Ford Muscle Cars Tech Forum banner

1 - 2 of 2 Posts

·
Premium Member
Joined
·
557 Posts
Discussion Starter #1 (Edited by Moderator)
Have you ever been really excited to install a new part, only to find that there is not enough clearance between it and existing parts on the vehicle? A perfect example of this would be a disc brake upgrade. You spend the time, remove the old drum brakes, install the new disc brake parts, get everything else put together, then when you go to put the rims on you find that there is not enough clearance between the caliper and the rim. In some cases the fit is so far off that you must replace the rims and tires, but what do you do when the difference in fit is so small that you feel the parts could be “persuaded” to fit together?

"What do you mean it doesn't fit?"
I have had this happen to me twice in the last few years. The first time was, as you would guess from the statements above, on the front disc brake upgrade I made on my 65 Mustang by replacing the old drum brakes with Granada front discs. The passenger’s side install went with out issue, I got the brakes on, bolted up the 14” slot-rim I was running on the car, gave it a spin and all worked just as it should. But when I repeated the process on the driver’s side and tried to give the wheel a spin, nothing happened. The rim was locked against the newly installed brake caliper. The castings on the driver’s and passenger’s side calipers were just different enough that the passenger’s side caliper cleared the rim but the driver’s side caliper did not. Knowing the fit was really close I had no doubt that I could use an angle grinder to “persuade” the driver’s side caliper to clear with out any fear of weakening said caliper. Unfortunately at the time, I did not take any pictures of the process.

As I mentioned before that was the first of two times that I have had to clearance a part. The second time involved interference between a new clutch pressure plate and a T5 bellhousing. This time when I clearanced the parts I took the opportunity to take some pictures, and the following is the pictures and process I used to make the parts clear.

If this is information on clearancing a pressure plate you may be wondering wht I began with the story about my Granada disc brake swap. The reason I mentioned it is that it is probably the most common place that you will want to “persuade” something to clear and since the exact same process can be used in both applications I wanted to address the brake clearance issue. Keep in mind the techniques that I am about to describe for clearance a pressureplat can be not only be applied to clearancing a pressure plate or caliper, but to almost any application where minimal material removal is required.

Technique
How hard is it to use a grinder and remove some metal? Its not hard, in fact it is easy, too easy and there in lies the challenge. What ever part is being clearanced was designed with a specific strength in mind and removing to much metal can weaken the part so you want to remove just enough metal from the contact points with out taking to much material or removing material from areas that already clear.

Clearance a Pressure Plate
As I said before the second interference issue I had was between a new pressure plate and my T5 bellhousing. The issue was discovered when I first fired up the engine after the install. The interference created a loud knock that made my gas powered engine sound like a diesel. After pulling the transmission and the bellhousing I was able to see the contact points on both the pressure plate and the bellhousing. There were three tabs on the pressure plate that were contacting the lower section of the bellhousing.



The first thing you must decide when clearancing parts, is which parts to remove material from. In the case of rims and calipers you do not want to modify the rims so all the material needs to be removed from the caliper. In the case of my pressure plate and bellhousing I was concerned with the structural integrity of the bellhousing especially since it is aluminum so most of the material had to come off of the pressure plate.

A small amount of material did need to be removed from the bellhousing but the reason for doing that was not an issue of clearance. I removed material from the bellhousing to eliminate a potential crack point. Anytime you have a structural piece such as a bellhousing you do not want to leave any non OEM sudden groves or sharp cuts in the surface. The reason for this is a sudden change in the surface of a structial part will cause an uneven distribution of stress in the grooved area during use, and may result in the part cracking. A simple way to eliminate the sudden stresses is to smooth out the area in question, which will distribute stresses more evenly.

Since the bellhousing was aluminum a quick pas with a die grinder and grinding stone was all it took to remove the majority of the grove. After that a quick pass using a pneumatic angle grinder with abrasive pad was all that was needed to finish polishing the grove out of the bellhousing.



The next step in the process was to check to see if the material removed from the bellhousing was enough to eliminate the problem. To do this I put two layers of masking tape on the bellhousing, where the contact points had been.


I then also put two layers of tape on each of the tabs on the pressure plate.


The reason for using four total layers of tape, two per contact part, is that it creates a total thickness of .015” and marks easily so that I could easily see exactly where the parts were coming in to contact with each other. To mark the tape the bellhousing was reinstalled and engine was rotated by hand. As the engine rotated I could hear and feel the tabs coming in contact with the bellhousing
When I removed the bellhousing I could see the contact points on both the bellhousing and tabs.




As I said before I wanted to keep the material removed from the bellhousing to a minimum so I did all my grinding on the pressure plate and removed a small amount of material from the contact points marked by the tape. From there the same clearance test as before with one exception. Instead of putting two layers of tape on both the pressure plate and bellhousing to get my four layers, I only put the tape on the pressure plate but still used four layers. With new tape on the pressure plate the test was repeated and once again material was removed.

I continued to repeat the testing and material removal process until eventually enough material was removed that markers were no longer being left on the tape. Since four layers of tape were a total .015” thick and the pressure plate with the tape on it was no longer coming in contact with the bellhousing I new I had at least .015” clearance between the parts, which should allow for expansion as the parts heat up.


When I clearanced my bellhousing It took me six test fits before I had removed enough material. I probably could have done it in less than six test had I been more aggressive with the grinder but I wanted to remove the minimum amount of material to get my .015” clearance.

As I said in the beginning the same technique can be used for clearancing brake calipers to fit in rims that are only slightly to small. There are however a few differences. First I recommend eight layers of tape rather then four so that the end result is .030 clearances. Also in the early stages of grinding, in order to be able to rotate the rim, you may need to loosen the lug nuts just enough to free up the rim keeping in mind it needs to be tight enough to still mark the tape.
 

Attachments

·
Registered
Joined
·
744 Posts
What clutch and year transmission bellhousing were you using? I had this same issue with my t5/Spec clutch combo in my 69 mustang. I talked to the tech guy at Spec and he said the earlier (82-86ish) bellhousings weren't tall enough to accept a taller, aftermarket clutch. He said hes been with Spec for 10 years and has heard of that twice.

It was weird because it did not make any noise at first but got progressively worse. Made kind of a ticking noise. Clearanced the bellhousing and put a new clutch in it and everything worked out fine.

Just glad I'm not the only one who ran into this problem.


Here's a thread with some pics attached of what I did.
http://www.fordmuscleforums.com/garage/496936-clutch-fork-fulcrum.html
 
1 - 2 of 2 Posts
Top