Cause of high engine rev? (auto trans)

[Hutch998]

I've got an 84' k10 with a 305 and th400 transmission. I don't have a tachometer, but its very noticeable when driving it that it waits forever to shift. I'm concerned not only for the health of the engine, but somewhat my fuel economy. The guy I bought this truck from said the transmission was rebuilt. My dad is saying this is caused from the guy having racing gears installed? I'm somewhat new to this, especially auto transmissions. Any help would be appreciated. I'm clueless on what was done to the transmission, however for a 305 it definitely takes off. I have new mud tires on it now with perfect tread and it'll squeal tires up to about 15 mph. If there are racing gears on there, do I need to do any work to help the engine? or is it perfectly fine? I'm just not sure if there's something wrong or not.

 

[HotRodPC]

Check #1 Vac Modulator and Vac Line. Make sure you have vacuum going to the line and it's connected. If that is good, then Check #2 is the governor. If it's Really a Th400, then it's a square cover with 4 bolts on the passenger side. You'll be looking for either a broken plastic gear on the end of the governor, or a stuck valve inside it.

It's going to be one of the 2 most likely. If neither of those 2 fix it, then next thing to check is that the Kickdown switch may have power going to it full time. Check #1 and #2 and we'll go from there.

 

[Hutch998]

Okay I'll check those first thing in the morning! If I'm not mistaken, the idiot before me pulled most (if not all) of the vacuum lines off when he put an edelbrock 650 carb on. He rigged everything up with zipties and I think theres some exhaust wiring in there somewhere.. The amount of work I need to put into this truck just to get it working right is insane.

 

[Hutch998]

Also I just read another post of yours about th400 problems? You said no vacuum would mean a very late and hard shift? Could that be the entirety of my problem? If so, how would I go about hooking all of that back up properly? What all is necessary with the vacuum system?

 

[HotRodPC]

Yes, the vacuum line or failing modulator can entirely be the problem. This causes late hard shifts. Late because it's not getting a vac signal from the engine, and a hard shift because the rpms are up so high, that pump pressure is high.

Now if it's the governor, it's likely not to ever shift out of first but it still can if you don't have a shift kit that prevents shift protection but will also shift very very late, probably almost to floating valves and very high engine rpm late. From what you describe, I'd be almost certain 1 of these 2 easy things to check will be the problem. Check vacuum first cust it's easiet and most likely. If that does it, then no reason to check the governor. It's likely to be or the other and not both. But at least you won't have to pull the trans or pull the pan even.

 

[Hutch998]

Well I just got underneath my truck, and I don't see a modulator? That's the passenger side view. I'm kinda confused..

 

[HotRodPC]

Total different ball game now. That's a 700r4. 4 speed overdrive. Not a Th400. First thing to check is that the TV cable is not stuck out leaving the TV valve activated. This is critical on the 700r4.

 

[Hutch998]

Well.... Now I feel really dumb, So would it be the same scenario with the vacuum lines? or is it something different with the different transmission? Thanks for straightening that out too haha.

 

[Hutch998]

Also how would I figure out if its stuck closed? Sorry to ask so many questions, I'm new to this stuff.

 

[HotRodPC]

The 2 transmissions are 2 totally different animals. The Th400 uses a Vac Modulator, Governor and Kickdown Solenoid to determine shift points and is a close to bullet proof 3 speed auto. The 700r4 is controlled by the TV cable at the linkage on the throttle body and a governor only. No Vac modulator. It's also far from bullet proof, has an overdrive with lock up converter via Solenoid with a signal from the ECM. It is very critical that the TV cable is properly adjusted or the transmission will not only not function correctly, it will burn up the transmission. If the TV cable is to tight, meaning pulling on the cable more than necessary it will shift late and shift hard. If it's to loose, meaning it's not pulling enough, it will shift very early, soft and maybe slip due to low line pressure which will cause overheat pretty quick and cook the 3/4 clutch pack first, then the dominoe affect and take out the whole transmission, and this can happen relatively fast like in just a couple to few hundred miles. So I'd get with adjusting that TV cable fairly quick. If it does not adjust, then it's safe to assume the TV valve in the trans pan is likely stuck applied.
Did you mention someone was working on the TBI? Chances are they didn't connect or adjust the TV cable properly when reinstalling the TBI.

 

[MadOgre]

The 700r4 is not vacuum operated its line pressure is controlled via the "TV" cable. Stands for Throttle Valve cable.

It is connected to the throttle linkage so that how much throttle is applied determines how much line pressure is applied. This equates to shift points.

So the other end of that black cable should be hooked to the throttle linkage on the Carburetor.

Correct ?

Also do not drive this vehicle until you have ensured that the "TV" cable is hooked up functioning and adjusted properly!

 

[Hutch998]

Well I'll have to drive it tomorrow, but tomorrow night I'm going to my ASE class, I'll have the gm master tech take a look at it. Hopefully a simple adjustment. And yes, The PO replaced the stock 4bbl rochester carb with an edelbrock 650, it doesn't seem very well installed... I'll take pictures tomorrow. I think the cable (from what you guys have told me ) is too tight, causing the late and hard shifting. I know absolutely nothing about this so I think I'll push my luck tomorrow and hope nothing catastrophic happens.. My guess is that mechanic will be able to fix it. If not I'll hit the books and gain some expertise on tv adjustment.

 

[MadOgre]

You must be registered for see images attach

Oh well you need this TCI part # 376710

I believe it can be had in A B&M and Edelbrock version.

Your TV cable will not adjust properly with out it.

 

[MadOgre]

PS driving it anywhere with out this is gonna burn up your tranny. Your way better off trying to hitch a ride or something

 

[MadOgre]

Well I'll have to drive it tomorrow, but tomorrow night I'm going to my ASE class, I'll have the gm master tech take a look at it. Hopefully a simple adjustment. And yes, The PO replaced the stock 4bbl rochester carb with an edelbrock 650, it doesn't seem very well installed... I'll take pictures tomorrow. I think the cable (from what you guys have told me ) is too tight, causing the late and hard shifting. I know absolutely nothing about this so I think I'll push my luck tomorrow and hope nothing catastrophic happens.. My guess is that mechanic will be able to fix it. If not I'll hit the books and gain some expertise on tv adjustment.

Don't hope. In the mechanical world there is no such thing. Drive it and you will burn it up!