Y 6486 - Rear Shock Absorber conversion

By Gilles Bachand

 

Before reading this, you must first read what Richard Prior has written on the subject. The following information is complementary.

 

The shock absorbers I used are KYB Gas-a-just #552-018: available from minispares.com They seem to have been recently discontinued as they do not appear in KYB's current catalog. However, many Classic Mini parts suppliers still have them in stock.

Their characteristics are:

     ●  Extended: 12 ¾ inches between eyelet centers

     ●  Compressed: 8 ½ inches between eyelet centers

     ●  Total travel: 4 ¼ inches.

 

I asked a talented machinist to laser cut the upper mounting bracket from Richard's drawing and in 3/8 inch steel. They do not need to have an opening in them when designed for a YA. The emergency brake (hand brake) cable follows a different route from a YB.

 

I then designed new lower mounting brackets which would replace the stock Lower Spring Saddle Plates.

 

This is the rough sketch I sent to the machinist.

All dimensions are in inches. These pieces were laser cut. To ensure that the 3/8 bolts I would use could comfortably fit in the holes, they had the latter be cut 0.010 inches bigger. This is not necessary if your parts are prepared in a more traditional fashion.

 

When assembled with the shock absorbers, the parts looked like this:

 

I used Grade 8 bolts, 3/8 inches in diameter and with fine thread (24 per inch).

 

They are 4 inches long to attach the upper bracket to the frame and 3 inches long to attach the shock absorbers to the brackets.

 

In both cases, the threaded section is a bit too long for our needs. The reason I chose those lengths is that the non-threaded section is present where the shock meets a bracket or when the upper bracket meets the chassis. This provides maximum shear protection.

 

A few washers were used to avoid the shock absorber body being too close to the brackets.

 

Those bolts can be torqued to 30 ft/lb. (Remember, these are Grade 8 bolts)

 

The next thing to think about is that you must redesining the rear axle rubber bump stops. Maximum shock absorber travel is 4 ¼ inch. When mounted on the car, the shock absorber must not be allowed to hit its limit or else it might self-destruct. Therefore, I reduced its travel by ¼ inch in either direction by having the rear axle reach the rubber bump stops that much earlier. The lower rubber pad is now ½ inch thick. As for the new upper rubber bump stop, look at the difference with the original one:

 

I sculpted the new bump stops from a bow rubber stop used on a boat trailer:

I glued the new rubber parts on the existing steel straps with an extraordinary glue named E6000.  You can read more about it here: http://www.eclecticproducts.com/e6000_retail.htm  I bought a 3.7 oz tube on Ebay for $6.

 

Please note that this measurement is such when the rear axle is resting on the lower bump stop.

 

It is recommended that you change the U-bolts whenever you work on the leaf springs, particularly if they are old, because they will have stretched and been submitted to much stress already. I have ordered a new set from NTG.