Gearbox Clutch CVs - Gear change reluctance

From VW T25(T3)-Tech
Jump to navigationJump to search
HarryMann: Slow into second when cold or synchromesh reluctance in very cold weather is fairly common on many boxes
and the T25 can suffer this too, particularly as the miles build up and synchro hubs wear. Here's a few tips...


Many boxes, not just ours, have this problem, of slow into 2nd when cold, one coming to mind being Lancia FWD boxes of the Betas, Deltas and Prismas. Otherwise, good and (very) strong boxes, but as the comments below make clear, lack of mechanical sympathy over a few years will eventually degrade first of all, 2nd gear synchromesh. As this is the first change-up of the day, when pulling away from cold, if it's dragged into gear screaming & kicking before the hubs can equalize the speeds, or the dog-teeth engage, then wear, even damage occurs. Some also try to rush this gearchange as the rolling speed of the vehicle is slow between 1st and 2nd - some hints follow - learn the foibles of your car/van/truck and drive accordingly.

The problem with getting that change wrong and persisting is making it progressivley worse as the hbs wear and the sharpness wears off teeth of the engagment rings - I'll see if I can't get a good photo to show what happens.

Exploits, workarounds

There'a few tricks one is to double-de-clutch - Clutch down and slip it into neutral, let the clutch up quickly as you blip the throttle just the right amount, clutch back down and ease it firmly into 2nd gear (no yanking that lever, just firm pressure). All before the vehicle has slowed down too much, so if going slightly uphill, don't chang up too early - quite a common sin. Letting the clutch up when the lever is in neutral speeds the gears up again, ready for meshing at the correct speed, whereas just blipping the throttle speeds the engine back up OK, but not the mainshaft as well. It's a technique that takes a bit of learning to be fluid, but anyone starting their driving in the 50's and 60's ought to be pretty proficient. Another time to use D-D-C'ing is when slowing for a big range change, typically up a hill with a Major Road Ahead that requires to be in 1st ready for an immediate take-off. Coming out of 2nd and using just the Synhromesh to force it into 1st is just Ugh! - painful to witness sometimes ;-)

Another trick, when starting on the flat or downhill, is to take 1st a bit further than normal and go straight and quite quickly into 3rd. With some gearboxes of old, when very cold, you'd virtually have to do this as they would often be far too heavy to drag into 2nd (Lancia Betas), and if you succeeded, the gradual damage described above would occurr - anyone with much mechanical sympathy would soon know harm was being done. Anyone else would be wrecking the box fro the next owner!

When running light, on the flat or downhill, you should be able to simply pull away in 2nd gear. The clutch is designed as a wearing replaceable item, the gearbox isn't! Don't slip it for ages, hardly any wear at all occurs just letting it in quite quickly with the right revs and throttle.

If you test a vehicle when warmed up and it 'snicks' going up into 2nd or 3rd, this is the reason, someone's been assuming that synchromesh relieves them of the duty of changing gear considerately, just dragging it in regardless of any complaints or reticence to synchronise when cold (or racing the change when warm). Only the best of the smaller and lighter units can usually cope with this.

Once the baulk rings and synchro hubs are worn, there is less chance you will get a good change when cold, whatever the oil, though Redline & some others do seem to make a diiference - if you can afford it. They advertise it as having an ideal dynamic friction coefficient curve, and is often advertised for Golf GTs and the like, so it's unlikely this is a vehicle specific problem..

The rear-engine layout necessitates a complex and often well-worn selection mechanism on T25s which doesn't help either - if this is all in good condition it definitely helps the driver feel the box into gear, or realise quickly it is just not interested!

Just don't even try going into 2nd when around freezing outside from a coldstart if box is like that... fast idling it a while in neutral might help a bit (never a good idea to slow idle for long periods ~ older engines should be warmed up by driving or fast idled).

(Linkage) Adjustment isn't always the answer unless it's been messed up previously or really worn its bushes. It's really all the joints right throughout the selection mechanism that need to be in good nick, without congealed and dirty grease stiffening it. Checkout this topic:


Poor gearchange

Aidan on gearbox oil

Please can the references to Redline MT90 be pulled from the WIKI, I do not recommend this oil at all, every box I've known that has had it has had issues, and there is a lot of evidence from the states of excessive wear with this product, Daryl at AA transaxles has been looking at this problem and now he no longer recommends it and on the Vanagon forums it's been spread about that it's not good - unfortunatly the UK importer is targeting the T3 market on ebay, based on old recommendations

the carplan 75w/90 gl4/gl5 is what i use now that the Fuchs is no longer readily available, if you want to spend a lot of dosh then use Millers, and if you want to spend a fortune then use the SWEPCO, but personally I go with the £20 stuff regularly changed and from what I'm seeing on wear after 5 years that advice stands

This is not all about oil or viscosity either, though a thicker oil would be expected to make things worse in winter.

But first of all, what's above assumes the box has the right quantity of oil in it - draining T25 boxes to find next to no oil is not that uncommon. Oil level on Syncros is reckoned to be just less than an inch below the bottom of the filler hole.