Serpent Diff and Axle Tips

Ok

If you are using anything other than zero offset wheels then I think (like me) that you will find the short length of the Serpent axle a bit frustating. He I have pictured it next to a HB 12X axle for comparison.

We really need the longer axle to allow the use of shims to widen the rear track width when we use Jaco or Parma tyres etc. If you use the Serpent part there is not going to be much axle "meat" left in the clamping hub. My solution for now is to use the HB axle shown above. The D rings are just the same. I think the CRC axle would work also. I hope Serpent will sort this issue and change the part. Another 10mm will do the trick! Thankyou!

Watch out! Trust Race Order

Serpent have used the original (and best!) Slapmaster type outer thrust race. The manual does not explain or show that the two thrust washers are different. The inner washer has a larger internal dia of approx 4.25mm and the outer washer is smaller with an ID of 3.97mm. Make sure you put them in the correct order. The axle needs to rotate inside the inner washer without touching or binding on it. This is why it is larger in terms of internal Dia.

Notice that the grove track in each washer should face the thrust ball race. I know this sounds obvious but I have spotted people rebuilding the diff in the pits and missing this point already!.

Do it Like Slapmaster

Now onto another problem. The orange spacer that sits between the hub ball race and the inner thrust race washer could be better designed. The original Slapmaster system used a black plastic spacer that had a locating lip machined onto it. This lip centred the spacer on the hub via the bub ball race without it touching or binding on the axle that was free to rotate inside it. The Serpent part unfortunately has two issues:

1. The orange spacer internal dia is too tight and needs opening out to about 4.25mm. This is easy to fix with a Dremel!

2. There is no locating lip centering the spacer to keep it off the axle.

Left to Right: Standard Orange Serpent : Slapmaster : My Modification

hmmmm: I have two possible solutions here.

First I used my lathe to machine a lip on the spacer as shown right. Ok this is not possible for everyone and to be honest I did not make that good a job of it so....

My second idea was to super glue the orange spacer onto the hub ball race. Now this needs a deft hand, some degreasing and a very light application of cyano. Get this wrong and you will super glue up the ball race (done that! the first one went in the bin).

I have shown below a little trick using paper to ensure the oversized spacer is still centred on the axle as you bring it into contact with the ball race flange (pre-painted with a thin film of glue). Apply your thin film of cyano to the outer flange (only!) of the ball race, then slide the orange guy down the paper'ed shaft to meet it. Apply some pressure while the glue takes.

Now you can remove the paper. The hub ball race and the orange spacer should now be one and the same part. The orange spacer cannot shift to bind on the axle as it is held centre via the positioning of the ball race.

Now follow my old general diff building tips (posted here ages ago!) and you should have a great diff.

Cheers

Mark

Serpent S120 Link Build Tips: Dont Tweak The Tweak Brace!

My tips for mounting the mono shock to the cross brace are as follows.

1. Make sure the alloy carriers are an easy fit onto the cross brace. Open up the the holes in the carbon if neccesary to enure the ally carriers "fall" into place without forcing.

2. Ensure the mono shock shaft fits between the carriers without any twisting or stress. The shaft should locate in the carrier indents without bending the carbon brace in any way. Work the tollerences by opening up the location holes and screw holes with a file if things are tight.

3. Find some plastic washers as shown above to clamp down onto the shaft. This will allow the shaft to seat without being twisted as you tighten down the clamp screws.

Accurate Side Spring Placement. The Tweak Bar

It seems to be the case that the correct starting point for the side spring position on the link car is to just have it touching down onto the link arms.

To achieve a predictable "touch down" it is important to have the spring's tweak screw nice and true to the cross brace. If the tweak screw goes in square to the brace then there is a chance the spring will be square to the chassis and link arm.

What I do is to use an M3 die to form an accurate positioning tool for the tweak screw.

This is laid down on the tweak brace as I thread the screw down it to ensure I start to cut the thread at right angles to the brace. A little black grease is used on the thread to aid a clean cut into the carbon.

See the result?..... Nice! If you can do this by eye, then good luck to you!

Serpent S120 Link Build: Link Love

I have two tips with regards to the chassis-to-pod link arms.

First I would advise that you open up the internal diameter of the top of the hole for the ball just a little. The ball is going to be inserted from the bottom anyway. I am taking about 0.1 to 0.2mm away here with a body reamer.

The objective is to be able to tip the link moulding from left to right without the top flange of the hole binding on the upper surface of the metal ball.

Secondly.... The link clamp screws MUST clear the material on the outside of the moulding and thread into the material on the inside. If this screw is threading into the plastic both sides of the slit then it is never going to act as a clamp.



So what I am doing is using a drill or other tool to just open up the hole on the outside of the slit so that the thread will only bite on the inside. In this way you will get a clamping action with minimal effort on the screw. If you dont do this, you will strip the fine hex head sooner or later... I have warned you!

Cheers

Mark

Serpent S120 Link Build: Getting the Main Pivot Just Right

I am tring to get two things right here.

Firstly I found that the main chassis was sitting higher than the rear pod in terms of ride height. The error was about 0.3mm in my case. To get this just right and end up with a "flat" chassis including the pod, I decided to grind a little off of the pivot ball.

As a check I am suggesting that the target for the overall length of the ball and shoulder is 4.70 mm as seen below.

Secondly, in my opinion there is too much play in the seating of the ball in the pivot mouldings. I want to be able to use the clamping screws "just" tighten down onto the ball and then back off a fraction. To get this a little more accurate I am grinding away the top surface of the main lower moulding and taking some off the lip of the lower moulding to create a tighter fit as shown.

I found I needed to get the top moulding down to about 3.50mm for it to sit into the lower moulding. Remember I have also removed material from the top of the lower moulding.

Sorry if this is all a bit picky but it is in my nature!

Mark