Marina Diff

[listerjp2]

I have just been looking on eBay for Marina parts and found an interesting statement from a guy who is selling a 1300 diff.

He says that the internals for his diff was taken from a Triumph 2000 auto which slotted straight into the original diff housing and gave him a 3.27:1 ratio.

If this is so what would that do to the power output across the range on a 1300 Marina lump?

Has anyone else got any info on this mod?

Adrian

[stevejgreen]

I have never tried to match parts, but it does not sound right.
The weak link on a Marina axle tends to be the halfshafts and they are very different.

Off out for a while, will give it some thought.

[donsayers]

I know that the marina axle was Triumph sourced from the rear drive Toledo/Dolomite/TR7 range, and these it turn were based on innards from the Herald/Spitfire//GTV6 range. The dolomite diffs will fit the Marina axle, with the exception I think, of the Sprint one. The 2000 was a much bigger car I doubt very much if the diffs would fit. Having said that the ratio is the same as the Dolomite 1850 Auto but then there are not that many different tooth ratios.

OK so having sifted through the part numbers on Rimmer Bros I stand corrected, the 2000 did seem to share at least some crown wheel and pinions with the Dolomite range. My best guess is that diff is essentially the same as the Dolomite 1850 Auto, and these are known to have been fitted into Marina axles. Probably the ratio is a little high for a 1300, but I have certainly been looking at it for an 1800. Then again the car is light and if you don't have an overdrive, it will reduce the noise on the motorway.

[stevejgreen]

OK, I have a little I time, and I agree generally with Don. This is a Ratio 3.27 Teeth 11/36 Part No TKC2768 Source Dolomite Auto / 4sp TR7 Auto / Ital 2.0 Auto

As far as I recall, Triumph 2000 used a differential style that has a different design, similar to a Dolomite Sprint, The access being form the rear of the axle body, rather than a separate casting from the front.


Triumph 2000, 2500 etc


Dolomite Sprint


Marina/Dolomite - Differential casting

The weak point as I suggesed was the halfshafts that are Marina/Dolomite only a heavy duty modification by Rakeway http://www.rakeway.co.uk/page37.html is an alternative. The current crop of failures are possibly due to 40 year old mechanics and original lubrication.

The Dolomite Sprint halfshafts are completely different.

Reference http://www.fastmarinamagazine.com/vi...rential#p38655

[donsayers]

When I speak of differentials I am talking about the parts inside the casing. I agree that the Dolomite/Sprint and the 2000 have different diff carriers, however given that they share crown wheels and pinions, I very strongly suspect that a marina diff could be rebuilt, IE talking every thing out of the casing not just exchanging assembles, with parts from a 2000 or a Sprint axle for that matter. However rebuilding a diff is beyond the scope of a home mechanic without access to the shims and or collapsible bushes and the data sheets on clearances and preloads.

As for half shafts, I have not known one fail on a road car, and certainly on the 1300 Marina they were well up to the job. The 1300 diff on the other hand was a known weak point as the pinion had only 9 teeth. The 1800 is much stronger as the pinion is bigger with 11 teeth.

[stevejgreen]

Did you see how much that diff centre finally sold for £130.00.
Silly money, unless you were desperate.
Unless it was going in a daily driver, I would hold out. Ive seen them go for less than half that.

[Mike]

........................try getting hold of a Ford Sierra 3.14 diff. They make over £350 !

[christopher.bogue2011]

Re: Marina Diff

A bit late in the day, but for info, when I rebuilt my Roadster a few months ago the one thing I wanted to do was to get the revs down when on the motorway. I replaced the Marina 1.8 Diff centre with a Triumph TR7 4 speed Auto from Rimmers. This has a ratio of 3.27:1 and fits straight in to the Marina casing. 80mph now gives only 3100 rpm (Fiat 2.0L Twin Cam with five speed box). Not a cheap mod but well worth it in the end!

My decision was all thanks to Steve Greens expert advice. Best thing I ever did!!

Chris

[stevejgreen]

Re: Marina Diff

Only too pleased to be of help. Much of what I wrote is simply collated from many sources here, on FastMarina and many other places.
Its all documented at http://www.fastmarinamagazine.com/vi...rential#p46404

What gearbox do you have, has it an overdrive?
With a Ford Type 9 overdrive @0.825 in fifth and a Dolomite Sprint axle at 3.45, I am down to 2.84 total final drive ratio from the original 3.63.

