Take a look at my engine;

http://www.facebook.com/photo.php?pid=456486&l=6e3833df4e&id=1811331443

http://www.facebook.com/photo.php?pid=456484&l=3b099a5a1c&id=1811331443

http://www.facebook.com/photo.php?pid=456482&l=69f5d6e1fa&id=1811331443

Am I just missing where it is, or am I just missing it all together? I thought the 90 6.2L had a Vac Pump, and not an electric module? Maybe I am just looking in the wrong place. or in the wrong way.

If you have one it's belt driven on the front of the engine...... maybe under the p/s pump?

You probably don't have one though......

ok. so if I dont have one here is the issue, I have posted about it before, but wont bring up that old post. When shifting the engine red lines before lunging into the next gear. I was thinking that it could be due to a bad vacuum pump, but if I dont have one, what would be my next step to determine what is going on?

Some of the info that I know:
It did leak a little tranny fluid, this afternoon I found several bolts that had not been tightened at all, they were about half backed out around the pan. So hopefully that will fix the leaking.

The Transmission was replaced in 2004-2005, I have the paperwork from the shop, but the date is hard to read. The Trans was a rebuilt.

Did we ever determine what transmission you even have?

not yet.. it was not on the paperwork, where or how can I figure that out? is there a plate or something like that on the trans? trying to google it has not helped much.

look at the pan for it...... http://www.transmissioncenter.net/PanShapes.htm

based on the info I can find they only had one 3-speed transmission that was available on these trucks and that was the THM400. I know I am only shifting up to third, so if there is a 4th then I am missing it completely and that is another story :)!

Then you will have a vac pump.... it's gonna be belt driven though...

I gotcha. and you said behind the PS pump right. I will look there tomorrow, wonder why it seems like I never hit 4th, maybe because of the vp being bad?

I would check the pan, I got a 89 Silverado and its a 3spd auto. If you have a 1/2 ton then you may have a 4spd.

Here are better pics of the difference in pans.
http://www.hotrod.com/techarticles/identifying_gm_automatic_transmissions/photo_02.html

all the NBS trucks had either a belt driven vacuum pump or no vacuum pump. the cam driven pump was for the OBS truck ONLY. your engine has a "dummy shaft" in there to drive the oil pump. if your truck is a 3/4 or 1 ton its got the TH400 in it. if its a half ton its got either the TH400 or the 700R4. the TH400 is operated by vacuum, and the vacuum is varied by a deal on the side of the ip with vacuum lines going in and out of it. if its a 700R4 its got a TV cable(throttle valve) and it does the same job as the vacuum, it tells the transmission the throttle position so the trans knows when to shift. i think the TH400 wont go into 3rd unless it has a vacuum source.

I have a 1990 K2500 and I believe the vac pump is on the upper passenger side. My truck has few options (no A/C) and a serpentine belt. The vac pump is a large diaphragm enclosure looking thing on the top.

It should be in the top of this picture:
http://www.timekill.org/photos/truck/alt-out-1.JPG
http://www.timekill.org/photos/truck/alt-out-1.JPG

I am somewhat new at this, so please correct me if I am wrong...

thats it for sure :thumb:

I have a 1990 K2500 and I believe the vac pump is on the upper passenger side. My truck has few options (no A/C) and a serpentine belt. The vac pump is a large diaphragm enclosure looking thing on the top.

It should be in the top of this picture:
http://www.timekill.org/photos/truck/alt-out-1.JPG
http://www.timekill.org/photos/truck/alt-out-1.JPG

I am somewhat new at this, so please correct me if I am wrong...

That's it, and on trucks with A/C, the A/C compressor will be there and the vacuum pump should be below it.

