sure you allow for the boss that encloses the rod oil seal and scraper.

 bump stop rubbers

 

Shrouds

The original Vincent shroud cannot be used because the AVO damper has a larger diameter.

The AVO dampers are well protected and a shroud is not essential, in fact I do not use one at the back. For the front, I eventually made a shroud, partly for cosmetic reasons and partly to reduce a slight tendency for the cables to chafe on the damper.

Suitable tubing is 1 7/8” x 18G ERW steel tubing. The supplier I used is here: http://www.mkmetals.co.uk/product/5205/0

A spacer ring is required between the D8 mounting and the tube.

 *How and Where to Purchase AVO Dampers*

 Before placing an order you need to choose: -

  •  TA1445 or TA1446 rear damper?

  •  Thumbwheel or Allen screw adjustment?

  • The part number for the front is TA1447.

Order from: -

AVO UK Ltd, Caswell Road, Northampton, NN4 7PW, phone 01604 708101.

 Price £80 + £10 p&p +VAT.  (At time of webpage creation.  Contact AVO for current price details.)

 They quote delivery as 3-4 weeks, but they can often supply from stock.

 AVO have now sold well over 120 of these dampers with no reported problems.

 I would welcome feedback on any technical issues about these dampers, email me at: -

 Rob Staley, 28 January, 2016

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