Hello Everyone,

I’ve been a “silent reader” until now, but I’ve run into an issue I couldn’t find discussed here.

I own a 1956 Olds 88. Recently, I rebuilt the engine and swapped the original 2-barrel carb for a new Edelbrock AVS2. The car ran great for about a month, but after a drive involving a lot of manual shifting, the Jetaway transmission stopped shifting into 4th gear. Gears 1–3 still work fine.

The transmission specialist my workshop works with tried several linkage adjustments but eventually concluded that a rebuild is necessary. His quote is €5,000 (around $6,000) including installation. Before committing, I contacted another builder for a second opinion. The first thing he asked was whether I had changed the carb. He mentioned that he’s seen similar issues after carb swaps because the geometry changes, which can lead to insufficient pressure for the 4th gear shift.

Since a rebuild is quite expensive, I wanted to ask: Has anyone experienced this issue before? If yes was it a linkage issue?

Thanks in advance for your help!
P.S.: Here’s a picture of my car.




built engine

 

I agree that these transmissions are sensitive to carb linkage adjustments,
I would suggest that you go back to the two barrel and put all the linkage as it was.
Then adjust the linkage as per the 1956 Oldsmobile Shop Manual.
If it still won't go in to 4th gear then the trans is obviously damaged and will need to be re-built.

 

The only thing that seems a bit odd is that it was working fine before. Still, it looks like there’s no way around your suggestion.
I’m hesitant because the engine currently runs beautifully and starts instantly, even when cold—but as I said, it seems this is the only option.
Thank you for the suggestion

 

I might be wrong but if your car is an 88 (not a Super 88), I believe it would have still had a hydra-matic and not a Jetaway. I suspect the problem is in the linkage since you did a carb swap. Linkage adjustment is critical. I hope that is your problem.

 

Two questions. 1st. Do you have two transmission cooling lines going in to the bottom of the radiator? 2nd any pictures of the linkage hookup to the trans?

 

The cooling lines would be a sure way to determine which transmission you have. The quickest is if you have a P (Park) position on you gearshift selector. If not, you have a hydra-matic.

 

Hi Glenn,

it is a Jetaway, I have a P and also the cooling lines are there.

 

I don’t have that picture yet, but I’ll take one later. However, I do have a picture of the linkage going to the carb. One of the transmission guys mentioned that he still believes the issue is related to the throttle lever radius on the new carb—he suspects the radius is too small, which might result in insufficient pressure to engage 4th gear. Unfortunately he is a 7 hours drive away from me and can not look at it in person as he seems quite knowledgeable.
I will check the radius on the old carb and compare it to the current radius.

 

Myself, i believe the carburator replacement should not be a big factor if you have all the original factory throttle linkage bolted to the intake manifold. Then the only difference would be how the carburator throttle plates are attached to that factory linkage. The piece that looks somewhat odd, is that round bent piece attached to the throttle. Did that come with the carb? Or? If that trans worked fine before the change, then i would have to think it should still work. Just hard to believe that it would go bad at this point. Maybe read thru this thread and see if it helps you. And look at his linkage setup. https://classicoldsmobile.com/forums...roblem-186632/

Have to add this. In your first post you stated that you did a lot of manual shifting and it worked fine. After the engine rebuild, did you try driving it normally in drive? Meaning no manual shifting.

 

the round bent piece is actually the "new" throttle linkage that was done by my repairshop to fit to the new carb. I need to doublecheck with them if they have bent the original linkage or took a new piece and adjusted it.
I just found pictures from the old carb setup and also when looking at the pictures from the thread you recommended it seems they adjusted the linkage that it bolts on the upper part and not on the lower part of the throttle lever.

I did the manual shifting after the engine rebuild. Actually i only drove the car 2 or three times before the rebuild and that is some time ago, thats why it is hard to do any comparisons for me. The manual shifting was mainly because i was driving on a steep and twisty roads thats why i isued Lo and S quite often.

 

I think your trans guy may be right. That radius is very important.
As a general rule the lever on the side of the trans should be all the way forward (against it's internal stop)when the throttle is at warm idle position.
And all the way back when it is at wide open throttle.

If you have the original carb , you may be able to determine that radius by measuring the distance from the center of the throttle shaft to the center of the hole where the linkage attached.

 

Hi Charlie,
thanks for your opinion ... i will try to adjust the radius and keep you guys updated.
If that does the trick, I definitely owe you guys a couple of beers! 😄