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12-26-2018, 01:19 PM
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#1 |
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Registered User
Join Date: Apr 2005
Location: Austin, Texas
Posts: 300
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Why do I have a transmission relay?
I have the fuel pump relay on the firewall and next to it is a transmission kickdown relay. I have an 87 TBI truck with the 4.3L and a TH350 trans. I think (Not near the truck right now) the truck came with a TH350 new and I think that is what is in there now. It's either that or a TH350C.
I attached a pic I found on the internet to show what I am talking about.
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My mother is a recent cancer survivor and this truck build is for her |
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12-26-2018, 05:50 PM
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#2 |
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Registered User
Join Date: Oct 2009
Location: .
Posts: 2,187
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Re: Why do I have a transmission relay?
They came equipped on trucks with the M40 RPO(TH400) transmission.
Do you have a switch on the accelerator pedal? Can you post a pic of the SPID? |
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12-26-2018, 06:54 PM
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#3 |
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State of Confusion!
  
Join Date: Jul 2002
Location: Gulfport, MS USA
Posts: 47,269
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Re: Why do I have a transmission relay?
If it is a T350, then it is a T350C model for the later years. Not sure about the relay part as I don't remember one on my 81 (250 w T350C). Since your's is an EFI 4.3, then it may need it.
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Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God! |
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12-27-2018, 11:17 AM
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#4 |
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Registered User
Join Date: Jul 2005
Location: CT
Posts: 278
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Re: Why do I have a transmission relay?
Your truck did not come with a TH350 so if it has one, someone swapped it. The TH400 Detent solenoid is energized via the relay which is energized by the ECM.
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01-03-2019, 06:12 PM
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#5 |
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Registered User
Join Date: Apr 2005
Location: Austin, Texas
Posts: 300
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Re: Why do I have a transmission relay?
Low and behold, this truck came with a TH-375. I never knew that existed.
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My mother is a recent cancer survivor and this truck build is for her |
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01-05-2019, 01:26 PM
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#6 | |
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Registered User
Join Date: Apr 2009
Location: New Freedom Pa.
Posts: 1,335
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Re: Why do I have a transmission relay?
Quote:
The TH 375, is simply a TH 400 with a long output shaft that mates to the smaller TH 350 drive shaft yoke. This can be identified by "375-THM" cast into the tail housing. Internally the clutch packs originally had fewer friction plates. The 375 rating was a result of the smaller yoke and fewer clutch friction plates. To confuse the matter, some heavy duty TH 350s were also designated THM375-B. The key to telling the difference is the shape of the pan.
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