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Discussion Starter #1
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.

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 :confused:)

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
 

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Dereck;
Why go to a totally new TV cable when they are so simple to adjust? You just need work the throttle crank through the ENTIRE range of travel after having pushed the release button and take up any slack. There are quite a few posts going over the proceedure.
Mine (the '85 van) was shifting late and hard from 1st to 2nd when cold; turned out someone had OVER-filled my tranny by about a quart. Took that much out through the dipstick via a pump and it shifts much better.
My '82 motorhome had a 700R4 installed to replace a trashed TH400 that was original from the factory. The shop that installed it was having trouble finding a TV cable setup for the 1-ton chassis so I had them set it up for pure internal pressure shift points. I will recheck that next time I have the doghouse opened up on the MH. I had read it was possible with a certain part.
Hope that helps in your case.
 

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Discussion Starter #3
My '82 motorhome had a 700R4 installed to replace a trashed TH400 that was original from the factory.[/QUOTE]

Funny you said that. Cause I just bought this truck a couple weeks ago. The gear shift indicator says "overdrive" which I thought to mean the truck was a 700r4 this whole time (causing me a ton of head ache and confusion). I just looked at the oil pan and the truck actually has a th400 tranny. Someone switched trannies on me!

Any ideas this time? Engine is still working wayyyy to hard from the 1-2 shift.
 

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Mad (Sean) Max
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x2. Bad vac pump. Check the levels. Should have 20+" at idle. A bad vac pump will give the exact symptoms you describe. Not actually the worst thing for the trans but it is a very uncomfortable drive. Unfortunately vac pumps are over $150 here (high priced Canada). The "pod" (round top part) from a 6.5 will swap over and may be easier to find used and working at a wreckers. \


Good luck
 

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Keep in mind that this probably doesn't have a VRV like a truck with the TH-400 original from the factory would. So it is possible that the vacuum modulator is seeing 0 vacuum all the time. Thre are two ways to solve this. Either get a VRV (Vacuum Regulator Valve) and install it on the pump (good luck finding one) or install a cable operated modulator such as the one listed here http://www.400raptor.com/ about 1/3 down the page. The description of the part is:

#4X. 350 / 400 Cable Operated Modulator, no vacuum needed. This works well for superchargers and on diesel motors without a vacuum regulator. This modulator uses a 700R4 throttle valve cable. Cost $128.00

There may be others available from other manufacturers, so search around. B&M used to sell one years ago as well for used on supercharged engine applications, where the vacuum modulator would get messed up by boost pressure and cause erratic, or delayed shifting, or even no shifting.
 

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Discussion Starter #7
Hey,

Thanks for all the input. I actually do have a VRV (surprising I know). The hose running from the vacuum pump to the VRV is kinda worn and spongy. You think that could be the problem? I know i am being optimistic hear.

Next, the fact that my truck is shifting means the vacuum modulator on the tranny is working right, just not receiving enough vacuum?

Lastly, I have been reading that there are adjustments on the VRV and on SOME vacuum modulators. The fact that the tranny is shifting 1-2 at 30 and kicking really hard leads me to believe that this a beyond just a mere adjustment and that perhaps i have a bad vacuum pump?

What do you guys think?
 

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Discussion Starter #8
Update:

I took the line from the Vacuum pump to the VRV off and determined there is vacuum. 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?

So the problem should now lie somewhere from the inlet of the VRV to the vacuum modulator pump?
 

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Yes but no. Did you just pull it off the VRV? The vac lines are T'ed off to the emissions and to the heater controls also right by the vac pump. Mine had a bad solenoid and a leak to a air flap in the cab for the heater.
 

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A vacuum hose should not be spongy, so replace it with a new one of the proper type; that's just good maintenance. If it were so worn out it could collapse at higher vacuum numbers thereby not allowing enough to get to the VRV or anything downstream of that.
 

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Discussion Starter #11
, 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
 

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Discussion Starter #12
Bigboytoys,

To answer your question. The valve coming off the vacuum pump is T'ed,but the side opposite the line to the VRV is plugged off. There are rubber hoses running towards the driverside from the vacuum pump.
 

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Dereck;
Have you tried pulling a vacuum on the hose/line running to the modulator? Either that or blowing compressed air through to make certain there is no blockage in that line. In these older vehicles vacuum and other rubber lines have a tendency to split or otherwise deteriorate. Some rubber hoses will get interior chunks that can fall off and plug things up internally and still look OK from outward observation. If it can be easily gotten to, it might be worth just replacing the line from the VRV down to the tranny modulator.
Just my 2-cents ;^)
Chris
 

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Ok, so I have to add to this. I have a 1984 GMC Sierra Classic 1500 with the 6.2 and a 700R4. Here's my problem, I think it's related. I just swapped this transmission in after having another one that was cracked around the bellhousing (happened before I bought it). This trans is a 4wd with transfercase and the truck is 2wd. Yes, I know that's not wise but I needed the truck online and had the crossmember, rear drive shaft and all from the donor truck which also had the 6.2 in it. Here's what's going on: It shifts from 1-2 antwhere from 17-19 mph, sometimes it shifts harder. 2-3 at around 32-35. 3-4 is anywhere from 54-60 depending on the throttle. Also, should note that the speedo is WAAAAAAY off. As in 22mph off at 40, You're doing about 57 at that point. The other morning I took it out for a run, it was around -10 when I took it out, and it shifted late as usual, but would not go into 4th. This was new, Correctly adjusted TV cable, clean fluid on a fresh filter less than a week old.
 
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