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Author Topic: How To Race-Prep A 700 Series Transmission  (Read 7302 times)
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Chris
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« on: March 26, 2007, 07:58:47 AM »

PLEASE keep in mind that you MUST retain your reverse gears & chain for off-road use! Racers do NOT need the reverse chain & gears because they don't have a need to go backwards, we as off-roaders NEED reverse. Please keep this in mind when following these procedures!



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
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« Reply #1 on: January 14, 2008, 08:22:20 AM »

Here's a writeup with pictures from TOM FOX:

http://www.heymow.com/index.php?topic=5644.msg62944#msg62944

Due to size...this topic is being split up...it will follow step-by step...but give me a few moments to post all sections of the build-Thanks!



I just race-prepped my 700 series tranny and documented STEP-BY-STEP what was done.

First and foremost…..I would have not attempted this without the help here at HEYMOW!!! The advice given here is priceless and just want to do my part and give some back to you guys!

This is pretty much the same as George’s RACE PREP procedure..except with some pictures and a few of my own additions.

For part numbers and other specifics…please read Georges post http://www.heymow.com/index.php?topic=192.0


First thing that was done was the tranny was taken completely apart. The only items left in the case was the input needle bearings.

The case halves, gears, shafts, keys…ect were complete cleaned and given a very close inspection for wear and any cracks.




The four shaft bushings WERE NOT cleaned in a solvent. They were just wiped off  and checked for wear. They were just fine and will be reused.

Reverse gears/chain went in the scrap pile…will not be used in a race tranny.

I installed 4 long bolts into the lower case to act as a stand while putting tranny together.









Once all your parts heve been inspected and/or replaced…it is time to start the assembly:

First thing I do is to get the needle bearing on the input snout repacked with grease.

This is done by pushing some good quality automotive grease into the input snout.
You then take the input shaft in one hand and with your other hand/finger cover the opposite end. SLOWLY push the input shaft into the snout.









This shaft acts as a plunger and forces the grease around the needle bearings.

Once you feel that there was sufficient penetration of grease into the bearings, you can now remove the shaft and wipe away the excess grease that came out of the snout.


Posted on: January 14, 2008, 10:12:26 AM
From the factory, there was a O-RING on the bottom of the snout and the top as well. These will NOT be installed.

A SEAL will be installed on the bottom of the snout.



I  placed the seal on the snout in the proper orientation. Squared it up and SEATED it with a proper size pusher (socket) and lightly tapped it into place.





I installed the retaining clip onto the input shaft “PULLY” side as well as a washer. I now inserted the input shaft into the snout from the BOTTOM . By placing the input shaft in from the bottom, you will not “ROLL” the lip of the seal and cause a leak.


Now with the input shaft pushed all the way up into the case…the next thing to do is install the needle bearing that goes under the pinion gear. REMEMBER….DO NOT install a O-RING….The gear oil will not be able to lubricate the input bearings if the O-RING is installed.








Now install the pinion gear and clip….I now “FEEL” the end play of the input shaft assembly…If it feels loose, you can add another shim to tighten it up….if it feels to tight..you can remove the top washer right below the pinion.




That takes care of your INPUT.
Posted on: January 14, 2008, 10:12:45 AM
Now onto the gears!!!

MAKE SURE you inspect the keys for wear!! Look on the sides and top corners…if they show wear..REPLACE!!!!




Now Check the shift gears….look for nice and square corners,,,if rounded or chipped…replace



Now inspect the output shaft splines…if these are worn or damaged don’t even bother using it…get another one!!!



Now remember…EC sells sprocket adapters for both the FINE and COURSE type shafts.

The 2 sides of the shifting
gears are different. One side is flat and the
other side is cut out. The flat side of the gear
is placed onto the shaft towards the shoulder
of the shaft or towards the shifting keys.



Shoulder



The newer style SHIFTING WASHERS hade a raised radius ring..this raised ring goes toward the shoulder of the shaft.





I then install the shifting collar with the keys. The collar has a wide side and a narrow side



The wide side faces the shoulder on the shaft.

I take the keys and hold them in place with my fat thumb.




I then just slip it onto the shaft, and slide it down a bit so it self retains itself as an assembly.





Posted on: January 14, 2008, 10:13:11 AM
Now we can start installing the shift gears onto the shaft.

