Help with a new purchase

[FishPony]

So I bought a truck and I have a few questions. Been lurking this site for a bit now and from what I can tell this is the info I have gathered.

1986 Mack MH 612

E6 275 w/ Maxitorque T2050 5 speed trans

Symptoms:

shifting, sometimes it shifts perfect other times you get a bit of a grind. Downshifting is nearly impossible. Maybe user error or clutch adjustment needed. 

top speed is only 43. This makes me very sad lol I just want to go faster. Please help!

History:

the truck belonged to the county and has 124k original miles and the interior shows it. It’s in fantastic condition. The guy before me bought it to restore and sell on eBay for profit but it didn’t work out for him. It sat for about 8 years under a car port.

 

I have it now and so far all I have done is drain the fuel tanks, washed them out, put new fuel and filters and it seems to run and drive just fine other then the symptoms mentioned above. I have a ton more questions but I guess we will start there. I was hoping to use this as a work truck to transport cars/freight locally. Like hotshot kind of. Overkill I know but I hate new and love to bring older trucks back from impending doom!!

 

[doubleclutchinweasel]

Not to offend, but grinding while downshifting a non-synchronized transmission usually IS user error.

MUST match RPM...regardless of whether you use the clutch or just "float" it.  Will slide in easily then.

Of course, there COULD be other issues.  But this seems to be the most common problem.

Oh, and welcome to The Pound.

[67RModel]

I don't know there is lots of missing information here. Is the speedo accurate? Check it against a GPS phone app. A T2050 has a 0.6:1 overdrive. You would have to have 8.88 gears or something crazy low like that in your rear end(s) to only be doing 43 in 5th gear. Are you getting it into top gear? 5th is all the way over to the right and back against the seat. Is it a tandem or single axle? What is the engine governed at? What are your RPMs when you are maxed out at 43 mph? Yes grinding is most likely operator error. The Mack extended range transmission takes some getting used too and a "reprogramming of your brain" to get the hang of. They are not like other heavy duty transmissions. The steps between gears are comparatively huge. 

[doubleclutchinweasel]

Like he said, the steps are BIG on a those boxes.  Remember, the steps are a certain percentage drop, not a fixed RPM drop.  So, if you shift at lower RPMs, the steps appear smaller (same percentage, smaller RPM difference.  Those engines pull hard at lower RPMs also.  I used to keep the revs fairly low through 4th.  Then wind 4th pretty high, drop into neutral, take a nap, then drop it into 5th!

Downshift only when the RPMs pull down to about 12-1300.  Don't try to downshift at 17-1800 like we did with the compound stick on the Quadruplex boxes.

Big steps!  Big, wide steps!

If the revs are, say 2/3 of what they were before an upshift, the equivalent downshift would be 3/2 the revs.  So, if the revs drop from 2100 to 1400 on an upshift, then you have to pull down to 1400 before downshifting and rev it all the way to 2100 to get it to match up on the downshift.

You'll get the hang of it.

I am very curious about the RPM/MPH that 67' asked about.  That OD trans should do more than that unless something (tach, speedo) is off calibration, or the rear gears are insanely low.

[FishPony]

Ok I might be missing something here. Let me go check with gps brb. Thanks for the responses and no offense taken. I am not used to these style trucks and the guy that sold it to me did not grind a single gear but also never downshifted.

[Geoff Weeks]

Also county owned stuff can be weird, they spec it for a job and may gear it low to prevent clutch wear and speeding. Many times if you are employed by a government entity you don't have to have a CDL. I've seen ex county stuff with real weird spec 's  45 top speed. I saw a Loadstar tandem axle dump, 392 gasser and juice brakes on a 40K  GVW.  I doubt you could get that thing over 35 mph fully loaded, but you'd be crazy to want too with juice brakes.

 When the county or other agency spec's it, resale value is not even on the table.

[FishPony]

Ok I’m going to risk sounding like an ass here but it is what it is. I’m new here and want to remain honest so future readers can learn from my stupidity. He said 5th was down and to the right. I tried that many MANY times and there was never a gear there. Until, I just went out now for a drive around the block and thought, these guys know more then me let me force this bischhh in just to see. When I use two hands and a hell of a lot of strength it pops right in without even a hint of a grind…

I was coookin’ down these back farm roads doing like 65 lol. Thanks soooo freakin much u guys are legends.

