700r4 problems. 6.2 Diesel

[dchough]

Hey everyone.

Thanks a lot for helping me with my last problem. I replaced the lift pump like you all said, primed the system, and my '82 6.2 fired right up. You guys on dieseplace and here on 67-73chevytrucks are awesome!

Now onto another problem... My 700r4 shifts REALLY late.

1-2 **** occurs at 30 MPH on the dot every single time. The 2-3 shift occurs at 43 mph every time. I have never had a 3-4 shift, even at 65 on the highway. Letting up on the throttle DOES NOT produce an up shift. The 1-2 shift is also very hard -it jolts into 2nd. Less so with the 2-3 shift. Once the shift is made, stomping on the pedal DOES NOT produce a downshift.

The tranny fluid is a nice red. Doesn't smell new, but doesn't smell burnt either. It might be a little low, but should not be enough to cause such problems (or at least I think )

I have searched for weeks on this problem and I have narrowed it down to:

1. A bad TV Cable
2. Stuck valve
3. Bad governor

The 1-2 shift at 30 mph would mean its shifting at full line pressure, right? I feel like simply loosening or tightening a cable couldn't fix the shifts when they are EXTREMELY late, or could it? Am I looking at probably replacing the TV cable as opposed to adjusting it?

Also, what the hell is a stuck valve? It involves dropping the pan and cleaning the insides, right? Wouldn't a stuck valve produce more irregular shifting? the 1-2 shift comes every single time at 30 MPH.

Lastly, I read once that if there is a pin or ball or something that goes bad, the 700r4 has a automatic device that will send the tranny into "late shifting mode." Any thoughts? What would cause this?

Pretty much, what do you guys think is the cause of my shifting problem, given my symptoms?

Thanks a lot more looking out for me and reading this ridiculously long post!

-Dereck

[lindstromjd]

Originally Posted by dchough

Hey everyone.

Thanks a lot for helping me with my last problem. I replaced the lift pump like you all said, primed the system, and my '82 6.2 fired right up. You guys on dieseplace and here on 67-73chevytrucks are awesome!

Can we say "I told you so"? In a good way though.

I hate to bring up a stupid question... but are you positive you have a 700r4 and not a TH400?

[MadManAndrew]

Originally Posted by lindstromjd

I hate to bring up a stupid question... but are you positive you have a 700r4 and not a TH400?

Guy at Napa asked me that yesterday, "Are you sure you have a 350? You know, they put turbo 400's in these trucks too." I just looked up and stared at him until he went back to searching, lol.

[dchough]

OH MY LORD.

I bought this truck 3 weeks ago. Probably spent an hour checking it. Thought it was a 700r4 right off the bat. Even looked at the oil pan...

lindstromjd, when you asked that question, I thinking in my head, what a silly question, of course its a 700r4. The gear indicator panel even says "overdrive" indicative of a 700r4 4 speed tranny. I could have sworn i looked at the tranny pan and seen the rectangular pan, but when I went outside to check the oil pan shape again, just to be sure... sure enough its a th400. Someone must have replaced the 700r4 with a th400 at sometime.

Hahahahahaha. I am a moron. For the last 4 weeks I have been spending hours a day google "700r4 shifts late and hard."

I don't know whether to laugh or cry.

Having sorted through that MINOR detail, I still feel like the shifts are still late. Sounds like the engine is working wayyy to hard on the 1-2 shift and it still kicks.

Any ideas? Jeeezzz. Hahahaha I am a complete idiot.

[lindstromjd]

Ok... No hard feelings. I'm going to say that you're probably not getting enough vacuum to the modulator on the back of the transmission with that late of shifts. I wouldn't worry about the hard shifting; that's usually indicative of a shift kit. Slow, soft shifting and taking forever to grab the gear is a problem.

So... where are you getting vacuum from for the transmission? From the vacuum pump of the back where a gasser distributor would go? Or from the side of the injection pump? I'd almost say that with that late of shifts, and the no downshifting, you might not have any vacuum to it at all, and it's acting like you're going balls-out, wide open throttle at all times.

[dchough]

I think you are right. I don't have any vacuum. I wonder if any adjustments are needed to be made when switching from a 700r4 to a 400th behind a 6.2, like the vacuum. The 700r4 doesn't have a vacuum modulator line right? I wonder if the previous owner just dropped in a th400 without making the necessary changes to make it compatible. The guy I bought it from said it has shift late ever since he had it.

What do you think? I can take pictures of the setup and post them. Maybe you can spot something I can't?

-Dereck

[MadManAndrew]

Yes, the tranny will shift with or without vacuum, the vacuum just makes the tranny shift more accordingly to the motor than the standard shift points.

