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1987 TBI Vacuum to TH350 Transmission

magik235

magik235

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I have a 1987 350 TBI with a TH350 transmission. The transmission failed and I am getting it rebuilt. I want to assure I have everything right when I reinstall it. I have searched and read many posts regarding this issue but haven't found a definitive answer.

What is the best place to connect the vacuum line to the TH350's vacuum modulator on the TBI setup?

Is the quote below from TCI transmissions accurate?

3. Don’t attempt to use a kinked metal or all rubber hose to connect your vacuum modulator if applicable. Proper installation is a metal line carefully bent, with just a few inches of rubber hose on either end for connection.
 
I am pretty sure you want strait manifold vacuum. I think TBI has a port right behind the TB on the pass side intake runner to get it from.
 
my old 87 did.....:thumb:
 
Yea, you want full manifold vacuum from the TBI routed how they say. If you use rubber all the way it can degrade and collapse.
 
Are you sure you have a TH350? 1985 was the last year for a TH350 in a blazer, your 87 should be a 700R4 UNLESS someone swapped in a TH350. The info about a nicely bent steel line with a short piece of rubber hose at either end for connections purposes is correct though for any trans using a vacuum modulator and it MUST e manifold vacuum not ported vacuum.
 
4X4HIGH said:
Are you sure you have a TH350? 1985 was the last year for a TH350 in a blazer, your 87 should be a 700R4 UNLESS someone swapped in a TH350. The info about a nicely bent steel line with a short piece of rubber hose at either end for connections purposes is correct though for any trans using a vacuum modulator and it MUST e manifold vacuum not ported vacuum.
Click to expand...


My Dad bought the 87 new. It came with a th350c....It had 220k miles before my ex #2 wrecked it....

They were still out there....Of course, my 86 burb came with the 700r4 .....:dunno:
 
Currently the TH350's vacuum line is connected to the port behind the TBI but there is a T in the line with the other hose going to the cruise control, heater controls and a vacuum reservoir . My assessment is the TH350's vacuum line should be independent of any other lines. Where should I connect the lines going to the cruise control, heater controls and the vacuum reservoir?

The TH350 is a transplant. The Jimmy came with a 700R4.
 
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If the other stuff needs full manifold vacuum too, I would get one of the fittings with 2 ports on it and feed the trans modulator off one then the other stuff with the other port, if nothing else just to keep everything clean and neat in there.
 
As long as it's manifold vacuum (it should be from your description of what it controls) it doesn't matter how many things share the same port.
 
In the picture below of the manifold is the plug just to the top right of the TBI flange a plug for a vacuum port?

350Swap017.jpg
 
First, it's doubful that you'd be able to remove that plug, second, that's a large NPT thread and you'd have a VERY HARD time finding a fitting that would fit and then have a nipple small enough for the hose you want. You just need to find a fitting that fits the circled NPT thread that has however many hose nipples that you need. If you need 3 or more then Fords are a good source and they used a fitting with up to 5 or 6 hose nipples of various sizes.
 
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