Hello all -

As you can gather from my other threads, I'm in the process of returning my dad's '68 F-85 to the road after a 6 year hiatus (with very limited driving 5 years before, after the first time it was resurrected). When it last was on the road, we noticed a small leak of transmission fluid, which was regularly topped off. During the 6 year period it sat, there was a massive leak (something I've gathered the Jetaway is famous for when it sits after use for a while). This weekend, I completed work on the manifold and carb swap, filled the trans to the dipstick level, and backed out with no problems. However, there was a noticeable clunk shifting into drive, but then no issues shifting from 1st to 2nd. However, when downshifting while slowing down, there was a noticeable clunk that would occur - but only when downshifting, not upshifting! Fluid levels are full, I used DEX/MERC as I had in the past.....any ideas what could be causing a clunk when downshifting or shifting into drive from park/neutral when stopped?

Pics of new top end parts included, just because.

 

Looks like a fun project. You are going to get a lot of people suggesting that you drop that Jetaway and replace it with either a TH350 or 200R4, and I am definitely in that camp. Doing any work to the Jetaway is not worth the trouble nor the money. The car will drive so much better with a TH350 or 200R4, and both of these more or less drop in.

 

First I would check that your modulator is connected to manifold vacuum, next would be Ujoints.

 

Way back in the '70s (when Dad still owned my Cutlass) it exhibited these same symptoms, most noticeable was the hard clunk when slowing to a stop at the downshift from 2-1. Discovered that Dad had set the idle speed too high. Once that was adjusted back to spec, the clunk went away. I high idle speed would also cause a clunk when shifting into gear. Considering you have a new intake/carb, I wouldn't be surprised if something similar is going on.

 

Sorry for the very late (necro thread!) reply, but just wanted to say thank you for this - I ended up swapping carbs with a buddy, as we suspected the used carb I got needs a rebuild, and the new idle speed from his carb eliminated the clunk altogether. I've since adjusted the idle with no clunk return, so you were spot on. Thank you again!

 

Great, glad to hear you got this solved, and thanks for the feedback to this thread. BTW, the carb you had on there previously should've been capable of dialing back the idle speed to the same spec as the OEM carb. The trans should know no difference in carbs if they are set to the same idle speed.