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Author Topic: RACE PREPPING A 700 SERIES TRANNY  (Read 76136 times)
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George Herrin
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« on: November 26, 2005, 09:56:40 PM »

Here’s what I do to 700 series trannies, I find them in Junkers and pay as little as possible for them generally horse trade or whatever, Anyways here goes... I first off clean all the benonite grease out of them that’s that black muck that you find when you open them. Clean them thoroughly. Do not put the brass bushings in degreaser or spray them with carb cleaner, they are impregnated with oil and yes I use them. I do not put needle bearings on the shafts. Once everything is clean I inspect all parts, The shift keys get a good look at the engagement tips, if they are chipped or show signs of much wear REPLACE them. Everyone has their own opinion on how many shift keys to use, some like the 4 key shafts, which only come in the newer trannies, and if you order one for the older that’s what you will get they don't make the two keys anymore. I use what’s in them. I have run a two key shaft every since I started running the 700 series Tranny. I have never broken a key. Only had one dnf for a tranny and it wasn't a key I bounced real hard never lifting and ripped the input out but it was two years old. (Race wise). Now look at the inside of all gears off the shift shaft make sure all the corners are square and not chipped or rounded. If everything is in good shape great. If not you will need to replace the damaged gear. Now check the input shaft for wear and the needle bearings, if all is good then I put some automotive grade bearing grease in the input shaft keeping a finger over one end I put the shaft back in which presses the grease into the bearings packing them well. I do not put the O-ring back in I replace it with an oil seal which can be gotten from Tecumseh or even a Napa store. I sometimes put an extra flat washer on before I put the snap ring back on to remove all the play. If you have to replace the input shaft bearings I use an old bearing and grind the ends down to make a spacer between the two bearings to keep them from walking towards each other. They have been known to do this on some cases once bearings have been replaced. Now I do replace the input and bevel gear with steel gears, if the rest are not steel no biggie, that’s what I use, I use what is in it, and have never broke but one gear and it was 5th gear the 19 tooth 5th gear counting the one on the shift key shaft. I also remove the reverse chain and sprockets. I do not put spacers back in their place. Everything will work fine without them. Now I gear to race in third, which both gear’s in most trannies especially a 5 speed will count 25 teeth each. If you forget which gear matches what, no worries the two from each shaft will always add up to 50 teeth. Now I add a touch of the bearing grease on the ends of the shafts before I put the brass bushings on. This gives a little lube before the oil gets to them. Once everything is assembled and before you put the top case on put some perma-gasket of your choice on the bottom case to seal the top to it. I also lift each shaft and put a little under each bushing and then a film on top of each, only if it’s an open case type end though, this is one less place the oil can leak out. While that’s setting up add app. 8 ounces of gear lube, type and weight is your choice, I use 80/90 Wal-Mart brand. If you have no way of measuring the amount of oil, with the case level, simply add enough oil to cover the input gear. Now I use all 6-mount holes to bolt it down and the whole I cut for the input shaft is a very snug fit. I only use 1/4-inch thick plate for a tranny plate. Now for the do it yourselfer E.C. Distributing has a cnc precision cut trans plate that will fit most anyone’s application in building their race mower. They sell for 55.00. They also have an idler sprocket bracket assy. Bolts to the bottom of the trans plate and can bolt a idler of your choice to it. They have two plates specific dimensions are 10.5 wx8 and 13wx8. The first being designed to be an exact fit for a Murray wide body and the second being a direct fit for the box frame MTD chassis. Both are universal and usable in many chassis setups. They come with a bushing that once you bolt the tranny in place it slides over the input shaft centering itself on it and supports it all the way to the base of case. You weld it in place and end result you have one heck of a tranny plate. That pretty much sums what I do to them simple, cost efficient except the two gears that you replace, and works very well. I don't hot rod my mowers nor run them on pavement very much. And if the motor is running, and I am not moving, the clutch is in. Look at it this way its less wear and tear on the tranny pulleys and belts, basically the whole drive train. Now below is all the part numbers for everything I use in or on the tranny from Tecumseh.
700 series parts and no.
7 tooth sprocket      786077
8 tooth sprocket      786047
10 tooth sprocket    786076
12 tooth sprocket    786095
15 tooth sprocket    786111
Steel bevel gear       778154
Steel input gear      778153
Shifter key            792089A
Flanged Bushing    780105A
Input oil seal               788083
Input Needle Bearings 780086A
Input Shaft   776135

