Mack 6 Speed

[d8pete]

I have a 1984 R686ST with the 300 and 6 speed 2 stick transmission. I love the truck and use it to haul my antique caterpillars for my hobby. My question is why does the 6 speed have so many repetitive gear ratios? Why were they not set up like the duplex to allow split shifting and have 10 different ratios available? I told a friend once, if I designed a 10 story building but told the owner he could only use 6 floors, I don't think I would be designing buildings for very long. It seems as though the step from 4th to 5th is quite far? I would appreciate any info. thanks.

[randyp]

I have a 1984 R686ST with the 300 and 6 speed 2 stick transmission. I love the truck and use it to haul my antique caterpillars for my hobby. My question is why does the 6 speed have so many repetitive gear ratios? Why were they not set up like the duplex to allow split shifting and have 10 different ratios available? I told a friend once, if I designed a 10 story building but told the owner he could only use 6 floors, I don't think I would be designing buildings for very long. It seems as though the step from 4th to 5th is quite far? I would appreciate any info. thanks.

I have a 61 with a duplex and most of the time i just drive it like a 6 speed cause its too much shifting and hard work scratching to try to do a lot of splitting. I have driven triplex and quads and i think the duplex is by far the hardest one to use. I didnt really think the six speed had a lot of repetitive ratios though,,,my opinion anyway,,,randy

[daveigou]

The 285 & 300 hp Maxidyne engine with 6 speed transmission is probably one of the most sucessful power combinations for any truck manufacturer ever. If used as intended, there are no duplicated ratios, in that low range on the compound section is intended to use only with first gear on the main. It was never intended to be driven as a splitter type transmission. The other big advantage is to have multiple progressively shiftable reverse ratios.

I believe there may have been other rare variations, maybe someboidy else can jump in here, I think there was a very rare overdrive 2 stick six speed with direct and overdrive only (no reverse) on the compound section. But I think those were only built for a short time, probably mid 60's to mid 70's, and were no longer available long before your truck was built.

Dave

[HK Trucking]

The 285 & 300 hp Maxidyne engine with 6 speed transmission is probably one of the most sucessful power combinations for any truck manufacturer ever. If used as intended, there are no duplicated ratios, in that low range on the compound section is intended to use only with first gear on the main. It was never intended to be driven as a splitter type transmission. The other big advantage is to have multiple progressively shiftable reverse ratios.

Yes, although the TRXL1071 6 speed did have a couple "splittable" ratios (not recommended by Mack) such as shifting from 2nd lo to 1st direct with 2 hands.

I believe there may have been other rare variations, maybe someboidy else can jump in here, I think there was a very rare overdrive 2 stick six speed with direct and overdrive only (no reverse) on the compound section. But I think those were only built for a short time, probably mid 60's to mid 70's, and were no longer available long before your truck was built.

Dave

That was the TRDXL 1070.

.

[randyp]

I have a 1984 R686ST with the 300 and 6 speed 2 stick transmission. I love the truck and use it to haul my antique caterpillars for my hobby. My question is why does the 6 speed have so many repetitive gear ratios? Why were they not set up like the duplex to allow split shifting and have 10 different ratios available? I told a friend once, if I designed a 10 story building but told the owner he could only use 6 floors, I don't think I would be designing buildings for very long. It seems as though the step from 4th to 5th is quite far? I would appreciate any info. thanks.

on my duplex, most of the time, i shift 1 thru 5 low, hood sets up a good vibration, air starts to get thin, afterburner temp starts wasrming up, lots of cars are lined up behind me, waiting on me to face that ole demon, they must be excited cause they honk and yell a lot and give me the number one sign, I ease my goggles down, reach over and slip box into 5 high (with trembling sweaty hand) take the collar off that 673 and let her graze. WHEw,,,according to my fancy dancy GPS i have just achieved maximum velocity of 58.241 MPH again! Man, what a ride! I love beating that ole demon

[randyp]

I have a 1984 R686ST with the 300 and 6 speed 2 stick transmission. I love the truck and use it to haul my antique caterpillars for my hobby. My question is why does the 6 speed have so many repetitive gear ratios? Why were they not set up like the duplex to allow split shifting and have 10 different ratios available? I told a friend once, if I designed a 10 story building but told the owner he could only use 6 floors, I don't think I would be designing buildings for very long. It seems as though the step from 4th to 5th is quite far? I would appreciate any info. thanks.

d8 pete, what kinda antique cats you got? I would like to see some of them on here. Im kind of an antique cat operator myself. couple of years ago, Holt cat held a 100 year celebration at their store in longview, fed everybody catfish, gave away prizes and all. I had a good time, they had several antique cats there. I told them to be sure and invite me to their next 100 bash, somebody may have to chew my catfish for me then though.

