This is a freshly rebuilt th400 rmvb with 2nd and 3rd gear issues.
1. Fluid is at full mark
2. Linkage is double checked and is right
3. Yes it's a rmvb shifter

After installing tranny the first time p,r,n,1 worked fine and as soon as shifted into 2nd tires would lock up and some thing for 3rd.

I dropped trans and took it back to the builder and I reinstalled the trans and this time p,r,n,1,2 work and tires locked up in 3rd.

after notify the builder of the issue I was told a check ball was accidently left out of the tub. I was told it was an easy process and that i could do it. After installing check ball in location i was told and put everything back together I'm at square one again. P,r,n,1 and 2nd and 3rd lock up.

I'm probably going to just cut my losses and take it somewhere else.

I have read some threads on ls1tech about this issue but there like a decade old and it just goes ghost. No response if issue was fixed or what the root of the problem was.

I just wanna get this issue resolved already and I'm sure there are some very knowledgeable guys on here. Thanks in advance.

 

My best guesses would be either the low reverse band is to tight or otherwise being applied during 3rd or the 2nd gear overrun band is applied however it is usually omitted with the RMVB I have worked with,

 

What valve body is it using?

 

I'm not sure of the VB brand that was used.

 

Update? having the same issue