The $2000 CLUNK!

[swissarmychainsaw]

Here is LilRed (1984 Silverado, 305/700R4 No AC):




I have had this truck about 4 years, and love it. It's a hobby truck, meaning it sits mostly and only gets out on long stretches for vacation or out dirt biking and stuff. (127K miles) It's all stock.

The trans has leaked the whole time I have owned it, something I know these 700R4s tend to do.
I have made pitty-pat repairs to the trans over the last few years, meaning I wasted money on not really fixing the leak, which is clear to me: It needs a rebuild.

I just took it on a three hour cruise towing a dirtbike trailer, and coming home, after dropping off and unloading everything I backed into a parking spot and BANG!

I stopped real fast, got out to inspect the damage. I was SURE I had either hit a car, or the telephone pole behind me. I got out, and I was about 4 feet away from the pole. Hrm...

I pulled forward, then put it into reverse again... Clunk (normal) then take my foot off the brake, give it a little gas, and BANG! there it is again!

The short version (although I might have passed that point already) is that in reverse it bangs like that every couple of feet? Needless to say I was not driving it around or anything after that.

It reminds me of when I broke the yolk in a van years ago, but that time the drive shaft ended up on the ground.

Drive shaft feels sold, feels like its in the tranny. The tranny has always felt messed up, so I'm happy to "fix" it. Did not downshift when you stomped it, felt like you had to floor it to keep it from shift really early.
The good side was it got really good gas mileage.

So my real question is this:
What do I do now?
I see 700R4 on Craigslist (here in San Fran area) for like $700 supposedly rebuilt already. Is that too good to be true?

Or do I have this one rebuilt, or do it myself.
I don't know jack about transmissions, but am a capable mechanic with the right manual, but don't have much time (three year old at home). I'm not broke though either.

I *would* like to make this truck a little bit more capable as a tow vehicle. Nothing crazy but I'm thinking not having it shift as quick would be good, maybe a cooler.

So if I go shopping for a transmission what do I look for?

It seems that the Torque Converter is what determines when the transmission shifts, i.e. where a "shift kit" goes, right?

Thoughts appreciated!
--Nick

[Krwright]

Shift kits go in the valve body. Most of the time it just consists of a new plate, springs and removing check balls. Converters control stall speed and have nothing to do with shift points. The tv cable controls shifting and kick down.
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[Krwright]

If you change trannys be sure to properly adjust the tv cable. You can junk a good trans in a hurry. 700r4's are picky about tv adjustment.
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[ElGracho]

Make sure the pinion nut on the rear end hasnt loosened before you get into the trans.
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[71swb4x4]

The first thing I would do is pull the differential cover and look things over real well.

[old Rusty C10]

Originally Posted by 71swb4x4

The first thing I would do is pull the differential cover and look things over real well.

this is what i was thinking too.. and i would have it done up at a shop if indeed this is a trans problem..

[BigBlocksRule]

Pull the drive shaft, jack 'er up and check the diff...that should isolate the problem. It could be something fairly easy.
Good luck, hope it's easy and cheap.

[wilkin250r]

I'm with the other suggestions. Most of the clunks I've known have either been driveshaft problems (usually U-joints) or differential problems. Pulling the covers off the differentials is a simple, fairly cheap method to eliminate one very likely possibility.

[Your41Plague12]

I'm also thinking rear end on this one. If a tranny clunks going into or out of gear, it's relatively common. But while in gear every couple of feet or so, it seems to have something to do with the rotation of your gears. That's the first place I'd check.

[butch86]

i agree with everyone else check your rear end first. sounds as iff your pinion nut has backed off or you have a bearrin in the rear end housing gone bad

[swissarmychainsaw]

Ok, what is the best way to "check the differential"?

Right now I'm planning on pulling the drive shaft (mostly because it's easy); checking the Universal joints.

Then just turning the rear wheels and listening to the rear end.

OR should I open the diff cover? I assume I will need a new gasket and (duh) oil, if I do that.

Thanks for the replies!
--Nick

[notyo_cheez]

Pull the cover and inspect, it's the only way to remove all doubt. You assumed correctly.

[swissarmychainsaw]

So I drove it today from the parking spot to my garage (one block).
I tested it forward and backward and it did not make the clunk again.

I then drove it around the whole block and backed it up the drive to the garage, a short but steep hill. No noise.

When climbing a hill I shifted into first and the made some whirring noise, but kind of expected too, it downshifted.

In my experience, things like failed drive shafts and rear ends, once they make noise, it is there to stay.

This leads me to think its transmission again.

It's up on jack stands in the garage, but I don't want to needlessly take the driveshaft off and open the rearend if I don't have to. LOL
I guess it would be different if I had a lift!

For now I sprayed the u-joint holding bolts (rear yolk) with some penetrating oil, and will have a look again in the morning.

[N2TRUX]

Do you know if it has a locking rear differential? One thing I didn't see mentioned is the possibility of a locker unlocking as your source of big bang. My thoughts are you should pull the cover and inspect the dif. If its in good shape, you rule that out, and give it fresh lube at the same time.

[swissarmychainsaw]

I ended up taking the truck in to a Differential shop that had looked at it in the past here's the rundown:

U-joints both replaced (rear was stiff).

Rear-end was serviced, said there was some metal in the fluid, more than should have been, but nothing broken off or obvious.

The trans was serviced, also had some particles in it. These guys had pulled the 700R4 last year and replaced the front pump seal which was leaking.
Good news is that it is NOT leaking from there. The last leak seems to be from the Shift input shaft, so they fixed that. FINALLY a non-leaking transmission! I hate leaking stuff. just hate it.

I debated on a rebuild, the quote was 1600 for the trans plus 300-400 installation (three year national warranty) but decided against it. (he had slightly cheaper options, but not by much)

I contemplated selling the truck. Actually that was the deal I made in my head. If I don't fix the tranny I'm going to sell it (which I hate to do, pass the pain on to someone else). The guy at the shop was like, "oh man, I don't think I would sell this truck. I drove it, and it makes *no* noise, no squeaks, no rattles, it's just like new truck!"

That of course is why I like this thing. It IS a nice truck.

same guy said, "just keep driving it, and when/if it fails, THEN replace it."

So that is what I'm going to do. Change the fluid really regularly, and just take it easy as she goes.

So I took about a one hour camping trip with it, and it seems to be doing fine. Meaning it's far from perfect but is still working about like it has in the time I have owned the truck.
It sometimes wants to shift out of first late (25mph) but after an hour of driving it stops doing that.

For now, I'm going to live with it, and start shopping for a reasonable alternative to the $2000 rebuild.

What have you guys done to fix/replace the 700R4?