[cdow]

Re: Marina Diff

So are we saying that a Rakeway Upgrade kit and TR7 diff from Rimmers will have the rear axle sorted for good, albeit at a price?

[stevejgreen]

Re: Marina Diff

Have you been off reading on Fastmarina? Not seen you there....
If only it were that easy... The Rakeway kit solves the halfshaft problem where they snap at the keyway transition, usually after kerb hopping.
With a standard (and there really is no other) diff centre you are limited to around 120Bhp or so regardless of ratio, though some say the larger toothed 4.11 ratio is stronger, you loose on top speed.
Since you have a Type 9 overdrive, perhaps not a big problem unless you go motorway cruising your 3.63 Marina axle.
Only the Sprint axle takes power greater than 120Bhp.

In normal service I would not expect the halfshafts to break, a call to Redline in Caterham will give you a price for standard sizes if and when you do, much cheaper than Rakeway conversion. The diff centres still come up second hand, some people have spares, so provided you catch it before it goes very quiet they can be swapped out pretty quickly. I do not think its practical to rebuild your own diff centre. So choose the ratio you want from Rimmer Brothers and get an exchange unit.

My advice for what its worth, is check the availabilty of spares, buy if you are concerned and join the AA.

Any more info? PM me for my phone number.

[John_Mulvaney]

Re: Marina Diff

With a Cabrio I'm not a frequent reader of Roadster tech stuff these days but you gents brought back memories.........................

Although a while back now I can vouch for Rimmer's diffs. All blued-up to check the meshing surfaces it was worth the money when it replaced 2 "reconditioned" units that failed in quick succesion, although the first one of these did come from YKC's hillclimb car!
I went through a slightly different thought process when seeking to change from a 4.11:1 diff. My car ran a MG Maestro 2.0 Efi with a SD1 5 sp gearbox and I reasoned that the lesser weight of the Roadster would still allow good performance if the diff ratio went from the 20.3 mph per 1000 rpm I had to the 23 mph per 1000 rpm of the donor car. My info. was that 2.0 Maestro + Montego and 1850 8v Dolomite in o/d 4th were all in the range 22 -24 mph /!000. With the SD1 0.833:1 5th ratio and a 3.63:1 diff this gave what I required and a calculated 3044 rpm at 70 mph, not too different from what Peter seems to be getting (tyre size can make 3% difference if not more). My goal was not to have an "overdrive" cruising gear but something that would "drive" at 70 and a bit more beyond - I needed to keep my licence for work! The result was a car that happily accelerated up the majority of m'way inclines in top but was much less stressed around the 70 mark. It gained 2nd fastest Marlin of the day up the Brooklands test hill 2-up with luggage from a standing start in second all the way so the 25.6 mph / 1000 rpm with a 3.27: diff would have been worth a try had I still got the car!

For the Marina gearbox 4.11:1 = 16.9 mph/1000rpm; 3.89:1 = 17.9; 3.63:1 = 19.2; 3.27:1 = 21.3 (all data based on best I had at the time and from reasonably reliable sources)

Hope this helps folks select the ratio that best suits their requirements,
John

[stevejgreen]

Re: Marina Diff

Thanks John. Always nice to hear the old and new data pretty much match up. Good to hear your experiences.
Yes, despite the cost Rimmers do a good rebuild, not a job for a keen amateur to set the end floats up.
Luckily I know Chris's car, he's not too far from me, and I have a few differential spares stored away.
I think the crucial issue when doing any differential repairs is cleanliness. Ideally the axle casing should be off the car and washed through removing all traces of old lubricant and potential metal particles that it holds. Stuff in there could be 40 years old!

[trevor_ford]

Re: Marina Diff

Had a look under the car today and the problem that I thought was propshaft u/js appears to be the differential. There is a slight clunking while driving which gets worse on decelleration. Are the Ital 1700 and Marina 1300 diffs interchangeable ? As far as I remember, the diff in the car is from the Marina 1300 and I have the Ital 1700 diff in the garage. Is the axle casing the same and can I identify the diff in the garage easily ? Once again, thanks in advance for any info. : )

[trevor_ford]

Re: Marina Diff

The diff in the garage is marked ST 1003 R