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coach handling after engine swap
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tom gleason
Posted 2017-04-17 4:28 PM (#4522)
Subject: coach handling after engine swap


Contributor


Location: Corcoran MN 5340
I got my coach from my uncle and he had replaced the 440 engine with a 6.9 diesel out of a Ford pickup. This destroyed the handling of the coach, it wandered all over. I since installed a rubber helper spring from Recreational vehicle services, Jim Black the owner was a FMC engineer when these were built. They ran into the same problem when they first offered a diesel engine as an option. This made a great difference but it didn't completely fix it. Has anyone else swapped engines and had a similar problem? What did you do to over come it? Thanks in advance
Tom
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LCAC_Man
Posted 2017-04-17 10:11 PM (#4524 - in reply to #4522)
Subject: Re: coach handling after engine swap


Elite Veteran

5001001001002525
Location: Oceanside, CA
The Timbren "spring" is a glorified bump stop and really just provides a very small amount of rear spring rate and won't come close to offsetting the 6.9 (a previous owner put them on mine and they were/are a joke (IMHO).
You can go at fixing it two ways:
1. Offset the added weigh of the 6.9 by adding weight up front, it's going to take 2 or 3 times the additional weigh of the 6.9 because of the front tire position being closer to the added weight up front.
2. Add rear air bags, this is a tough (but better) fix as you'll have to do some considerable fabrication work...there is no "kit".

Another great steering improvement mod is to install a "Safe-T-Plus" stabilizer...google them...they work.


Edited by LCAC_Man 2017-04-17 10:12 PM
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5Dollar
Posted 2017-04-17 10:34 PM (#4525 - in reply to #4522)
Subject: Re: coach handling after engine swap


Veteran

10025
Location: Bethune, SC
Len

Are there pictures in your album of the Safe-T-Plus installation?

How much fabrication did you have to do?

I am assuming you have a front steer.

Which model number did you get and what mounting brackets?

I think I will give it a try.

Henry
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hemi354az
Posted 2017-04-17 10:58 PM (#4526 - in reply to #4524)
Subject: Re: coach handling after engine swap


Extreme Veteran

50025
Location: Scottsdale, Aridzona
The single Timbren deflection/load curve of the size that is most often used on a FMC is shown here - http://timbren.wpengine.netdna-cdn.com/wp-content/uploads/2015/06/S...
They have been making kits for hundreds of different trucks/delivery vans for 50 years - http://timbren.com/media/
Many 440 Gas engine FMCs developed steering wander that seems to be solved with a set of Timbrens.
Suit yourself . . .
Lou #120
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BigRabbitMan
Posted 2017-04-18 12:06 AM (#4529 - in reply to #4522)
Subject: Re: coach handling after engine swap



Expert

100010010025
Location: Cottage Grove, OR
As the coaches aged, handling issues started showing up. Timbrens on the rear provided a stabilizing factor to the rear of the coaches. With them and a properly maintained front end the coaches handle well.

Adding weight to the rear of the coach does affect handling. How much depends on how much weight is added. When I did my conversion to diesel, the weight factor was a prime consideration in my engine selection as the Duramax is the lightest small modern diesel. My engine has had an effect on the handling of my coach but not near the degree that those with other engines have described for their coaches.

You don't have a choice of engine as the coach came with the engine that it has. The Ford is a heavy engine and heavy engines have caused handling issues like you have described. As Len has stated, at this point you need to ensure that all front end components are as they should be: not loose nor do they bind. Once that is done, then either add front end weight or/and add rear end air bags. Both methods have worked to rebalance coaches and make them fun to drive.
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LCAC_Man
Posted 2017-04-18 7:17 AM (#4530 - in reply to #4525)
Subject: Re: coach handling after engine swap


Elite Veteran

5001001001002525
Location: Oceanside, CA
5Dollar - 2017-04-17 8:34 PM

Len

Are there pictures in your album of the Safe-T-Plus installation?

How much fabrication did you have to do?

I am assuming you have a front steer.

Which model number did you get and what mounting brackets?

I think I will give it a try.

Henry

Yes, pictures here (this one and the one after it) http://www.fmcowners.com/mbbs22/photos/show-album.asp?albumid=127&p...

I used the mounts from a P32 Workhorse Chassis and modified them, it's a 3-4hrs job.
Yes I have a late coach so you need to keep that in mind when looking at the pics.
Safe-T-Plus model number 31-140.


Edited by LCAC_Man 2017-04-18 7:17 AM
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