MK4 Golf TDI alternators

[Will T]

Hi,

It seems I need a new alternator on my Golf Mk4 2002/3 TDI 130 estate (ASZ engine). Is it Bosch alts that were fitted originally? We plan to keep the car (it's wonderful!) so I don't plan to 'go halves' on replacing it if I can help (afford) it. I'm assuming around £200 for a Bosch replacement (120 amp?). Here's what happened:-

Broke down yesterday on our way back from somewhere - I'd stopped for a break, after which the engine wouldn't turn over properly and re-start. Symptoms of a flat battery, "Workshop" message on dash display. Had to call the AA. The AA tech diagnosed a flat battery because because the alternator wasn't supplying the necessary current. Also there was a lot of 'dry bearing noise' coming from the alternator area. The tech restarted the car from a portable power pack, took some readings, stopped the engine then charged the battery from his van for 20 mins, just enough to get us home in case we had to turn the engine off for any reason en route. And of course I followed his advice and switched off all unnecessary electrical systems (radio, heater/AC fans etc). Got home OK, albeit with a lot of loud mechanical 'whirring' noise coming from under the bonnet!

The techs recommendation was a) replace the alternator b) possibly replace the idler/tension wheel (said it wasn't possible to ascertain it's bearing condition until the alternator was removed). To my question re renewing the brushes and/or rectifier he said if the bearing was on it's way out it would make more sense economically to change the whole unit.

Any info from those that have been here before most appreciated!

Will T

P.S. The lower half of our red dashboard display, which has been out of action for a long time (showing a single vertical line) suddenly came back to life, presumably because the low voltage condition forced it to reboot! But the radio is fine and hasn't required the security code to be entered...?

[vwcabriolet1971]

It would make sense to check brush lengths and auxilary belt tensioner before rushing in to spend £200 for a new alternator. New voltage regulator about £25 and new tensioner est. £20. Your MK4 golf aternator removal will be a lot easier than my old '99 model as yours doesn't have the power steering pump/motor at the top. The alternator has to come out any way so its worth checking once it's out.
Most garages will sell you a new alternator rather than check and fix the old one as it's more profit for them.

[Will T]

Well, when I took the car in to the garage they immediately suspected the alternator "clutch pulley" because they've seen these fail before. On pulling back the belt tensioner with a tool and grabbing the pulley, the pulley just flopped about and wobbled on the shaft! The mechanic said it would have sometimes been freewheeling resulting in the alternator not spinning and therefore not charging the battery. As for the alternator itself he doubted there was anything wrong with it. However he said sometimes the pulleys were so seized on the shaft they couldn't remove them necessitating a new alternator.

Luckily they got mine off and the alternator itself and battery got a clean bill of health, so I got away with a bill of around £100 (the pulley and a new belt were around half of this). The serpentine belt had to be renewed too because it was badly worn (cracking across the 'ribs'). The engine was much quieter when I picked the car up - it was surprising how the pulley noise had been creeping up over the last few months! Until now I'd never heard of a clutch pulley for alternators so I've learned something. And my red dash display is still working...

I don't know if the garage checked the alt brushes etc, (should have asked) but they are very thorough as a rule. They're certainly not in the business in ripping off customers, they've been established for a long time and specialise in German cars and diesels, and have a long standing customer base. I feel lucky to have them nearby given the stories you sometimes hear! (plus my own previous experience).

Thanks for the input.