I have posted this on another site also just to make sure I have as many people covered on this subject as possible.A friend of mine the other day was travelling down the freeway in his 2005 Monaco Windsor when he heard a big bang and scraping noise. He pulled over. His engine was still running but the whole front of the engine had dropped forward which resulted in the transmission sitting on the ground in pieces and his drive shaft broken. He got towed in by Coachnet to a large Peterbuilt dealer who is a Cummin/Allison dealer. Upon inspection it was determined his front motor mounts had given way and broke allowing everything to drop forward and take everything else out with it. I was startled when I heard this but the dealer said this can happen on these Class A motorhomes and in transport trucks. Again. I was shocked to hear this.My question is for anyone out there with any knowledge on this type of incident, what are the chances of this happening and why would this happen? Up to yesterday, I had never heard of this. Maybe one mount was cracked and let go and took the other one with it?As you can appreciate this is a very expensive fix with a rebuilt transmission, new drive shaft and a new bell housing on the front of the engine plus lots and lots of hours of labour costs.Any input would be appreciated.Toban

Short answer, I for one cannot recall any incident as you have described it. Do you know what kind of chassis?

Did the dealer say why it happened?Just saying it can happen does not tell us much. Something obviously failed.

JohnnyT wrote:Short answer, I for one cannot recall any incident as you have described it. Do you know what kind of chassis?That vintage Monaco would be on a Roadmaster chassis, Monaco's proprietary chassis.

It's a roadmaster Monaco chassis.The dealer apparently said they have seen diesel pusher motorhomes with this problem in the past but is more common in transport trucks. I'm just getting this from the owner so I can't say exactly what the dealer said.Would this be a wear and tear thing? I've never heard of owners having to change motor mounts as a maintenance item. It is a concern though when you hear this. I thought the mounts are part of the engine from Cummins but someone else said the mounts are separate from the actual engine? Then if this is true, the chassis manufacturer would be the ones putting this onto the engine when they install the engine to the chassis when the MH is being built?Lots of questions. I believe the bill will be $20,000.00 plus.Toban

According to the Monaco brochure, the chassis is the Roadmaster RR8S, which is not the Roadmaster chassis with the trailing arm problems. .

Cummins engine mounts broke with serious damage

11 Replies

toban
Explorer
Apr 28, 2015
My friend said the mounts were not part of the chassis. He said they ordered the mounts from Cummins.

Anyway, it a heck of a mess. I thought there would have been some sort of warning something was going on in vibrations etc.

Hope it never happens to any of us on the road and thanks for all the replies.

Toban
Ivylog
Explorer III
Apr 27, 2015
Each motor mount is made up of two right angle brackets with a rubber cushion between them. One is bolted to the frame and the other is bolted to the bell housing and sits on top of the one on the frame. There is a bolt between the rubber cushion that holds everything together so under enough torque one side does not lift up too much.

The odds of these brackets breaking is slim so the bolts coming loose is a more likely option. Even if one side broke, the other would hold the engine up for a while. Doubt you would hear or feel this movement on a DP.

Here are some pictures of a Cummins ISC bell housing mounts but they would be pointing down when bolted to the bell housing. The mounts on my ISL are much heavier and not of cast iron and yes I went and checked mine... not something I would normally do.
Bruce_Brown
Moderator
Apr 27, 2015
I think the question that needs to be answered is were these the mounts supplied by Cummins on the motor itself or the mounts installed on the chassis by Monaco.

In other words, was it the actual motor mount, or the chassis mount the motor attaches to.
randallb
Explorer
Apr 27, 2015
Motor mounts do not just break. They start to tear or settle. Both of these occurrences will give you some type of symptom. If it tears you should feel a shift from the power train assembly on take off. If they settle a driveshaft vibration is normally felt. If these symptoms are not noticed or ignored then what occurred to you friend is the final result.
Randy
mpierce
Explorer
Apr 27, 2015
Would depend on which "mounts" broke. There are matching "mounts" on the engine, and the frame. With a "rubber" cushion between.

I have heard of a mount breaking. But, NEVER of an engine "dropping". I think the broken mount is essentially always on the frame, so it is not a motor problem, but a frame problem.

It is NOT COMMON.
Kennedy64
Explorer
Apr 27, 2015
Had this happen once with a 90's Grand Prix I owned. Went to turn right on to a road....instead lost steering and went straight and blocked three lanes of traffic.
Called the dealership the next day and found out there was a recall on that particular body style of car (affected several models and years).
Pretty darn scary and I was very grateful I needed money from the ATM otherwise I would've been driving around S curves at about 45 mph at that time.
rgatijnet1
Explorer III
Apr 27, 2015
According to the Monaco brochure, the chassis is the Roadmaster RR8S, which is not the Roadmaster chassis with the trailing arm problems. .
toban
Explorer
Apr 27, 2015
It's a roadmaster Monaco chassis.

The dealer apparently said they have seen diesel pusher motorhomes with this problem in the past but is more common in transport trucks. I'm just getting this from the owner so I can't say exactly what the dealer said.

Would this be a wear and tear thing? I've never heard of owners having to change motor mounts as a maintenance item. It is a concern though when you hear this. I thought the mounts are part of the engine from Cummins but someone else said the mounts are separate from the actual engine? Then if this is true, the chassis manufacturer would be the ones putting this onto the engine when they install the engine to the chassis when the MH is being built?

Lots of questions. I believe the bill will be $20,000.00 plus.

Toban
smlranger
Explorer
Apr 27, 2015
JohnnyT wrote:
Short answer, I for one cannot recall any incident as you have described it. Do you know what kind of chassis?

That vintage Monaco would be on a Roadmaster chassis, Monaco's proprietary chassis.
gbopp
Explorer
Apr 27, 2015
Did the dealer say why it happened?
Just saying it can happen does not tell us much. Something obviously failed.