To overdrive, or not to overdrive, that is the question

[Ian Perry]

Now the Spitz is on the road, I am facing the next question. It works fine (well, there are a few niggles as always, but hey), but...

It's a 1977 model 1500, with a non-overdrive gearbox. I have a second-hand OD gearbox (with gear lever and apparently working switch), crossmember, prop and speedometer drive. I have no idea the condition of the box, whether it works or is quiet, whether the synchro is all banjaxed, and no idea at all whether the overdrive works. I assume that in theory it would be a "relatively straightforward process" to pull the old box and prop out, put in the OD and reassemble everything around it... but then discover that the box or OD are u/s and start the whole blimmin show all over again. And put right all the new niggles that I've created by giving it the old "fresh air treatment". And also noting that I'll be doing it all on my tod.

I apologise for the heretical question, but... Is it really worth it? Does the overdrive really make that much difference?

[sparky_spit]

It all depends upon your intended use of the car.  If you are going to use the car for relatively short runs out, pottering around the countryside at speeds that the car was originally designed for, then it may meet your needs perfectly without the expense and bother of adding overdrive.  If you intend driving the car longer distances, including a reasonable amount of motorway and fast A roads, then overdrive will be become much more desirable, not just for your ears and body but also for the car itself.  It can be very tiring driving at 4000 RPM in 4th gear to keep up with traffic for a couple of hours, and if you intend doing any longer distance runs or events, having an overdrive reduces RPM at the same speed by about 1000 RPM or so, depending on which specific car/engine/diff you have and really becomes a must-have.

Iv'e got a J Type OD in a Mk3 Spitfire and wouldn't want to be without it. I drove back from Holland some years ago with a non-working OD after an overnight event, and it was very tiring at autoroute speeds; not something I'd want to do again.

[glang]

Agree a lot depends on you. Apart from cruising another benefit is on overtaking where its quicker to drop out of OD third than from 4th but if thats not something which appeals then maybe OD isnt for you....

However dont forget though that I think OD now adds more than 2k to the sale value and desirability of most cars...

As to the condition of your replacement gearbox thats less straight forward as although the 1500 single rail unit is the strongest of all the versions (with bigger tip bearing and synchros) all units are pretty old now and its highly likely it wont be perfect.

[Clive]

I would not want to be without OD, and the 1500 spit needs it more than most. 

OK, if all town and no more than maybe 50mph, but anything more and OD transforms the driving experience.

[Ian Perry]

Gents, many thanks - all sounds convincing... Bonus ball question then - engine out and do it on the workshop floor, or pull the interior out and do it through the cabin?

[Amy Wade]

1 minute ago, Ian Perry said:

Gents, many thanks - all sounds convincing... Bonus ball question then - engine out and do it on the workshop floor, or pull the interior out and do it through the cabin?

You need to take out the tunnel to get access either way. It's up to you how you do it, it's not the easiest thing taking the box out through the cabin but it saves you removing everything needed to get the engine and gearbox out together. 

[standardthread]

1 hour ago, glang said:

although the 1500 single rail unit is the strongest of all the versions (with bigger tip bearing and synchros) all units are pretty old now and its highly likely it wont be perfect.

Not sure about that, prefer three rail boxes.

As for a change of box, it depends if you are lucky enough to have an aluminium bellhousing in the mix. I just take gearboxes out without engine removal.

I wouldn't be without an OD on my 1360 Herald.

Edited November 12, 2022 by standardthread

[glang]

25 minutes ago, standardthread said:

Not sure about that, prefer three rail boxes.

As for a change of box, it depends if you are lucky enough to have an aluminium bellhousing in the mix. I just take gearboxes out without engine removal.

Yes Ive heard that before about people prefering the action of the the three rail design but theres no doubt Triumph incorporated the larger mainshaft tip and synchro rings (and possibly other changes) in the single rail because these were weaknesses in the older design☹️ 

Agree that an OD gearbox especially single rail with cast iron bell housing will be quite a lift in through the interior of the car and having an assistant is definitely recommended...