Here is my trans pan, looks just like the TH400 to me:
http://www.facebook.com/photo.php?pid=457484&l=3c18d5e191&id=1811331443

On another note, I was fishing around looking for the Vacuum Pump, which I think I found right under where the AC compressor would be if it were installed;
http://www.facebook.com/photo.php?pid=457486&l=fa2ff3d25a&id=1811331443
and came across this cable coming out of what I think is the throttle body, it is not connected to anything, but it should be hooked up to the same place as the throttle cable:
http://www.facebook.com/photo.php?pid=457487&l=fc110dc6c4&id=1811331443
http://www.facebook.com/photo.php?pid=457488&l=4b732628c0&id=1811331443

Here is my trans pan, looks just like the TH400 to me:
http://www.facebook.com/photo.php?pid=457484&l=3c18d5e191&id=1811331443

On another note, I was fishing around looking for the Vacuum Pump, which I think I found right under where the AC compressor would be if it were installed;
http://www.facebook.com/photo.php?pid=457486&l=fa2ff3d25a&id=1811331443
and came across this cable coming out of what I think is the throttle body, it is not connected to anything, but it should be hooked up to the same place as the throttle cable:
http://www.facebook.com/photo.php?pid=457487&l=fc110dc6c4&id=1811331443
http://www.facebook.com/photo.php?pid=457488&l=4b732628c0&id=1811331443

Looks like a THM400 to me too and you seem to have found your vacuum pump. Diesel's don't have throttle bodies. What you're looking at there is the cruise control cable.

If you determine that you aren't getting any vac and you are looking at a wrecker, one from a 6.5 is a direct swap (I'm pretty sure) Those suckers aren't cheap new.

RC - still have that newby smell to me! Sorry for misspeaking there. I should have just asked what the cable was! :)

As far as checking for vac, can I just pull off the top line and connect a guage, or do I have to do something fancey? What would be "good" vac pressure? On my first post about this issue JoeAirForce had mentioned 20" was good. But I am not sure since he was thinking that I had the vac pump that was behind the engine.

Thanks

RC - still have that newby smell to me! Sorry for misspeaking there. I should have just asked what the cable was! :)

As far as checking for vac, can I just pull off the top line and connect a guage, or do I have to do something fancey? What would be "good" vac pressure? On my first post about this issue JoeAirForce had mentioned 20" was good. But I am not sure since he was thinking that I had the vac pump that was behind the engine.

Thanks

Unless it was in another thread, I never said how much would be "good vac" :p:

The position of the pump won't affect the readings it should have.

and yes, just pulling the hose off and sticking a vac gauge in it will work fine. :thumb:

if you have vacuum presure you have some serius problems :p: . but yea 20" is the lowest that is acceptable.

I think that was me telling you about the vac draw a few weeks ago in another thread.

As 4320 said 21" is spec and higher isn't bad but much lower and you'll have problems. Below 15" and you'll start getting real high hard shifts. At no vac you'll redline into 2nd and never get to 3rd

ok.. pick on the guy that does not know the right terms :)> Keep it up. In the Marines we called this hazzing! here we will just call it breaking me in.

Sorry Joe for mis representing, it was smackzed that was giving that tip. Thats for the correction smackzed!

Lots of topics were covered in this post, which I try not to do. So to wrap it up for today I will be doing the following this weekend:

1- Checking Vac DRAW
2- Looking into fixing the cruise control linkage

I will post back with any results I have. Thanks again gentlemen... and I use that lightly around these parts! :)

I got to check my pump this weekend, having hard shifts and the idle wanders some so either a leak or the pump is starting to go.

the idling wander has nothing to do with vacuum. the vacuum pump on a diesel is just for accesories, it has NOTHING to do with engine operation. the injection pump is what meters fuel so check for an air leak because if air is getting into the system the idle likes to play around.

I am guessing that a compression tester would not work to test the vacuum draw? I happen to have one, and if I dont have to buy something new my wallet would like that.

an engine vacuum tester gauge is worth about 10 dollars.

I cant find one for less than about 25-30.. which i will pay if I have to. I am a cheap skate, what can i say.

I lied... I just found one for 12 bucks from harbour freight tools! now that is what I am talking about.