These are all Tecumseh part no. There is an after market oil seal also it is a Federal Mogul no. 340387 you can obtain at most car parts stores i.e. Napa etc and CR number is 6106
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George Herrin #6
Indian Power.. You gotta Go big to beat em or Go HOME
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« Reply #1 on: November 27, 2005, 10:09:26 AM »

Excellent post on the 700 buildup...especialy having the part numbers all in one spot.. Cool

Question do you do anything to the "top" half of the case, like run a strap over the top mounting lugs and down to plate to help stabilize the aluminum case...

Or is there no worries in the upper case flexing or lifting if the lower is securely mounted...?
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Randy Stys
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« Reply #2 on: November 27, 2005, 10:13:41 AM »

I can see "sandwiching" the trans for stability (over top and down to plate), but I have seen guys bolting the top of trans to "tunnel" or seat mount with no direct connection to lower plate...

Seems like with frame/body "twist" this would cause more movement and binding than it prevents...???
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Randy Stys
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« Reply #2 on: November 27, 2005, 10:13:41 AM »

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George Herrin
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« Reply #3 on: November 27, 2005, 10:36:18 AM »

The very first bp build I did I did that. Was a terrible pain if you ever had to work on it or service it. So the next and every other since then including my two time championship bp's I have not done this. If the threads in the bottom case are good and you remove the reverse chain and sprockets this will not happen. The only time I have ever seen the top case damaged was when a chain broke wrapped itelf around the sporckets imploding it from the inside out. Another time 5th gear broke and broke out the case halves in the gear area. Both times though it never pulled the case screws out. AND if you use an E.C. Distributing tranny plate with the lower input case support you will have nothing at all to worry about.
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George Herrin #6
Indian Power.. You gotta Go big to beat em or Go HOME
8 time ARMA National Champion
4 time USLMRA National Champion
Retired from BP
www.herrinmowersports.yolasite.com
www.allamericanmowerchampionships.yolasite.com
My other racer is a 1/5th scale Dirt Late Model!!!!
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« Reply #4 on: January 02, 2006, 06:45:00 PM »

hey guys
was runnin my mower and toasted the shift keys   does anyone know where to get them cheaper than 10 bucks a piece
just wonderin
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Brian Singsime
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« Reply #5 on: January 02, 2006, 07:24:47 PM »

Best I've found was $7.95 if you buy 20 at a crack...

Talk to Eric H. he goes thru a ton and asked me to find a bulk rate...

If he's ready to order maybe you/we could split a pack...

I only need a pair for "spares"...
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Randy Stys
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« Reply #6 on: January 02, 2006, 10:30:42 PM »

George I was wondering from your write up at the top I understand that you dont shift when you race. do you just change pulleys for different tracks to get the gear that you want. That is what I do and it is a lot easier on the drive I feel. You got to bring it home or you cant be first.
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David Peters
George Herrin
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« Reply #7 on: January 02, 2006, 11:06:34 PM »

