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1991 Suburban 4wd, 350

Last week my transmission went wonky on me. It normally shifts at about 18mph, about 32mph, then again at around 50mph.

Now on the upshift it misses the 18mph shift, shifts at around 32mph then again at around 50mph. It never gave any indication of trouble until then.

I checked the fluid level, and had to add a couple of quarts. No improvement.

We changed the fluid / filter a couple of days ago, and noticed some 'mud' in the bottom of the pan. Not a lot, but enough to cover the bottom. When I saw that... well, I suspect a rebuild may be in order.

My son has a junked out Firebird that has a 700R4 (rebuild, about 2000 miles on it) that he wants to put in my truck. I'm dubious, but since I bought the $1100 transmission for him anyway, it'd be nice to be able to put it to use.

Question:

  1. What kind of transmission came in the '91 Suburban (assuming stock)?

  1. Is a rebuild of my transmission in order?

  2. Can we use his 700R4 in my Suburban?

  1. What modifications will need to be made to his 700R4 in order for it to work well in my Suburban (daily driving, occasionally towing a

16-1/2 ft boat (tow package already in place on my truck))?

TIA

Reply to
tomh5480
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As long as it is a 91 or earlier 700R4 it will work fine and bolt right in, Later models are electrically controlled. As far as enhance durabilty, it sound like you have 3.42 gear and stock or larger tires. The burb is a heavy beast (I have a 89 4x4 GMC that I have had since new and original tranny is still great after 175K miles) YOu need a aux tranny cooler fopr one and you should look into deeper gears if you are towing more than a few thousand pounds. 3.73, if your tires are stock and 4.10's if you are running 31's or so. Properly geared and cooler the

700R4 built in 87 and later is a sturdy unit
Reply to
TheSnoMan

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I guess it depends on whether it is a 1/2 ton or 3/4 ton. I have a 3/4 ton

91 suburban with an 4L80E which is not interchangeable with a 700R4, I guess I would climb under and see if there is a speedo cable coming out of the trans. If there is then the 700R4 will work if there isn't then you will have to go with a rebuild as you have an electronic trans. If I remember correctly I chose a 3/4 ton due to the heavy duty emissions and the newer trans. Now the real problem is whether you plan to reinstall the transfer case? To mount a transfer case on a 2wd trans requires some of the internal shafts to be changed. You can't (as far as I know) just slap on the adapter in place of the tail shaft housing. A good trans shop can do the conversion cheaper then a complete rebuild. It won't be a direct bolt in...

Good luck, mark

Reply to
r_d

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