rear end vibration
 

I have a vibration in the driveline,about 2500 rpm,you can feel it,go in and out,i have martins kit in my car,rebuilt t-5,stock mustang drive shaft cut down and balanced twice,7.5 rear end completely rebuilt,new hub bearings on both sides,replaced trans tail shaft bushings,have added washers on front differential mount,to change diferential pinion angle,up and down,does not seem to do anything,running out of ideas,wondering if some body has run into same problem to help me out,i don't know if a aluminum driveshaft would help.

You mentioned the problem changes at 2500 RPM but not at any different speed. A drive line vibration is very rarely RPM sensitive, it's usually speed sensitive. If it really changes only with RPM the problem has to be from the input shaft of the trans forward because everything rearward of that changes with speed not RPM.

Have you done the trans mount reinforcement to the floor? Basically you just bolt it to the floor right next to the tunnel where it is 3 layers thick. If so that maybe be transmitting a engine vibration to your butt. The biggest mistake I made was putting a polyurethane trans mount in. It rattled the change in the cup holder so bad I couldn't hear the radio. I went back to a stock rubber Camaro trans mount and it is as smooth as can be.

On shimming the rear end have you actually measured your pinion angle? It takes a $35 tool and a half hour to do.
https://www.v8miata.net/attachment.p...ine=1394532320

http://www.sears.com/craftsman-digit...3&blockType=G3

See also https://www.v8miata.net/suspension-d...xplained-1292/

I used to solve these types of issues when I worked for Ford. Are you sure that it is a driveline vibration & not a wheel/tire vibration? They feel totally different. If you can provide a little information, I think I can help you. Is it speed sensitive or RPM sensitive? If so, what speed or RPM? Can you reproduce the vibration in another gear, at a different RPM or MPH? Does it occur on acceleration, deceleration, coast, any combination of the latter? I can P/M my phone number if you would like to discuss the issue.

I rotated the tires,no help,seems smooth 1st through 4th,when I put it in 5th gear,at 2500 rpm at 65 to 70 mph,i get the vibration,it goes in and out,i checked the driveshaft angles they seem ok,i don't know if the trans is causing it,i have the stock mustang trans mount installed,and poly bushing on the front of the differental

thanks for the info

I am running a modified mustang trans mount

Any vibration in 1st through 4th at 2500 RPM? Did you try 65 to 70 MPH in 4th gear to see if it is different? Is it smooth at 75 MPH +?

This is the key to finding which end of the car it's in.

BTW you mentioned your pinion angles look good but did you measure them? There is a lot of different specs for different applications but a good rule of thumb is to have the yoke of the drive shaft and the flange at the diff within 2 degrees of each other and dead on parallel with each other.

I had the same problem with mine. Found it to be slop in the trans crossmember. I bolted it through the floor like Jim explained. Problem solved

if I try to go 65 mph in 4th gear,i am pushing 3500 rpm,no vibration at that rpm,i checked the angles,they seem to be about 1 to 2 degrees,at each end

Have you checked the angles from side to side? In a Ford conversion the engine is centered but the diff pinion is off to one side. If the engine and the differential center lines are not parallel in all planes you could have a vibration.

-Jason

Don't care you need to try it. My money is still on driveline and I bet you get the same vib in 4th at 3500 as you do in 5th at 2500.

We’re trying to help here but you need to clarify a couple yes or no things for us please.

Do you or don't you have the vibration in any other gear at 2500 RPM?

Is your trans mount bolted to the floor at the edge of the tunnel or not? These are 2 extra bolts not normally used in Monsters kit.

FYI Jason check out the angle in the V8R GM diff set up.
https://www.v8miata.net/attachment.p...ine=1394646590

Mine with the 8.8 Ford is not that far off but the point is we're all in the same boat on this one!

at 2500 rpm is when I have the vibration,when you are shifting,the rpms are in the higher range of rpms,when I shift into over drive,of course the rpms drop,to 2500 that's were the vibration is,i have a modified mustang crossmember,very strong,i have to drive it again,and see if I get the vibration in the lower gears,i don't remember