Type 9 Gearbox in a Roadster

[john cole77]

Re: Type 9 Gearbox in a Roadster

When I checked the input flange on my axle it was not 90 degrees to the floor
I had to make a 3 degree wedge to put between the axle and leaf springs to rectify it.
Sorry for the fuzzy wedge picture

[andyf]

Re: Type 9 Gearbox in a Roadster

I'm wondering if that's the problem or if I have the tail end of the gearbox too high as well

[ggrum]

Re: Type 9 Gearbox in a Roadster

I seem to recall that the original spacer block between the axle and spring was tapered anyway to deal with this problem.

[jon_cox]

Re: Type 9 Gearbox in a Roadster

I seem to recall that the original spacer block between the axle and spring was tapered anyway to deal with this problem.

Not the spacer block itself but a wedge. There appears to be some confusion here though.
The original mk1 marina was designed with a zero degree rake on the axle. It caused loads of issues though with UJ's wearing out really quickly. They do not like being run constantly inline (zero degree angle) as the needle bearings do not move and therefore all the pressure and forces always act in the same place. Therefore BL (Morris) fudged it by adding a 3 degree block. Later they changed the jig used to weld on the axle pads to remove the need for the block.
Propshaft design references put the optimum angle anywhere between 2 and 4 degrees.
Here is the page from the Marlin build manual.
Axle Angle Pads.JPG

[andyf]

Re: Type 9 Gearbox in a Roadster

That's how I remember it too. If the gearbox flange is vertical the diff should be as well otherwise there will be an agle difference in the two UJs which causes them to speed up and slow down loading the gearbox and diff bearings.

[duncan]

Re: Type 9 Gearbox in a Roadster

I have moved the engine/gearbox centerline in my car - ensuring that it is still parallel with the chassis

This gives more space for the pedals and it ensures that the UJ's always run with a small amount of movement

The key is ensuring that the "plane" of the gearbox out is parallel with the "plane" of the diff input

[dogoncrazy]

Re: Type 9 Gearbox in a Roadster

I have a pair of lowering blocks which DO have the taper built in.

[jon_cox]

Re: Type 9 Gearbox in a Roadster

I have a pair of lowering blocks which DO have the taper built in.

Funny you should mention this....
On eBay at the moment there is a pair of Marlin lowering blocks.... https://ebay.us/B9oU6f
The picture would seem to show them as having a taper as you suggest.
My blocks, purchased in 1986 with the kit, are not tapered.
So does that mean there were 4 options?
1. Square block with no wedge
2. Square block with wedge
3. Tapered block
4. Tapered block with wedge (to compensate for later axle with angle spring seat if tapered block was what you had)
Any more options?
s-l1600.jpg

[andyf]

Re: Type 9 Gearbox in a Roadster

Thanks guys, that's good to know. I've ordered a magnetic inclinometer so that I can measure the angles. I'm expecting the problem to be at the gearbox end. When I changed the mount to fit the type 9 I probably didn't position the tail end of the gearbox properly, I was certainly not thinking about UJ working angles so it would be a fluke it it is correct

[dogoncrazy]

Re: Type 9 Gearbox in a Roadster

The e bay ones are in fact mine and as of a few minutes ago sold to a club member. Thanks, Alan

[andyf]

Re: Type 9 Gearbox in a Roadster

Ok so I've measured the angles and the UJ working angles are out by 2 degrees. The Diff Pinion angle is 3.5 degrees up and the gearbox output shaft is 1.5 degrees up. Looking at the numbers it seems that I need to use the 3 degree shims to correct the diff angle and to reduce the gearbox output shaft angle by 1 degree as well. So I found a pair of 3 degree shims online with a smaller spigot hole so I've bought those with the aim of drilling out the hole to suit the Marina spigot size.

UJ Angles.jpg

[jon_cox]

Re: Type 9 Gearbox in a Roadster

Hi Andy
For a leaf spring based solid rear axle car these numbers, if I have understood your diagram correctly, look pretty spot on. There should be a 2-3 degree difference to compensate for leaf spring wind up under load. You have 2 degrees, considering the light weight nature of a Marlin Roadster, this would be about right for the change in pinion angle whilst driving.
Jon

[stevejgreen]

Re: Type 9 Gearbox in a Roadster

It’s worth bearing in mind that in service the diff rises and falls quite a lot especially as it reaches the suspension bump stop.
Go for a drive with the top cover of your transmission tunnel off, it will surprise you looking at the angle that the prop goes through.
when I fitted my Sprint axle, the diff nose was horizontal, quite deliberately ignoring the taper wedge.

[jon_cox]

Re: Type 9 Gearbox in a Roadster

Hi Andy,
As Steve has alluded to... There is a BIG difference between static loading and Dynamic loading of a mechanical system. The rear suspension on the roadster is very basic and has many degrees of movement which constantly change in the dynamic state which is the real downside of leaf springs with no anti-tramp bars or any other locating geometry.
You have measured your car, no doubt, in a static unloaded state. Just by loading the car as it would be driven (2 adults and full tank of fuel) you will find the diff angle will change with the nose of the diff turning upward due to the change in the geometry due to the leaf spring flattening, the rear shackle hanger moving rearward and the rubber in the bushes being compressed. Next, taking all these things into account, you have to look at something called leaf spring wrap which is basically the leaf spring changing shape into an S shape due to the turning moment of the axle. All these things, depending on weight of car, strength of springs, power etc all add up to give you a nose up angle on the diff during driving conditions.
Suspension specialists will give a value of 2-4 degrees difference in pinion angles in the static state to compensate for all these changes whist driving.
Image-3.jpg

[andyf]

Re: Type 9 Gearbox in a Roadster

Plenty of food for thought... Tonight I'm going to measure the angle of the spring plate to see if I have an old axle or one of the newer ones