th-400 problems

[Ssmnt408]

talking to a guy about buying his th400 he says sometimes when you shift to second it just free revs other times it goes right into gear. He said it had a fairbanks manual valve body kit in it. is this an internal problem or could it be his linkage not properly adjusted?

[DonWG]

Free reving shifts are not a linkage problem.

[Ssmnt408]

any insights as to what the problem could be?

[DonWG]

That is a very strange symptom for a 400. I'd have to test drive that one.

[87buickracer]

Originally Posted by Ssmnt408

talking to a guy about buying his th400 he says sometimes when you shift to second it just free revs other times it goes right into gear. He said it had a fairbanks manual valve body kit in it. is this an internal problem or could it be his linkage not properly adjusted?

Problem could be in the valvebody.disassemble and inspect.

[chris718]

This sounds like the 2nd sprag is rolling over .I saw this 2 times and based on ttorque input to the sprag itll either hold or roll over.

[DonWG]

I thought about the sprag too. But even if the sprag had rolled, you'd still be in low. The 1-2 shift would just feel like you stayed in first. Some people that don't recognize a rolled sprag could assume that the trans went into neutral and is free reving. Hence why I suggested that someone with more knowledge of transmissions should test drive the car.

The shifter adjustment should be checked also. Wondermatic shifters are notorious for giving the impression that second gear is not there. I just had a customer yesterday that went to the track the weekend before and had no second gear running down the track, but had second on the return road. Transmission experts that happened to be at the track that day were, of course, offering their opinions of doom and gloom. "Oh, I've been doing transmissions for decades and I do everyones transmissions here at the track. It's the sprag." This was a 350 by the way, with a HD intermediate sprag. Not the stock roller clutch assembly. I know. 350? It's what the guy had and what he wanted to stick with. It was like pulling teeth to get him to at least go with the aftermarket sprag assembly. The guy called us and we asked him to bring the car in so we could check it out before we offered an opinion. As soon as we took it down the road, we recognized the famous wondermatic shifter syndrome. Adjusted the shifter and all is well. We had built the transmission and installed the shifter last year. The car left the shop with everything adjusted properly. It turns out that the customer removed the engine and transmission, for whatever reason, and when he reinstalled everything, he obviously didn't get the shifter adjustment right. Good thing someone didn't just pull the trans assuming a busted sprag. That tech would have found a nice surprise.

Never assume anything. The first step to properly diagnose this problem is to have a qualified and knowledgable person test drive the car.

[chris718]

Alot of times we get an incorrect description of the problem,however the sprag can hold and then let go and this would put it back to low but freewheel .Most customers couldnt relay that concept to us in a language that makes sense.What is a wondermatic shifter

[bison]

Sounds like a failing sprag/roller clutch. I would be most pronounced on gear changes.

[DonWG]

Originally Posted by chris718

Alot of times we get an incorrect description of the problem,however the sprag can hold and then let go and this would put it back to low but freewheel .Most customers couldnt relay that concept to us in a language that makes sense.What is a wondermatic shifter

A Wondermatic is a shifter that's so far out of adjustment that it makes you wonder what position your in when using it.