GM400 Gearbox will not change up gear

I have a 1984 XJS HE with original gearbox a gm400. Recently I removed the fuel rail to replace all the fuel lines as one was weeping fuel. After putting everything back together started the engine up took for a drive and gearbox is reving to 3500 rpm 40km an hour but will not change gear.
In the past 3 months the Governor spindle has been replaced and the modulator has been replaced. The vacuum line to the modulator is holding a vacuum and is fine. any ideas???

Well, since you were fiddling in the area, I’d check to see if the kickdown switch is somehow permanently engaged.

Ok will check that out tomorrow. I have ordered a replacement modulator and governor just in case due to arrive next week some time

From past experience the PCV valve can produce a similar problem.

I am curios now - what is connection between PCV valve and gearbox performance?

I’ll bet that Trev had a “Senior Moment” and meant to put his post on the “Idle too Slow” thread.

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As the inlet been disturbed - I would start from checking vacuum value. Look for leaks in the vacuum line, try to disconnect the vacuum from gearbox and blank the port, see if there is any difference during the ride. I assume your gearbox runs on 1st gear only? (or 3rd gear maybe?)

PCV valve jammed open will cause loss of vacuum.

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No senior moment then. Darn. I have them all the time!

As a very much senior, I feel entitlement !!!

Thank you for that wisdom of advice, you hit the nail on the head, wrong connection on the microswitch keeping box in permanent kickdown. Just had her out for a quick drive 100 km an hour and 2k revs, changing up and down very nicely. Great appreciate your help. thank you

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Glad I could help!

20 char

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Guess I wasn’t thinking clearly about failed open PCV valve effect on vacuum - thanks

Yipppy !!!

Best as it can. simple fix, all is well…


PS: fixed my elecrical issue. Thought I over loaded a house circuit with gadgetry. Blew a fuse. Used meter to check them for continuity. Not quite done. Meter went dark. Marginal 9v battery died. Lottsa batteries here, except no more 9vs. Could dash to the store and get some. Nope, I am still in quarantine…

Check main box. Reset master breakers. Whadda you know, the lights came on. All circuits powered…

Should I rob my analog meter of it’s battery and repower the digital?

I will add 9v’s to the shop list. Forgot when I bought up a bunch of rechargeables. Goal is all rechargables…

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Analog stuff is retro cool, but I would not trust an old analog meter for real work compared to a modern digital meter. I rebuilt an old Robin meter for a friend and had to create a voltage source out of button cells to replace a weird battery that no longer existed. It was a lovely thing to hold and use, but only could get to 5% of my digital meters that were all within 0.5% of each other.