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m211 front-end not pulling in reverse???????
- Thread starter byrd
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The G749 trucks use a sprag-type coupling much the same as the early Reo G742.
The unit is told which direction to turn via a rod from the automatic transmission selector. It may be out of adjustment, stuck, or the sprag itself bad.
dg
The unit is told which direction to turn via a rod from the automatic transmission selector. It may be out of adjustment, stuck, or the sprag itself bad.
dg
rizzo
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In the 5 ton t case there are 2 sprags. One for forward. One for reverse. the trans should tell the t-case which sprag to use.
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This is not the same as the 5-ton or the 2.5 ton Reo.
The 5-ton shifts the transfer with air.
The Reo used both a mechanical linkage for the sprags, or positive lock with an air piston and no sprags.
The GMC does, however, have the sprags in the transfer like all the others.
Rather than a solid poppet rod coming out of the transmission, it uses a smaller connecting rod much like a throttle linkage from the 8-speed automatic selector to bias the sliding clutch in the transfer from fore to aft, selecting which rotation the sprag will engage upon wheel slip.
A simple test is to jack up one side of the front axle and rotate the wheel & tire whilst the transmission is in gear (engine off).
If it will go one way and not the other, things are OK so far. If it turns freely, look to see if the drive shaft is turning...if not, the differental gears or axle shaft is suspect. If the shaft is turning simutaneously, then the problem is in the transfer or the adjustment of the signal rod going into it.
Repeat this proceedure with the trans in reverse. The tire should rotate only in one direction, although the reverse of the last check.
dg
The 5-ton shifts the transfer with air.
The Reo used both a mechanical linkage for the sprags, or positive lock with an air piston and no sprags.
The GMC does, however, have the sprags in the transfer like all the others.
Rather than a solid poppet rod coming out of the transmission, it uses a smaller connecting rod much like a throttle linkage from the 8-speed automatic selector to bias the sliding clutch in the transfer from fore to aft, selecting which rotation the sprag will engage upon wheel slip.
A simple test is to jack up one side of the front axle and rotate the wheel & tire whilst the transmission is in gear (engine off).
If it will go one way and not the other, things are OK so far. If it turns freely, look to see if the drive shaft is turning...if not, the differental gears or axle shaft is suspect. If the shaft is turning simutaneously, then the problem is in the transfer or the adjustment of the signal rod going into it.
Repeat this proceedure with the trans in reverse. The tire should rotate only in one direction, although the reverse of the last check.
dg
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G744 has the test right on, jack it up and turn the wheels. Only difference is that the GMC does not use an over-run clutch (sprag or roller), it has a dog clutch, which almost never gives any trouble (unlike the clutch in the M-35s) other than adjustment. The adjustment is REALLY critical. But once set properly as close to trouble free as it gets.
Thanks, Squirt-Truck for the help I did as G744 said and they turned together(shaft and wheel).Is it hard to get the adjustment correct? The frontend works fine in foward just not in reverse . I would like to get that fixed if someone could share some more knowledge with me. THANKS, Squirt-Truck and G744 for the help so far!
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I will try to detail the test and adjustment (please excuse the errors it has been 20+ years since I did this last...)
Place truck on a reasonably level place, chock rears.
Engine should not be running for this test.
Jack up a front wheel, stay clear just in case there is some wind-up in the driveline.
With transmission selector in forward position (level, hilly, high or low, does not matter) turn front wheel. With transmission in ANY forward position, tire should rotate freely forward but lock going backward.
Repeat with transmission selector in high or low reverse, wheel should rotate backward but lock going forward.
Now the memory part............
Best I recall, the transfer front drive selector is pulled by the shift selector bell crank. It has a clevice and pin end attachment. Rmove the pin, free the jam nut and adjust the rod to a shorter length. (Please not that this may be reversed and need to lengthen...) With the shift rod freed, and the wheel still jacked up, verification of operation of the drive clutch is easy, just move it from front to rear and confirm engagement. (BE SURE APPROPRATE SUPPORT IS UNDER THE FRONT AXLE). Final adjustment is to split the distance the selsctor rod moves from the center position and engages with the selsctor shaft in the transfer. Be sure all shifter pins are in place and not excessively worn.
Good luck, let us know.
Place truck on a reasonably level place, chock rears.
Engine should not be running for this test.
Jack up a front wheel, stay clear just in case there is some wind-up in the driveline.
With transmission selector in forward position (level, hilly, high or low, does not matter) turn front wheel. With transmission in ANY forward position, tire should rotate freely forward but lock going backward.
Repeat with transmission selector in high or low reverse, wheel should rotate backward but lock going forward.
Now the memory part............
Best I recall, the transfer front drive selector is pulled by the shift selector bell crank. It has a clevice and pin end attachment. Rmove the pin, free the jam nut and adjust the rod to a shorter length. (Please not that this may be reversed and need to lengthen...) With the shift rod freed, and the wheel still jacked up, verification of operation of the drive clutch is easy, just move it from front to rear and confirm engagement. (BE SURE APPROPRATE SUPPORT IS UNDER THE FRONT AXLE). Final adjustment is to split the distance the selsctor rod moves from the center position and engages with the selsctor shaft in the transfer. Be sure all shifter pins are in place and not excessively worn.
Good luck, let us know.
John.Westlock
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I have had the same problem with my 54 XM215. Another problem is that I had to warm it up and go backwards and forwards to get it to go into low. It also comes out of low some times. I know I should fix it but haven't figured out what it is exactly and how to fix it. There is linkage from the transmission to the carburetor. As I changed the head gasket I think the linkage rod might have been tweaked just enough to mess up the adjustment- readjusting this might fix it. Any ideas? Thanks.
rizzo
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what was it? the linkage?