I've got this 1987 Bounder 30ft motor home that has a 454/th400 . Is there a way to tell if it has the 275 gear without tearing it apart. I might want to keep that core . Anyone run across them and can tell what to look for. My understanding is they put the275 first gear th400's in limited amount of those motorhomes of the 1980's . Bell housing has a big HD on the top of the bell housing it but know doesn't mean anything , any ideas?

I don't know much about GM transmissions but the TH400's-to my knowledge-came factory with 2.48 low , 1.48 intermediate. Unless someone dropped a 2.75 planetary set in it?

^^^^^^^^^^ THIS ^^^^^^^^^^
All factory TH400s are 2:48 to 1 low gear. Aftermarket world offers 2:75 low planet.

Now back then in certain BIG GM based vechicles (14500 GVW, MHs, Bread Trucks, Dumb Trucks etc) had what is called a TH475. Same trans and gear ratio as a TH400, but have straight cut gears.

Code tag on trans should have the year and 2 letter code. Get that. Might be able to identify for you.

Never heard of that gear set in a factory unit, but who knows?
Why would you want a 2.75:1 gear?

Those heavy motor homes of those years . They put them in very few of those motor homes of those years. The 2.75 1st gear was never put into a 1 ton truck. a 20,000 lbs 40ft 200 hp 454 needed all the help it could get. If you ever seen those th400 of those years that are in the motor homes they mount the emergency brake to the housing of the th400 . Too much weight for the parking brake mechanism to hold with all that weight. They want 100.00 for the core for the exchange , for that price if indeed it has the 2.75 first gear its worth hanging onto it.

There is a good chance that the 2.75 gear set may be from the Allison 540, many of the internals are the same as a TH-400?

I have parted out two MH in the last four years. One of which had the parking brake as described. I would love to keep one if they had 2.75s. I hope someone can come up with some way to find out.

I will go tear mine apart just to find out.

quote:

Originally posted by VX96:
^^^^^^^^^^ THIS ^^^^^^^^^^
All factory TH400s are 2:48 to 1 low gear. Aftermarket world offers 2:75 low planet.

Now back then in certain BIG GM based vechicles (14500 GVW, MHs, Bread Trucks, Dumb Trucks etc) had what is called a TH475. Same trans and gear ratio as a TH400, but have straight cut gears.

Code tag on trans should have the year and 2 letter code. Get that. Might be able to identify for you.

This is the correct information. Its the strait cut planetaries you want.

I kept my core for 100.00 worth it any way you look at it. I smoked the forward drum welded it together form what my buddy says, no neutral or reverse . When you put into neutral its like it has a another gear . I will also tare my old th-400 apart with my buddy and see when I get some time know the weather above 40 degrees . There is a chance but a small one in my old 1988 motor home its on a 1987 Chassie only 30ft . The longer the motorhome the better of the chance, my 30 ft er might not have the 275 fist gear but a 40 ft would have a way better chance. Wish I learned how the build transmissions . Ive killed about 5 th400 in 20 years a racing. I can build everything else but a transmission on a race car. Bought into the Hype of a couple so call tranny experts in my area got screwed bye both. I have someone I can trust that wont Lie to me to my Face . I know **** brakes but don't straight up lie to my face and except me to buy into your lies . POS so called Tranny expert and you know who you are. I'm sure you've read this topic come see me anytime at the track Sacro/Sonoma Maybe I help you figure out how to put a lip seal on a pump correctly, so called tranny expert.