Lubrication for Transmission Rebuild....GL5 or ATF...

Here's one I was presented with today. I decided to let a professional Transmission house rebuild my FS5W71B 5 speed transmission. They suggested to fill it with ATF, after the rebuild, being as it is very cold up here in Quebec city, and Martin the owner of the company claims that using ATF in the manual transmission rebuilds he does, is working out much better than standard oil. The issue he claims is with lubrication and the cold, the ATF he says works much better, and his customers are very happy as he has had no returns. He says on cold days, that the GL4, and GL5 is too thick, and the bearings & other parts, starve for lubrication, which is causing bearing failure at an earlier interval. What do you think Tiger Racing? and Datzen Mike, and other Oil specialists? Should I go with the ATF? or stay put with the GL4 - GL5 ?  Id' like your input on this...DAttsun Al, 

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    I bought a '70 Dart Swinger 340 new. At the end of the summer the transmission was growling loud enough to hear over the exhaust. I took it to my local garage and they said the bearings and also mentioned it was full of ATF. I took it in under the 5 year 50 thou Chrysler warranty and they agreed it was the bearings and it was rebuilt and returned to me. I asked them about what fluid was used and they said 80 w 90 but in Canada there were complaints about hard shifting in the winter and ATF was used or mixed? with it. I drove it to my local garage and yup, they had refilled with ATF which I promptly had them drain and refill with the thick stuff. I never had a problem after that... But in the coldest part of the winter I had to park it in first gear at night or would have to let warm up to get it in gear in the morning. Got stuck on a snow drift once and it was 6 hours before I could dig it out. I started it to warm up and the rear wheels would spin in neutral because the oil was so thick.

    This experience would say that ATF doesn't protect a standard transmission. (although this was 40 years ago) It does work in an automatic but there are no 'gear' changes in it. Instead clutches and band brakes select planetary gear sets to transmit power. There are no synchros nor coupling and uncoupling of gears.

    I would like to learn more about how this would affect a Nissan 5 speed.

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    Sorry if its was already mentioned i just made a post about this in another thread but i think is worth reposting because is good info.There is a Technical Service Bulletin from Nissan advising not to use GL-5 on older manual transmissions because the sulfur and phosphor content can corrode "Yellow Metals" like brass and bronze.This is a very well known fact among the 240sx,Sentras,200sx and many other Nissans with transmissions that have bronze Synchros.Since many 720 share similar transmissions as those found in 200sx i guess is not recommendable for your trucks neither. 

    I used in my 240sx and my 200sx Redline MT90 which  is GL4 is phosphor and sulfur content is very low and you will notice  a difference in shifting.There are some other good brands like Amsoil that also meet this criteria.GL-4 Is not easy to find at local stores, only race stores and some napas have it and it usually expensive, Redline is  $11 per quart same as Amsoil  but to me is every penny worth it

    Also want to add this is not a myth here is my own story.Me a and few of my Nissan friends  decided one day to meet up and work on our cars changing fluids and tunning up our cars.I told them about we all buy in same store to get a discount but 4 of them  refused due to high cost of GL4, those 4  went and bought  GL5 at local auto parts.I insisted but none listened, 3-4 months down the road first transmission broke, few weeks after that on the way to the track another, about 1 month later another one.Common factor? GL5 in all of them, the last guy decided to flush and add GL4 but damage was already done it lasted like  1 more month.

    Just wanted to share this info with you guys,This are tough times and I know how expensive repairs can be .By the way I'm not advertising anything at the end you do whatever you want to, I'm just a Nissan freak owned like 8 of them so far from 1980 200sx Z20E to a 400whp 240sx/sr20det and anything in between.

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      scott felsen

      Just an update... I have driven my truck over a year with ATF in the 5 speed transmission. It was just rebuilt last year when I started this. I have driven over 30 thousand miles in the truck with no problems at all with the transmission. No leaks, no shifting issues. Nothing so far. I will update you next year or sooner if problems occur. I will be changing the ATF this week and will report any problems then also.