Nope I don't shift and I don't change pullies. I run a 8 on motor a 5 on tranny, and 12 on tranny to a 44 to 48 on axle. If and I say If I need to make a change I do it on the axle sprocket. Nine times outa 10 though I never do that. The setup I have is generally so close at any given track I go to I do not worry about changing the sprocket. Keep in mind this is on my BP. But the same went for the SP also. I have never had but 1 tranny caused DNF in 6 years. only 2 chain dnf. The rest were belts.
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George Herrin #6
Indian Power.. You gotta Go big to beat em or Go HOME
8 time ARMA National Champion
4 time USLMRA National Champion
Retired from BP
www.herrinmowersports.yolasite.com
www.allamericanmowerchampionships.yolasite.com
My other racer is a 1/5th scale Dirt Late Model!!!!
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« Reply #8 on: January 16, 2006, 08:38:01 PM »

hey george does peerless make any sprockets bigger that a 15 tooth??
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Brian Singsime
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George Herrin
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« Reply #9 on: January 16, 2006, 08:44:29 PM »

No but if you have an aps catolog go to page 206 look at the bottom left there are sprockets with 3 bolt holes. They go from 17 tooth to 27th they are aluminum. You can use an azuza steering wheel hub bolt the sprocket to it and it fits the splines of the tranny.
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George Herrin #6
Indian Power.. You gotta Go big to beat em or Go HOME
8 time ARMA National Champion
4 time USLMRA National Champion
Retired from BP
www.herrinmowersports.yolasite.com
www.allamericanmowerchampionships.yolasite.com
My other racer is a 1/5th scale Dirt Late Model!!!!
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« Reply #10 on: January 16, 2006, 09:44:51 PM »

THANKS GEORGE
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Brian Singsime
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« Reply #11 on: January 28, 2006, 12:18:07 PM »

Which I could figure out how to delete this message!!!!  I done figured it out.

Dale, in Michigan
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« Reply #12 on: January 28, 2006, 01:26:17 PM »

So I see one output is for the brake, the other for the drive sprocket.  According to the manual, makes no difference which one is which.

NOW!  These transmissions are real simple on the inside, but the grease, oh the grease!!!  Previously everything I've had apart used gearoil.  It was amazing!   LOL

The specific question I now have relates to the 700-078 transmission.  Not my first, or even second choice, but out of stock and back orders can do that to a guy.

According to the schematic, the large bevel gear is number 778154.  The gear commonly known as a steel gear, though it's not listed as such on this particular schematic.

The input pinion gear is part number 778176 and is listed as steel, though it's not the common number used of 778153.   For insurance, I ordered the 778153 to make sure I had the steel gear.  Only it's at least 50% taller than the 778176 stock gear.  Unless there is some compression trick I don't know, it isn't a gonna fit!

WHAT do I have????   Should I just remove the chain and sprockets, ALL that grease, switch to a seal on the input shaft, put oil in and run  it?  Right now, I don't  see any other way.

Just for kicks, it does have 4 shift keys!  Some parts of this little gem appear to be pretty tough.

Dale, still transimission prepping in Michigan
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« Reply #13 on: January 30, 2006, 07:48:41 PM »

does anyone know what the part number for the long input shaft fot the 700 is
wantin to build a spare but havent seen the long shaft
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Brian Singsime
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George Herrin
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« Reply #14 on: January 30, 2006, 11:19:31 PM »

Dale the original input gear will have 2 thrust washers and a bearing under it. remove one washer and the bearing and it will fit. All have a 42 tooth bevel gear whether steel or stamped. The pinions are 14 tooth with some models having the shorter with washers and bearing. I do not run that and have never had a problem. Now as for the reverse gears and chain, toss them out. remove ALL grease add oil seal and 8 onces of oil and go racing. So schematics will list the input as steel and not the bevel as steel. If one is steel they both are. SO the original parts will work just fine or do as I listed above and the new input will work also.
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George Herrin #6
Indian Power.. You gotta Go big to beat em or Go HOME
8 time ARMA National Champion
4 time USLMRA National Champion
Retired from BP
www.herrinmowersports.yolasite.com
www.allamericanmowerchampionships.yolasite.com
My other racer is a 1/5th scale Dirt Late Model!!!!
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