tyson Posted January 31, 2005 Share Posted January 31, 2005 So I have a 280XT with 90,000 miles on it, 14psi/intercooler/SVO injectors/3" downpipe (only exhaust on the car right now). What I always wanted to do, but I dont have the time is to swap it to a 5 speed...hopefully in a year or so I will be able to do it. Now, ever since I raised the boost from 10psi to 14psi, the automatic just does not hold up, it has trouble shifting under boost, and it slips as well, the shifts are soft and sloppy instead of firm. I think for this summer I am just going to have the transmission rebuilt and beefed up a bit. One thing is I dont know anything about automatic transmissions. We have quite a few race shops in Minnesota that deal with transmissions (mainly Ford/GM though). If I bring in my transmission will they be able to source/make the right parts to firm up the shifts and make it able to send the power to the rear wheels? I know for sure they will have to make a new torque converter...but thats the only thing I know about these transmissions. Any advice? BTW, I am not looking for just drag performance...while that is a plus, I want to autocross my Z and possibly roadrace it this summer. Quote Link to comment Share on other sites More sharing options...
Bernardd Posted January 31, 2005 Share Posted January 31, 2005 I've been looking into this for a while as well. Here's a link to a website that specializes in Jatco's. http://www.keas.com.au/default.asp They've sent me a rebuild tech sheet for holding up to 700hp. They have valve bodies for full manual shifting as well as transbrakes. He quoted me 1800 AU for a built tranny plus shipping. I can forward the tech sheets to you if you want to have it looked at by a shop. I also have a shift improver mod sheet that I can send over. I had my trans done by a local shop two years ago. It started slipping again last year so I took out the trans for a look at it. The shop that did my rebuild didn't do the valve body mods correctly so that's most likely my problem. I've found that the servo piston is really small on our trans so I'm going to swap it out from a 4n71b if it fits. I'm also going to install a couple of extra clutch disks. If the line pressure is increased enough, along with shift kit mods, the tranny is plenty strong enough. Quote Link to comment Share on other sites More sharing options...
drzed Posted January 31, 2005 Share Posted January 31, 2005 Bernardd - in what gear is your trans slipping? I've done some minor valve body mods to my 3N71B last year and it worked great all year until the last day at the track - then it started to slip in 2nd only. I was told that this is one of the weaknesses on this trans as 1st and 3rd have multiple clutches while 2nd only has a brake band (like a brake shoe) - or so I was told anyway. I am going to pull my trans in the next few weeks and see whats up. I would be interested in seeing your shift improver sheet to see if there is anything else I can do. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted January 31, 2005 Share Posted January 31, 2005 Just a random thought.. My 93 King cab is an auto, and iirc the 3.0 engine is basicaly the same as your 300zx (block I mean) so in theory, could you not pick up a cheep used truck tranny? I drove mine for the last 3 years (quite hard sometimes..) and it NEVER gave me trouble.. Shifts smooth, but there's a 'switch' of some sort that lets it rev out and shift harder under WOT (there is a togle on the dash to engage it whenever you want, but it will turn on by itself under sudden throtle application.. goes right to red line and feels like a manual shift when it kicks into the next gear).. kinda cool really.. The write up in the owners manual actually says it it intended for "towing/hauling loads on steep grades, or 'spirited' driving" Quote Link to comment Share on other sites More sharing options...
Bernardd Posted January 31, 2005 Share Posted January 31, 2005 Bernardd - in what gear is your trans slipping? I've done some minor valve body mods to my 3N71B last year and it worked great all year until the last day at the track - then it started to slip in 2nd only. I was told that this is one of the weaknesses on this trans as 1st and 3rd have multiple clutches while 2nd only has a brake band (like a brake shoe) - or so I was told anyway. I am going to pull my trans in the next few weeks and see whats up. I would be interested in seeing your shift improver sheet to see if there is anything else I can do. Mine doesn't actually slip, it's a slow shift from 2-3. Revs up before grabbing. I asked (and was charged for) a shop to shim the pressure reg valve and the pressure modifier valve along with enlarging the holes for the 1-2 shift and the 2-3 shift in the separater plate. I bumped into a guy that works on tranny's all the time so he's going to help me out with some tools. I'm going to modify the tranny as per the tech sheet from keas. If all is good I'll pick up a full manual valve body. The other thing is the servo piston. It needs to be bigger. Quote Link to comment Share on other sites More sharing options...
