Harsh shift 1 to 2 and "clunk" getting in gear?

I have searched and I think I have some ideas, but before I drag it back to the tranny shop, I am hopeing to get you folks opinions as well.

From park into R there a pretty good jolt/clunk coming from the tranny. The 9" rear was also went through in the process. Unless they screwed it up, the lash should be OK. Then there is the same jolt coming out of neutral into D.

And then from 1st to second, the shift is pretty stiff too. From 2nd to 3rd its softer, bout right IMHO.

I am running Supershift Amsoil ATF which they spec for Type F. Amsoil says it will tighten shifts. If 2nd to 3rd were tight as well, I think I would just assume that its my oil and forgetaboutit.

But I have never driven a C4 before, so I am worried. Do harsh shifts lessen the life of the tranny? I chose the synthetic amsoil becuase I want maximal life out of the oil, not because I race or tow much.

Could the bands be out of adjustment? Or just my agressive oil choice?

This a used tranny, but I had it freshened up -- the shop said they replaced all the seals and couple of clutches (everything that looked bad at all). It was newly rebuilt less than 5k miles before the prior vehicle (302 Mustang) was wrecked. Then it sat for 5 years in a garage till I traded for it.

It has a stock 12" convertor on it, which if I understand things, has a low stall speed. I have the truck idle set at about 900 - 1000 RPM. I backed off the idle speed and it didn't make much different though, and it became doggy from a standstill during "casual" driving, which is what I mostly do.

Thanks

I had the same problem and adjusting both bands fixed it up.

With your idle at 900 - 1000 rpm you should be getting a very uncomfortable shift from park or neutral into any gear but it will be worse in reverse.

There are two things that may be causing this. Your high idle is definitely one but when your transmission was worked over they probably raised the line pressure. That will add to the harsh shift.
It will not harm the C4 but it is hard on the rest of your driveline components. U-joints should be checked more often because they are the first that will show wear. The splines on the output shaft can be affected but not for several years of very harsh abuse.
Let me help you understand what is happening. In park at 1000 rpm the pump is in full by-pass. That means that pump pressure is very high while line pressure is more or less nill. When you shift into reverse the line pressure spikes very high - higher than when you are in drive. The forward clutch bangs into the locked position with the engine and the converter at 1000 rpm. All the slack in the transmission is immediately removed and the whole gear train is shoved to the rear of the C4 case. As all that is happening the reverse band locks the reverse drum as it tries to spin backwards at 1000 rpm. That shock is transmitted to your driveshaft about the same time the gears in the planetaries begin to spin. Pressures are still as high as they can be at the rpm. The rpm drops because of the stall speed of the converter (about 1200) but the torque is on its way to doubling (that happens when your rpm is 1200 rpm above your road speed. Nothing in the transmission is turning yet because your foot is on the brake. When you release the brake you instantly begin to accelerate because your engine is still trying to turn 1000 rpm. Your transmission has to slip to wear so it isn't producing any wear. The fast engagement keeps that from happening.
As for the reduced speed of high gear engagement - it is an illusion. The shift is just as fast but you are already cruising and the converter is able to absorb most of the shock. If you set your idle as low as possible without stalling in drive it will eliminate most of what you feel. 550 - 650 in drive for a stock engine is about right. Be very happy that your rebuilder did such a good job in building your transmission. I would not recommend doing any adjusting without consulting your rebuilder first - I don't know what mods were made or what the critical clearances are - they will. When I build a C4 I adjust the bands very differently than the factory suggests - if they are adjusted to factory specs it will generate a great deal of heat and wear. So don't adjust anything without dicussing it with the rebuilder first. I do recommend that you lower your idle - a lot! to make the fist shift into gear more comfortable.

Wow, great reading, though I find some of that over my level of understanding/need.

I will say that my "builder" is a local guy that really just freshened the tranny up. We did not discuss any mods or performance settings/adjustments and I assumed that I was not getting any. My engine is producing a mighty 140 HP!

As for the idle, I had it a about 650 when I had the manual tranny. With automatic tranny, I found that it idled rather slow once in gear, such that it would cough/hessitate a little off the line, so I adjusted the idle up to 950 or so.

But the harsh shift was occuring at 650 idle as well.

It is possible that the tranny had been reworked for more performance by the prior rebuild -- I got it from a fellow who's son had it in a warmed over mustang with a 302. It had been rebuilt less than a year before the stang got wrecked.

I will heed your advice and not jump in there to start adjusting things.

Paul is the man. I often feel like we owe him for the lesson.

The C4 was probably beefed up when the prior owner had it - That would make sense with the added HP from the "warmed over" 302. You are not likely to hurt the transmission with your 240 six. Harsh engagement into reverse is common when the mods in the valve body are made because the restrictors to the low reverse solenoid are drilled for faster engagement and release. The same is true for second gear servo. Higher pressure is also needed with a performance C4.
Take your idle down and adjust the air fuel mixture, accelerator pump and timing to keep it snappy from a standing start. The 240 has a lot of torque on the low end so you should be able to make use of it.

BTW: My "standard" street build for the C4 is good for 350 -400 HP. I don't do stock rebuilds.