First rebuild of a Turbo 400 desired input

[master53yoda]

I'm in the process of planning on rebuilding a turbo 400 trans for my 24' class C motorhome. This is the first auto trans rebuild i have done but have substantial mechanical experience including rebuilding a gear vendors overdrive. The motorhome has a 6.2 that I put twin turbos on last summer, it is putting out about 210 to 225 HP. The trans has a GV overdrive behind it, the old tranny failure was a bad pressure reg on the pump and i didn't notice the minimal slipping in 2nd and overdrive until to late.

The kit I'm looking at comes from ebay at 235.00. It has ALTO red Eagle Friction Clutches and Kolene Steels. and the high end Red Alto Band Clutch, and all the rest of the seals etc. adjustable modulator and pump and output shaft bushings. It is the only kit i have found that has the band in it as well as the modulator.

Is there a reason to go with a modified stall RPM torque convertor. My thinking is that i would want a LOWER lock-up RPM rather then a higher lockup. I'm not finding any lower lock up torque convertors.

[rustyk]

I had the TC replaced with a Sun Coast build when I had the tranny rebuilt - much more roust than the stock (which had failed). Well worth considering: http://www.suncoastconverters.com/sh...ue-converters/

They carry a lot more variety than what is shown on the website.

[TrenchFoot]

If you're interested in heading over the mountains I'll make you a deal on a professionally rebuilt T400 and HD torque converter. I had one built up with a TransGo shift kit and various HD parts for my Jeep then decided to go with a 700r4. It has a Jeep-specific tail shaft that I will have the shop swap over to long or short shaft as needed.

If interested in a trip to North Bend, reply with your email or phone.

[Robyn]

One thing to really pay close attention to on a TH 400 is the center support lugs in the case.

**These are the large lugs in the aluminum that the center support slides into**

Now with the case clean and dry, carefully inspect the area where the support sits in the lugs, if there is a worn area and the support can rock back and forth radially the case is no good.

The support should just slide into the lugs. if there is a worn "NOTCH" its case time.

This sort of wear allow the center support to move and it will lose its seal, causing the high clutch pack to fail.

The center support "BOLT" that goes through the case under the valve body and fastens the center support. This bolt is hollow and feeds the oil into the support.

This is one of the few places that a 400 fails, that is a critical issue, and is missed every so often even by large shops.

Good luck

Missy

[jtraik]

Hi Robyn,

I am attempting a rebuild on a TH400 from a '68 Cadillac. I bought Cliff Ruggle's book on how to rebuild and modify a TH400, it is step by step with pictures. However during disassembly, when I got to the center support I am unable to remove it. In the book he shows to remove a bolt that is within the valve body channels, however mine does not have that bolt... there is a hole where it would have been but it is NOT threaded. I have also come across another picture on the internet showing the location of another center support bolt, just outside the area of the valve body channels. I have that threaded hole but there is no bolt. The center support is in there tight and cant figure out how to remove it.

I would appreciate ANYONES help!!! thanks.

[Diesel 4 blood]

If you want you can call the shop I have all my transmission work done its in Spokane on market the shop is called mayfield transmission talk to shane I won't take a transmission to anybody else and he can answer pretty much any question you ask

[OIL BURN]

Just a thought,wasn't there an upgrade to the later say 70's center support,which I think was a tad longer to allow deeper engagement into the lugs to spread the load on the lugs to avoid damage to them?I think this change over occured 1969 or 1970 in which all later 400's had the longer center support. As far as the center support bolt located in the oil vallery cast into the case, you would clearly see it if it was there. I cant imagine the trans lasting this long since it also serves as an oil port to the cenetr support. If as you say the bolt was missing,it may have accidently not installed, goes to show the 400 is one tough trans.

Any used trans parts seller would have the later center support, as far as I can remember some of the trans kits like trans go or superior recommended using the later longer support. Memory says the threaded section the bolt goes into is in the support itself,so when installing the support get the threaded hole lined up as centered as possible so that the bolt screws in easily.

Sometimes the center can be diffciult to remove when there is some lug damage,so wiggle it and find a opening in the case to lighlly tap and coach it along it will come out,its somewhat heavy. Minor lug wear/damage is usually not a problem and again if memory serves me right a longer later center support would contact the unworn area on the trans lugs.

Buy yourself a Haynes 400 trans overhaul manual ,you can find them at autozone,pepboys,etc,. These manuals employ a step by step pictorial with written comments on the disassenbly and assembly of the 400. The 400 is one of the simplest and toughet trannys out there, G.M. hit the bullseye with the 400. Get the manual ,read it first and become fimiliar with the parts/sections of the trans,take your time and absolutely keep every clean! When disassembling,lay you parts out in an order on your bench in line,don't pile them up,makes inspection alot easier to find damage,unless your are a professional trans builder.

I build my own 400's simply because I enjoy doing it.The only time I've had problems was with rebuilt assemblies like the output carrier to reaction carrier thrust washer contact surface.When the pinions were sweged in place, the thrust washer mating surfaced was nicked causing a minor raise surfaced, it acted like a cutting tool and shaved 3/4 of the surface of the thrust washer.So, pull, disassemble,clean,resassemble,with another rebuilt reaction carrier,of course checked for nicks,reinstall and trans works great so far over 60000 miles in a 74 crew cab utility truck.Check all thrust washer contact surfaces,you can use a used one and rub it against the mating surface to check for smoothness,if rough then dress down to remove nicks.Just check ALL rebuilt assemblies.

One additional item,the torque converter.It has to be on the money with reguards to locating hub center line in front that fits into crank ,topump drive at rear.Had a bad one once,went for a test drive,truck shook like a washing machine out of balance,watched the converter at idle,it moved up and down like it was bobbing for apples.I shut it down and lucky not to damage the front pump.You may want to check Robyns posts on torque converters and trans rebuilding,very good information.As always,any members that can add or correct my information is welcome to do so and appreciated.

GOOD LUCK WITH YOUR REBUILD.

OIL BURN

[Robyn]

I have never seen a 400 without that center bolt.

Many times the large lugs on the center support will wear into the case and nurf up a bur in the case lugs, making it tough to get the suport out.

If this happens the case is usually junk.

The cause of severe center case wear is commonly attributed to someone slamming the tranny from reverse to forward withe the vehicle moving, or doing this to "rock" the vehicle out of snow, mud etc.

This activity if done long enough takes its toll on the case lugs. Eventually the wear becomes great enough that high gear goes away due to loss of oil pressure to the high clutch.

Did you remove the snap ring just in front of the center support ???

The ring holds the center support in the case.

Missy