The Stovebolt Site Forums The Parking Lot Big Bolts T.'F. 2-Speed Re-Build Tips/Tricks-"THE DIAPHRAGM"

Hello,Everyone! These tips may come in handy,for some of you guys,trying to figure out how to get your 2-speed up-and-running. Maybe helpful,if swapping a 2-speed rear,for a single-speed,as well! I bought the T.F. '55 Chevy Shop Manual,just for that purpose,but NOTHING is covered in the manual,except for the rear-ends,themselves! This should be in the "Tech Tip" section,but I wasn't able to access it,so here goes... When I bought my truck,the components were dis-assembled. No flex hoses to the diaphragm,and steel lines were clogged with mud dauber stuff. P.O. drilled a hole in the top of the "Pancake",and used a coat hanger to switch the 2-speed!DANGER!! If you're not parked on level ground,and the axle doesn't shift,it's in neutral,and you're under a 10,000-pound RUN-AWAY truck! If your truck is un-fortunate enough to be set-up like this,PLEASE Chock the wheels! Setting the E-Brake,isn't going to help,if the rear-end is in "NEUTRAL"!! O.K. The first thing I did,was remove the 3, 9/16th bolts that attach the "pancake" to the axle. (I didn't have the flex-hoses,but I would've dis-connected them first.) I put the unit in a vise,sandwiched between a couple of chunks of wood, to protect the housing. I removed the screws,that attach the 2 halves of the "pancake". I didn't have any of the diaphragm material left,(as a pattern),so I went to a truck-tire shop. I was Gladly given a couple of "flaps",since they're a couple of plies thicker than the tubes. First,I sandwiched the "flap,(cut over-size),between the 2 halves. Using an awl,I punched holes at 12:00,3:00, 6:00,and 9:00. I then tightened the screws,which will leave an indentation,around the circumference. Remove the screws,and find the "Center" of the diaphragm. Cut a SMALL X,(SMALLER THAN THE DIAMETER OF THE SHIFT ROD),and push the shift-rod through,until it "seats". Make sure that you have washers sandwiching the rubber. Tighten the "rod nut" securely.(I put a drop of "loctite", on mine. I used neoprene,to seal the diaphragm to the rod,and all mating surfaces of the "pancake" circumference. Align the holes already punched,and finger-tighten the screws. Punch-out the remaining holes,then make sure all the screws are tight. (I did mine like doing a head)12-6-3-9-1-7-etc... Let it cure for a day. Use a vacuum source to check for leaks,(in a bucket of water is helpful), and the movement of the shift rod. Your pancake should be as good as new! Make sure that you use a sealer where the housing joins the axle,or it WILL LEAK!! Stay Tuned!!

This isn't covered in the T.F. '55 truck manual,either. My truck didn't even have one! The 2-speed switch,is mounted to the SM 420 transmission,with a bracket. The switch has five ports. Two vacuum lines,(front of the unit), attach to the engine,one attaches to the speedo. "regulator"(smallest port),then the rear two ports, are plumbed to the rear-end. I bought one from Oregon,and recently re-built it,for fellow "Bolter" IronClad,for "Brutus"' 2-speed swap. I'm shipping it BACK to Oregon! This is a Bendix unit,with 2 rubber "stoppers" that actuate the Hi/Lo function. The unit had the hoses dis-connected for YEARS,by the looks of the mud dauber nests,INSIDE the air-chamber! I soaked it for 4-days,to soften-up the 55- year accumulation of grease and mud,them took a toothbrush,and cotton swabs,to give it a thorough cleaning. The cable was froze,so I used lithium grease,and a couple of vice-grips,to twist the (cable)housing enough to "free" the wire. If you remove the 2 bolts from the bracket,you gain access to the inside of the switch mechanism,to adjust the cable,or periodic maintenance. I'd use "Permatex Form-A-Gasket",to seal the three pieces together,since I'm not sure if the origional gaskets are available. This thing was actually pretty easy to work on. There are two video's of this particular switch,in my "Photobucket" link. 9/27/2013. "Freed Cable". Hope this helps someone.

O.K. So you found yourself a 2-speed rear-end! Did you purchase a "switch"? How about a "Manifold"?? I just added a large "T"-fitting,and plumbed it into my vacuum source,on the intake. Installation can be seen in my "Photobucket" link,on Page 4,titled "Bill Hickey's 1955 Chevy 2nd-Series 6500". No vacuum-lines,since your truck didn't have a 2-speed? A simple and inexpensive alternative to steel lines,is Hi-pressure Agricultural hose,sold by-the-foot,at most any tractor/ag supply store. Not stock,but a lot less labor-intensive,and the fewer the fittings,the likelihood for leaks diminishes. "Try IT,You'll Like IT"! I've had DOZENS of people look my truck over,and Nobody's said anything derogatory about the lines not being stock. They-re well-hidden, and most people don't give the inside of the frame a second look. If you can't locate a switch-cable,a cheap alternative is a choke cable. Available at your F.L.A.P.S. I even found one with a period-correct button,for about $5.00! Nice thing is that you can trim these to the length you desire. (Mine was 5') Have FUN!!

My '54 350 has the 1350 rear with the vacuum 2 speed;it UP shifts GREAT,but I can't make it DOWN shift without stopping and waiting for it to finally catch up. I've thought of re-building the system,but I recently discovered a friend has an old truck (about a '58 GMC 350),not currently running,so I'm going to try to arrange to trade into it and use its 1350 ELECTRIC 2 speed punkin in my '54 and put my vac. 2 speed punkin in the '58. (It's an old County truck with a telephone pole auger on it. I'm thinking to get it operable again,but it'll only need low in the 2 speed.)
Sorry if I highjacked the thread.
Speed

I'm GLAD you did!! More info on the electric 2-speeds is MORE than WELCOME!! Sounds like you may have a small leak,somewhere in your "return" line. With the engine idling,(in Neutral,wheels chocked),spray each fitting with "WD-40".Don't forget the circumference of the "pancake"). Listen for the engine to increase R.P.M.'s slightly. when you hear that,you found your leak. If that doesn't work,you may have to replace your diaphragm. Just follow the instructions. I had FUN doing mine! Hope this helps.

wetwilly,

When was the last time you tried that trick with WD40? The old original WD40 had propane as the propellent which made it a starting fluid and worked as you discribe for checking for vacuum leakes, but they stopped using propane over 10 years ago...now it won't start a lawn mower.

Mike B

Well...to tell you the truth Mike... It's been about that long ago,since I used WD40 for such a purpose,but now that you mention starting fluid...Just Don't Smoke while Troubleshooting!! Please-BE SAFE!!

A simple, effective vacuum leak checker that leaves no mess at all is a Propane torch. Just crack the valve open a little and search for the leak. The engine will rev up or smooth out when the gas gets sucked into the leak and there's no liquid to make a mess like WD 40 or carburetor cleaner leaves behind. I've also used acetylene from the torch to do the same test.
Jerry

Thanks fir the tip,Jerry!