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1500 overdrive gearbox, replacement, pitfalls. Advice request.


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Spitfire 1500 with single rail, overdrive, box. Possibly originally a Dolomite box.

Issue is this: Box is making a fizzy/rumbly noise at idle which disappears when clutch is depressed. So I'm assuming likely cause is input shaft front bearing. Probably go for an exchange-recon box.

Gearbox in and out no problem for me. But removing and replacing the o.d. unit is not something I've ever done. I messed up badly when replacing the o.d. on my GT6 and had give the whole assembly to a specialist to make good.

Haynes makes the process sound easy peasy. But what in practice are the likely obstacles to trouble free removal and replacement? Any advice would be much appreciated.

 

Thnx

 

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A noise like that may only be the release bearing; rattles in neutral but goes away when clutch pressed. I'd try that as the easiest first step; of course the box does have to come out for access, but it's cheaper to solve than many other problems...

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As Colin says it would be nice if it was the release bearing but these normally make a noise under load (pedal pressed). Much more likely a source than that or the front bearing the noise is the needle roller between mainshaft and input or possibly the layshaft needle rollers. These have a reputation for being much weaker than the main roller bearings and stop spinning if the clutch is disengaged when stationary.

I thought the OD just unbolted as one unit and then separates from the mainshaft but sure an expert will be along soon....

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1 minute ago, johny said:

As Colin says it would be nice if it was the release bearing but these normally make a noise under load (pedal pressed).

That's typical; I would have to have the odd car where mine rattles and whirrs like mad until the clutch is pressed...

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Does yours stop with the very slightest pressure on the pedal? If so that might be a way of distinguishing between the two sources otherwise it will be difficult but unfortunately I think the needle bearings are more likely☹️ 

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easy to refit an overdrive 

no faffing around trying to align the shaft splines 

when the unit  is partly on but wont go the last couple of inches  take 2 decent screwdrivers and from the outside introduce them each side to locate in the operating bar plates and prise them open( away from the pistons  the whole inards is free to rotate and self align but mind when it drops to keep the finges out the way 

squeaky noises can be throwout skidding on the diaphragm fingers   a light touch on the pedal solves it

noise at idle can be just gear backlash  , and wiith tunnel off some alarming clatter is normal

test that at idle  just puch the gearstick into 3rd , it wont engage but loads the gears ,cuts out backlash clatter

input earing   all you need for that is a dummy short lay shaft spindle  drop the cluster and knock the input shaft out the box 

the rest is easy 

Pete

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Sounds exactly like my 3 rail box sounded, I would guess mainshaft tip wear. If I recall J types are easier to refit (no alignment of the splines), just give it a good clean out.

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8 minutes ago, DanMi said:

Sounds exactly like my 3 rail box sounded, I would guess mainshaft tip wear. If I recall J types are easier to refit (no alignment of the splines), just give it a good clean out.

J types, use Pete's method splines do need to be aligned, couple of thin bits of wood for when the overdrive drops can save fingers.

Regards

Paul

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3 minutes ago, 68vitesse said:

J types, use Pete's method splines do need to be aligned, couple of thin bits of wood for when the overdrive drops can save fingers.

Regards

Paul

OK wasn't sure as haven't had a J type for 35 odd years

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