Wiper wheelbox

[John Larkin]

I have discovered that I have two different wiper wheelboxes on my 1967 Elan. The one from the left side of the car shows part number 72761A, and has wheel 1.212" diameter with 27 teeth. The wheelbox from the right side of the car is 72776A, 1.423" diameter and 32 teeth. The latter looks older (rustier). Can anybody tell me which, if either, is correct?

John Larkin

[garyeanderson]

Hi John

In the Robinshaw Ross book it lists wheelboxes as following

1963 -1964 S1 & S2 as 72776A
1964 -1965 S2 & S3 as 72774A
1966 -1968 S3 as 72776A
1968 -1973 S4 /Sprint as 72761B/D superseded by 72841

Gary

[John Larkin]

Hi Gary, I knew you'd have the answer!

So the rusty big wheel version is correct. I'll order one tomorrow.

Thanks!

John

[garyeanderson]

Hi John
The answer isn't mine, I just know where to look or how to find. Then all I have to do is figure out if it the correct answer...

Gary

[Frank Howard]

Hey John,

Unless you insist that every part on you car is "correct", I'd consider using what you have and here's why. Let's say you have your wiper motor set up so the wipers park on the right. You'd want the right wiper to cover an area that slightly overlaps the area covered by the left wiper but you'd want the left one to sweep farther to the left. If you used the big wheel box on the right and the small wheel box on the left, you'd accomplish that. The result would be that the left wiper would move slightly faster and cover more area. There are plenty of modern cars that use this system. One that comes to mind is the Chrysler minivan, where the wipers overlap and point toward each other when they come to a rest. One has to get there before the other or they'll interfere with each other. It's possible that the PO deliberatly ordered the smaller wheelbox in order to increase the wiping arc on one wiper only.

I noticed the unlike my Europa (as well as most other modern cars), the locations of the Elan wiper pivots are symetrical. In other words, they are not offset to the right or the left. While this makes it easier to manufacture a car the can be set up for left or right hand steering, it is not the ideal arrangement for placement of the wipers. My car has left hand steering and I have set up the wipers to rest on the right so they are away from my line of sight when I'm driving in dry weather (99% of the time). I have actually considered moving the left pivot a few inches to the left to improve the coverage. I didn't realize there were two different sized wheel boxes available. Having two different sized wheelboxes could accomplish the same thing. Kind of a cool improvement that's visable only when one sees how much better the wipers cover the windscreen.

[John Larkin]

The 27 teeth wheelbox was put in by a Lotus "specialist" in the UK in the mid-90s. The installation must have caused him some problems as he compromised the insertion of the drive tubes into the wheelboxes.

In the top photo you can see a pair of horizontal slots to the right of the rusty wheel, and a pair, further apart from each other, to the left of the wheel coated in black grease. These slots locate the flared ends of the drive tubes. They are 32.5mm apart on the rusty wheelbox and 51.5mm apart on the greasy one. Using one 51.5mm unit the wiper spindles centres would be pushed further apart by half of the difference (i.e. by 9.5mm) if the drive tubes are located properly in their slots. Mine were not --- they were inserted far enough so that the wiper spindles were correctly located, and then the wheelbox backplates were tightened up over the wrongly located flared ends. I'm surprised it stayed together all these years.

John

[661]

So, what did you do John?
I'm starting from afresh with a new shell so could move the pivots slightly to a 'more desirable' position. I too am RHD, will park to the left.
I have an original Lucus 72774A and went to SCParts to get the other wheelbox.
Like yours it's longer with a smaller pulley and therefore greater sweep. That might be useful on the L side wiper??
Anyone else used different wheelboxes by design?

[John Larkin]

So, what did you do John?

Hi Graeme, I regret that I cannot recall what I did in the end. My wipers park on the left (RHD car) and swing through a similar arc angle in operation, so I suppose both wheel boxes are the same.

[661]

It was 5years ago and was not meant in anyway to be a Government health agenda question to spot early Alzheimer's!
I think I'm in the same boat.

If you put the one back that you described, they can't be the same, but it must work. Because of the shape of the screen you are a bit limited by the sweep of the driver's (right) wiper.
I spoke to Alan Turner the DR2 wiper motor guru who says for a 130 degree sweep motor, the rack plunge will be 2.68 cm. Having calculated amount of rack movement to make each wheelbox go through 360 degs ( 9cm for 72774 amd 7.5cm for the new box) I estimate the sweep is 107 degrees for the original box (72774) and 129 degrees for the new box. I will probably give this a go.