TOPIC:

WOW, again looking really nice JR!!! That body works out well with those wheels i think!
Nice job.

Cheers, Bram

Looks Great

Worn halfshaft end is top right ...





Finally got to use the Frog hex adapators ...





Only having 3 wheels meant I had to buy a pair ... I'm thinking the spare one tied on to the rear bumper?




Bought a set of Frog universal driveshafts:








Finished ... sort of ...





Test drive showed up a few flaws - balljoint pulled out of the servo saver, rear bodymount vibrated to bits, and the gearbox makes a horrendous noise I'm thinking the diff now, even though there was nothing visibly wrong with it ... maybe it's getting forced apart under load, so I guess the bolt together mod would be a good place to start

Sounds like it needs a pitstop.
Looks very cool - nice universals!

Way to prove the diff - find a smooth slippery surface (Water on lino, shopping center?), steering full-lock & nail it. Do the same on a grippy surface (Mud, grass, tarmac). If it only clatters on the grippy stuff &/or at full-lock, it's definately diff. If it does it in a straight line (Without veering off to one side), it'll be something else.
If you go for the water on lino testing option, chances are you'll forget the gearbox noise fairly rapidly anyway!

I opened up the gearbox - it had to come apart anyway - the small side of the spur gear is now missing a tooth & the bits seem to have got run over by the large side & the pinion, pretty much burning off three teeth there too

I couldn't find the correct spur gear (52/17T), but the spur gear from the FAV re-re gear bag (19335607) is the right size on the large size (52T). Unfortunately the small side is one tooth bigger at 18T ... but on the plus side the diff is one tooth smaller (47T vs 48T) ... so it should all mesh together. No doubt the gearing will be wrong, but at this point, badword it

DOH!...?
At that point I'd be looking at how much slop there is in the spur bearings & related shaft fixings, same with the next meshing gear - there's not a huge amount of force involved that early in the geartrain, so it's gotta be due to something insecure wanging about causing poor meshing. How good a fit are the plastic bearing cup things on the ends of the shaft, in the sideplates?

Just been having a gander at the pics of the assembled gearbox (To double check my previous rattlings) - yeah.... from memory those plastic cups that hold shaft bearings for the spur & diff are usually a really poor fit in the sideplates, & given that they appear on BOTH parts of a meshing gearset, I can only point & say "Well there's your problem". How bad a fit are they? Enough slop to cause say less than 1mm mesh?

What spurred that outburst was, whilst thinking about the nut+bolt diff fix, I thought, wouldn't it be better to re-make the sideplates from something stiffer (Say 18swg (1.2 th'k) stainless) & replace the crappy plastic cups with proper press-fit cups? The cups would be better made from something with less "give", but the biggest improvement would just be to have them a better fit. I'm sure that mod would address both the diff issues of the MB AND poor meshing of the Frog type gearbox.

Whilst I'm scrutinising, have a look at the main plastic gearbox moulding - is there anything in the way to stop crap finding its way down the hollow suspension arms & into the 'box? - might be an answer to the "fanned motor" creating a vacuum & dragging stuff in from somewhere (Looking at the fan I think it's designed to pull air in at the front & spit it out at the vents at the back cos it's a centrifugal fan)

eddrick wrote:

Just been having a gander at the pics of the assembled gearbox (To double check my previous rattlings) - yeah.... from memory those plastic cups that hold shaft bearings for the spur & diff are usually a really poor fit in the sideplates, & given that they appear on BOTH parts of a meshing gearset, I can only point & say "Well there's your problem". How bad a fit are they? Enough slop to cause say less than 1mm mesh? ...

I've seen some pretty sloppy fits on Frog-type gearboxes, but no - those cups were some of the best fitting ones I've seen. I'm thinking I had "fixed" the "noisy gearbox" with the new driveshafts, the broken tooth I think was probably the plastic being weakened by age or incorrect lubricants, and I just found it out by trying to wheelie it - nothing to do with the reported "noise" issue. The chewed teeth on the outside of the spur I'd guess were caused by the pinion taking the path of least resistance (chewing through them) when the spur gear momentarily stalled against the diff ...

eddrick wrote:

... What spurred that outburst was, whilst thinking about the nut+bolt diff fix, I thought, wouldn't it be better to re-make the sideplates from something stiffer (Say 18swg (1.2 th'k) stainless) & replace the crappy plastic cups with proper press-fit cups? The cups would be better made from something with less "give", but the biggest improvement would just be to have them a better fit. I'm sure that mod would address both the diff issues of the MB AND poor meshing of the Frog type gearbox...

Assuming you could machine it accurately enough (by that I mean it's not something I could do with a pillar drill in the shed ) then that would work... apart from not fitting in the sticky out bits of the chassis without fettling the gap a bit wider, which is doable, although it would be easier if there was a step machine in the plates ... the trailing arms I guess could effectively be spaced out with washers (or a machined shim plate) between the outer pivots & the chassis, I think there's enough slack in the driveshafts for that. Based on past experience I'd say the chances of there being any money in that I'd say is pretty remote - but it would be sound engineering if you found a Frog gearbox that has floppy shafts

eddrick wrote:

... Whilst I'm scrutinising, have a look at the main plastic gearbox moulding - is there anything in the way to stop crap finding its way down the hollow suspension arms & into the 'box? - might be an answer to the "fanned motor" creating a vacuum & dragging stuff in from somewhere (Looking at the fan I think it's designed to pull air in at the front & spit it out at the vents at the back cos it's a centrifugal fan)

I'm not sure where that myth developed - the outside pivots on the Monster Beetle are closed caps rather than the ally loops on the frog/brat ... and besides that, the gap behind the inner pivot points on the gearbox sides is not open to the rest of the gearbox anyway

See what you mean about the rear arms etc, & now I've seen the pic, I remember now... (Haven't seen one up-close since the early/mid '90s!)

Sideplates - 18swg was a guess... how thick are they? (Was thinking same thickness, stiffer material).
As far as "How to" goes, I was kinda thinking "Too much effort to do on the mill", & I'm pretty sure that if you were careful enough, a bit of drawing around what you've got would probably be good enough. If I were gonna do it, it would be a drilly filey job. Something flat & stainless from Poundland might be a good starting point....

Looking at the pic of gears, the diff pinions look like they'd get awfully close to the spur, or is that just the pic angle? You don't suppose they could be twatting it, do you?