This is the second part of an article dealing with the destruction of a VW T3 Syncro Gearbox. Part one can be found here. https://vantopia.ie/vw-t3-gearbox-destruction/
After cleaning and inspection of the box it was found to be mainly scrap the following was found
Mainshaft The Mainshaft has suffered from heat damage upon all bearing surfaces from running with lack of oil and is scrap. shaft on the right is a good used one to show contrast with heat damaged mainshaft note the blackening of the metal
Third and fourth gears have also suffered heat damage and fourth gear has welded itself to the syncro ring. Third photo shows a good used gear for contrast also note the blackening of the bearing surface in pic 4
PInion shaft again suffering form heat damage on all bearing surfaces and debris damage in the reverse G gear area
Pininon bearing lock ring/ first gear inner race showing heat damage
Pinion shaft gears 1st 2nd 3rd and fourth all showing heat damage
R/G Synchcroniser Hub
Reverse gear and G gears note damage in bearing surface from needle bearings etc
G Gear note the brass and other materials gound into the teeth
When did this happen ?
Customer stated that when that this happened when driving on the motorway at 50 mph on a long drive he started seeing smoke. When he dropped below 50mph it was ok but when accelerated to 70 mph smoke remerged and when customer tried to change gear the problems started. It then sounded like a bag of bolts in a washing machine. He then limped the van home. Customer is running a 2.5 Normally aspirated engine from a Subaru Legacy.
Why did this happen ?
Main damage to this VW T3 syncro gearbox was due to oil starvation and continued driving after oil loss. This has led to heat damage on all bearing surfaces and gears evidenced by blackening of the material.
Discoloration or darkening of the bearing due to metal-to-metal contact, which raises temperatures. Discoloring on races and rollers is common. In mild cases, discoloration is from the lubricant staining the bearing surfaces. In severe cases, heat discolors the metal itself. After suffering this kind of heat effect the material will have degraded and lost whatever physical properties it had for this application such as hardness and its surface will have become rough if examined under a microscope. Thus rendering the component unusable even though it may look ok apart from the colouring.
The mainshaft bearing also failed which led to damaging of the gears and led to other bearing failures and interface between the reverse and G Gears and the Synchroniser which subsequently exploded
The root cause and conclusion
Wait for it :)
It is very hard to say what was the root cause of the destruction of this VW T3 Syncro gearbox. One of the things it was not was the rebuild It was built to the correct specifications. Pinion height was spot on and all circlips or what remained of them were present so I can see no reason for that to be a contributing factor. The rebuild was over seven years ago and if there had been anything amiss it would have shown itself before now.
From what I see the main contributing factors to the destruction of this syncro gearbox are as follows
1) Continued driving after oil loss. Failure to regularly inspect the vehicle and look underneath for any warning signs such as oil leaks etc.
2) The damage to the nose cone and a possible oil leak from there. This may have been due to a prop shaft failure or a Viscous Coupling locking up ??
3) The damage to the reduction housing arms. Either by bolts working their way loose? or a fitting error? It is very hard to say.
4) The crack on the cover plate. This may have been caused from a bump start previously but probably was a result of the destruction in the reduction gear carrier.
Conclusion
After speaking with another gearbox builder a similar instance of a nose cone fracturing was noted on a motorway drive, this was attributed to a propshaft failure. The Viscous Coupling was tested but ruled out as it appeared to operating ok. From this instance the probable root cause maybe this leading to gradual oil loss over a distance to the eventual failure of the mainshaft bearing, dmage of the gears and subsequent explosion of the R/G synchoniser fragments of which went through the GGear and the idler gears rupturing the cover plate and leading to further oil loss eventually ending in oil starvation with continued driving.
Is this the end?
At Vantopia™ nothing is wasted. Despite the nose cone reduction gear housing the pinion shaft and by default the crown wheel ( they are a matched pair and cannot be used with another) the mainshaft and the entire gear train along with the rev gear shifter and various other smaller componets are scrap the box will be reused. All the damaged parts have been kindly donated by the owner to be reused in making a display box for educational purposes for your viewing pleasure. The other usuable components will be used to rebuild a box for the customer along with components from another box that I have in stock so it will live to see another day. :) tune in for the resurrection
