C4 squeals on gear change and burns clutches - Page 5 - Ford Muscle Forums : Ford Muscle Cars Tech Forum
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post #61 of 69 (permalink) Old 04-16-2019, 02:22 AM
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Re: C4 squeals on gear change and burns clutches

I'm at a bit of a loss with the pressure .
Reverse IMO is actually high , and Forward gears low .
I can't help thinking something odd in the pressure reg boost valve area .

The circuitry is very similar between early and late styles .. The ports in the cases are different so they shouldn't be interchanged anyway . I know that's not what you've done just answering the question.

Now have any parts components been switched between valvebodies ?

Reason I ask , In the late 70 on valvebodies , there are actual few different castings , I'll say 3 I know for sure in some comparisons i've done , maybe more.

There are 3 different size 1-2 shift valves , and 2 different seperator plates . The plates are close to same looking but a couple holes slightly different .

The gaskets in the kits usually have the holes to suit both plates ..

You do have the correct gasket for the 40-3 kit ???? It is different to a standard gasket .
The cutback valve can have a ball fitted , but just to prove it check that orange spring , I think you'll find it wont allow the cutback to move enough to actually function to drop pressure.
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post #62 of 69 (permalink) Old 04-16-2019, 04:17 AM Thread Starter
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Re: C4 squeals on gear change and burns clutches

hello greg, thank you for confirming the differences in valve bodies as i have read they are not interchangeable i didn't know why.
items changed between valve bodies are only those found in the shift kits as i move from one vb to another.
i agree with you as i have 3 different vb's and 2 different separator plates all of which have been kept together for use later if need be.
i have noticed differences in the galleries within the vb halves and also the different hole positions and sizes.
yes the gaskets are correct for the 40-3 and all holes are clear (not blocked) as per the visual light test and are not standard.
i will try the cutback spring for bind and install steel ball just in case.
now for the boost regulator,

does the boost regulator work identically in all forward gears if so what could cause a different pressure between them?

what do i look for with its condition?
i know that i have at least 2 different boost regs as the spool valves do not fit the other sleeves.

how can i diagnose boost valve problems?

wow thanks this is getting deep, also i was driving it and at low rpm it would change harder if i held the rpm at say 3000 for a couple seconds then got on it and changed. it sort of felt as if it had to build pressure which didn't show up on the gauge.
what happens when the modulator valve is stuck all the way in so it doesn't move?
thanks again
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post #63 of 69 (permalink) Old 04-16-2019, 06:16 AM
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Re: C4 squeals on gear change and burns clutches

Well I am starting to think the problem may not be the valve body,
unless you are making the same mistake on every one (unlikely),
or there is something wrong with the Shift Kit. (also unlikely)

I assume you have compressed air and know how to air check the clutch packs with the valve body off?

Possible leak in the high clutch circuit?

The video below shows air checks,
but I would use a rubber tipped blow gun to get a really good seal on the passages, not just a piece of hose.

You want to pressure up the circuit and try and hold pressure and listen for excessive leakage.
There will be a small amount of air leak but it should not be excessive.

Don't forget that the front servo release passage is also in the high clutch circuit.
(have a look at the oil circuit diagram when the trans is in high gear)
Wear at the servo pin in the case can cause issues.

That's all I got for now....


Last edited by galaxiex; 04-16-2019 at 06:19 AM.
 
post #64 of 69 (permalink) Old 04-16-2019, 03:52 PM Thread Starter
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Re: C4 squeals on gear change and burns clutches

hello Galaxiex, well i have no idea, any of my ideas went out the window long ago.
with the vb's, i have laid the items out in there positions on my table relative to the vb so i cannot mess it up then clean inspect replace
i chose transgo as recommended to me due to there quality and accuracy however i have never used them before.
you are correct, i do have air and know how to air check and to make sure i was doing it correctly i took the stator support and clutch drums too a transmission specialist to verify my work and it checked out perfectly.
when i assembled the box before installing the vb i again air checked the drums and bands for correct operation and yes there is a slight amount of air getting through whilst the items are functioning properly, i put this down to air is thinner than oil. maybe i am wrong, will have to check that!
i am going to have a look at the circuits to better understand.
this is great thank you guys
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post #65 of 69 (permalink) Old 04-18-2019, 03:30 PM Thread Starter
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Re: C4 squeals on gear change and burns clutches

Hello Galaxiex, after taking your advice, i looked at the schematic of the reverse circuit and understand how that works.
the rev circuit bypasses all other's so how is it's pressure regulated?
how are the forward's pressure regulated?
where would be a loss in pressure in the 3rd gear circuit? (PA intermediate servo installed)
looking at those circuits are producing more questions (and a headache) than i expected, certainly no smoking gun i could see.
thanks again, i appreciate your help
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post #66 of 69 (permalink) Old 04-20-2019, 12:28 AM
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Re: C4 squeals on gear change and burns clutches

Quote:
Originally Posted by lenoaust View Post
i chose transgo as recommended to me due to there quality and accuracy however i have never used them before.
you are correct, i do have air and know how to air check and to make sure i was doing it correctly i took the stator support and clutch drums too a transmission specialist to verify my work and it checked out perfectly.
when i assembled the box before installing the vb i again air checked the drums and bands for correct operation and yes there is a slight amount of air getting through whilst the items are functioning properly, i put this down to air is thinner than oil. maybe i am wrong, will have to check that!
i am going to have a look at the circuits to better understand.
this is great thank you guys
Transgo is good stuff .. You are correct , air checking is different to oil flow when the trans is running . The oil would seal better . You always hear some minor ring leakage .
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post #67 of 69 (permalink) Old 04-21-2019, 02:17 AM Thread Starter
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Re: C4 squeals on gear change and burns clutches

thank you Greg for confirming that idea. i took a look at the reverse circuit and i get that (well sort of) pressure, and noticed it bypasses the throttle pressure valve altogether where the forward gears are run past it to bleed off pressure. do you think line pressure would rise considerably if i shimmed it with a couple of washers?
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post #68 of 69 (permalink) Old 04-21-2019, 11:57 PM
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Re: C4 squeals on gear change and burns clutches

You know , at this stage it really can't hurt . My only concern would be you don't really want reverse any higher .

I'm still trying to figure what the noise is , very unusual for something internal to make a noise like that .
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post #69 of 69 (permalink) Old 04-22-2019, 05:51 AM Thread Starter
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Re: C4 squeals on gear change and burns clutches

hello again, that is good to know so how much do you think will be enough shim thickness to see a difference?
i found my dads vacuum gauge and did a vac test 9inm at idle 1000 rpm and 18 at 3000 rpm with a corresponding drop in line pressure which seems normal to me, what do you think?
thanks again Greg much appreciated
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