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MG TD TF 1500 - Tach reduction gearbox

About four years ago I bought a new gearbox from our reputable 'parts source', you guessed it, it crapped out. I took it off thinking something came loose and the shaft turned without any resistance. When I opened the case rhis morning, much to my surprise, there were plastic gears that were completely stripped off. Is there anyone here in the states that repairs them with original steel gears? I will do without before I spend another $120.00 for this JUNK. Slammed again! Thanks, Russ
RAH Russ

Can you measure the OD and count the number of teeth on the gear?

If they are "US" DP gears I might be able to find a source.

Jim B.
JA Benjamin

Hi Jim - No, both the drive and driven gears are stripped down to the base plastic and the teeth are shards in the grease. The gears are held on to the steel shafts so it must be a press/interference fit. I don't know how that would be possible, I would think over time a/the gears would slip. MAYBE that is exactly what happened. Not sure but someone out there might have a good original case apart and could check with a micrometer for US. Russ
RAH Russ

Abingdon Spares lists a repair kit that I think is the gears. Call them and ask. "35 088a Repair Kit for Reduction Gear Box" For years there were no tach drives available, and unfortunately the original batch of repros had plastic gears. I think the repros are metal now. I suggest calling your source up and discussing, while out of warranty they may cut you some slack. George
George Butz

If someone needs a gearbox just email me ( have 3 )
Gerard
Gerard Hengeveld

I second what George says. At least give them the opportunity to tell you to "pound sand"... before assuming they would. Regards, tom
tm peterson

George - thanks for your note. I did check with the Calif company, the gears are a composite material like micarta they said, a step above plastic I would think. I also checked with ASL about that kit, I seem to recall that is for the coupling end, not the gears. I had heard that B/G in the UK had the gears, I haven't hear back from them yet. Also looked at FTFU and they don't seem to have repair parts either, feels like I'm running around in circles. I do remember there was someone doing repairs on them with NEW hardened gears but I lost/misplaced the details. ASL did carry the gears in 2010 @ $31.00 each, NOT shaft mounted. Russ
RAH Russ

I just stripped out a spare (old and worn) reduction box. The gears appear to be metric with the following specs:
small gear: 24 teeth, 13mm OD, 4.3 mm thick, 4 mm bore
large gear: 54 teeth, 30mm OD, 4.3 mm thick, 4 mm bore

If someone finds a source, please post the details here.
Lew3

You can get them from Speedograph Richfield at: http://www.speedograph-richfield.com/index.html You want the R141 - AT17 Cheers - Dave
DW DuBois

Thank you Lew & Dave - Yes, I'll contact S/R and see if they do in fact sell the repair parts and advise. Russ
RAH Russ

Great link, Dave! And they have both originals and their own substitute for these so that once the originals are gone there is still a source.

BobbyG
Bobby Galvez

I just checked again. I found the large gear is a little smaller than I reported above. The teeth on my original are worn down badly so I overestimated the size. The diameter is closer to 28 mm, but the other details are correct.
Lew3

Those gear are very close to American/imperial 48 DP gears. (DP=Diameterial Pitch)

DP may be (approximately) calculated by counting the number of teeth adding 2 and dividing by the OD in inches. (Round to the nearest even whole number)

48 DP gears with the correct number of teeth are available from Boston Gear (and others). Boston gear sells only through distributors but there is a distributor finder on their web site.

The available ones, in the BG catalog, have a hub, which would need to be turned off.
The 54 tooth gear would have a 1.125 OD a bore of 0.250 and a face or thickness of 0.125. the hub projects 0.25 and is 0.50 in diameter.
In brass the part number is G143
The 24 tooth gear has a 0.500 OD a 0.187 bore and does not seem to have a hub. Part number is G136
These are 14-1/2 degree pressure angle gears.

There are similar gears using a 20 degree pressure angle (PA) also.

I believe the 20šPA is a more modern design perameter and I suspect these would have been 14-1/2 degree PA if, indeed they are US/Imperial and not Metric.
I do believe, if Metric they would more likely be 20šPA.


BG's Website is difficult.
Go Here:
http://www.altraliterature.com/brands.asp?brandID=3&litType=product#cat9
And download the "Rotary Drive Products" catalog.

Jim B.
JA Benjamin

Jim,

Thanks for that! I hope to find a distributor for Boston Gear and order a set or two.

However, I'm not sure I agree with you on the hub dimensions. Whereas, my metric dimensions could very well be inch sizes, neither gear I have has a hub, and both gears' bores seem to be just a shade under 4 mm or .157 inches. The shafts that the gears are pressed onto are closer to 6 mm than 1/4 inch, but the tips are turned down to 4 mm and pressed into the gears.
The gears are 4.3 mm thick which would leave no room whatsoever for a hub inside the case.

It is the shaft dimensions which originally led me to believe the gears to be metric.

Cheers,
Lew
Lew3

Yes Lew. I know the hub on the Boston Gears is not on the MG ones. It would need to be turned off.

Nothing is quite perfect.

Jim B.
JA Benjamin

Jim,
I saw that after I reread your message. The biggest problem, at least with trying to match MY gears, is the shaft diameter. The Boston Gear 54 tooth has a bore of .250 inches and I need 4 mm or 5/32 inch.

So I'm now trying to 3D print some. Once I get the design right, I may then try to print in bronze.
Lew3

This thread was discussed between 21/08/2016 and 25/08/2016

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