ok guys, I went and test drove a new to me dump truck. I wasn't able to get the results I wanted out of a 2 spd rear end. usually I rung gears 1 through 5 then drop into neutral up shift rear end then back into high. this may not be the proper method but served me well on all the old ford trucks I drove. they were gas burners if that makes a difference. The truck i just test drove was a 3126 cat with a 5 spd and 2 spd rear in a gmc, can anyone tell me the correct sequence to shift up and down as I don't know what I am doing right and wrong
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2 spd rear end
- Thread starter wrc
- Start date
Wes J
Senior Member
Most of the ones I have seen worked fine like you described. Or, you can start in low and go to high before shifting to second gear. The Cat may have enough torque to just forget the 2 speed.
Most of them are electronically shifted or work on vacuum (gas only) and they don't work very well. Maybe the shifter is goofed up.
Most of them are electronically shifted or work on vacuum (gas only) and they don't work very well. Maybe the shifter is goofed up.
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4H may be "higher" than 5L, in which case if you need the ratio you'd shift from 4L-5L-4H-5H. It's been a little while, but most of the rear end shifts don't need neutral or clutch, do they. Pull the switch up, let off the pedal and get back on the pedal just before it catches.
Agreed, I never clutch for a rear end shift, unless I have lugged the engine too low and need to break torque to allow the shift, but I try not to wait that long.
Well, for that matter, I never clutch to shift the main either. In my opinion, a clutch is something to use to get moving, then leave alone. I find it lasts longer that way.
Well, for that matter, I never clutch to shift the main either. In my opinion, a clutch is something to use to get moving, then leave alone. I find it lasts longer that way.
there should be a shift pattern over the visor or in the manual!! but Delmer is right on his shift pattern on the GMCs
Shimmy1
Senior Member
Most 5-speeds that are paired with a 2-speed rear are synchronized transmissions, and require the clutch to shift properly. That being said, you don't generally need the clutch to shift the 2-speed, but it tends to take the "clunk" out of it.
Shimmy1
Senior Member
My guess is by taking it out of gear to shift the 2-speed, you are not allowing the driveline to "break torque" to allow the shifting mechanism to move from low to high. Try it again, leave it in gear, clutch engaged, and just let off the accelerator pedal when you shift to high. If it still doesn't shift, there might be other issues.
It sounds like you're used to driving a ten speed, the five speed with two speed rear you need to split gears. I generally start in second low if it isn't a heavy load, upshift the rear, then you take third and downshift the rear at the same time. Rinse, repeat. Down shifting is the reverse, you drop the rear from high to low, then when you drop a gear in the main box you flip the switch back to high. You're basically taking a half gear at a time, up or down.
When upshifting the rear end don't take the tranny out of gear, flip the switch and then either depress the clutch slightly or just slowly let up on the gas, it will pop right in. If you take the tranny out of gear while the rear is trying to shift, the driveline is adrift without a paddle and neither end will synchronize.
When upshifting the rear end don't take the tranny out of gear, flip the switch and then either depress the clutch slightly or just slowly let up on the gas, it will pop right in. If you take the tranny out of gear while the rear is trying to shift, the driveline is adrift without a paddle and neither end will synchronize.
RonG
Charter Member
The rearend should be half a gear which works good for splitting your shifts,going from third high to fourth low for example should give you half a gear based on a full gear in the transmission.Many trucks when shifted from fourth to fifth are only half a gear anyway,yours may differ so you will have nine ratios total by using the two speed to split them shifting up starting in first.You are right,the electric two speed works better than the vacuum activated two speed.I have not seen the vacuum two speed for years.The vacuum two speed will pop out of gear on a long pull.Ron G
What made alot of vacuum 2 speeds jump out was they wasnt given time to full go in were they would stay then half way in the vacuum was holding then get on a pull engine vacuum droped bam rearend jumps out of gear. I always use the clutch on a hard pull when shifting the 2speed it takes the presser off and allows it to fully ingauge. The best thing about 2 speeds were the money i made parting trucks out years ago. I think most 5 speeds in trucks with 2speeds have a short 4.
capt_met
Well-Known Member
My truck is 5speed with 2 sped axle. there is a shift pattern sticker that says to always be in high when changing transmission gears. after switching gears then change to low range. would it damage the truck to go through the gears in low then upshift to high when it gets moving?
I think they don't want you shifting both at once, as lantraxco explained in #8 above. You're in 3H, leave it in high, shift to 4 then use 4 to speed up the driveshaft to catch low, rather than rev up 3 to try to catch low, then slow down enough to catch 4, or be stuck without a paddle, so to speak. I'd have to think about downshifting, I can't remember how that works... I think you do want to shift to high before downshifting the transmission, so you don't have to rev as high to catch the lower gear, or can you shift the axle in neutral going down?
No problem that I can see shifting through the gears in low, then changing to high only in the top gear.
No problem that I can see shifting through the gears in low, then changing to high only in the top gear.
Wes J
Senior Member
Most of these combinations have the same problem as the old duplex, triplex, quadraplex, etc two stick transmissions. There might be as many as 20 combinations of gears, but many of the combinations would have almost exactly the same ratio. So, 3 on the main and 2 on the aux, would be the same ratio as 4 on the main and 1 on the aux. They didn't really fix this problem until the SST transmissions where everything was in one unit.
This is what the "short 4th" refers to. The spread from 4 to 5 is the same as the 2 speed in the rear, so 4-hi is the same as 5-low.
This is what the "short 4th" refers to. The spread from 4 to 5 is the same as the 2 speed in the rear, so 4-hi is the same as 5-low.
Truck Shop
Senior Member
Gear overlaps. / Think about driving a super ten- that's all a 5 and 2sp is really. That's if you have driven a stuper ten.
Truck Shop
Truck Shop
RZucker
Senior Member
I had a C-65 chevy that you hit 4 lo then 5 lo, then 4 hi, then 5 hi. Confused the heck out a lot of guys.
Comparing a 5and 2 to a super ten is like comparing a laser cutter to a chainsaw. They both do the same job but one takes some skil to master.
Wes J
Senior Member
Wait, which one is which? I'd think a laser cutter would take a lot of skill to master.
Off topic, but I worked on an old International twin screw truck once that had 2 2 speed axles. You can guess how well that worked. One shifted into high and the other didn't and the difference in ratios burned up the power divider.
Shimmy1
Senior Member
Those were labeled as 3-speed rear ends. When both were in low, you were in low. When both were in high, you were in high. When the rear was in high, and front in low, that was called intermediate. Yes, they were hard on power-dividers. Only use intermediate for short periods of time.
Birken Vogt
Charter Member
More commonly they just both shifted at the same time (or were supposed to)
The 3 speed deal was an International thing I think.
Truck Shop
Senior Member
Well I don't know about Skill I guess. I do know the first 5 and 2sp I drove was when I was nine on the farm, 51 years ago.
Then a super ten in the early 90's. You make the same moves and splits with either trans. But really there both chainsaws IMO. But I do like driving a 9 and 4.
Truck Shop