M1028 tranny shifting vaccuum pump question.

[sowchinook1]

Hey All,

My 1028 seems to enjoy shifting gears only at near redline rpm, I gathered through other posts that this may be due to insufficient vacuum either from leaks or a failing pump. I'm going to check the lines, but in the event the lines are fine, I'll have to assume the pump is bad. So I checked autozone and a new pump is 129 bucks. My question is, will this pump be identical to the one on my truck or is there a mil version? The autozone of course didn't have a 1987 m1028 reference so I queried 1987 V30 4x4 6.2 diesel for the part search. Also, on a separate note, I was wondering if the cucvs use some kind of military/offroad shock absorber vs. a standard one found on civi trucks. The reason I ask, I've had a few 1 ton 4x4s in the past, 4x4s SRW and when I jump up and down on the bumper the civilian trucks are rock solid barely moving up and down at all. My 1028 however, will bounce up and down quite a bit. Are the shocks just worn down or different style, and no I havent gotten fatter so I'm sure it's the truck!

Thx

 

[tlm47201]

The M1028 uses a pump that mounts where the distributor went on gassers. On the civis, I believe they used a belt driven unit, but (and this is the million dollar question) I think civi units with a/c used possible the military unit. Not 100% positive tho.

 

[CUCVFAN]

If the pump makes vacuum, check the rubber lines at the tranny and vacuum valve (pass side of the IP). Also, try to adjust the vacuum valve. Rotate the top of it all the way toward the rear of the truck and test drive it. If it makes it better (or shifts too soon now), you need to adjust it. If no difference, it might be bad.

Basically, if you don't give the tranny any vacuum, it's going to shift on the governor, which means pretty much full speed shifts all the time. They are pretty harsh, too. If the shifts almost bark the tires, then you might not have vacuum at all.

 

[CUCVFAN]

That I am aware, all 6.2 vacuum pumps are "distributor" style. A.I.R. pumps are belt style, but only on gassers, as far as I know.

 

[CCATLETT1984]

when telling the parts store what you have, list a 1985 K30 6.2
The cucv's used older style parts from what the '86-plus civilian trucks used.