What's a Retarder and a Power Take Off?

**RickO** · 10-31-2010, 11:54 AM

Ok, it was a slow Saturday night and I was reading my Alison 4000 manual before bed last night. It reference two things that were new to me but I couldn't really find an explanation of them. My forum search turned up vague references but I'm still unclear.

What is a Retarder and do I have one? It sounds like a form of transmission brake but....?

Also, there was reference to PTO. What's that?

Thanks much....

Rick

Clonetrooper · 10-31-2010, 12:08 PM

Power take off is an output shaft from tranny, found on dump trucks, work trucks, fire engies etc used to power pumps etc with out truck moving. Like having another engine on a truck to power things.
Retarder uses engine or compression or tranny down shift to slow vehicle, it uses the drag of the engine while it is not producing power. More to it than that but that is justa simple answer.
You should have a retarder, it uses early downshifts to slow vehicle in stead of brakes.
Kelly

Mike Canter · 10-31-2010, 12:11 PM

The retarder on the Allison is a brake option. The one I test drove had a little lever on the armrest that I could slide back and forth and it slowed the MH down. It could be adjusted so when you let up it would automatically engage and start slowing you down. I believe it shuts a valve internal to the tranny to apply an internal brake. It is not an engine Jake brake or an exhaust brake. It is hard on the tranny because it generates a lot of heat. This MH I drove had a Jake brake and a transmission retarder.

The PTO is the driveshaft output. Power Take Off

**RickO** · 10-31-2010, 12:49 PM

Thanks guys. Interesting but sounds like niether one applies to me.

Rick

**Route 66** · 10-31-2010, 04:19 PM

Nope.

I believe Foretravel is about the only MH with a transmission retarder and I understand using it can generate a lot of heat in the trans.

Mike Canter · 10-31-2010, 04:47 PM

Dirk, you are correct. It was a Foretravel I was driving that had one. I believe if you a tranny retarded you have to change ATF and filter as prescribed under "severe" usage.

**Route 66** · 10-31-2010, 05:21 PM

If the Trans retarder was all that great, we'd see more of 'em.

I haven't driven a Foretravel, but my engine brake is quite sufficient.

**RickO** · 10-31-2010, 07:20 PM

I did notice the service tables in the manual had a special schedule to follow if a retarder was used. Their "do not exceed" temps also showed much higher temps for retarded equipped units. I'll bet some pretty violent stuff goes on in there when the retarder is in use.

Rick

Clonetrooper · 10-31-2010, 08:53 PM

I drive a newer GMC 7500 with Allison automatic tranny(almost as big as a semi tractor) sometimes, it has a trans retarder that you can select, and I have only used it a few times. It comes in handy when towing heavy trailer in heavy traffic while raining. It feels like it is gonna yank the rear end or tranny out. Violent stuff is right.

There is a switch labeled Rtrdr on the dash of my 2000 Discovery equipped with Allison tranny. When you switch it to ON the tranny will down shift early while driving, slowing the vehicle. This seems to be hard on the engine and tranny. My Landgrebe tow dolly has excellent hyd brakes and I dont drive in mountains often so I don't ever need to use engine/tranny retarder. I don't have an exhaust brake which tend to be noisy and illegal to use in some cities, main target here is semis. Looked in my tranny book and it referred to retarder briefly, but I remember reading more about how it works in online Allison info site. Maybe this was only available on this model, I don't know.

frankdamp · 11-01-2010, 09:51 AM

It's interesting that everyone's opinion is that the retarder gives the transmission a hard time.

When I was driving transit, all our coaches had Allison transmissions - some 5-speed, some 6-speed. Our instructions were to have the retarder on at all times except in very slippery conditions. We had to notify dispatch if we turned it off for any reason.

You could certainly tell if it wasn't working, but I don't remember any particularly strong braking effect, even at freeway speeds. Most of the miles for the fleet were at 35 mph or less on city and local county roads, so maybe the retarder use didn't cause any additional maintenance efforts.

Mike Canter · 11-01-2010, 10:31 AM

It is Allison that states the retarder changes the maintenance schedule. The Foretravel I drove with the transmission retarder had a lever control that adjusted how much retarder force was applied. It came on very smoothly in the normal position. One could adjust it so it would in normal driving conditions alsmost bring the MH to a smooth stop without applying the service brakes. It was great

JohnFreyja · 11-01-2010, 11:13 AM

RickO,

Mostly Foretravels and they seem to love the retarder over the Jake. The PTO on my Country Coach runs the variable fan and also the power steering pump and if they are the permanently lubed (greased) they need to be serviced regularly. I had mine converted to the "wet" lube. If it is not maintained you could loose power steering at an importune time!
Jake (engine) brakes are often illegal in many cities but exhaust brakes are not that noisy.

John