Marina Axle Upgrades

[cdow]

I understand that the Marina axle can take about 150BHP, but not being that technical I don't really understand where the weak point is.

If it's just the diff, could it be a simple (albeit expensive) solution of fitting a Quaife diff to the standard axle?

Or is there a bit more to it than that? If so, which is the simplest upgrade path that retains the existing wheels with a 3.75" PCD?

Cheers

[lil_red_roadster]

Re: Marina Axle Upgrades

Well, it reputedly has a habit of chewing through crownwheel & pinion teeth if abused, and the halfshafts aren't particularly strong either...and the locking taper design (hub to shaft) was archaic even in 1970. It was after all what Triumph referred to as their "light duty" axle (basically the Herald/Spitfire diff made into a live axle).

The Dolly Sprint used the "large car" Triumph diff (from the 2000/2500) with tubes to make a live axle. Same track as the Marina and same PCD but can allegedly withstand c 200bhp. Early cars had 3/8 studs (a la Marina) whilst later ones had 7/16.

The only other axles of similar dimensions with Marina PCD are the cooking Triumph Dolomite & TR7 (4 speed & early auto)...the 1500/1850 Dolomite flavours were to all intents and purposes the same axle as were the early TR7, though this differed IIRC in that it had slightly longer halfshafts and hence wider track. Later TR7 (5-speed and TR8) used a cutdown SD1 axle but the TR7 had 4-studs rather than 5 and retainined the 3.75" PCD...so a late TR7 unit could also do the job (though might have a slightly wider track).

[cdow]

Re: Marina Axle Upgrades

Is it not possible to get stronger crownwheel & pinion/halfshafts? I'm quite keen to avoid having to fit a different axle and the undoubted problems that it will bring with it.

[lil_red_roadster]

Re: Marina Axle Upgrades

I've not discovered anyone who offers this yet (shame its not a Midget...Frontline do hardened shafts for that one)...they may be out there but it'll be a case of asking around. Good place to start might be Canley Classics and other specialist Triumph shops, plus the Marina boys.

Or just lay in some spare half-shafts & diffs and drive normally...!

[ggrum]

Re: Marina Axle Upgrades

Chris,
What power output engine have you got fitted? I have had a 130BHP Alfa engine in my Roadster driving through a standard 3.66:1? Marina rear axle for the last 12 years or so without any problems. Providing you avoid tyre smoking standing starts where the pressure on the gear teeth is highest I think you should be ok. I nearly fitted a Dolomite Sprint rear axle but it would have meant flaring out the exit from the tunnel which is a problem with a SWB car like mine in that it limits how far the seats can go back. The other option would have been to remove some of the strengthening ribs on the diff casing which I know some people have successfully done.

[cdow]

Re: Marina Axle Upgrades

It's putting out 143BHP at the moment, but I'm thinking about throttle bodies and taking it up to about 180BHP. I'll have to do some digging for the uprated bits...

[daniels917]

Re: Marina Axle Upgrades

I have about 160BHP, and driving fairly gently (i use the roadster every day) i stripped the crownwheel teeth off a standard 1.8 axel, now replaced with a dolly sprint unit, it went in quite easily, and the speedo now reads accuratly, so a bit of a bonus

[cdow]

Re: Marina Axle Upgrades

I might have to go the Sprint route. Trouble is that given I can't do the work myself, the faffing making stuff fit soon racks up the labour cost, which is why I was after strengthening up the existing layout…

[lil_red_roadster]

Re: Marina Axle Upgrades

This may be the usual internet myth but I found reference deep in the bowels of the MMOC forum to Quaife at one time offering uprated half-shafts for the Marina axle.

They are no longer listed (though the diff of course is) but it might be worth talking to them...if they still have the drawings who knows...

This would not be a cheap route though...the Quaife diff goes for 550+ and as an indicator Capri shafts are about 100+ each...

BTW...I meant to ask if you ever worked out which terminal in the sierra fuel sender was the right one...? I'm having trouble getting a meaningful readout through mine.

Cheers

Jez

[stevejgreen]

Re: Marina Axle Upgrades

In no particular order, and tying not to write a book.

I stand to be corrected on some technical issues but.....

Quaife list LSD units for Marina and Ital (different) they are only the LSD, effectivly replacing the Sun gears and their casing. They do not make new Crownwheel and Pinions, the main input gears. They used to supply halfshafts for the Caterham racing boys but there was a fault in the manufacture. Quite probably the bearings were sliding on the shafts, the usual problem. They have no intent to remanufacture.

Spare, standard, halfshafts are avaulable from REDLINE COMPONENTS LIMITED, Timber Hall, 19 Timber Lane, Caterham, Surrey CR3 6LZ Telephone: 01883 346515 these are available for about £120 a side. I beleive they can also supply hubs. They manage to keep many Marina axled cars on the road.

Bearings and seals should not be an issue as they seem to be readily available on ebay. Most should be available from Motor Factors or Bearings suppliers. Gaskets can be home cut.

Being simplistic that leaves the crownwheel and pinion assy's. It has been suggested that they are the same as a 4 speed TR7 as it has the same ratio (the rest of the TR7 axle is different) but I dont know of anyone who has tried, nor do Rimmer Bros though they agree, these diff assys and parts are getting rare but are on their shelves.
It may be that Rimmer, or any capable motor engineers, would be prepared to rebuild a complete Marina axle if you were to supply all the necessary parts.

All of the above should give you a 'new' axle that would replace an old, worn unit but will not necessarily handle more power.

I would hazard a guess that the Marlin being lighter than the average Marina would launch at a lower torque, so unless you are suffering axle tramp, you are still within the capabilities of the Marina axle.
If you are thinking of throttle bodies it may be possible to use the Engine Management system to provide limited Launch Control that could protect the diff from undue strain.
As a rough guide, maximum torque will occur around 3000rpm, but max power produced at 6000 revs.

Finally you could source another Sprint axle and then persuade an engineering company to follow my 'How to' post on the MMOC website. It's there because I can edit significant posts as I go along.

The only other alternative will be to convert a Ford axle. These are used by so many racing outfits that parts are generally available. The downside is the change of gear ratio, wheel track, and studs etc. and quite an engineering challenge.

[stevejgreen]

Re: Marina Axle Upgrades

Addendum
This info needs confirmation but....

Triumph Dolomites, not Sprint, used the same crownwheel and pinion etc. and possibly the same halfshafts so I would guess the same track.
Equally rare.