48re No Overdrive - Bad OD piston seal

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Diezl

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Aug 20, 2019
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My 48re started not wanting to go into OD then finally wouldnt go at all so troubleshooted until it led me down the path of a failed OD piston seal( had 15-30psi at the OD port).

So I think i am going to "rebuild" the OD unit put new frictions and steels and set up my clearance right along with the new piston seals. Just took it out last night so haven't fully taken all frictions out, but i have attached a couple pics of the first couple, what do you think bad frictions? that one steel has weird markings on it.

But im wondering if its a bad idea to just rebuild the OD unit and not taking the whole trans apart and clean everything in case of debris?
Truck shifts through 1-3 perfect, has lots of good parts in it dont think it needs a full rebuild but most people ive seen that replace the seal dont take it all apart but i talked to a local reputable builder and he said he would take it all apart and clean everything.
I'll add I did take out the VB before this while trying to troubleshoot and replace my solenoids. Also, to go over and see if anything was blocking the orifices in the 3-4 and other bores. Did not find any debris anywhere just slightly darker fluid than what was in the pan. Cleaned it up and put it back in drove another mile or two to see what my pressure was at the od port then tore out the od unit.
 

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zstroken said:
What did the pan look like?
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Pan and fluid looked good. This was the drain plug on the PPE pan which is smaller in diameter than stock, think its a little misleading in the pic maybe mainly because when i wiped it off and most of the material on it was the light silver dust/fuzz. Not sure on last fluid change I've only driven the truck maybe 3-4k miles since buying it. Sorry pic is sideways.
 

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I'd rebuild the od direct with gpz's and regular steels, od brake with gpz's and alto steels. Put a seal in the piston and go with it. Especially with that low of miles.
 
thatguy69 said:
I'd rebuild the od direct with gpz's and regular steels, od brake with gpz's and alto steels. Put a seal in the piston and go with it. Especially with that low of miles.
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Not sure when the trans was rebuilt thats just how long ive had it for. It was built prior to me. No receipts but was told it was suncoast parts built by local guy. So all from just what ive seen so far has a grey billet converter with no markings, suncoast dnj gm gov solenoid, suncoast accumulator piston, trans go shift kit, billet band strut and anchor, and just saw the billet output shaft because of this so that made me a little happier lol. I would guess proboblly a billet input too, who puts in a billet output without an billet input but dont think theres a way to tell unless take the trans out.
Anyways, i was thinking gpz's too. When i was looking saw alot of different thicknesses, still gotta research how to know which ones.

Do these seals just go bad from normal use or not? Ive read they go bad because the clutches wear down and the piston has to travel too far then not too sure
 
Was the overdrive piston shim missing. Looks like overdrive piston came out to far and ripped seals on edge of retainer/center support.
 
Workin man said:
Was the overdrive piston shim missing. Looks like overdrive piston came out to far and ripped seals on edge of retainer/center support.
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No, if its called "thrust plate" in the atsg it was there. Did a measurement on it and the spacer or thrust plate would need to be thinner. i have a .198 plate and based on my measurement i would need a next size thinner .183-.185 plate. But that is with my worn clutches, i just took the top set of clutches and steels out and they dont look good like those first two i posted. I will post a pic of them
 
first couple looked good then got bad. Just dont want this to happen again so trying to figure out what happened.
 

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Maybe those lipseals just got tired on ya. Sonnax sells a overdrive piston housing. It fits the piston a bit tighter than oem. I have used them before, it is a nice upgrade. Did your housing have sharp scoring? You might have just had bad luck. Has the snap ring in the overdrive housing that connects to the big bearing moved or not in its respective grove. This could lets the overdrive guts move away and hyperextend the piston?
 
Workin man said:
Maybe those lipseals just got tired on ya. Sonnax sells a overdrive piston housing. It fits the piston a bit tighter than oem. I have used them before, it is a nice upgrade. Did your housing have sharp scoring? You might have just had bad luck. Has the snap ring in the overdrive housing that connects to the big bearing moved or not in its respective grove. This could lets the overdrive guts move away and hyperextend the piston?
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Seemed like the housing was smooth but didnt take the closest look at it just yet, and ill check on the snap ring as well. Thanks for the suggestion. Would i be in trouble if i just put in new frictions and steels to rebuild the od unit and not take the whole trans apart, guess because of clutch material ?
 
I’d take the valve body apart and clean it. Are you running 5 or 6 frictions in the overdrive brake clutch pack? I run borgwarner in mine and never had slipping. I run line pressure at 180 in overdrive.
 
I use a drill bit too check the piston to steel plate clearance. I use koleen steel too. Use the drill bit like a feeler gauge.
 
Take a caliper and measure the thickness or the worn pack vs the new when you put it back together to see how much the difference is. That will also show you if the piston traveled ou too far and damaged the lip seals.
 
Disregard my post where I said alto steels,had a brain fart. Working man is correct, there koleen steels
 
So i checked the snap ring in the housing and looks like it might have worn a groove in the housing and i can push and pull on the output shaft and move the guts a fair amount not sure if thats normal. But ill have to take the guts out tomorrow and try to look for the groove. It might need the housing shim ive seen. I didnt pay attention how many in the brake pack so ill have to get back to ya, this working during the day stuff sucks lol only get a couple hours to mess with it a night. I have heard of the drill bit method but i will need to research that more, i did that measurement i posted earlier with a straight edge across the mating surface. Not sure how i can do the first measurement that is explained in the atsg on the intermediate
 
I set the OD unit vertically with the output shaft down. Then stack everything up, and use a dial indicator raising the stuff until it hits the piston. In this application more clearance is better than tight. Too tight you will be applying clutches before the others have released and will heat things up in short order.
 
Still contemplating if i should just rebuild the OD unit and stick it back on or have the local builder take it all apart and see if i need anything else. Rebuilding the od doesnt seem hard just dont want to have to pull it out again want to get it right the first time.
Also, having a hard time sourcing the right gpz frictions and steels there seems to be quite a few different sizes you can get. Ive been looking at wittrans.com because i can order the parts sperate including the seal. Should i just measure the ones i have and get whatever is close?
 
Diezl said:
Still contemplating if i should just rebuild the OD unit and stick it back on or have the local builder take it all apart and see if i need anything else. Rebuilding the od doesnt seem hard just dont want to have to pull it out again want to get it right the first time.
Also, having a hard time sourcing the right gpz frictions and steels there seems to be quite a few different sizes you can get. Ive been looking at wittrans.com because i can order the parts sperate including the seal. Should i just measure the ones i have and get whatever is close?
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Goerend sells a lot of parts, and is very helpful as well.
 
You should take the overdrive assembly apart and check it for any problems and make sure the sun gear has no pitting on it.
 
So took the guts out, need to make a press tool to go further but i only had 5 frictions in the od brake section
 
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