POSTM Posted February 3, 2005 Share Posted February 3, 2005 They've sent me a rebuild tech sheet for holding up to 700hp. They have valve bodies for full manual shifting as well as transbrakes. He quoted me 1800 AU for a built tranny plus shipping. I can forward the tech sheets to you if you want to have it looked at by a shop. I also have a shift improver mod sheet that I can send over. Bernard, I've thought about this for a few days, and I may be able to help. A larger servo would help (like Corvett servo for th700r4). Also, getting as close to minimum clearence as possible in direct clutch pack. I never modded a jatco, but I've modded tons of TH 350, 700r4, and c4s. You can also play with the accumulators. Shorten springs, lenghten springs, spacers. If I had more information, I could give you some more direction. Could you send me the tech sheets? I'm also interested because I own a 280Z with an automatic. Quote Link to comment Share on other sites More sharing options...
Bernardd Posted February 3, 2005 Share Posted February 3, 2005 I'll send the sheets over. I've found a B&M shift improver kit that I've purchased so I'm going to look over that as well. I have the servo out of a 4n71b. It's a 80-44 compared to the stock turbo servo which is a 72-44. As far as I understand it's size is the limiting factor as to how much pressure and ultimately grab the servo band can apply. Bernard Quote Link to comment Share on other sites More sharing options...
POSTM Posted February 4, 2005 Share Posted February 4, 2005 I've used B&M kits in many GM trans and results are good. Most people I built trans for were not looking for performance, but if I could keep slippage to a minimum I could minmize come backs. I always shot for a seamless shift but very soft at light throttle.The information and parts B&M kit can be used in variety of ways, as to please any one from grandma to the full time racer. The key to longivity I found to be increased line preasure and close to minimum clearance in clutch packs, slippage = come back.Iff your engine revs while wating for 3rd up shift you probably have bad seal and/or worn clutches. This can be pin pointed by doing a preasure check, I would expect to see the preasure gage drop at the 2-3 upshift. I test with wheels off the ground, and use brake to apply load. A larger apply servo will increase aplied force,and with increased line preasure force is multiplied.For a firm 2-3 upshift I would do valve body mods and minumize clearance in direct clutch pack by adding a clutch plate if possible,I sometimes use thinner steals to acomidate an extra clutch. Having not worked on a Jatco trans in over 20 years I can only go by my experiace with other trans mostly TH700r4 (I love this trans it made me lots of money). This being sead the Jatco seems to be solid unit. Bernard you are one the right track and I would sure like to see those tech sheets from Keas and B&M. Quote Link to comment Share on other sites More sharing options...
Bernardd Posted February 5, 2005 Share Posted February 5, 2005 Check your PM POSTM. In the tech sheet from KEAS he shows how to delete cushion plates and replace them with (all) frictions and steel plates. I'm going to do this to both drums and replace the band with a new one from Borg Warner. The clearance is also reduced from .085 to .035. I haven't checked to see if the larger servo will bolt straight in yet but in the event it doesn't, what can be done to make it fit. I'll probably end up rebuilding the entire tranny seeing as it's going to be totally apart anyway. Quote Link to comment Share on other sites More sharing options...
tyson Posted February 5, 2005 Author Share Posted February 5, 2005 Thanks for the replies guys. So I assume any reputable performance transmission shop in the area should be able to diagnose/order and install the parts into my transmission? Valve bodies and clutch packs? Quote Link to comment Share on other sites More sharing options...
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