9 to 8 speed

[Flying Pig]

I’m looking at a truck with a Mack 9 speed.  Can I swap in an 8 speed in the same place.  Is there any difference in length between the two?

[terry]

What make of eight speed mack or fuller?   terry

[Flying Pig]

Mack please.  Wondering if the 8 speed is the same overall length or if a different length driveshaft is needed.

The 8 speed has lower low gear ratios which would suit the job better.  I’m sure the 9 speed would work ok, but the lower gear would be better.

[880joe]

The 8 speed will also have a higher overdrive ratio 

[Flying Pig]

I am wanting that too.  I built a custom Fuller with a .6 of but I only use it when empty.  The Mack I’m looking at will be geared lower than my Ford.

[terry]

The only drawback is the engine infront of the nine speed is not made to be lugged down like it will be with the mack eight speed transmission,   terry

[Flying Pig]

Terry, Where would the lugging come from?  Lower low gear will let me use a little rpm while still going slow.

[Geoff Weeks]

Wider ratio gap between gears, means  the engine speed may be too low for the load in the next higher gear but too high in the present gear. 

Torque rise of the engine has to be matched to the gears available.  An engine set up for a 9 speed with closer steps will not be matched to a transmission with wider steps.

Edited 22 hours ago by Geoff Weeks

[Flying Pig]

I guess I’m at a bit of a loss.  A 300 can use a 5,6,7 or 8 speed but a 350 can’t?  The 350 would have more torque.  Please help me understand.

[Joey Mack]

[Joey Mack]

I thought I would post these to help you know the ratios. 

[Geoff Weeks]

1 hour ago, Joey Mack said:

I thought I would post these to help you know the ratios. 

I think what he needs help with is the torque rise of the engine in question, and why some need close ratio steps and others in the Mack family can work with wide ratio steps. The engine torque rise has to work with the steps between gears.

You know Mack engines better than I and can advise.

[Joey Mack]

If he posts the engine he has, theres a good chance i have the charts.

[Geoff Weeks]

23 hours ago, terry said:

The only drawback is the engine infront of the nine speed is not made to be lugged down like it will be with the mack eight speed transmission,   terry

 

11 hours ago, Flying Pig said:

I guess I’m at a bit of a loss.  A 300 can use a 5,6,7 or 8 speed but a 350 can’t?  The 350 would have more torque.  Please help me understand.

The issue @terry and I are trying and failing to get across, is that an engine built to run in front of a close ratio 9 sped is fundamentally a different engine than one built to run in front of a wide ratio transmission. The 350 and 9 spd has higher torque and hp but in a narrower band than a 300 designed to work with a wide ratio box. Maxidyne vs Econodyne. 

I hope showing the Charts for the two types would get the point across.  While placing a broad torque band engine in front of a close ratio trans will do no harm but not use the engine to its best, going the other way (placing a narrow torque band engine in front of a wide ratio box) can do some serious damage as the engine will lug at every gear change and may never have enough torque to make it into the power band of the gear it is in.

[terry]

As geoff said, i had a 285 which is a engine you can lug down to about 1100 or 1200 RPM's i had it with a mack 12 speed and loved that combination.  terry

[fjh]

My self I would install an 18 sp fuller more selection is in my mind always best regardless of engine band width ! More choices! That said if you already got that trans then its up to you! Also In my area the 18 is more widely available! 

[Freightrain]

12 minutes ago, terry said:

As geoff said, i had a 285 which is a engine you can lug down to about 1100 or 1200 RPM's i had it with a mack 12 speed and loved that combination.  terry

My 237 worked well with Triplex.  It could pull down, but seemed better with tighter splits available.  Granted I am not pulling 80k lbs.

My 300+ had a 5 spd behind it.  I know the transmission was original to the truck but not sure the engine was.  I bet it was a dog with only 5 gears.

[terry]

4 minutes ago, Freightrain said:

My 237 worked well with Triplex.  It could pull down, but seemed better with tighter splits available.  Granted I am not pulling 80k lbs.

My 300+ had a 5 spd behind it.  I know the transmission was original to the truck but not sure the engine was.  I bet it was a dog with only 5 gears.

Yeah before my285 and 12 speed, my truck had a237 and a quad, liked that too, but that quad was a no no on lugging way down. hard on that single countershaft trans.  terry

[Freightrain]

I didn't take mine below 1500.  Maybe 1400 if I was easing off the throttle before downshifting.

[Flying Pig]

The 18 speed Fuller has no lower low gear than I have now in my 13 speed.  I could split the bottom range but that won’t help a bit loaded heavy in a spongy job site.  My trans mission in the current truck is a14609b which I added a splitter.  About the same as the 18 but I now have a bigger OD option.

What I’m looking for in all this is the super low crawling gear for off road deliveries.

Also to clarify, don’t yet own the Mack in question.  I’ll be test driving that Sunday.  I’m just trying to find my best results for what I’ll be doing with it.  My current truck is toes up at this time requiring a large cash infusion.  I’ve done the same work with the Ford but worry about destroying a driveshaft at times.  Eventually the Ford will get fixed and back to highway hauling while the Mack will be used for shorter trips with off road deliveries.

[Geoff Weeks]

A 14069B has a low of 12.57 Where as a 15618 has a low of 14.71 so that is not true. However what the low ratio is doesn't tell the whole story, it is the steps between gears and what the power band of the engine is that will make or break the set up. 

An Eaton 18 has a low of 14.71 and a top of .85 with 17 steps between

The Mack 2080 B has a low of 20.08 and a top .67 with 7 steps between.  Each step has to be huge to make that spread, and if the engine isn't built to allow that RPM drop between gears it will lug and may not even make enough torque to get to its powerband to be able to use that spread.

[Geoff Weeks]

3 hours ago, Flying Pig said:

T worry about destroying a driveshaft at times.  Eventually the Ford will get fixed and back to highway hauling while the Mack will be used for shorter trips with off road deliveries.

If your worried about spitting a driveshaft, you have the math backwards. Lets say you have 600 ft.lbs at the flywheel with the engine at idle, clutch engagement. If you have 12.57 low ratio, you have 7542 ft lbs into the driveshaft (assuming no losses in the transmission) if you have  20,08 low, you have 12048 ft/lbs into the drive shaft.

 In most cases you'll loose traction before you stall, front wheels sink in and the drive tires don't have enough traction to move you forward. Lower gear will not help with that. once the torque exceeds grip of the tires they will spin.

Lower gears come in handy when moving heavy loads slowly, but if your tires can't grip enough, it doesn't matter. Soft ground it is all about what your tires can transmit to the soft ground.

 I did heavy haul and started loads of 170K with 12.56 low gear. backing that load in a tight space, a lower gear would have been handy, but risks the driveshaft if the operator isn't careful.  

Only way to increase reduction but not stress on the driveshaft is a lower rear ratio, either single speed, two speed or planetary hub.  Superload prime movers use planetary hubs to lessen the strain on the driveline all the way to the hub.