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andy anderson

6 Speed Problem

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My R model has a Mack 6 speed and it jumps out of high gear when going down hill. Could it be the gear or the fork?

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Which 6 speed the t2060 or a 2 stick'r, I've got both and had the problem with the t2060, ended up being the slider clutch in the transmision, requires tearing down the transmission to fix but its a pretty easy job...

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My R model has a Mack 6 speed and it jumps out of high gear when going down hill. Could it be the gear or the fork?

2 stick

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My R model has a Mack 6 speed and it jumps out of high gear when going down hill. Could it be the gear or the fork?

Unlikely the fork. The fork will wear a little which will cause the dog clutch to not throw in as far and the teeth will round off, so as soon as the load comes off it, it wants to jump out, but the culprit will be the dog clutch. But I did have a bolt come loose on the shift rail on our X1070 2 stick and it wouldnt select reverse properly.

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My GMC's 4 speed had a crack somewhere on the top plate where the shift lever entered. 2nd gear would sometimes jump out, or it might not even want to catch at all.


-Thad

What America needs is less bull and more Bulldog!

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My R model has a Mack 6 speed and it jumps out of high gear when going down hill. Could it be the gear or the fork?

You might take the main shifter loose and check the 3 springs under the shifter, might be a weak or broken spring, high gear is the one on the left. i think the high is a stiffer spring. Ron

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You might take the main shifter loose and check the 3 springs under the shifter, might be a weak or broken spring, high gear is the one on the left. i think the high is a stiffer spring. Ron

It has been awhile since i had a mack transmission out, but i looked at my 5 speed today, there is a little plate behind the shifter with two bolts the springs are under there, i think a 6 speed is the same.

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I noticed last night that the trans had a 3/8" gap at the bell housing at the top. Some bolts were broken off and some were missing and the remainder was loose. I tightened some and replaced the missing bolts. The trans worked great today for about 4 hours untill more bolts snapped and the trans moved backwards again. The truck is in a local shop now waiting to have the trans pulled. The bellhousing will need repaired or replaced. Anderson

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I noticed last night that the trans had a 3/8" gap at the bell housing at the top. Some bolts were broken off and some were missing and the remainder was loose. I tightened some and replaced the missing bolts. The trans worked great today for about 4 hours untill more bolts snapped and the trans moved backwards again. The truck is in a local shop now waiting to have the trans pulled. The bellhousing will need repaired or replaced. Anderson

Sorry mate Ive been out for a couple of days, Why is your gearbox fallin out? Your mounts mustve been worn? Sounds like you may need to sling a rear support across the top of the box like a Roadranger. Ive seen a similar result on a V8 with a quad box. The bolts came loose and it fretted and chipped the back of the flywheel housing where it mates against the block. As for jumping out of gear our F model was doing it, it has a 15spd roadranger, we put a heavier detent spring on top gear selector and replaced the mounts and it solved our problem. Obviously the lenngth of the gear linkage had a bit to do with it. Be interesting to hear from you mate. Cheers :mack1:

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Sorry mate Ive been out for a couple of days, Why is your gearbox fallin out? Your mounts mustve been worn? Sounds like you may need to sling a rear support across the top of the box like a Roadranger. Ive seen a similar result on a V8 with a quad box. The bolts came loose and it fretted and chipped the back of the flywheel housing where it mates against the block. As for jumping out of gear our F model was doing it, it has a 15spd roadranger, we put a heavier detent spring on top gear selector and replaced the mounts and it solved our problem. Obviously the lenngth of the gear linkage had a bit to do with it. Be interesting to hear from you mate. Cheers :mack1:

I got my truck out of the shop yesterday. Trans was pulled and the broken bolts were replaced, the bellhousing checked out OK. The mounts for the bellhousing were replaced as well as the carrier bearing and the cross member realigned. The guy who worked on my truck said this was a common problem. The truck shifted fine on the way home.

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