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musicjon1975

FAV Gearbox not got any torque so car stationary

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Hopefully someone can help me :-D This is my first post and am really struggling with a vintage FAV. have totally taken it apart and rebuilt it. When I put power through the motor the gearbox runs ok - is noisy but is ok. the short shafts turn fine. When I connect the long shafts it seems to lose any torque so much so that the wheels don't turn once on the ground. Any ideas what I am doing wrong. Have had a look at all the elements and they seem fine (not worn out etc.)

Thanks in advance for any help you guys can give...

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Is the motor running when you put it on the ground? I'd hazard a guess that the battery is not providing the voltage required to run the motor under load (especially if it is an old battery), or the motor itself is very worn and can't do the same either.

As far as  I know the FAV doesn't have any friction-based connections in the drivetrain, so if the motor is spinning freely it would be because a part is stripped, but still has enough material on it to drive when there is no load.

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Thanks for the reply... Yeah is a new Sport Tuned Motor and a reasonably new 7.2V battery. think I might just have to replace all the gears / parts just to make sure nothing is slipping. As soon as i put the wheel fixers (sorry not sure of the name - bit that sits behind the wheel when you put on axle) it seems to hold enough friction to stop the axle turning...

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I would double check they are the right parts and that they haven't been deformed. If you are talking about the wheel adapters, they are the kind of thing that people often over-tighten and damage.

Take the motor out, and roll the car along the ground. It should be completely free rolling when the wheels are attached.

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I would check is the grub screw. 

540-sized RC motors have a flat facet on the shaft.  Grub screw should be fastened on that. (BA6 in bigwig instruction, but it's the same 3x3mm screw)  If you miss that flat spot, the pinion will not transmit power.  It also gets loud.  The pinion stays still, but the shaft rotates. So the grub screw goes around the shaft, making louses.  So, if it's "louder but won't go," that'd be the first suspect.  

adDUnZh.jpg

 

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Was also going to say to check the pinion is mounted correctly and grub screw tightened.

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With the motor removed, does the drivetrain spin freely?  All bearings/bushings in the correct place, no gears binding or pinched on shafts?

Does the pinion have the correct # of teeth?

Is the motor mounted in the correct position in the gearbox with respect to the # of pinion teeth?

Are the motor mount screws too long and protrude into the armature?

Is the battery voltage at least 7.2 volts?

EPA (end point adjustments) on the radio are 100%?

 

 

 

 

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How did you get on?  I still think its a pinion spinning prob,not on the motor shaft flat. If its your first car it is surprising how "noisy" this sort of driveline is. I think the added drag of the shafts and wheels is causing the pinion to slip.

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Morning all, thanks for all the ideas / comments. Going to tackle it this evening and will let you know. Pretty sure i did the pinion correctly but will check for sure.

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Just another suggestion, it might be the hex drive shafts that fit between the gearbox and axles are rounded off. I had this problem with an old frog that had the same design shafts.

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4 hours ago, musicjon1975 said:

Yeah I do wonder about the hex drive shafts... will take some photos later and upload and maybe that might help diagnose... thanks again

Sorry, I see the vintage mentioned BUT overlooked "have totally taken it apart and rebuilt it" So it could be worn hex`s on the drive shafts.

Ignore my previous input

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Evening gents,

OK so have taken the whole gearbox apart and this is what I learnt:
1. Pinion Gear was in the right location and grub screw also in correct location - tightened to the flat part of motor axle
2. With Engine out car rolls ok but sounds a little crunchy
3. When i put the gearbox back together it just isn't smooth like one of the gear is slipping
4. When I put the motor on (attached to gearbox) the main gear runs off it fine but then the gearbox sounds noisy and like something is slipping.

I think the problem is in the gearbox itself - the hex shafts all look a little worn but not unduly so.

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From the photos, the gears look like they're in good shape and the motor bolts are Tamiya brand, presumably for this model.  Bearings spin freely? Axles/dogbones aren't binding due to extreme angles?

Here's the manual: https://www.tamiya.com/english/rc/rcmanual/58496.pdf

Is it assembled as the manual indicates?

The only other instance where I've heard of something like this is where an owner used a screw to mount a trans that was long enough to protrude into the gearbox and chafe on a gear.