[rcbildr]

****So let me see if I understand this right. There is a vacuum modulator on the passenger side of the transmission. This tells the transmission what the engine is doing based on vacuum pressure, and thus directs the transmission to shift accordingly. So then a hose runs from the vacuum modulator directly up to the vacuum pump, and then from the vacuum pump to the injector pump, which is linked in some way to the throttle?*****

You have all the parts just not in the right order. Starting at the vacuum pump there is a hose that goes from the pump to the vacuum regulator valve (VRV) on the injector pump, then from the VRV there is a hose that goes down to the vacuum modulator.

In addition to being able to adjust the VRV you can also adjust the vacuum modulator too. I was able to on mine, I'm not sure if all TH-400's have and adjustable modulator. Inside the nipple on the modulator is an adjustment screw. All you need is a small flat tip screwdriver and IIRC when you turn the screw in it make the shifts later and firmer.

[78maliburat]

[QUOTE=MadManAndrew;4761498]Yes, the tranny will shift with or without vacuum, the vacuum just makes the tranny shift more accordingly to the motor than the standard shift points.[/QUOx-



THE GOVERNOR WILL SHIFT IT

[spudz]

You probably don't have a diesel governor.

[dchough]

Update:

I took the line from the Vacuum pump to the VRV off and determined that there is in fact vacuum suction. I could tell the line was actually oscillating and sucking in and out just by looking at it. So I can now check a bad vacuum pump off my list, right? Or perhaps its not enough suction?

So i am assuming the problem is somewhere between the inlet of VRV and the vac modulator. What are the chances the VRV itself isn't working? What should I look for? Something disconnected?

Also, what are the chances this shifting problem is indicative of a simple adjustment at the VRV or Vac modulator?

Thanks guys. I am learning a lot and really starting to get a feel for this system.

[rcbildr]

I think you are at the point to where you need a vacuum gage. Disconnect the hose on the VRV that goes to the modulator, hook up the vacuum gage on that port of the VRV, and then rev the engine and see how the gage reacts.

[dchough]

Alright, So I think I have narrowed down my search.

I ran a vacuum test on the vacuum pump from the line that goes to the VRV. After it warmed up a bit, I got the vacuum to run at 18". I replaced the cracked and worn hose from the vacuum pump with a brand new one, and that bumped the vacuum pump reading up to a steady 24" once it was warm. So I am assuming my vacuum pump is good.

Then I hooked up the gauge to the outlet port of the VRV (the line that goes to the transmission modulator). After about 15-20 seconds of the needle slowly rising, it stopped and stayed at 8".

So I am getting about 24" into the VRV and only 8". I tried adjusting the VRV, but the VRV is already as straight up as it goes. Any adjustment brought the outlet VRV suction down from 8" to about 6".

I also ran a vacuum test at the tranny modulator, which was 0". So i am getting no vacuum at the tranny module, which is probably the cause of my shifting woes. (Additionally, when I disconnected the line to the modulator, there wasn't any tranny fluid, so I am assuming the tranny modulator is ok.)

So I am assuming I need a new VRV? Does this sound right? Is there anything on the VRV that I can take out and replace or rebuild, or is it better just to replace the whole thing?

Thanks again!!!!

-Dereck

[rcbildr]

There is another adjustment on the VRV, I'll have to go look at mine again so I can describe what to look for/at...I'll post up when I do.

There isn't much to the VRV valve. I was able to take mine apart and clean it up to get it working again. You should see high vacuum at the VRV and then it will drop when you rev the engine.

I'll be able to go out and look at mine in a couple hours (I'm at work right now) and I'll let you know.

[rcbildr]

Ok, let's see if I can describe this right. Looking at the top of the VRV you will see the 2 nipples for the hoses. IIRC the top hose comes from the vacuum pump and the bottom hose goes down to the modulator. Just below the lower nipple is a collar with 4 prongs 90* apart. You can twist that collar to adjust the amount of vacuum going to the modulator and it also affect how the vacuum drops off when you rev the engine....you will have to play around with it to see which direction to turn the collar. I hooked up the gage to the lower nipple and adjusted mine to about 14" of vacuum. If I remember right that was where the vacuum would drop off when I would rev the engine. The drop should be proportional to how high the engine is rev'd. It took me a while to get it right and at first the collar didn't want to turn. Hope this helps.

[dchough]

Hey,

Thanks for the description. I'll check that out and report back. So i twist all 4 prongs?

[dchough]

RCbildr,

So i twisted that collar thing you were telling me about and IT WORKED! You were right, it was hard to twist, but once I cleaned it up and sprayed it with some PB Blast, I was about to get it moved. It was all the way down, screwed on tight to the bottom. I twisted it towards the top and I also unscrewed that pivot screw on the side of the VRV itself (not where it attatches on the IP) And I was able to get about 11" out of the VRV. I took it for a test drive and the 1-2 shift is at about 16-17 mph, and the 2-3 shift is at about 32-33. Still alittle high, but I am going to mess around with it.

Thanks again! And thanks to everyone for their help! You guys saved me over $100 for a new VRV!

[GmtGmt]

wow is that a true red block engine?

[dchough]

Yup!!!

[rcbildr]

Awesome!!! Glad to hear you got it.