Hello,
I have a 1975 Barth 25' chevy p30 chassis 454 motor and a t400 transmission.The transmission is making noises like it wants to be rebuilt.And I am wondering if there is an other transmission that would bolt on the 454 that might be an improvement over the t400. Any suggestions? thanks

Iam

I read that the "475" was introduced in 1987.

http://en.wikipedia.org/wiki/Turbo-Hydramatic
http://www.hotrodders.com/foru...75-trans-164852.html

If you went 4 speed, it would mean you'd need a computer to control also.

happy motoring!
Matt

Check this site :https://www.novak-adapt.com/knowledge/chevy_standard_shift_info.htm. There are a number of options including non-electronic swaps and the latest electronic shifting transmissions. I would recommend contacting a GM truck service center and have them help you. It is likely you may need a new driveshaft and upgraded universals in addition to the transmission. The necessary electronics can be found in junk yards or from aftermarket builders, like Novak who created the web page above.

A lot depends on what and how much you will use the RV. If in fact the trans is bad, I would strongly consider the 4L80E as a replacement. It is basically a 400 with the addition of an overdrive gear which will reduce engine RPM and noise. Will bolt right up to the 454.

It will require an aftermarket electronic trans controller and maybe a driveline change/mod.

These can be picked up at most any truck dismantler relatively cheap. Santa Clara Truck has a bunch of these and are guaranteed.

Much of the cost will be determined by how much if any of the work you can do.

Most all RV with the 454 around and after '91 came standard with this trans.

quote:

www.novak-adapt.com/knowledge/chevy_standard_shift_info.htm

I have a SOB (1984 Chevy chassis 25 foot xplorer) and am going to change to a 4L80. I have the transmission, a buddy of mine has reworked it a bit, and I will install. It bolts up to the bell housing without a mod, and you will need to shorten the drive shaft. Then add a transgo manual shift kit and be good to go. Or add a stand alone controller, around $600 or so. Another option is to get a 1991 (I think) stand alone controller from a diesel powered van. That is what I am doing. Good luck.

Chuckd
stillwater mn, where we are still having winter
1976 Barth Class C

Thank you all for your recommendations.The 4L80 sounds like a good upgrade.I will be driving a lot on steep roadways and intend to use the low gears to engine brake on the downhill to help save the brakes. So I wondered if the Allison transmission is a more heavy duty transmission for this type of driving? The 454 is easily up to the task.

Iam

Another option is to install a Gear Vendors unit as I have on my 85 Regal. Then you end up with 6 speeds. No electronics required, just a shortened drive shaft. And the Gear Vendors unit is stronger than the 4l80, according to my son-in-law, aka jet pilot, aka rock crawler builder, aka Camaro restorer, as well as Gear Vendors themselves. Because of the 1st + first overdrive, 2nd + 2nd over drive, and 3rd + 3rd overdrive, I would do the GV again. It might be a little more expensive but in the long run give you a lot of flexibility in driving conditions.
Jim

I may be wrong, but I believe the 4L80 has a lockup torque converter whereas the T400 does not. Makes a difference coasting down a mountain.

quote:

Originally posted by Iam:
I am wondering if there is an other transmission that would bolt on the 454 that might be an improvement over the t400.

IMHO Find a good transmission shop to rebuild your T400. The T400 is one tough tranny. Changing to a 4 speed would require a rear end gear change to make the best use of gears. With a 454 and a 25' unit you have plenty of power to pull hills. Put your money in your brake system.(hoses, pads, shoes, lines, and new calipers, master cyl. and wheel cylynder).

quote:

Originally posted by Gary Carter:
I may be wrong, but I believe the 4L80 has a lockup torque converter whereas the T400 does not. Makes a difference coasting down a mountain.

It does, but the TC unlocks coasting. However, I've run down 7%+ grades several miles long (in 2nd), and the temp barely rises. I had mine upgraded by Suncoast Converters, and the tech said there are no problems caused by downshifting for retarding.

quote:

Originally posted by Doorman:


IMHO Find a good transmission shop to rebuild your T400. The T400 is one tough tranny.

Yes, and if you have money to spend, go for a Gear Vendors. with your lighter coach, the 3rd OD could save some gas and engine wear on level ground. 2nd OD is really useful for climbing, but your 25 footer should already climb decently.

Barth put overdrives on some of the larger gassers.

I have a pickup with a 4L80E, and the 4th gear and lockup converter are useful for easy driving, but of limited advantage when pulling a load or climbing.

GM says not to use OD when towing. That means heavy loads, which would mean never use OD in a motor home.

I would be curious to see if GM made the same rec on motor homes with the 4L80E trannies.

quote:

GM says not to use OD when towing. That means heavy loads, which would mean never use OD in a motor home.

I had my 4L80E upgraded to handle the torque from the new engine, but OD was not an issue (relying on tranny temp). However, I run in "D" in hilly country (or when encountering headwinds), to avoid repetitive up- and down-shifts. Otherwise, I run in OD. Tranny temp sticks at 145°F, and turbo boost and EGT are low.

quote:

Originally posted by Rusty:

quote:

GM says not to use OD when towing. That means heavy loads, which would mean never use OD in a motor home.

I run in "D" in hilly country (or when encountering headwinds), to avoid repetitive up- and down-shifts.

That could be part of why GM makes the rec.