Gearbox advice please

[norfolkstag]

Gents,

Hoping someone can help me with some gearbox advice. As long as I have had the car (5 years now) when it gets warmed up I get a fairly noticeable jolt/jump when the car changes down (its a '72 auto) or when I select reverse. It's not noticeable when the car is cold and its most noticeable on selecting reverse.

My local garage reckon that the auto box is 'tired' and should be replaced. They have also advised that I should source a manual box and get it refurbed before fitting. They have seen and worked on a lot of stags and have assured me moving to the manual will transform my stag driving experience!

Anyone experienced similar issues with their Auto and/or made the switch to manual??

Thanks

[73stagman]

I would think that changing the gearbox from automatic to manual should be your choice, driven (sorry no pun intended) by your driving style, the need to "mix your own gears" rather than the "garage" suggesting it as way of a fix for a tired auto box. Whether or not the auto box is tired is another discussion, and I reckon that as your Stag is 1973 it will be a BW35 and the swap to a manual will be quite involved and costly. (The engine rear plate needs changing as well as the flywheel, the prop shaft, the pedal box the slave and master cylinder all have to be found) There is also a wiring change that needs doing (its easy but easily forgotten as well!)
The way the exhaust is mounted is different from one box to the other as well as the actual gearbox mounting itself...
That's before you find a gearbox that is functioning aswell... you may end up with a manual box that is tired and needs overhauling!

I think that although it might be difficult to get the BW35 gearbox overhauled economically it probably isn't impossible but maybe a better option is to change the type of Auto Box!

[DJT]

Could well be gearbox brake bands need adjusting. The BW35 is a trifle agricultural compared with modern autos, but shouldn't be that rough. What is the tickover RPM? Anything above about 650 will amplify this problem? What about the driveline universal joints. There are 6 of them and any play will also result in rough changes.

Our guru on these matters would be able to advise, but he no longer posts. If he is reading this he may send you a PM.

[wilf]

I like the way the auto drives - makes the whole car seem more relaxed as a cruiser for me.

I greatly improved the behaviour of my BW35 by adjusting the kickdown cable a touch. Got it about right now.

Much banging and thumping putting it in and out of gear was cured by a new propshaft and drive shafts, i.e. new UJs all around. I didn't change them due to this issue however, the improved behaviour when selecting a gear was a by-product of curing other issues like propshaft vibes and the "twitch" due to seizing plunging joints on the drive shafts.

[V Mad]

I had an auto stag with BW35 that did that, but I never tried to cure it. Manual or auto gearbox is a personal choice, so you may find a manual stag not to your liking. Try a drive in one before you convert, or consider the conversion to ZF 4 speed auto.

[richardthestag]

My stag started out as a bw35 and is now an manual j-type overdrive.

Both boxes have their advantages and disadvantages.

Drive an manual od car before you make the jump!

The conversion wasnt too bad. I bought all my bits from martin dimmock. The box looked recon already :-)

That was a win

Need gearbox obviously, engine adapter plate, flywheel, spiggot bush, clutch gubbins including hydraulics, the gearbox of course. Make sure you get the bolts that go either side of the engine adapter plate. Standard unf iifc connect it to the engine block. But there are a couple of dowel bolts that you will need also.

Ontop of that is the pedal box, not too tricky to change, propshaft. Gearstick and surround. All the wiring should be in place, so long as your gearbox comes with its own loom.

Driving experience for me...

Manual o/d

I sometimes like to exercise my right foot a little, from stand still using the full rev range the manual box makes the engine sound incredible, double declutched downshifts make the hairs stand up on my neck. And if i am careful on a run i just kiss the wrong side of 30mrg.

Downsides, the eiffel tower gearstick means that i cannot easily get my foot off the clutch when in 4th gear. Clutchless upshifts are easy and double de clutch down shifts must be mastered but the rewards are great. That said round town, 3rd gear od is pretty much the same as 4th gear non od. So get it up to 3rd and then flick the switch in and out.

Getting the clutch to work correctly meant me getting the box off twice, grrrr works beautifully now grin.

Bw35
Suits the car better imho, is relaxed and laidback, the exhaust note round town sounds much smoother, as the torque converter does its magic. On the road it feels less involved but then there is more time to smile

Downsides, leaking atf out the dipstick hole all the time - well mine did. Agricultural 3 speed, never bettered 23 mpg with it! Managed on one spirited drive to average 11, but that was a good run. Lastly autobox specialists used to be in every town, not any more :-( and diagnosis really should be done with the box in the car and it running.

Not ideal for me as a home mechanic.

When i did the swap if i could have afforded it i might have been tempted by the zf4 speed autobox. May well be the best of both worlds

Have fun

[Mike Stevens]

Excess play in the drive-line after the 'box will exaggerate the problem. Prop and drive shafts have already been mentioned, but the diff itself can have excess play in it when the sun/planet gear thrust washers wear. I have been 'playing' with a saloon diff (much the same design) and changing these thrust washers has made an amazing difference!

I think you need to find out where the play is before condemming the autobox...

Cheers,
Mike.

[norfolkstag]

Gents,

Many thanks for the great advice.....has now got me thinking that a deeper examination of the 'clunk' problem is needed.....and maybe i should stick with the Auto box. Most seem to think it suits the car better.......

[jleyton]

Just to further muddy the waters I was looking for an auto when I bought my car. As has been said, I thought it would suit the car better however the car I saw and fell in love with is a MOD and I'm well pleased. My first Stag, many years ago, was an Auto and I had fond memories of that.

Ok, my everyday car is an tiptronic auto so I can use that if I want relaxed driving but the main advantage of the manual over a standard auto, for me, is the gear ratio. In OD top you're doing nearly 25mph/1000rpm whereas in a BW 35 or 65 it's closer to 20. That means that at 70, the engine is under 3,000 in a MOD but over 3,500 in an Auto, or thereabouts.

Although we all love our engine sound, I just find the manual more relaxing in this respect and the added bonus of instantly being able to flick in and out of overdrive is brilliant.

Having said that, as has been said, maybe the ZF conversion gives the best of both worlds ?

Just by two penn 'orth

Cheers

Julian

[gray]

Some useful automatic auto box bw35 info

Julian

take a look at this, chapter Fd. It's for the MGB but this chapter is for the BW35 used in the auto version - which I have. Same as yours.

You may find that the problem you are experiencing is covered on page fd14, which suggests adjustment of the downshift & throttle valve cable. The downside is that it does require a specialist tool so a classic gearbox garage would need to take a look, but on the upside it's an engine/gbox IN adjustment which may be just a few pounds.

the chapter really has some good stuff in it an a recommended read for any auto owners. lots of diagnostic tests and ....

hope you fine it useful. I am looking for advice on changing the front oil seal in the BW35 as it is totally stuck (my engine is going back in this weekend) and I don't want to remove the box.
G