Gearbox

[nickbowler640]

Help needed my gearbox jumps out of reverse so i either need a replacement or somewhere that can recondition at a good price!!!! The gearbox if from a 1800 B series. Any ideas ?

[stevejgreen]

Re: Gearbox

We have exchanged emails elsewhere. I now understand your problem a bit better.

I am afraid it is not very good news, and I have written a book.


If it is jumping out of reverse then it could be a few things. The down side is that whatever the problem, the box will have to be removed to identify and resolve the issue. You may be lucky and track down a replacement box but only Marina 1.8 or Ital 1.7/2.0 use the same gear clusters and input shafts, and are truly interchangeable. You may find a commercial gearbox rebuilder who will take on the job but parts, especially the gearsets, are rare and costs high.

There are no other like for like replacements. The same pattern gearbox is used in several Triumphs but their input shafts are internal gear clusters are different. Some Marlins have been fitted with Triumph Dolomite gearboxes but the clutch spline length is shorter and may be prone to premature failure. These boxes are more common as the basic box was used in several Triumphs.
One thing is for sure, metal particles will be in the gearbox oil, the internal magnet should keep them out of the works but bronze particles will still be circulating around.

I have a spare Ital 1.3 box, but it is not suitable for your application as the input shaft is different from the 1.8.

I can see a winter project on the horizon.

So back to your problem.
It could be:
1. The reverse gear selector fork could be worn. A long shot as most of the ones I have seen are fine to reuse.
2. Possible the selector shaft is worn but more likely to cause other gear selecting issues first.
3. The reverse selector fork pin is the side of the box could be loose and this can be checked and re-seated without stripping box if you are careful with locktite etc. If so the gear cluster and reverse idler could be shot as well.
4. My favourite is that the outer gear on the 1st / 2nd syncro hub and reverse gear are worn out. As reverse has no syncro to engage it so the tips of the teeth wear, any slight crunch going in to gear (ie. car still going forwards when selecting reverse) knocks off the tooth edges. I have seen one so worn there are hardly any straight part of the tooth left to mate with to give drive in reverse so could bounce out easily.


There are two different reverse idler gears that have been used. Down to BL parts bin engineering I think, with slightly different tooth angles.
Outer ring gear on the 1st / 2nd syncro hub are hens teeth.
If it is the reverse gear that is worn it also wears out the 1/2 syncro hub outer and the gearset but they can be found.
Also bear in mind that laygear, 1/2 syncro and reverse idler gear must match and 2 and possible all 3 are hard to get.
Someone else may offer some advice on here.
Finally, register on the Fastmarinamagazine forum, loads of info there and users like Jubileenut who has rebuilt a couple of boxes and whose knowledge I have used to help me answer your question. They may also be able to source a serviceable second hand box.

[jon_cox]

Re: Gearbox

Nick,
There is on on eBay.....
http://www.ebay.co.uk/itm/Morris-Marina-gearbox-1700-1800-cc-/300605903016?pt=UK_CarsParts_Vehicles_CarParts_SM& hash=item45fd8210a8#ht_500wt_1203

[donsayers]

Re: Gearbox

I have actually rebuilt a Marina gearbox, which is waiting to be fitted to Wee Beastie. There is a design fault with the gearbox which spoils what is otherwise a sound box.

When reverse is engaged all the other selectors remain in place and the reverse idler is mover forwards to engage with the teeth on the outside of the first/second synchro ring and the layshaft. At all other times it is tucked away to the rear of the box, out of mesh with everything.

All is fine until you select first, when the first/second synchro ring moves rearwards to engage first, but in doing so it half meshes with the idling reverse idler. If the synchro ring is spinning it chips pieces off itself and the reverse idler.

If the box were 1/4 of an inch longer there would be room for the reverse idler to sit further back and there wouldn't be this problem. (See the Ford type 9?)

As it is the life of the box is compromised by little bits of chipped geartooth circulating in the oil. (That's what the magnet is for folks!)

BL partially addressed the problem with a minor redesign for the Ital, when the teeth on the idler layshaft reverse gear and the first/second synchro ring were made bigger, more robust and fewer in number. The parts are not interchangeable, obviously.

So the moral is be very gentle when you select first. I believe this fault is also inherent in the very similar Triumph 'box from which the Marina box was derived.

The reputation of the early box (split upper deck type) was spoilt because the machines made to use it were ex Triumph and were already worn out.

[dogoncrazy]

Re: Gearbox

Why not convert to Ford type 9 box if rebuilding the 1800 box isn't viable.

[stevejgreen]

Re: Gearbox

I am pretty sure the gearbox on ebay is an ex Ital 1.7.

For someone who is not necessarily mechanically skilled, its a straight swap with the existing box. The old box with a damaged reverse may be a good spares or repair for the likes of Don and myself, or others, so will not necessarily go to scrap.

Fitting a Type 9 is a more expensive and labour intensive task, though the benefit of overdrive and a shorter gear lever etc are significant. It may be that the Type 9 will need maintenance itself if this is done commercially, costs soon escalate.

Don's analysis of the Marina/Triumph box is pretty much spot on though I am unclear of a definate changeover point, as I have seen the larger gear on a Marina box. It could have been upgraded or swapped at any time though. The original Marina style box could be 40 years old and rebuilt more than once in its life, only opening it up will reveal the secrets within.