[d8pete]

Thanks guys for the replies - I am only a novice truck driver at best and do it only for my hobby which might explain part of my situation. However looking in the Mack manuals for the trxl 107 mack states that the use of low range in 2,3,4,5 is not recommended as the ratio of 3rd in high is the same as 4th in low, 4th in high is the same as 5th in low,and the same for the lower gears. I love having 5 reverse speeds but when accelerating heavy or climbing a gradual grade the step from 4th to 5th is a little long and with no Jake trying to downshift to hold yourself while going down a long grade is difficult. Randy I will try and post some pictures of my truck and trailer with the Cats. Caterpillar wise I have a 10,22,30,40,60 D2,D6,RD-6,and RD-7. Like I'm sure you've heard before I'm one of the guys that likes to play with Cats and Dogs.

Pete

[HK Trucking]

Thanks guys for the replies - I am only a novice truck driver at best and do it only for my hobby which might explain part of my situation. However looking in the Mack manuals for the trxl 107 mack states that the use of low range in 2,3,4,5 is not recommended as the ratio of 3rd in high is the same as 4th in low, 4th in high is the same as 5th in low,and the same for the lower gears. I love having 5 reverse speeds but when accelerating heavy or climbing a gradual grade the step from 4th to 5th is a little long and with no Jake trying to downshift to hold yourself while going down a long grade is difficult. Randy I will try and post some pictures of my truck and trailer with the Cats. Caterpillar wise I have a 10,22,30,40,60 D2,D6,RD-6,and RD-7. Like I'm sure you've heard before I'm one of the guys that likes to play with Cats and Dogs.

Pete

Keep in mind that the operating range of your engine is 1200 to 2100 RPM.

As long as your RPM's are in that range, it's all good, hence the wide spacing between the gears RPM wise.

.

[Chuck C]

Pete, did you here that Alan Smith passed away yesterday.

Chuck Czaplewski

[d8pete]

HK - Yes I do stay in my operating range and maybe go down to 1000 rpm. At about 2000 rpm in 4th high my truck is going about 38mph or so the speedometer tells me. 5th high takes me from about the 38mph to 72mph at 2050rpm. When downshifting from 5th high to 4th high I have to get the truck down to 35-39mph with the brakes and no Jake and once I'm in 4th the motor is already on the top of the rpm range and provides little braking action to hold back the truck and trailer, so once again the brakes do all the work. Thats why if there was a split or another gear between 4th and 5th it might be easier. Just my two cents.

Hi Chuck - yes Jeff Moyle told me about Al Smith's passing. I saw him at Bowling Green and he looked pretty good. Very sad, the Mack and Cat guys lost another great supporter and great friend.

Pete

[Lmackattack]

Pete

sound like you have some fast rear ends. Most Macks with a 6 spped had 4.17 for on/offroad and 3.87 for highway. sounds like you have something around 3.87s? the only down side with the 6 speed was shifting the higher gears in the hills. Great all around trans untill you want to keep your road speed up pulling a good hill. 1000 rpm is fine as long as the truck can still accel. most other engine MFG cant touch 1200 rpm and pull a grade. this is why old macks were always good in the low speed offroad market. Many times if im in the thick mud I will put the aux box in low. then shift the main 1-2-3 untill I have the road speed up. at that point I then shift the aux back into direct(leave the main alone)accel through direct 3rd. then make the last 2 shifts in direct 4-5 gives you a total of 6 forward speeds.

[d8pete]

LMACK - How do I tell what rearends I have, is there a marking on the castings somewhere? Like I said before, I love the truck but I just don't think this truck was set up for heavy loads and hills both. 54,000 lbs with moderate grades and I'm fine.

[fjh]

LMACK - How do I tell what rearends I have, is there a marking on the castings somewhere? Like I said before, I love the truck but I just don't think this truck was set up for heavy loads and hills both. 54,000 lbs with moderate grades and I'm fine.

Look on the front of the diff just off to the lower passanger side of the input housing there is a flat spot top right hand corner you'll find the ratio.

Your looking for nos like 3.87 / 4.17 / 4.42 / 4.64

[Lmackattack]

Look on the front of the diff just off to the lower passanger side of the input housing there is a flat spot top right hand corner you'll find the ratio.

Your looking for nos like 3.87 / 4.17 / 4.42 / 4.64

Ya and bring a small paint scrapper and wire brush so you can see the stamped numbers on it!!

[d8pete]

fjh and LMACK - I looked last night and the truck has 3.87. Where do I look to find the weight rating of the rearends while we are on the rearend topic? Thanks.

Pete

[daveigou]

Looking from the back of the truck, look at the rear rear, just to the right of the check plug, you should find numbers like "SS38C", the "38" would be 38,000# cap.

