700R4 question

I have a freind at work with a 86 chevy truck and a 700r4 tranny, he woudl let me have it, but it is worn and slipping. My question is how available are these?

I know it would need to be rebuilt and I do not plan on using it in my car but for the future...

Are they expensive at the boneyard?

Would it be worth it?

Also what type of rear are in these trucks (86 chevy) and are they any good?

 

I think the 1986 model 700R4s are junk. It seems that the years you want are 87 or 88 and up.
They aren't hard to come by, but plan on it being almost twice the cost of a TH350, depending on how crazy you go with it. From personal experience, make sure you have a LOW axle ratio if you are going to use one, my 2.73 axle and the OD means that there is NO torque and relatively low vacuum while cruising. So, if you are accelerating, as soon as you touch the gas pedal, the vacuum goes to "0" and dumps fuel in. Moral of the story, get LOW gears.

 

The best 700R4 guys I've met are at Bowtie Overdrives in Hesperia, CA. I think its www.bowtieoverdrives.com. They specialize in these transmissions and even custom-fab the critical TV linkage to ensure they work right. When I get to the point in my build when I'm ready for a new trans, I'm going with one of their 700R4s. They told me they'd work with me directly to ensure it works right behind my Buick Straight 8. Nice guys with real pride in their work.

 

Crosley is the tranny man that will know for sure, but I think that by 86 GM had the improved input shaft and pump. So the 86 should be OK, the rest of the parts can be upgraded when it's rebuilt. 86 is good for a couple reasons, it has hydraulic valve body and it has speedo gear drive. Later 80's and up to 91 are better units, but I think yours would be OK to use.

Price depends on the yard, but 700R4 are still fairly common.

The rearend in that truck is essentially a 8.5 ring gear 10-bolt GM rearend. So it's pretty strong for almost any abuse short of slicks and big engines. The two problems are that it is wide and has a 5 on 5 bolt pattern.

The best advantage of the 700R4 is that you can run high 3/low 4 rear gears and the fun low gear acceleration, but then have the 0.7 OD so you can cruise the freeway. If I were building a car from scratch and was running a Chevy V-8, I would definitely use a 700R4 trans for an auto trans choice.

 

Yeah, I remember hearing that my '86 Caprice had the updated style trans in it. It lasted for 180,000 till the motor blew. We replaced both out of hand, cause we had a new engine and new trans laying there. It was still working great when the engine blew though.

 

87 up has the better input shaft, valve body, plus some other improvements, Cases are the same, so the 86 and older can be updated.
Yards around here are getting $150 for smoked cores.

 

amazing answers.

I will post this answer along the thinking lines that you are driving this setup regularly and not beating the shit out of it.

The 86 is a fine unit to build. Have it built by some person that knows 700r4's and all will be fine.

Updated to a later fwd input sprag setup if you wish. Definitly replace the sprag with new.

Open the lube circuit up some.

Stake and loc-tite the pump bushing.

Drill the drain back holes in the pump and stator support.

A TransGo jr shift kit and drive it.

Oh btw, the cases are not the same from mid 1987 up when compared to early non aux v-body units. Moving valve bodies and separator plates around without any knowledge of what you are doing will most likely result in trouble even without changing cases.

 

[ QUOTE ]
...Drill the drain back holes in the pump and stator support.....




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Crosley,

What symptoms can one expect if this isn't done?
Cold this be the fix I need on mine('88) for it losing (bowing) fluid out the front pump area if I'm pulling a grade at 70+ with the tranny downshifted (high engine rpm)?

 

DrJ,

is the fluid coming out of the pump area or from the breather on top of the main case?

Usually the pump converter hub seal blows out and the oil never stops running out

Drilling the drain back routes on the early 700's will help avoid the pump hub seal from blowing out of the pump housing.

 

It happened about 100,000 miles ago, on the way to Zion Nat. Park. I was pulling a long grade at "highway speed" and the tranny was downshifted, at least into 3rd, possibly into 2nd? at 70-80mph.
When we stopped at arest stop Wife noticed the back doors of the van were all oily, so I looked onderneath and it was running out of the flywheel cover there was nothing on the dipstick so I asked around the rest stop and there was a guy with a couple of quarts of ATF so I traded him a couple of quarts of motor oil, which I had, and drove backto a station I saw 10 miles back down the road. There I put two more quarts of ATF and a Quart of "Stop leak and conditioner" in it. and continued on because there was more civilization ahead than there was behind. Well It lost another quart that day so I put another quart of stop leak in it and it quit leaking. I changed plans (we were on our way to Lincoln via Vail so Ithought twice about driving over the Rockies so we went north and took the I-80 I drove like an old man the rest of the trip so It didn't down shift and since then it only leaks if I do some of that high RPM stuff pulling hills so I just don't. (It's only the go to the grocery store car now)
So, if it was the hub seal I was damn lucky because it stopped or maybe it's the big seal that goes around the outside of the pump housing?
Anyway, when this Van dies I was going to part it out for the tranny but I was just wondering what to look for and what to modify to fix this. You've given me some good possibilities..
Thanks.
Maybe see ya out there the last week of the year?