FMX

bogdanator · May 18, 2024

Hi everyone
I need help with my mustangs FMX transmission , I have a 1973 Mach 1 with 351C and auto fmx , tha car is shifting very late, everything is hooked up ok , oil is good so I’m thinking about replacing a vacuum modulator but there’s so many different ones, some with blue stripes some with green and so
Can someone tell me witch one to get, witch is correct and will work
Thanks

Hemikiller · May 18, 2024

The '73 FMX w/351 would use the Black band modulator - TM-18 or D3AZ-7A377-A. There's a couple on eBay. You can also use Standard Motor Products TM-27. The current version is a single area diaphragm, the original was a dual area diaphragm (two ports)

https://www.ebay.com/itm/256162378227?chn=ps&mkevt=1&mkcid=28

bogdanator · May 18, 2024

Can I use a single diaphragm one , will that be ok. I do not have a egr any more and I think the second port connects to egr

Hemikiller · May 18, 2024

The TM-27 from Standard is a single area diaphragm designed for the 73s and eliminates the second port for the EGR compensation.

bogdanator · May 18, 2024

Thank you for your help

bogdanator · May 18, 2024

The TM-27on ebay is showing as 2 port , is ther any other single port I can use or I just cup one port?
Thanks

Bentworker · May 18, 2024

See below. The vacuum modulator should be chosen based off of your engine vacuum. How wild is your camshaft?

https://7173mustangs.com/threads/fmx-valve-body-info.39371/

bogdanator · May 19, 2024

Everything is stock , just rebuild the engine, trying to stay simple
Thanks

Hemikiller · May 19, 2024

The instructions that are supplied with the Standard TM27 show it is a single port design.

https://www.rockauto.com/en/moreinfo.php?pk=45220&cc=1132995&pt=8500&jsn=2067

Bentworker · May 19, 2024

Get a handheld mityvac pump and test the one you have. The modulator softens the shifts under lightly loaded (high vacuum) driving. If you have a bad vacuum leak, pinched or clogged hose / line it will present like a bad modulator.

FMX

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