To think i don't have a speech impediment

[McColonel]

To me, F and TH are pronounced exactly the same. E.g. three and free - I say them in exactly the same way.

My wife says I can't pronounce th, and I always pronounce an F when it should be TH.

Does anyone agree with me, that they are pronounced the same? Or is she right, and I can't speak properly? My brother agrees with me.

OP, in noticed in one of your posts you wrote that if you said "What do you fink about that?" you would expect to be understood, but if you can't say "th" surely you would say "What do you fink about fat?". Is that right?

This is strange. I've had these exact conversations with my husband as he 'can't' say 'th' in that context either. Although he can if he tries, similarly to when you have tried, sticking your tongue forward etc. Only difference is he admits to not being 'able' to pronounce it.
With him it's partly his accent (from Essex). Annoyingly it meant we couldn't use a couple of baby names as he can't say them properly (at his own admission)!

I wouldn't call it an impediment as you're not actually being impeded from pronouncing 'th' correctly by anything other than an unwillingness to change.
I'd place it in the same category as "them things". I'd understand you generally (unless there was confusion over "three" "free", for example) and I would assume you either hadn't been taught correctly and hadn't noticed other people speaking correctly, or that you knew the difference but struggled/were unwilling to correct yourself.
If I had been pronouncing something incorrectly my entire life I'd try to fix it. As a matter of fact my brain wants me to say "peridott" not "peridoh" because someone else always pronounced it that way and correcting myself feels very artificial. I do it, though, lest people think I'm thick. ☺

Grunt

In the two examples you give, the /th/ sound is pronounced slightly differently.

In think - the /th/ is 'voiced' - there's a breathy element to it and the tongue pokes further out
In that it is 'unvoiced' and the tongue makes a sort of vibration

try it out

Maybe that's the difference. Dunno

I know when we used to teach Jolly Phonics the two sorts are taught separately

Hahahha! No no I don't say chain chacks. There is an 'r' in there. There's more t than ch but there is definitely a ch sound in there.

Rereading the OP's posts I think that he must say "What do you fink of vat" in the example given.

Grunt

Yes, I think that's more likely, because the /v/ is fairly similar to the unvoiced /th/

Ah, so you say chrain chracks? Round here that's only something I might hear young children say, most adults manage to say the t clearly at the beginning.

No I think I say tchrain tchracks. I'm saying it so much now that it's hard to know. Certainly saying train with absolutely no ch within it whatsoever is pretty hard!

I get really annoyed when people say things like "should of" instead of "should have", "try and" instead of "try to", and confusing their/there/they're etc, but I don't consider mispronouncing "th" to be in the same category.

Everyone else does :)

You're rather judgemental of others' shortcomings, but not of your own.

Well said, sandwiches.
(What I wanted to say)

Now try to get people to buy that there's a d sound in jungle, Iguana.

I can say jungle without a d!

In think - the /th/ is 'voiced' - there's a breathy element to it and the tongue pokes further out
In that it is 'unvoiced' and the tongue makes a sort of vibration
It's completely the other way round.
/th/ as in think is voiceless. The vocal cords don't vibrate
/th/ as in the is voiceless The vocal cords do vibrate

derxa

Ah OK

I got the names wrong, but they do sound different

Not a SALT - just dredging stuff up from memory

It's OK Narp

The first time I heard a proper Londoner I genuinely could t understand one particular word he said, fort. I really struggled to followed his sentence and eventually realised it was thought.

I was familiar with the f for th (didn't realise then that it was a london thing, I thought it was a childhood thing) but adding an R into the word still baffles me.

Dropping an R, in the way some English people do as opposed to us Scots drrrrrragging out out Rs I get, putting an R in the middle of the word thought remains baffling.

People put in "r" sounds all the time to make things easier to say especially between two words which end/start with vowels:
Pamela Anderson - say it fast a few times and you get Pamelaranderson

Other words with extra sounds in RP -
Fence (t - fents)
Hamster (p - hampster)
Warmth (p - warmpth)

Must be an accent thing, I never would get pamelarnderson, or your other examples.

McColnel I'm also from Oxfordshire, I have an Oxfordshire father and london mother (muvva). I don't think it's an impediment, more like dialect/ lazy speech.
When I am comfortable around people I speak relaxed, birfday, muvva, farver, bruvva, anuvva.
Don't worry about it

Xmas2015Santa8473, I am also Scottish and, while I can understand, linguistically, why those with English accents add that extra "r" to make the words flow better, it does also annoy me I'm afraid, as it seems a bit lazy to me.

As a child I was always bemused by the Blue Peter presenters going on about "drawring" and during the Olympics I got really fed up hearing about our great sporting heroine "Jessicarennis".

This is a joke isn't it?

xmas - it's not really an accent thing - it's connected speech.

Intruding / r/
The media / r /are to blame.

Law(r)and order.

Intruding / j / (y sound)
I / j / agree.
They / j /are here!

Intruding / w/
I want to/ w/eat.

Please do/ w/it.

It's how your mouth moves from one sound to another.

But iguana it must be connected to accent to some degree (even if not caused by it) because Scottish people do not do this.

If I met a potential partner who said fink instead of think.........the potential would be lost.