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Post Info TOPIC: 68 GP TH400 / 396 trans vacuum line


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68 GP TH400 / 396 trans vacuum line


I am hoping to get some help or input on the vacuum line to the trans modulator for the above combination.  In a recent discussion with a previous owner of this 68 GP, I mentioned that the engine sounded like it was revving higher before the trans would shift into a higher gear.  Long story shortened is that I was informed that the original vacuum line to the modulator was replaced as there was issue with the original and subsequently a vacuum line that was 1/4 inch was installed as they were unable to source an original.  I was told that the original was a 3/8 diameter and a 1/4 inch was installed and perhaps this 1/4 line was affecting the modulator and shifting.

Admittedly, I do not have a hot clue whether the original vacuum line should be 1/4 inch or a 3/8 inch, so my question is, does anyone have any information as to what size the vacuum line should be for 396 / TH400?  Also, could a variation in the diameter also be a contributing factor in shift variation?

The car is stuck in storage for 10 more days so I can't access it immediately for any other info, but wanted to try and get some info on this topic.  Also, does anyone have an original part #?

Thx, Jake

 



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Earl36


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i am 100% sure it should be 1/4 inch

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Canadian Poncho Superstar!

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Without looking I'd say it's probably a 3/16 line Jake.

Classic tube, Fine lines or Inline probably has an exact shiny reproduction part. Or just do it yourself with brake line. I don't thing the size will have much bearing on the function of the modulator. Provided the modulator isn't stuck and the hard line and hoses aren't significantly kinked, it should not matter.

Funny you are asking about it, I will be making up that exact line this spring for my engine install, and have been actually thinking about it.

Cheers,



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67' Grande Parisienne. Ex Ottawa USSR Embassy car, 67- 68.
6977017306_dfca361bfc_m.jpg
 


Poncho Master!

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You should try and get a factory line if at all possible.

I believe the main line is 1/4" but the ends are reduced to 3/16" and have a "furl" to keep the hose secure.

They are very interchangeable so even say a pickup with a 350 Engine and a T-400 will work.

The line at the top actually fits inside the fitting in the intake and the hose slides over to seal them up.

Normally the fitting for the power brake booster also has a smaller nipple for the modulator line .

Most modulators have a secret adjustment screw to fine tune the shift.

The screw is inside the modulator hose nipple, the hose must be removed to make adjustments.

There should be no fluid inside the hose, if any is present it indicates a faulty modulator.

Looking at it turn the screw right to delay shifts and left for earlier shifts.

Thanks
Randy




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Sherwood Park
Alberta, Canada

1981 Parisienne 400



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Thx for the responses, it gives me some valuable info to explore when I liberate it from storage! 10 days and counting, hope Winnipeg weather cooperates!

Jake

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Earl36


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I should have an original one for you.

There's a couple different configurations, mainly dealing with the fitting on the intake manifold. On most, the fitting has the vacuum port pointing straight at the passenger side fender. However on some, the fitting has the vacuum port pointing almost 45 degrees towards the heater box. Which fitting do you have, and I'll take a look at the vacuum lines I have. (I grab these from the junk-yards as I was missing one on my 2+2 rag when I got it) As GLHS60 mentions above, the ends are reduced.

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70 2+2 convertible
70 2+2 hardtop
70 Parisienne hardtop
72 GMC Sierra

 

 



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Hello Seventy2plus2, I am not sure which fitting I have but I will take a look,...in ten days! The car is buried at the moment and I am going to take it out of storage at the end of the month. I doubt I will have a chance to have a look prior to that but your question is something that I am going to look at closely. I will let you know in ten days!  biggrin

 

Thx, Jake



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Earl36


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ricks first generation Camaro sells them ... all  BIG BLOCK AND SMALL BLOCK CHEVS ARE THE SAME THE LINES SHOULD FIT AND WORK



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Canadian Poncho Superstar!

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I'm sure I have a reproduction one for the fitting that points towards the heater box, and I'm sure I have a used one for the fitting that points towards the fender.

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70 2+2 convertible
70 2+2 hardtop
70 Parisienne hardtop
72 GMC Sierra

 

 

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