Rear end of my marina based Roadster seems high

[listerjp2]

Re: Rear end of my marina based Roadster seems high

Well the two sumo wrestlers (my wife and a mate) worked it has now dropped by 10mm.

Thanks for the advice.

Adrian

I would suggest the "slacken the bolts and use two friendly Sumo wrestlers approach"

Q67 after it's rebuild sat high, and here are pics of KEX when first built and when I picked the car up, after very few miles were done - note the shackle angle

To misquote John Inman, "It'll ride down with wear"

Yours looks a great job by the way Best DC

[b_caswell]

Re: Rear end of my marina based Roadster seems high

When I first moved my rolling chassis out of the garage the rear u/j was beyond its limits and jumping over itself.

I am sure some early Marlin kits were supplied with a lowering block that was 3 degrees tapered.

But the lowering kit supplied with mine were parallel blocks and the advice was to get the "Taper shim" part number FAM 1387 from my then friendly local BL dealer at a princely price of £5.60p. Problem solved.

I could be wrong, probably am! but I thought that as some kits needed these and others didn't, that perhaps BL revised the position of the spring plate, however there was no wedges fitted when the axle was in the donor 1973 1.8 Auto saloon.

[listerjp2]

Re: Rear end of my marina based Roadster seems high

Thanks Ben.

I will still check to make sure.

Regards

Adrian

[philcoyle]

Re: Rear end of my marina based Roadster seems high

Steve,
When I first got my Roadster one of the UJs was a rubber doughnut which was just about holding together by the steel band around it. This type of UJ is fine for diffs that are fixed to the chassis as in independent suspension , mine was built with a marina live axle and the rubber doughnut UJ is not suitable for a live axle as anything more than 2 degrees out or line horizontal or lateral only speeds up its inevitable wear, and its collapse. I replaced my propshaft with a purpose made one with proper UJs with grease nipples and 16 years later its still trouble free.

[stevejgreen]

Re: Rear end of my marina based Roadster seems high

Steve,
When I first got my Roadster one of the UJs was a rubber doughnut which was just about holding together by the steel band around it. This type of UJ is fine for diffs that are fixed to the chassis as in independent suspension , mine was built with a marina live axle and the rubber doughnut UJ is not suitable for a live axle as anything more than 2 degrees out or line horizontal or lateral only speeds up its inevitable wear, and its collapse. I replaced my propshaft with a purpose made one with proper UJs with grease nipples and 16 years later its still trouble free.

Clearly your car was not built in accordance with the Marlin MK2 build manual. Otherwise, a Triumph rear axle has no angular movement between the gearbox and differential.
Here lies the problem with advice, it needs to be specific.

[duncan]

Re: Rear end of my marina based Roadster seems high

A driveshaft with two UJ's is expected to run between points on two parallel planes

In other word the gearbox output should be perpendicular to the plane of the diff input

It's OK to move the engine gearbox up or down or right or left - but you should move the whole thing and still keep it pointing square to the diff - not at the diff

From the other POV the wedges could be used to keep the diff square onto the gearbox output

[stevejgreen]

Re: Rear end of my marina based Roadster seems high

On a vehicle with independent rear suspension like a triumph based roadster the diff is bolted to the chassis, so the prop shaft stays in line with the gearbox, it has no choice, but the two drive shafts and their UJ's have to account for the rise and fall of the vehicle.

On a marina based tgehicle the solid rest axle moves through about 120mm vertically when driven with gusto. At full upward deflection the diff drive flange is higher than the gearbox output flange on full downward deflection it is about 90mm below the gearbox flange.

That generates quite an angular deflection for the prop shaft UJ's to contend with. The wedge theoretically reduces the induced angle at maximum downward deflection but increases it on upward deflection.

It is my contention that with a full tank and two occupants, a rest mounted sparred tyre etc. is that on a Marina based car, the wedge is marginally counter productive in the conditions described.
However on lightly loaded car it may have a limited value only.

[duncan]

Re: Rear end of my marina based Roadster seems high

You are describing the wedges being used to rotate the axle so it is pointing downwards
That is BAD thing with UJ's!!
The up and down does not matter as long as the axle moves up and down - both of the UJ see the same angle - which is absolutely fine - up to quite a decent angle

But if the axle points downwards then the two UJ's see different angles - that is NOT a good idea - it will cause torsional vibration in the driveline - BAAAD!

If you are going to have different angles on each UJ then you don't use UJ's - that is when you need "CV" joints

[stevejgreen]

Re: Rear end of my marina based Roadster seems high

You are describing the wedges being used to rotate the axle so it is pointing downwards
That is BAD thing with UJ's!

Not at all. You have misunderstood what I wrote. It seems that I am more familiar with the peculiarities of a Morris Marina and a Marina based Roadster.
To recap. Original Marinas were not fitted with a thin wedge, at some undocumented point there was a ‘product recall’ and many cars were retro fitted with a thin wedge, but not all. Presumably intended to angle the differential nose up, towards the Marina propshaft centre mount, of its two piece propshaft, thereby reducing the load on the UJ’s.
That is unless there is a better explanation. Who knows the mysteries of BL!


When Marlin created the Marina based Roadster, I presume they adopted the same Marina geometry, but with the propshaft significantly shortened, the rear part being salvaged because it contained the sliding section, but still significantly shortened.
We can only guess that the leaf spring mounting points were in the same physical orientation as a Marina. I no longer possesses accurate enough measuring equipment to prove it.
Marlin then fitted a tapered lowering block, about the same angle as the previous wedge but significantly ‘higher’.
So with a shortened prop and a new tapered lowering block, the old Marina geometry is already compromised.


With a lighter car, a change in weight distribution and leaf springs that are past their most reliable, it’s quite possible that when driving with gusto, the normal elliptical curve of the springs becomes an ‘s’ shape, and all the mathematical calculations go out of the window, as they wind themselves up under heavy acceleration. Who knows what direction the nose of the differential will be pointing?


A Marlin Marina based Roadster is a massive collection of compromises, few of which relate to the donor car, or an ideal modern vehicle.