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Vacuum pump...VRV...TH400

B

BigJohnson

1/2 ton status
Joined
Jan 22, 2001
Posts
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Location
AL
Hello everyone!

Finally scored a 1 ton rig, 1985 CUCV M1008, and I trying to get it running right. I am having a lot of trouble with the TH400 shifting late and very hard. Right off the bat I had a bad vacuum pump, no vacuum at all. Got a remaned one from the parts store today and when I removed the original one it had a different gear and drive for the oil pump so I just swapped the remaned pod onto the old drive. The drive appeared in good condition so I just reused it. Did the CUCV trucks have different gear drives?

Now I have vacuum but I am still have shifting problems. What is the proceedure for testing a vacuum pump? With a vacuum gage hooked directly to the pump I get a very eratic measure off the scale of the gage. Is this normal or should it be steady?

I then suspected the vacuum regulator valve. With the bottom inlet hooked to the pump and vacuum gage to the top I am reading 9 in. hg at idle and it drops to around 5 in. hg at 1/4 or so throttle. I read the proceedure for setting the VRV but I don't have the appropriate throttle stop. Does anyone know the correct throttle postion or another way to set it?

I haven't done anything with the vacuum modulator yet. I think I will just get a new one to rule that out. The one I have seems to be non adjustable. Is an adjustable one better?

Thanks in advance for any help :bow: I need to get this thing in shape to put the 11R16 Michelin XLs on it:D
 
Have you pulled the tranny pan and inspected the condition of the tranny? Checked the governor on the tranny?
 
Thanks for the reply!

I haven't pulled the pan yet. The truck was a county truck and from the condition it looks like they drove and maintained it up until the starter broke and ruined the flywheel when they auctioned it off. The trans is a Jasper reman and the fluid is nice bright red and clean. I being optimistic and hoping for the best...maybe they replaced it and then decided to get rid of it:)

I put in a new vacuum modulator and got the same thing late hard shifts. I then connected the vacuum directly to the modulator bypassing the vrv. It shifts normally now but maybe a tad earlier than I want. It is driveable now.

That leads me to think that the vrv is to blame. Maybe an adjustment will fix it:confused:. I know a new vrv costs $90...ouch! I've here that without the vrv the trans will shift at low line pressure so it seems necessary.

So much for the being a cheap project....:D
 
I'm no expert but I have never heard anyone mention different gear drives for the 6.2 vac pump. You should get yourself a set of the Military manuals on the 6.2. It will help out a lot!
 
BJ
Try Jamie at the Diesel Depot for the VRV. My cucv didn't have one when I got it, they made me a good deal on a used one.
I dont think it is a good idea for a t400 to not have a operating vacuum system. As you see, with no vacuum, the trans thinks the engine is under load like it would be in a gasser WOT, so it shifts later and harder. If you hook directly to the vacuum source, the shift will be early and soft, you definitely dont want slow soft shifts all the time as it would cause excessive wear.
You can set the VRV without the stop using a little experimentation, it will be obvious when your adjustment is close.
BTW I had a set of 11.00 x16 michelins on my cucv that I no longer need, pm me if you are interested in them, I'm also in AL
 
Thanks for the info guys. I am going to work on the VRV some more....right now the project is on hold with a try to get a title for the truck. All I got is a bill of sale and in AL you can't get a title with just that. Pretty frustrating:mad:
 
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