Dave

[maxidyne237]

hey HK what are the most forward gears you can shift from a stop with a two stick six speed. never tried the 2nd low to 1st high but i will tomorrow. thanks

[Rob]

hey HK what are the most forward gears you can shift from a stop with a two stick six speed. never tried the 2nd low to 1st high but i will tomorrow. thanks

Be easy on it. Parts are expensive and no sense trashing something that is good.

That is a good transmission not designed to perform as you propose, although I've seen several do it.

Rob

[Lmackattack]

you only get 6 forward speeds total.

mack says to shift like this

"low" 1st- shift to direct 1-2-3-4-5 = 6 gears total

some like me do this

"low" 1-2-3- shift to Direct 3-4-5 = 6 gears total

over view

1st low is the lowest ger you have

2nd low is basicly the same as 1st direct

3rd low is basicly the same as 2nd direct

4th low is basicly the same as 3rd direct

5th low is basicly the same as 4th direct

5th direct is your highest gear

this is why you cant really split the gears, evertime you use the aux box it is nothing more than a dowshift or up shift you dont get the 1/2 RPM splits like the old B models transmissions did.

s HK said there were a few overlaping ratis but they were so close that they did nothing more than keep your hands busy or let you show off a little. HK should we let him know about geting the truck into gear without the clutch? or how about forward to reverse without the clutch LOL!!!

hope you can follow that some?

[maxidyne237]

" HK said there were a few overlaping ratis but they were so close that they did nothing more than keep your hands busy or let you show off a little. HK should we let him know about geting the truck into gear without the clutch? or how about forward to reverse without the clutch LOL!!! "Lmackattack

Let me know if you need any info on replacing driveshafts, replacing powerdividers, bull gears, side gears, or throughshafts next time you try that. Make sure you have your historical licence plates lock tite'ed on when you do.

"Yes, although the TRXL1071 6 speed did have a couple "splittable" ratios (not recommended by Mack) such as shifting from 2nd lo to 1st direct with 2 hands.

"HK Trucking

I was just wondering what gears made forward progress without being exactly the same. If they are close in ratio but still make forward progress in ratio I would like to know. Thanks

[HK Trucking]

" HK said there were a few overlaping ratis but they were so close that they did nothing more than keep your hands busy or let you show off a little. HK should we let him know about geting the truck into gear without the clutch? or how about forward to reverse without the clutch LOL!!! "Lmackattack

That's perfectly achievable, if the truck is rolling forward, you judge the speed and pick the correct gear and slip it in. If the truck is rolling backward, you put the compound in reverse, then you judge the speed and adjust your engine RPM accordingly and slip the main into the appropriate gear.

Let me know if you need any info on replacing driveshafts, replacing powerdividers, bull gears, side gears, or throughshafts next time you try that. Make sure you have your historical licence plates lock tite'ed on when you do.

Actually, that won't be necessary if it's done correctly.

"Yes, although the TRXL1071 6 speed did have a couple "splittable" ratios (not recommended by Mack) such as shifting from 2nd lo to 1st direct with 2 hands.

"HK Trucking

I was just wondering what gears made forward progress without being exactly the same. If they are close in ratio but still make forward progress in ratio I would like to know. Thanks

Actually, I've always had a reputation for shifting smoothly, making a manual trans shift as smooth as an automatic, I take pride in doing that, as that's the way a truck should be driven.

That said, I've never been afraid to "experiment" and try different techniques, always being cautious not to "jam" gears.

The 2nd lo to 1st direct with 2 hands works flawlessly with a TRXL1071. Notice I said TRXL 1071. The ratios in the TRXL 1071 are suitable for this, the ratios in a TRXL107 are not.

As a side note, if your clutch cable snapped and you couldn't disengage your clutch, would you call a wrecker or would you drive the truck back to the shop?

.

[Lmackattack]

HK wrote

As a side note, if your clutch cable snapped and you couldn't disengage your clutch, would you call a wrecker or would you drive the truck back to the shop?

HA HA Herb this is exactly how I learned to drive with no clutch at all. 3rd week on the job and the clutch cable got stuck when I pushed it in. I got the cable unstuck by hand so I could get back on the road to get the load off. had to use low 1st to get moving from a stop and reverse 1st at the pit. workes like a charm in a jam and not real hard on the trans if you can get some movement of the wheels before you hit the gate for the gear.

made my boss happy that day!!

[d8pete]

Hopefully this will help illustrate my question if I can get this to post correctly. Thanks again guys for all your input.

Mack trans 1.pdf

Mack trans 2.pdf

Mack trans 3.pdf

[HK Trucking]

hey HK what are the most forward gears you can shift from a stop with a two stick six speed. never tried the 2nd low to 1st high but i will tomorrow. thanks

Here's the ratios of the TRXL107 vs the ratios of the TRXL1071 as posted by D8Pete.

You'll be able to see why the ratios in the 107 are not conducive to 2 hand shifting.

http://www.bigmacktrucks.com/index.php?app=core&module=attach&section=attach&attach_id=5169

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