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Discussion Starter · #1 ·
Background: I have a stock (mark 1) donor build with 5.0, T5, and 8.8 with stock upper & lower control arms. I've always had a grinding noise from what I am sure is the drive shaft when going over large dips/bumps in the road at highway speed. Reading through the forum led me to beleive this is a problem with pinion angle that many people with the stock donor build have corrected it by shimming the back of the tranny up.

A couple of weeks ago I read that Mike Forte was selling nice billet "shims" for this purpose so I bought them. This morning I put the car up on jack stands to install them and was confused with what I found.

Right now the rear of the tranny is higher than the rear end differential so the drive shaft angles upward from the rear end to the transmission. If I shim the back of the tranny up another 1/2" to 3/4" with the spacers/shims I'd only be increasing the angle that is already there.

Does this seem correct? Do I really want to increase the angle to correct this problem?

[ August 17, 2004, 02:17 PM: Message edited by: Matt Kennedy ]
 

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What you're trying to do is make sure the differential pinion angle is pretty darn close to then angle of the output shaft of the transmission in all planes.

So get an angle meter - a simple one from Crafstman will work fine. Place it on the trans output shaft, and on the pinion shaft. The two angles should be the same at ride height.

Car Craft Magazine has a web site. They have an excellent article on setting pinion angle.
 

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Discussion Starter · #3 ·
Bob, thanks. I realize it may be lazy on my part but rather than doing all the research on setting pinion angle, etc. I figured that becuase I had a standard donor build for which there is a known fix I would just be able to "follow the recipe". In this case I had read in a number of previous threads that with the standard donor build you need to shim the rear of the tranny up 1/2" to 3/4" to correct this exact problem. The part I am confused about is the front of the rear end is already quite a bit lower then the rear of the transmission. As a result the driveshaft already angles upward quite a bit towards the rear of the tranny. Raising the tail of the tranny by putting in the spacers would only increase the angle. That is what I am confused about.

In other words the cookbook solution to the problem (as noted elsewhere) is to raise the rear of the transmission 3/4". This seems counter as it would only increase pinion angle as I understand it. But then again I am not very knowledgeable in these area and others including builders like Richard Oben state this is the fix. Unless I am mistaken.

So the bottomline reason for creating this thread is to confirm that the "fix" I am about to install is the correct one even though it seems incorrect to me.

Thanks,
Matt

[ July 05, 2004, 09:26 AM: Message edited by: Matt Kennedy ]
 

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Couple of things...

First I never had a problem with the T5 as far as shimming the rear up for alignment purposes. I did have this issuse when I went to a Tremec 3550.

Second...Sorry probably a dumb question but...Do you have jack stands under the rear end supporting the vehicle or are the jack stands just under the frame with the suspension hanging?

Normally U-joint bind is associated with the differential being at a different height when compared to the Tranny with the vehicle supported as if it were on the ground IE the drive shaft is at an angle severe enough to cause contact at the U-joint as the suspension travels up and down.

Improper Pinion angle normally manifests itself as Wheel hop under acceleration. Pinion angle is equal to the number of degrees the Pinion flange is off of 90 degrees when viewed from the side. Pinion angle is set to the negitive side(slightly downward when viewed from the side) so that as the differential rotates upward under acecleration the pinion angle come more into line with the driveshaft angle.

Clear as mud right ;) .

IMO you probably wont correct U-Joint Bind by changing Pinion angle. Unless for some strange reason your Pinion angle is WAAAYYY off to begin with.


[ July 05, 2004, 10:32 AM: Message edited by: Smitty ]
 

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Discussion Starter · #6 ·
Henry, thanks. I tried earlier this morning and figured they were closed when I did not get an answer.

Smitty, thanks. Ooops, I forgot that I needed to support the rear-end - I had the jackstands under the frame. I moved them to the rear end and that made a significant difference. In fact, now there is little to no angle. I'm thinking that with 2 people in the car and the force of going over a bump it probably moves even quite a bit further which now makes more sense in terms of adding the shims!

Thanks!
-Matt
 

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I thought the shimms Mike Forte was selling were for IRS cars.
 

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Matt,

The driveshaft angle needs to be the same on the transmission end as on the rear end pinion to properly, "phase", the driveshaft to eliminate vibrations or harmonics at certain speeds caused by different u-joint angles. You can adjust either the trans. or the rear,(if you have adjustable upper control arms), to acheive this. For example: if the difference between the tail shaft of the trans and the angle of the driveshaft is say 5 degrees, than you should attempt to acheive the same between the pinion yoke and the driveshaft angle. Good luck!
 