This is getting interesting...

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5 hours ago, SupraChrgd82 said:

From the photos, the gears look like they're in good shape and the motor bolts are Tamiya brand, presumably for this model.  Bearings spin freely? Axles/dogbones aren't binding due to extreme angles?

Here's the manual: https://www.tamiya.com/english/rc/rcmanual/58496.pdf

Is it assembled as the manual indicates?

The only other instance where I've heard of something like this is where an owner used a screw to mount a trans that was long enough to protrude into the gearbox and chafe on a gear.

This is getting interesting...

So have the original manual and worked off that last night. The 2 things that I wonder are:
1. I put race bearings in. Looking at the old images the plastic bearings that slot where the short hex bolts go through the gear casing have a small lip on them which isn't there on the race bearings - i wonder whether that is allowing a gap to form and so the differential is slipping
2. when i put the differential together and twisted under tension (my finger against the rear short hex bolt (the one they say you should tape to the casing to hold in place)) when I turned the differential the gear that sits on the 3 small gears wouldn't turn the whole time - it would slip...

Some more context - I thought that the angle of the drive shafts was to severe with the original suspension so I swapped for oil dampers to lower the ride height to give a more horizental angle for the drive shafts when under load but that made NO difference...

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In Pic 5, there are no splines visible inside the sleeve on the metal gear. It looks to me like it's been drilled out for some reason. Also the black grease on the main diff gear looks like it's got very small particles of something in, I suspect very tiny tiny pieces of metal diff gears... There is some wear visible on the teeth of the large metal gears. It would be worthwhile cleaning the grease of the whole lot so you can inspect for wear a bit better. 

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33 minutes ago, MadInventor said:

In Pic 5, there are no splines visible inside the sleeve on the metal gear. It looks to me like it's been drilled out for some reason. Also the black grease on the main diff gear looks like it's got very small particles of something in, I suspect very tiny tiny pieces of metal diff gears... There is some wear visible on the teeth of the large metal gears. It would be worthwhile cleaning the grease of the whole lot so you can inspect for wear a bit better. 

Was thinking of taking all the gears out and trying to clean them in the dishwasher? Is that a  good idea? then I can take photos and load up on here. Would also do the hex shafts etc.

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8 hours ago, musicjon1975 said:

 

Was thinking of taking all the gears out and trying to clean them in the dishwasher? Is that a  good idea? then I can take photos and load up on here. Would also do the hex shafts etc.

No, you'll clag up your dishwasher and your wife will chase you round the house with a rolling pin ;)

I would suggest a small glass bottle (Like a sauce bottle with an airtight lid), put some white spirit (Turpentine substitute) in it, dump in the gears, and clean them with an old toothbrush, being careful not to spray it into your eyes with the toothbrush. If you then leave the cleaning solution to settle, you'll be able to see how much shiny metal is actually in the grease.

 

 

 

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13 minutes ago, MadInventor said:

No, you'll clag up your dishwasher and your wife will chase you round the house with a rolling pin ;)

I would suggest a small glass bottle (Like a sauce bottle with an airtight lid), put some white spirit (Turpentine substitute) in it, dump in the gears, and clean them with an old toothbrush, being careful not to spray it into your eyes with the toothbrush. If you then leave the cleaning to settle, you'll be able to see how much shiny metal is actually in the grease.

 

 

 

Haha ok will try that in the morning. Have also ordered replacement gears but could only find original ones in the US so might take a bit to get here... Will clean them all and send pics - thanks again,

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9 hours ago, MadInventor said:

In Pic 5, there are no splines visible inside the sleeve on the metal gear. It looks to me like it's been drilled out for some reason

Good spot

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26 minutes ago, MadInventor said:

your wife will chase you round the house with a rolling pin ;)

Don't they all do that ;)

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I'm not seeing any 5mm shim washer or W3 spacer in your parts there , so you may be getting some sideways movement within the gearbox seperating the gear mesh

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overtightening of the motor mount bolts can cause the motor pinion the rub on the gearbox casing where the pinion vision hole is through distortion of the case

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Did I make a mistake and by replacing the W3 washer with a race bearing... did I lose a little bit that holds the gears in situ so now they can move around?

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