Transmission shift points very high RPM's-86 m1009

[86NavyT]

The TH400 tranny in my 86 m1008 shifts at very high RPM's from gear 1st-3rd

it was fine before it just started out of the blue. Sometime when I first start it seems like it shifts almost normal. But most of the time it has to be revved up pretty high befor it will shift. I've searched some and can across vacuum line problems but I couldn't find any broken under the truck (only saw metal lines no soft lines) I can only aaccess this site through my cell phone so searching is quite difficult on this little 2x3.5" screen. Anyone experience something similar to this? Thanks so much for reading this and any input you have!

 

[cucvrus]

Check all the rubber lines and the vacuum pump at the rear of the engine. 9 chances out of 10 that is the issue.

 

[MarcusOReallyus]

What Rick said. Rubber lines. Under $10 bucks to replace them all, and the chances are really high that that's all you need. Do that first, then get back to us if you still have a problem.

 

[stationjj]

I had the same issue. I agree with above, check your lines first.
After my vacuum lines checked out. It turn out my problem was the vacuum regulator value.
A vacuum regulator value can be purchased on Amazon.

stationjj

 

[rustystud]

Yep, what they all said.

 

[Russm]

https://www.rockauto.com/catalog/x,carcode,1050691,parttype,5172

Had the same problem.
My vacuum pump was bad

Now it shifts like it's brand new

 

[86NavyT]

Thanks for the tips everyone. Ill let you know what I find!

 

[M1008BOV]

I'm replacing my old dry rotted lines today as well. Couldn't find this vacuum piece at my local parts store. Any idea's what it's called and where to get one?

 

[cucvrus]

Don't need it. Just put Top line to Transmission modulator and bottom line to the vacuum source. If you really think you have to have it I will sell you one. But it is not needed.

 

[M1008BOV]

I wondered if there was a reason for that special connection and why I couldn't just direct connect the two individually?

 

[2deuce]

I had the line crack at that connection, only a tiny split on the underside. Fixed that and normal shifting resumed.

 

[cpf240]

That part is NLA. I *think* the purpose was to keep the lines connected properly, ie Top to Transmission...

 

[M1008BOV]

Ok, it wasn't shifting good still, so I removed that piece and just went direct. FYI, the line from the vacuum actuator goes to the bottom, the short one that connects to the hard line goes on top. Shifts good now.