VW Electrics Starter motor

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Technical Starter Motor Information, an insight into starter earthing and T25 specific issues plus their causes.

Aidan: our resident gearbox guru.. The early manual petrol wbx starter is smaller and lower power than the late one but they are interchangeable (except on 1985 MY petrol syncros with the short difflock pin)

VW standardised on the bigger starter in 1986 when they/bosch also used the same core starter on the TD montego gearbox they built for BL (TD needs more grunt to crank), the BL version however has a slightly different bolt pattern and I think different tooth pattern so is not interchangeable but looks just like the wbx one if you saw them together you'd have to look hard to spot the difference

I advise moving the earth to the starter motor on 5 speed boxes to reduce the electrolytic corrosive effects of sticking a 12V potential across a steel plate that has a 1mm gap to a magalloy case where with the aid of some salty water you can see massive corosion of the gearbox end case; the 4 speeds suffer much less from this though you will often see quite heavy corrosion of the bosses that the gearbox mount studs fix into; using the gearbox as the earth contact was just a production line simplification (engine and gearbox lifted up into engine bay and mount bolted on with earth in one action) and doesn't really do anything for efficient cranking Similarly the permenant live across the reverse switch on the gearbox together with the permenant earth to the gearbox causes corrosion of the case around the reverse switch housing and is why in late 1989 VW added a paper gasket to that mating face to mitigate the effects as by then they would have seen a lot of exchange gearbox cores coming back that weren't suitable for reuse due to the corrosion thus caused, and is why I have always fitted the paper gasket, now obsolete from VW and classic parts but which I make myself, though it has been remanufactured in america (but is a bit pricey)

Bad Starting when hot

Field winding insulation failing/breaking down

Starter bushing (in bellhousing) on petrols worn

Typical case?

Ally: When it snowed the other day, I went out and tried to start my van but it just kept turning over and nearly going. It got slower and slower untill the batterry died. I took the battery out and recharged it, it's a new and powerful battery. Now it just clicks when I try to start it and doesn't turn over at all.

Is my starter motor dead? There was a burning smell after I tried to start it the first time.

HarryMann: If it didn't spin it very fast, that is what you are saying, then:

1) the battery isn't being charged up enough (generator, leaving too long between runs, short runs, poor charging connections etc.);

2) the starter motor field windings are breaking down, new starter;

3) the starter motor bushing is worn badly, creating misalignment high friction;

4) the engine or gearbox earth straps/braids & connections need checking for high resistance, breakages (can double up gearbox straps);

5) the main starter motor lead /connections needs checking for high resistance, breakages;

6) you bought a cheap or too small battery or it never really got fully charged up.

NB. Locate the source of the burning smell ASAP. Could be the starter motor armature winding insulation getting hot, or more seriously a bad earth or damaged cable. This is probably No. 1 on your list, look for smoke and check the battery connections are good (clean and use Nocrode or vaseline on terminals - and be careful with shorts/sparks when a battery has been rapidly discharged, fumes, explosion).

Typical fixes


Quick video.


Intermittent starter spin although solenoid still clicks.

Its likely (if connections at battery and at starter motor are good) to be bushes inside starter - ie wearing out. As they do, commutator gets dirty, sometimes brushes contact (and it spins) and other times they don't (particularly if brushes are on their last legs) and nothing happens. Its possible to fit new ones yourself thereby saving £100+ and spending about £7 instead but you'll need a gas-powered soldering iron to get enough heat to solder on the new ones. Lots on Youtube regarding soldering brushes on starter motors. Flux suitable for external use (ie on steel) is recommended although I managed reasonably OK with the small five core solder (to a degree).

Totally dead starter.

Heres the end removed from mine. The failure was the braided cable which can be resoldered or replaced. Faulty braid may cause the starter to be intermittent to begin with but as it weakens and finally breaks, both solenoid and starter will go dead as the circuit will be broken. To verify, pop the end cap off and take a look - the problem should be evident.


Weak starter.

The oilite bush which the end of the starter runs in, can cause starter to bind, but shouldn't stop it trying to spin. If you do above, fit a new bush anyway - they cost pennies but can take an age to do due to old one being stubborn to get out. A suitably sized rawl bolt is reckoned to be the easiest method.

Bad brushes, poor battery connection and dying battery can cause similar symptoms so don't assume anything!

Poor main cables Few T25s have good main cables if they have not been replaced since the vehicle was new. This can impact both starting and charging.

See: http://wiki.club8090.co.uk/index.php/VW_Electrics_main_cables

Typical fixes where it's NOT the starter motor itself

WindySurfer: I've just had a new gearbox fitted and started having starter problems when I got it back. Every time I hit the solenoid with a hammer is would start so I though it was knacked and I'd get a new one. Luckly I check the old on directly on a battery before buying a new one as it turned out to be a bad earth between the bellhousing and the starter, when I hit it with the hammer in must have earthed. Worth checking before you spend any money

Weldore: WindySurfer had the same problem as me and we fixed it exactly the same way..just clean up the bellhousing face and the face on the starter that mates to it... also check the braid link from the solenoid to the starter for corrosion as mine also had gone there...in parts it was like rusty wire wool

Weldore: Jump off off the battery neg (-ve) and onto the solenoid body is a good check

Meggles: Tried the substitute earth.. nothing. Fortunately the starter packed up altogether so it was easy to check everything. Intermittent faults are such a nightmare :roll: Anyway, I removed starter, turned out to be a very badly corroded connection from battery+ side to solenoid. All is well now and no new starter to buy! Cleaned and lubed all other connections as a precaution.

Fitting a relay to starter

You can, over time, get appreciable voltage drop which means the starter solenoid doesn't pull in and make a great contact. This can cause intermittent, unreliable or even slow starting.

Heres how to add one: http://thelatebay.com/index.php?wiki/hot-start-relay/ - this also reduces the load on your ignition switch. As stated, if relay ever fails, you can reinstate the small blue wire back to its original position on starter to get you going.