MGB GT rear axle /diff

[Harry]

Evening all, My Marlin diff seems to be developing a little "Clonk" so I thought I'd replace it for a MGB GT diff, I located one + prop shaft down in Bristol, I drove down there on Saturday, it's a very scenic drive along much of the Welsh border, but it was very slow going ( In my Mondeo by the way ) I am sure I drove 200 of the 320 mile in 3rd and 4th gear only. Anyway, I've now changed my mind as it's inviting too much bother and work, besides the MGB axle is 2" narrower than the Marina unit and the PCD is greater too, so new wheels would be required. So it's plan 2 = wait for the Marina diff to die as the gear box did ! I must say though, the MG components are far better made / engineered than the Marina.
As for yesterday evening, took the Marlin out for a blast at 7.00 pm ish, over Minera Mountain as far as the Prospect Tea rooms, then down past the Sun inn at Trevor and back home over the Horse shoe pass, it's always a nice drive, but its so much better on a lovely sunny evening. There was a Morgan club meeting at Chirk castle over the weekend, I've never seen so many of them.

[stevejgreen]

Re: MGB GT rear axle /diff

The Marina differential centre has a pedigree from many Triumph sources. Dolomites and TR7's including Heralds, Spits etc use the same fundamental gear-set. Worth reading my document here or there.

If you are looking to change, the best option is probably a Dolomite Sprint complete axle that comes with a better ratio (3.45) for cruising than the original 3.63 found in 1.8 Marinas, though, like using an MGB axle needs extensive modification, but the PCD is standard Marina.

[angusgrooby]

Re: MGB GT rear axle /diff

Hi Harry there is a dolimite sprint axle on eBay at the moment http://pages.ebay.com/link/?nav=item...d=251956276454 a bit pricey but may well be worth it.

[Harry]

Re: MGB GT rear axle /diff

Thanks Angus, I think I'll pass on that, they can be had for a lot less, I only paid £35 for the MGB GT axle, but our local MGB center sells them for £150 -250, so maybe I'll stick it on Ebay myself at a profit eh ???

[Harry]

Re: MGB GT rear axle /diff

Hi Steve, thanks for the info, I'll keep an eye out for the Triumph axle, I don't mind the Marina diff, it's just that they are hard to get hold of and I don't want to get caught short with the one in use, but I like my parts nice and cheap and I'm patient ! I agree with you where the Marina diff is concerned however it was never meant to be used on a car of 90 - 100 hp was it, as you may well know, the Marina was never the car it was meant to be, but rather a collection of obsolete parts bin relics from another era. I did own a few of them back in the day, and well remenber the Knackered gear boxes, clonking diffs, broken springs and snapped torsion bars as well as a number of other suspension related embuggerment ----- oh and the water leaks, usually wetting the right foot = happy days !!
I never mentioned that I have fitted an MGB GT gear box to my Marlin and the overdrive makes cruising speeds more enjoyable, I just thought that fitting the correct rear Axle would be a cracking idea, but an idea too far eh ?

[angusgrooby]

Re: MGB GT rear axle /diff

Did you have a dedicated pair driving welleys to drive your Marina then lol ? I agree, with the price of the axle keep looking around if you are no rush I got a dolimite sprite axle for £26 but did have to go to the darkest depths of Norfolk to fetch it. I have not fitted it yet but is on the long list of jobs to do.
Steve when you fitted your axle you mentioned it over braked on the rear axle I think you over came that with fitting the Renault frount wheel callipers so would you advise doing the frount wheel callipers mod before fiting the dolly rear axle? My brakes run on a single circuit only so may well be difficult to alter the braking force going to the rear brakes.

[stevejgreen]

Re: MGB GT rear axle /diff

Strangely I am in Nottingham right now but I don't have the right vehicle or time to pick it up.

I did a full write up on fastmarina forum detailing the process.

[stevejgreen]

Re: MGB GT rear axle /diff

Did you have a dedicated pair driving welleys to drive your Marina then lol ? I agree, with the price of the axle keep looking around if you are no rush I got a dolimite sprite axle for £26 but did have to go to the darkest depths of Norfolk to fetch it. I have not fitted it yet but is on the long list of jobs to do.
Steve when you fitted your axle you mentioned it over braked on the rear axle I think you over came that with fitting the Renault frount wheel callipers so would you advise doing the frount wheel callipers mod before fiting the dolly rear axle? My brakes run on a single circuit only so may well be difficult to alter the braking force going to the rear brakes.

The standard drums on a dolly axle are larger. The mathematics of brake effectiveness are complex, brake pad area, slave cylinder diameter, pedal pressure etc, and then the balance front and rear, without complicating the issue with front brakes.
The Clio mod worked for me and others, better heat dissipation with a vented disk, but the Roadster is much lighter than a Marina and at the end of the day, braking is more a matter of tyre grip on a given road surface and conditions.
The Clio mod is mostly reversible, the only Marina part that is seriously modified is the torque plate that connects the caliber to the suspension upright. These rarely if ever fail so finding some on the second hand market should be relatively easy.

[angusgrooby]

Re: MGB GT rear axle /diff

Thanks for the info Steve I will up grade my frount brakes over winter then before replacing the rear axle for the dolly one. Hope this discussion is useful to you to Harry.

[Harry]

Re: MGB GT rear axle /diff

Hi Angus, yes, Steve's info is always handy to keep in mind, he's a mine of information, I find my Marlin handles quite well considering what it is, It corners quite well, I've not managed to leave the road yet but come close (Last Sunday) another 50 HP would be nice, as the old thing is hardly a ball of fire, but good enough for a laugh eh.

[stevejgreen]

Re: MGB GT rear axle /diff

Hi Angus, yes, Steve's info is always handy to keep in mind, he's a mine of information, I find my Marlin handles quite well considering what it is, It corners quite well, I've not managed to leave the road yet but come close (Last Sunday) another 50 HP would be nice, as the old thing is hardly a ball of fire, but good enough for a laugh eh.

Excellent, what can I say!