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Old 02-14-2018, 02:07 AM   #1
Smitty256's Avatar

Name: Smitty256
Title: Too Much Time
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Join Date: May 2014
Location: Killen, Al
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Questions on 47re and 48re

Ok guys I have 2 separate questions for 2 different trucks.

First question on on a 98 12v with a full billet full manual 47re. When I am driving this truck down the road it drives good under normal crushing power besides shifting 2-3 which I'm guessing is just a bind shift and the band needs adjusting. Now when you really get down in it and lock the converter it feels like it is slipping, this is a brand new billet triple disk converter with less than 10 miles on it and the trans. I do remember when I put the trans in, the converter was stamped 48re so I messaged the guy that built the trans and got the converter from and he said it would be fine and I'm beginning to think there is something going on with that. My main question is, is it ok to run a 48re converter in a 47re trans?

My other question is I have a 06 cummins with EFI, well the same guy above build this trans as well. The first time he built it it ran and shifted perfect. I broke the input in it and took it back to him and it ran and shifted perfect after that as well. So now the 3rd time the trans just quit pulling, I took it to him and he went threw it all and I had him put a billet input shaft and a triple disk converter. I got the truck back and it feels like every gear, besides lockup, is not pulling to its full potential. I'm not sure what is going on there. Low gear is sluggish but when the converter locks it throws your head back. Any suggestions for this?
95 12v Cummins in peices

98 12v Cummins under construction

06 Cummins dropped, EFI by Robert Ivey
Old 02-14-2018, 04:27 AM   #2
Big Blue24
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Name: Big Blue24
Title: Comp Diesel Sponsor
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47re transmissions are 100% compatible with 48re converters.

48re transmission are compatible with 47re converters however, there is a seal on the stator support of a 48re transmission that is designed to help seal the stator shaft to the inside of the torque converter; 47re converters are larger diameter in the region where this seal rides so the 48 seal no longer seals. This is not a major issue other than lowering the converter pressure a little similar to what a 47rh or 47re transmission normally sees. Many racing and hot street performance 48re transmissions are built and sent out the door with the stator seal missing on purpose. For good measure, when installing a 47re converter on a 48re transmission, most guys spend the 10 seconds to remove the stator seal so it doesn't have the possibility of popping free and potentially ending up somewhere else in the transmission.

To fix your 2-3 bind issue, you can make small improvement by loosening the band adjustment try 2.5 loosened from 72 inch pounds. For major improvement, you'll need to increase the 2nd servo release spring tension (double spring), change to a different style servo and/or lever ratio, or slow down the 3rd gear apply circuit (VB modification or restrictor orifice on 3rd apply passage).

To answer your second question, depending on the stall speed of your converter, it will never pull as hard unlocked as in lockup. If you have a higher than stock stall speed, like a 2400 V-10, you could be down as much as 200 HP unlocked vs locked on a 1000 HP truck. With a 1600 to 1800 stall converter, you'll still be down 50 to 75 HP unlocked vs locked on a 600 HP truck. By design, a torque converter is designed to slip when not in lockup, that's how it multiplies torque. If you get a super low stall/highly efficient torque converter, it will have much less loss unlocked vs locked, but it will also bog and cause the truck to act sluggish/increase turbo lag at low rpm conditions.
95' 2wd Junker Drag Truck
3/17/2018 10.55 @ 134 MPH
SXE 364.5 over HT80

Last edited by Big Blue24; 02-14-2018 at 04:29 AM.
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