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Matt your not going to get the drive shaft to be inline with the trans and rear end. you need to set the two( trans& rear) on the same plane not inline the drive shaft will be at an angle. hope this helps
Stacy
 

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In answer to your earlier concern, you still must make sure the drive shaft doesn't bind at full droop after correcting the angles for ride height. Just support the frame and let the wheels hang, and then rotate the driveshaft a couple times to make sure before putting it back on the road
 

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With the alignment issue corrected you should not have a problem with bind at full droop. If you allow the suspension to droop as low as it can the Coil springs will probably fall out before you get into U-joint bind. If you are running coilovers the shock will top out before you reach full droop. Neither of these are a good situation. Dont ask me how I know :eek: . That is why you have the limiting straps installed. You do have the limiting straps installed...right? Adjust the limiting straps so that you are getting full suspension movement while not allowing the Coil spring to drop out, or the coilover shock to top out (thats a great way to bust a shock)
 

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Discussion Starter · #12 ·
Cody, Mike (actually Cobra Cory on bahalf of Forte's) announced the new shims to raise the transmission in straight axle cars a few weeks ago.

Smitty, thanks and yes I have the limiting straps installed.

I go back to what I said originally. This is a straight donor build. If there is a problem with pinion angle on my car that causes binding on rough bumps at highway speeds with 2 guys in the car it should happen to every donor build under the same conditions. Along the same lines if someone has fixed the problem in a donor build it should work for us all. I don't see the need to do all the investigation/research on my car specifically if experienced builders are stating this is a "standard fix" that they install in their cars.

I will install the shims and post a follow-up to let people know how it worked.
 

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What is your rear ride height? If it is to low ?That could potentially cause a problem at full compresssion. Do you have coil springs or coilovers?
 

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Spend the $15 at Sears and get an angle gauge. Don't guess, actually measure. There are thousands of donor cars out there that followed the standard recipe and the pinion angle was fine. Because the shims are made and sold doesn't mean you actually need them. Some do, but most don't.

Measure, check, and measure again.
 

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Several possible problems come to mind. Low ride height is probably a big part of the problem. Another is the Mustang springs probably have a little more give than needed on full compression.

I do think the shims will help as the bind is happening only at full compression, on a bump, with two guys, and a full tank. We have never used them on a T-5 but they are must on the Tremec. Check the ride height, then put in the shims is still needed and see what happens. On our first car is only had driveshaft bind with 2 guys gas and a big dip in the road. When you get the extra dough get the coil overs. HTH, Cheers Richard.
 

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Discussion Starter · #17 ·
OK. Thanks very much for the feedback. I do own an angle gauge. What is the best way to support the car so that you can get underneath and accurately check the pinion angle (no lift available). I assume that you can just put jack stands under the frame in the front and under the straight axle in the rear. I did this yesterday but it still didn't seem like the springs/suspension were as compressed as when the car is on the ground. In other words it appears as though the tires are not as close to the body in the rear (not as far up inside the wheel wells) as they are when it is sitting on the ground. Am I missing something?

p.s Although I havn't checked in a while ride height was/is set to FFR spec all around (5"?). I'd have to go back and double check. The car has been on the road for over 2 years. At first I checked it frequently as it seemed to settle over time. Lately it doesn't seem to change so I havn't checked it in a while. I can usually tell due to spacing between top of tire and wheel opening.

[ July 06, 2004, 01:20 PM: Message edited by: Matt Kennedy ]
 

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The frame needs to be relativly level. Set jack stands under the front frame rails, and under the rear axle.
 

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Discussion Starter · #19 ·
I am posting this follow-up in case it could help others. I waited a while to be sure it was solved. Sorry - didn't take the time to figure exact pinion angle but here is the non-scientific approach I used.

I knew the problem only happened at full compression of the rear suspension (see post above). I double checked this by putting the car on 4 jack stands, putting a jack under the rear-end, and jacking up until the rear suspension was at full (or close to full) compression. With the car in neutral I then turned the drive-shaft by hand and there was obvious binding. In fact I could see where it was hitting. Nesxt I added the 1/2" spacer from Mike Forte to raise the tail of the T5 by that amount (along with a couple of new 1/2" longer grade 8 flange head bolts). I then jacked the rear again and tested again at full compression and no more bind. I then removed the jack and let the suspesion hang on the FFR supplied travel limiting cables and no bind in the other direction either.

I have taken numerous drives with full tank of gas and passengers and no more binding even going over bumps at highway speeds (bridge transitions were the worst).

Hope this helps.
-Matt
 

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Thanks for the info Matt, I was having this same exact problem and thought I was going to have to fork out $500 for the coilovers. Now I realize all I need are the shims.
 
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