First you install a shifting washer onto the shaft raised ring toward Shoulder on shaft….then install FIRSTGEAR with FLAT SIDE towards the shoulder



Now install another shift washer and SECOND gear







Another washer and THIRD GEAR







Another washer and FOURTH gear







One more of the raised washers and FIFTH gear







Now…you should have no more of those raised washers left…but you will have another washer that looks like this:



This washer has a lip on it that goes toward the shoulder of the shaft.



You now will have a completed output shaft assembly


Posted on: January 14, 2008, 10:13:33 AM
Now we can assemble the COUNTER SHAFT

Install bevel spur gear and smallest (first gear counter) to largest (fifth gear counter) gears to the splined end of the counter shaft.















We can now install the shaft support bearings onto the COUNTER SHAFT. First put some grease onto each end of the shaft. Now install the bearings.

 









Now place this assembly into the lower case.
Posted on: January 14, 2008, 10:14:33 AM


Now do the same for the output shifting shaft










Now make sure that the shift keys are not locked into any of the gears. If it is just pull back on the collar to disengage keys from gears. This is now in Neutral.



I now apply a little grease into the shifter pocket in the lower case



I now take the shifter rod assembly and place the pins into the grove on the shifting collar.



Now take the entire assembly and place into the lower case making sure that the shifter rod seats into its pocket.



Make sure that all 4 shaft bearings are KEYED into the case


Posted on: January 14, 2008, 10:14:49 AM
You can now use your gasket sealer/maker to coat the outside perimeter of the 4 bearings.



Make sure that when you place the shafts back down that the bearings are seated and keyed into location.

You can now make a bead of sealant around the case edge.



Now you can add your choice of gear lube into the lower case. Add enough to cover the top of the input pinion gear.



I then rotated the input shaft by hand to make the gears rotate and check for good lube coverage.




Before putting the top case cover on..I put a little grease onto the shoulder of the shifter rod to help lubricate it in the case.



The top half of the case can now be installed and secured with the 6 mounting bolts.



Now we need to install the shifter detent ball. I put some grease on the ball and insert it into it’s location





install the spring and set screw next.





I tighten up the set screw to about 2 threads into the case. This can be adjusted to personal feel of how the shifter feels


Posted on: January 14, 2008, 10:15:24 AM
Now we need to vent the case…..

The location of the neutral switch is a ideal location. I



I used a ¼ NPT brass fitting.




Now you need to shorten the threads on these fittings or they will hit the shifter fan and you won’t be changing gears!!



I took off about 3 threads..this gives me just enough clearance from the shifter fan.


I also installed a O-RING and a little RTV onto the threads before installing into case.

105 106 107








On the shifter shaft that protrudes thru the case, I also install a O-RING onto the SHOULDER part  of the shaft.




Here is the final product ready for install!!!!


Posted on: January 14, 2008, 10:15:41 AM
Only thing I see worng.... is there should be a thrust washer installed first before the brass bushing. NOW this does not apply where the cupped washer is installed at the end of the gears on the shift shaft.... Was there none there there or you forget or am I not seeing them. (3 altogether)



On this tranny 079...there were none when I opened up the case. By checking the SIDE-TO-SIDE movement of the shafts...There is around .010 movement...If I was to install washers there....It would be quite tight.....I'm sure I can order up some ultra thin ones to install to save on the wear that can happen to the bushings.



Very odd looking at the parts break down of the 079 it shows them 3 of them plus the two under the input pinion and the one on the output shaft covering the all the same washer same thickness and same pt# 780072. Never seen a 700 without them SOME don't use the cupped washer and use one there also but not all.



I too noticed on the parts sheet that they have washers there....And I'm 100% sure when I took it apart there were none there ( I carefully took the trany apart noticing each and every component--for it was my first teardown on one of these) I have other washers from trannies I took apart...I could always try them in there......Now I am using a counter and output shaft from a 002 transmission...not saying it makes a difference but just FYI.



The 700-002 and 002a uses them also. I would try to fit them in it doesn't take much for the gears to try and overlap on the edges and catastofic failure happens. Better to test fit em now than find you got a problem the hard way. Like I said I have never seen of even assembled one that doesn't use em.



WILL DO!!!

-------Just did.....Will update images later...But three washers have now been installed BEHIND the two brass bushings on the counter shaft and behind the brass bushing on the output shaft BRAKE side.

Thank you George!!!





Here are some updated pictures of the thrust washers installed onto the shafts.










Thanks again to George for pointing this out.

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