[Tim Bancroft]

Ian, if you plan to do the RBRR, its a no-brainer, fit the overdrive. I'd be loathe to fit without checking the box and overdrive out though. Put it in through the cockpit, just make sure the engine is at the correct angle. Bloody heavy unit is the Spit 1500 box and overdrive...cast iron bellhousing!!! Good luck.

[sparky_spit]

Changing the gearbox from inside the car is much quicker and easier and as Tim says above getting the angle right is crucial. To aid replacement, put a bellhousing stud (or a longer bolt with the head cut off) into the topmost threaded hole to help guide the gearbox's input shaft into the flywheel bushing.

I have heard of people testing the overdrive operation on the bench using a large heavy duty electric drill. I've never done it, nor seen it done, but someone on here may have more info on how to go about it?

Anyone?...........

Edited November 12, 2022 by sparky_spit

[Wendy Dawes]

15 minutes ago, Tim Bancroft said:

Ian, if you plan to do the RBRR, its a no-brainer, fit the overdrive. I'd be loathe to fit without checking the box and overdrive out though. Put it in through the cockpit, just make sure the engine is at the correct angle. Bloody heavy unit is the Spit 1500 box and overdrive...cast iron bellhousing!!! Good luck.

Try a  TR4a bloody heavy as an engine block  lol 

[Nick Jones]

OD on a 1500 is a no-brainer IMHO.

You can get some idea of gearbox condition with a few simple checks.

Try to wiggle the input shaft tip. 2 - 3 mm at the tip is not the end of the world, but much more than that suggests that the mainshaft tip bearing and/or input shaft bearing are tired.

Select all gears in turn and try rotating the input shaft and output shaft. Should feel smooth in all all with moderate drag. 

Drain oil. If already drained, take a look at the drain plug, which should be magnetic. A quantity of fine “fur” on there (which can look quite scary), is normal, provided there are no bigger chunks.  Whole teeth, rollers, bits of spring etc are bad signs.

Drop the rectangular cover of the bottom of the OD (new gasket for reassembly strongly recommended). There’s a filter gauze and a magnet in there. A little black slime/fine metallic sludge is normal. Chunks are not. Lots of black hairy stuff suggests the OD clutch lining is in trouble.

The above will tell you little about synchro condition or layshaft condition, though badly worn layshaft generally means lots of coarser “fines” on the magnet.

Not an especially difficult box to rebuild though good quality spares are not that easy to find if you need more than synchros, bearings and seals. Nearly all parts are interchangeable with your non-of box.

Personally, I like the single rail box gear change, especially if the lever is modified to remove the rubber isolator. It avoids the issues of the bushes falling apart in the remote that plague the 3 rail.

Nick

[Ian Perry]

On 12/11/2022 at 19:34, Tim Bancroft said:

Ian, if you plan to do the RBRR, its a no-brainer, fit the overdrive. I'd be loathe to fit without checking the box and overdrive out though. Put it in through the cockpit, just make sure the engine is at the correct angle. Bloody heavy unit is the Spit 1500 box and overdrive...cast iron bellhousing!!! Good luck.

Hi Tim,

Much as I would love to, I think there's precious little chance of trying to do RBRR in this, though might go for the Coast to Coast if I get all my admin sorted in time next time (also known as "getting all your sh.. in one sock"). I have a vague fantasy of touring in Northern Scotland in the Spitz though - which would definitely mean fitting the OD...

Thank you!  

[Ian Perry]

All, thank you so much for the responses and advice. I have a 'spare' day tomorrow* so will get the box on the bench and give it a proper poking.

 

* I am supposed to be making a sword rack, but I need some more dimensions before I can finish it (I'm the part-time armourer in a Regimental museum and we have about 60 swords that are currently in a bit of a heap... ). 

[Guppy916]

One of the best upgrades I did to my GT6 Mk3, J Type upgraded to 28% by TLD