So I do have some kind of adjustment issue here. That gear did not want to engage no matter what rpm I tried to shift at. I know I a new at this but man I have driven plenty of semi’s with all kinds of trans/motor combos and I have never had this issue. 
 

I guess I thought it was 4 forward gears and one reverse. Damn I’m dumb. Please help.

P.s. what the heck is that hose hanging out?

[tjc transport]

looks like  there is a grease zerk on the end. 

i always explained the mack 5 speed to multi range drivers like this:

"this aint no gear jammer trans. pull it out of gear, take a nap and when you wake up slip it into the next gear"

your E-6 should have around a 700 RPM band. so run it up to 2100 RPM, slip it out of gear, and around 1500 easily slip it into the next gear. 

same for downshifting. pull it out of gear and throttle up around 700 RPM and slip it into next lower gear. 

[mechohaulic]

hose hanging down is an extension hose going to the throw out bearing for grease,  depending on the maintenance schedule/ operation, i would take them off. history has found ; units with the hose and improper Maintenace program , the throw out bearing got sooo much grease(cause it's easy to get to) the grease spilled out to the clutch brake causing it to malfunction. if a "mechanic " had to reach up into bellhousing for greasing , less excess grease on clutch brake.

[Joey Mack]

tilt the cab and check the shifter shaft, u-joints and shift tower for excessive play..  there may be an easy fix for having to jerk it into 5th.. 

[Brocky]

I was told when I bought my Diamond T 921 cab over that it would not go into reverse.. Replaced the universal joint in the shift linkage and it worked perfect..

[mechohaulic]

does the MH have the extension on top of transmission to bring linkage out to driver side similar to the F models ?? '86 is tooo new for me to know. if so , two hands and lot of strength will bend/ break the top linkage going into the transmission rail selector. with ENGINE OFF I would jack up  one wheel allowing drive train to be movable , then check shift lever for operation in all gears . easier with cab over . 

[mechohaulic]

1 minute ago, Brocky said:

I was told when I bought my Diamond T 921 cab over that it would not go into reverse.. Replaced the universal joint in the shift linkage and it worked perfect..

speaking of Diamond T =NOT  to go off topic BUT trucking through CT on I- 84 mid afternoon was an east bound Diamond T (green ) with some type of extended sleeper on back. too much traffic didn't get best look at it. known to anyone on here, NOT Matt Pfahl  B model.

[Brocky]

Kenny Rex of Northampton PA (Allentown) Has green Diamond Reo conventional.. long wheelbase but NO sleeper that I remember?? It was at Macungie 2 years ago. Came in on Saturday Morning and was parked up by the pool across from the main trailer parking.

[FishPony]

So no to adjusting the clutch??? I saw a video online where a guy holds down the clutch with a 2x4 and tightens a bolt on the clutch and it solved his problem! 
 

im going to make a separate post introducing the big girl and maybe u guys can give me some pointers. Like maybe not be so oblivious to the 5th gear lol. 
 

thanks for going easy on me! Cheers

[mowerman]

5 hours ago, tjc transport said:

looks like  there is a grease zerk on the end. 

i always explained the mack 5 speed to multi range drivers like this:

"this aint no gear jammer trans. pull it out of gear, take a nap and when you wake up slip it into the next gear"

your E-6 should have around a 700 RPM band. so run it up to 2100 RPM, slip it out of gear, and around 1500 easily slip it into the next gear. 

same for downshifting. pull it out of gear and throttle up around 700 RPM and slip it into next lower gear. 

I owned a five speed 237 years ago, that thing  drove me crazy

[tjc transport]

5 hours ago, mowerman said:

I owned a five speed 237 years ago, that thing  drove me crazy

what do you mean? 

it could not drive you someplace you already are!!!  

[mowerman]

Do you know it was a good idea. I didn’t care for them at all especially running one of a lot of upgrades. They’re probably a lot more fun on flat ground haha bob

[mowerman]

I think mine was a six speed two sticks I do remember you could shift gears in reverse.. Bob 

[tjc transport]

Yup.

I had a bed engine brake plunger on my 79. So I wired up A two speed rear switch to work the engine brake.

Young guys would look in the truck and see two sticks and a two speed rear switch.

We would tell them it was a quad box with two speed rears.