I got one for $20 cnd (which translates to about $8 american, not because of exchange just cause everything is way cheaper below the 42? parallell) It dobles as a fuel pressure gauge tho which is nice. The dial has pressure on one side and vac (or negative pressure i guess) on the other

thats the same one i got smackzed. or very similar. i got mine from my dad, hes had it for years.

Just picked one up and it is the same way, Fuel and Vac.

Now the real question is how do I do the test? Just pull the top line and plug the guage into the line, or into the pump?

I am sure if I open the book it will be in there as how to do the test.

Either or. If you hook it to the pump it will tell you if the pump works however if you plug it into the line and get a bad reading it may be that the line has a hole in it. I would start right before the vac regulator (VRV) on the side of the IP and work backwards from there. If you get 20" or over tho at the VRV then vac supply is not your problem. Use some tape to get a good seal and so you don't have to hold it together the whole time.

just jam the gauge's hose onto the vacuum pump, start the truck and let it idle, then read the gauge. it should say at least 20".

I will do both. Thanks yall.

well I dont have good news. Less than 5"!!! now the real question is how do I fix it and where do I get the part(s)? Any ideas?

check some junkyards. if you cant get one, buy a new pod from the local parts store. but this is where being cheap is bad. the pumps run around 180 bucks.

definitley check wreckers and ask also for pumps for 6.5's.

found some on ebay for about 90. Might just make it easy on myself and get one of those.

Thanks for the help.

good price.

as far as getting a pump from a 6.5, do I need to get one from the same year range? I see one on ebay but it is for a 96 6.5, should that make a difference?

theyre all the same as far as i know. only the 82-87 truck 6.2 vacuum pumps are cam driven while the 88-93 truck 6.2's are belt driven like yours. and all 6.5 pumps are belt driven.

cool.. just looked at the junkyard website.. they have two k2500 chevy and one 3500 and a gmc 3500. Price for the pump... $16! Time to get out the wrenches and go do some pulling.

youll be darn lucky if you get one that actually works lol.

Is there anyway to test it in the yard? I am guessing not, unless the engine would turn over. I will check all of them and take my chances. maybe I will get lucky.

well id say if you can return them, take all of the vacuum pumps you can find. and try them untill you find one that works, then return the others.

Getting new to me vac pump sent to me. Should be here early next week. I will let everyone know how it goes.

It has been a few weeks and I finally got the new pump in! I am reading 25+ inches! This is great.. Now the issue is, the shifting is still really rough.

Does anyone know where on the transmission the adjustment screw is for the thm400? I have looked and dont really see anything that looks like what has been described. A picture is worth a thousand words.

Thanks,
Chuck

You might want to check at the tranny and see what you are reading might have a leak in one of the lines

A few things. The first I'd check would be for leaks in the vacuum line. Are you getting 14" at idle at the vac regulator valve (doodad on the passenger side of IP) which goes down with throttle. The VRV can be adjusted by loosening the bolts and pushing it up or down. This more or less adjusts how hard or soft the trans shifts and to a small degree how early or late.
Next I'd take the Vac modulator (canister looking thing at the end of the vac hose on the side of the trans, follow the vac hose down and you'll find it) out of the side of the transmission and replace it. They're fairly cheap and I don't think there's a test. If when you take it out there is a small screw inside back it out as much as possible and see if that helps. When buying a new one either get a black stripe one or a red stripe. Black stripe is diesel but it's big and get mashed up if you do any 4wd or off roading, red stripe is adjustable. The only test after any adjustments is to go for a drive and see if it's improved at all. Primitive but....

when you check your lines if there is trans fluid in the line then the modulator is bad for sure..if no fluid in the hose then remove it and suck on the inlet and hold your tongue over the inlet if it holds vacuum then its probably good..i didnt see where you checked the vacuum at (which side of the i/p switch) hook the vacuum gauge gauge to the outlet of the switch and see if you have vacumm that drops and raises as you open the throttle..hope this helps