Th350 shifting way late

[Joec123able]

My 77 k-10 shifts ridiculously late. It doesn't shift from first to second until 35 mph and at that point, it's revving so high it's almost almost redlining. It's a fun truck to drive but that just ruins it for me. Also I pretty much can't coast in it I have to basically stomp it til it shifts to the next gear then I can coast. Otherwise it will stay in gear and it feels like it's holding you back while coasting. Any ideas? I changed the trans fluid and filter and that had no effect on it.

[bd]

Check the vacuum line to the transmission modulator valve.  The rubber hoses at each end of the steel line have a tendency to swell and loosen or split.  Make sure the steel line isn't perforated.  While you are there, peer into the vacuum port of the modulator valve to see if there is any trace of red transmission fluid - replace the valve if there is and recheck the fluid level.

[Joec123able]

Check the vacuum line to the transmission modulator valve.  The rubber hoses at each end of the steel line have a tendency to swell and loosen or split.  Make sure the steel line isn't perforated.  While you are there, peer into the vacuum port of the modulator valve to see if there is any trace of red transmission fluid - replace the valve if there is and recheck the fluid level.

How would I check if there's a vacuum leak?

[bd]

Begin by inspecting the short 5/32" rubber hose at the modulator valve and the 1/4" rubber hose at the intake manifold vacuum fitting behind the carburetor.  Then inspect the connecting steel line for any obvious physical damage (e.g., rust, rubbing, breaks, etc).  If the steel line is still questionable following visual inspection, plug one end of the line and draw a vacuum on the other end to see if the line will hold vacuum.  With the line properly connected at both ends you could also spray the line with some B12 or similar aerosol while the engine is running to see if there is an RPM change - but watch out for exhaust heat.

[Joec123able]

Begin by inspecting the short 5/32" rubber hose at the modulator valve and the 1/4" rubber hose at the intake manifold vacuum fitting behind the carburetor.  Then inspect the connecting steel line for any obvious physical damage (e.g., rust, rubbing, breaks, etc).  If the steel line is still questionable following visual inspection, plug one end of the line and draw a vacuum on the other end to see if the line will hold vacuum.  With the line properly connected at both ends you could also spray the line with some B12 or similar aerosol while the engine is running to see if there is an RPM change - but watch out for exhaust heat.

Thanks a lot for the help! I'm gonna check that out, and probably just go ahead and replace the modulator valve and hope that solves it!

[Engineer]

Do what bd suggested first and let us know what you find.

If that doesn't fix your issue you may have a governor problem.

[rich weyand]

1) Replace both hoses first.  Cheap, and usually the cause of the problem.

2) Change the modulator.

3) Modify the governor.

You don't say whether this is a new problem, or existed when you got the truck.  If it was already a problem, the governor may have been modified already by an IPO who didn't know what he was doing.

[Joec123able]

1) Replace both hoses first.  Cheap, and usually the cause of the problem.

2) Change the modulator.

3) Modify the governor.

You don't say whether this is a new problem, or existed when you got the truck.  If it was already a problem, the governor may have been modified already by an IPO who didn't know what he was doing.

It's an all time four wheel drive truck and it has had that problem since I got it. I honestly don't know anything about the governor so I wouldn't know where to start with that but I'm gonna try to replace the modulator and fix any vacuum leaks tomorrow I'll let y'all know if it works out.

[Joec123able]

Begin by inspecting the short 5/32" rubber hose at the modulator valve and the 1/4" rubber hose at the intake manifold vacuum fitting behind the carburetor.  Then inspect the connecting steel line for any obvious physical damage (e.g., rust, rubbing, breaks, etc).  If the steel line is still questionable following visual inspection, plug one end of the line and draw a vacuum on the other end to see if the line will hold vacuum.  With the line properly connected at both ends you could also spray the line with some B12 or similar aerosol while the engine is running to see if there is an RPM change - but watch out for exhaust heat.

Okay I just found something on the trans that may be the cause, I found the metal line with a rubber end and there's a little nipple that it plugs onto on the transmission and it isnt hooked up, is that the vacuum line? If so it isn't even hooked up!!

Thanks a lot for the help! I'm gonna check that out, and probably just go ahead and replace the modulator valve and hope that solves it!

[Joec123able]

She's fixed!!! I'm so happy, it was just the vacuum line unhooked! Lol I'm so glad now it drives like a normal truck

[bd]

Good job!  Make sure the vacuum hose is a tight fit on the modulator valve so it doesn't come loose again.

[Joec123able]

Thanks so much for the help, getting that fixed made my week! So happy. I've had to fix a lot on this truck since I bought it but now getting that fixed, it's finally atleast a drivable truck.

[bd]

You are quite welcome.  Happy to help!

[Dr_Snooz]

1) Replace both hoses first.  Cheap, and usually the cause of the problem.

2) Change the modulator.

3) Modify the governor.

You don't say whether this is a new problem, or existed when you got the truck.  If it was already a problem, the governor may have been modified already by an IPO who didn't know what he was doing.

4) Check the kickdown solenoid.

I know the issue is resolved now, but for posterity, if the kickdown mechanism fraps out, it won't shift until 4k. At least that was the problem on my TH400.

[bd]

TH350 doesn't use a detent solenoid.