Shifting Gears loses powers when throttled

[MtnSea76]

I’m new to this. I just purchased a 1976 Bronco that has a completely rebuilt 302. Only a couple hundred miles on the new build. I brought the beauty from Utah to CA and since I’ve had it in CA, while in drive their is a delay between shifting from 1st to 2nd. If I drop it down and move it manually from 1st to 2nd to Drive it goes smooth. Seems to only lose power when in drive. Any recommendations on where to start?

 

[bronco t]

Welcome to the CB forum!

I would start by checking all of the vacuum hoses especially from the vacuum tree (behind the carburetor) to the vacuum modulator on the tail shaft of the transmission and look for cracked hoses, loose connections, missing caps, etc. Being a fresh rebuild who knows if the vacuum lines made it back to where they are supposed to be.

Also check to see if the kick down linkage from the carburetor to the transmission isn't binding and is moving smoothly (ask me how I know).

Here is a pic of my 77 vacuum tree that was missing a cap on one of the unused vacuum ports and the brake booster vacuum line coming out of the top of the tree was cracked. I have since replaced all of the vacuum hoses and it has run and shifted great since (knock on wood).

Good luck.

 

[DirtDonk]

Hey there. Welcome too!
Do you know if the transmission was worked on as well? Do you know if it’s a stock bronco C4?

 

[MtnSea76]

Welcome to the CB forum!

I would start by checking all of the vacuum hoses especially from the vacuum tree (behind the carburetor) to the vacuum modulator on the tail shaft of the transmission and look for cracked hoses, loose connections, missing caps, etc. Being a fresh rebuild who knows if the vacuum lines made it back to where they are supposed to be.

Also check to see if the kick down linkage from the carburetor to the transmission isn't binding and is moving smoothly (ask me how I know).

Here is a pic of my 77 vacuum tree that was missing a cap on one of the unused vacuum ports and the brake booster vacuum line coming out of the top of the tree was cracked. I have since replaced all of the vacuum hoses and it has run and shifted great since (knock on wood).

Good luck.

Thank you Bronco T. I will start at the Vacuum tree.

 

[MtnSea76]

The transmission was rebuilt as well. It is a stock C4.

 

[MtnSea76]

The transmission was rebuilt as well. It is a stock C4.

Correction: The gaskets and seals were replaced on the transmission, but the transmission itself was not rebuilt.

 

[Rustytruck]

Check the timing, stock is 6 degrees before TDC. which is a dog setting advance the timing to 12-15 degrees before TDC. Summer will soon be here shed the top and doors and run Naked it will step up your game too. Stock Broncos were dogs compared to modern engines today. Broncos that were dogs at 150 Hp at the rear axles are a beast with 300 HP. you don't mention tire size and gearing stock axle gearing goes to hell after a 30 inch tire. then you need 4.11 gearing at 33 inch tire. get the gearing right and they can be fun to drive again.