[Jack_K]

I was driving my 80 EC on the highway for the first time since rebuilding the engine and installing a used 700R4 tranny. I was in OD cruising about 60 or so (speedo is messed up with wrong gears in tranny) for 20-30 minutes when I started up a gradual rise. The car started bucking and jerking and losing power so I pulled over.

Temperature was below the 220 mark, oil pressure was 50 psi, battery was 13.8 volts, engine was idling fine. I looked under the hood and everything looked OK. Got back in car and goosed the throttle - sounded good, so I drove on.

Drove down the other side of the slight hill and started up the next rise. It started bucking again. I downshifted to D from OD and the bucking stopped. As the hill grew steeper the bucking started again, so I shifted down to 2 and the bucking stopped again.

Arrived at my destination and spent about 30 minutes there and then left. Drove home with trans in D and had no bucking, but I noticed the speedo was no longer working (it had been working before all the bucking started).

Arrived at home and checked the trans fluid level. It appeared low so I added maybe a quart. Haven't driven it since. I need to find out what happened to the speedo.

So, four questions:
1. Could low fluid level cause the bucking?
2. Why was it worse in OD?
3. Fluid level gets checked with engine running? In Park, Neutral, or Drive if running?
4. Any idea what happened to the speedo?

Jack
[edit] I have the correct TVE cable brackets for the 700R4 on the Holley carb and manifold and have adjusted the TVE cable properly.

 

[gentz]

I was driving my 80 EC on the highway for the first time since rebuilding the engine and installing a used 700R4 tranny. I was in OD cruising about 60 or so (speedo is messed up with wrong gears in tranny) for 20-30 minutes when I started up a gradual rise. The car started bucking and jerking and losing power so I pulled over.

Temperature was below the 220 mark, oil pressure was 50 psi, battery was 13.8 volts, engine was idling fine. I looked under the hood and everything looked OK. Got back in car and goosed the throttle - sounded good, so I drove on.

Drove down the other side of the slight hill and started up the next rise. It started bucking again. I downshifted to D from OD and the bucking stopped. As the hill grew steeper the bucking started again, so I shifted down to 2 and the bucking stopped again.

Arrived at my destination and spent about 30 minutes there and then left. Drove home with trans in D and had no bucking, but I noticed the speedo was no longer working (it had been working before all the bucking started).

Arrived at home and checked the trans fluid level. It appeared low so I added maybe a quart. Haven't driven it since. I need to find out what happened to the speedo.

So, four questions:
1. Could low fluid level cause the bucking?
2. Why was it worse in OD?
3. Fluid level gets checked with engine running? In Park, Neutral, or Drive if running?
4. Any idea what happened to the speedo?

Jack
[edit] I have the correct TVE cable brackets for the 700R4 on the Holley carb and manifold and have adjusted the TVE cable properly.

Fluid checked with engine warm, in neutral or park, it sounds like the bucking and surging is more of an engine issue than transmission by the way you describe. I would check for missfires or arching spark plug wires under a load. When it bucks and surges does your rpm rise alot then drop like slipping?

 

[black_on_black]

Your speedo cable could have broke happens alot when there that old + the jerking. One easy way to check if it the cable is to disconnect it from the tranny take your drill n put the end of the cable on it like it is a bit pull the trigger n watch the gauge. If it doesn't move try changing directions if it still doesn't move u found the problem.

 

[Jack_K]

Your speedo cable could have broke happens alot when there that old + the jerking. One easy way to check if it the cable is to disconnect it from the tranny take your drill n put the end of the cable on it like it is a bit pull the trigger n watch the gauge. If it doesn't move try changing directions if it still doesn't move u found the problem.

It's a new cable.

 

[DONE DEAL DONNY]

I agree with motor cause. You were running at lower RPMs each time you shifted to a lower gear raising the RPMs back up.
Also sounds like you need to pull the speedo and see if you can spin the cable. If it's hooked up to tranny you shouldn't be able to, gear may have striped in tranny
Donny

 

[ole george]

Although your torque converter clutch shouldn't dissengage under a light load , it sounds like it is staying locked up under load.If it did dissengage , it would cut down on the bucking. This ,of coarse , is addition to the root problem of power loss.

 

[Rob johnson]

Wow my E C does the same thing but i have no o drive it has the 4.3 , and clatters when this happens then runs fine when cold just does it when warm and up grades i cant figure this out???? someone help me

 

[rnhart3]

X2 on the converter still being locked. Saw many instances similar when working at a dealership..

 

[Jack_K]

It turned out that I had wired the vacuum switch so the lockup occurred at no vacuum and unlocked at vacuum. Here's drawing. I connected the wire to the wrong terminal.

 

[chevyefi]

Good job sorting it out.
Thanks for posting the diagram for others.