Auto to manual transmission conversion and more

[Fuelie74]

I got a little spring fever and decided that is was time to rip into my 74 and make some changes before spring. The main parts of this project are to switch from an automatic to a 5 speed manual and from hydroboost to manual brakes. I am not sure what else I will be changing for sure right now, but I am sure more will happen while its tore down.

I have a automatic pedal assembly for manual brakes and a manual pedal assembly for power brakes sitting on the shelf. I figure I would take them both apart and make a manual trans manual brake pedal assembly out of the two.

Once everything was tore down I found that the clutch pedal had a lot of wear on the shaft.




The shaft isn't available separately, so I decided to modify an auto shaft to work. I drilled the pedal and inserted pin and pressed it in.




Then I clamped the pedal into a jig I made and welded it back together.

 

[MYBAD79]

The 5spd conversion was by far the best mod I've done - so much more fun than the automatic. With my 3.55 gears I'm right around 2000 rpm at 70mph on the highway.

The pedals were the hardest part of the swap.

 

[Fuelie74]

Yeah I can't wait to get it out. It's only a T5 that I'm putting in, but at least its a GM world class T5. I had a lot of the parts already, so really it's being a cheap conversion. Hopefully in a couple years I can upgrade to a Tremec. My new trans has a 2.95 first and a .63 OD, so it's better on both ends than my TH400. My 3.08 gears will have to go for sure, I am thinking 3.73 will be just right.

Just got the pedal assembly put together and I found out that the brake pedal spring is a royal pain to put back on. Everything has been basted and powder coated. I also installed new bushings, pedal pads and trim.


I also got busy and pulled the TH400 out. That was alittle bit of a chore since this was a 4 speed fame with weld in crossmember. A previous owner did this and when they did it they decided to just touch the crossmember out and weld it back together. Yes that is 1/2 flat stock welded to it and you can see they never rewelded the top. This is not a new surprise to me, but I hate being reminded of it. I decided to cut it back out and take a different approach to putting it back in. I sure would like some suggestions on this. I have an auto trans crossmember from my parts car I though about using, but it looks I might have to pull the body to weld in the upper mounting points and I don't want to do that till fall.




I got my new bellhousing up bolted up to see how it would fit with the factory slave cylinder. I have heard people say that you have to modify the floor to use it. It looks like it is possible. The only think I can see being the problem it the fork itself. Since I am missing the fork and the slave cylinder I think I am just going to run a hydraulic throwout bearing. So I am thinking I will cut the slave cylinder mount off before I powder coat the bellhousing. Then drill and tap a couple holes in the housing for a block off plate where the fork went.

 

[Fuelie74]

Well I decided to replace the crossmember with a bolt in automatic crossmember out of my 73 parts car. I got the old crossmember cut out and the new one set in place. I still have to drill and tap the holes and finish the top bolt mounts. Going off my parts car frame it looks like the bottom bolts are 3/6 16 so that should be fairly painless.


Got the transmission bolted in for a test fit.


Looks like I will have to trim a very small amount out of the transmission tunnel.



Here is the Howe hydraulic throwout bearing I decided to run. I will be using a 3/4 inch Wilwood master cylinder with it.

 

[mrvette]

On your frame/crossmember mod there you had the same issue I did with my stick to auto conversion, going the other direction....I eventually cut the cross member same as your P/Owner, but when putting the thing back in, I had some 2" angle welded to either end on top/rear section, and some on the bottom also to form a box around the stub ends on the frame, then just ONE 1/2 dia. grade 8 bolt going fore/aft to hold it in place, been there for years....

then I got good and pissed having to cut the pipes every damn time I removed anyting in the way of a tranny/something.....and so on the cross member, I cut the bottom of the loops out at a nice wide angle, on top it was bridged and filled in about a inch down, but now it's kinda like a truss construction over the top of the loops, making it a snap to lower the pipes outta the way, in fact on my car I can drop the entire exhaust outta there in about 30 minits or less.....

except the headers, of course, :lol: but if time is no object, you can spend some MONEY and get a aftermarket cross member from BTO, I think.....

:crutches:

 

[Fuelie74]

Gene, I originally planned on fixing and modifying the weld in crossmember like you described, but they really butchered it up. Since I had a parts car with a bolt in member I thought I would be best off to go this route. I have looked at the BTO crossmembers there is no way I would spend that much money on one. Although if I didn't have sidepipes I would probably build a tubular member to go under the exhaust.

Measured for my driveshaft tonight so I can drop it off at the local driveshaft shop tomorrow during lunch and have them shorten it to 27 1/4 inches. My yoke is a small U-joint so I guess I will have to run a bastard joint. Looks like it will be a very snug fit between the yoke of the driveshaft and the tunnel.

 

[mrvette]

That does look close, looks like something already scraping, I had to cut/mod the pass side of my tranny tunnel for the 700/200 install, the pans being wider than the muncie tunnel construct allowed for,

I too have a driveshaft shortening under way...lovely,

:surrender:

 

[BBShark]

Are the holes for the automatic crossmember mounts, just threaded holes in the frame or are there weld nuts in there?

Nice job on the conversion. Do you have a neutral safety switch on your pedal assembly?

 

[Fuelie74]

That does look close, looks like something already scraping, I had to cut/mod the pass side of my tranny tunnel for the 700/200 install, the pans being wider than the muncie tunnel construct allowed for,

I too have a driveshaft shortening under way...lovely,

:surrender:

Yeah there are some rub marks in the tunnel. Non of the marks are fresh and there aren't any rub marks on the drive shaft. So I am going to assume that they are from a problem of some sort before I got the car.

Are the holes for the automatic crossmember mounts, just threaded holes in the frame or are there weld nuts in there?

Nice job on the conversion. Do you have a neutral safety switch on your pedal assembly?

I auto crossmember uses three bolts per side and the cross bolt is really what holds the weight. I am guessing by looking at the bolts that I removed the holes are just threaded into the frame. That's a good question though and I will crawl under my parts car this weekend to verify the mounting.

Yeah I have a neutral safety switch mounted on the pedals you just can't see it very well in the picture. I am missing the little rod that hooks it up to the pedal its self, but I will get that when I put my next parts order in.

 

[Fuelie74]

Well it's starting to feel like Christmas in March. My new to me C5 master cylinder just showed up. That reminds me I am missing the master cylinder studs for the pedal hanger. What size are they supposed to be?

 

[Fuelie74]

Looks like it was worth double checking. The holes do have weld nuts inside the frame. So now I am really looking for advice on this one. What would be the best way to go about this problem? Possibly a thread rivet insert?

 

[mrvette]

I was afraid of that mounting bolts shituation....

which is why I never rewelded my frame, and did that L bracket the way stated above....

:twitch::thumbs:

 

[Fuelie74]

Well I got my driveshaft back today and now I have another question. I am working on building the tranny mount and setting my driveline angle. I zeroed the gauge on the frame then measure the trans at 4.0 down, the drive shaft at 0.6, and the diff at 3.2 up. So I actually need to bring the back of the tranny down some so it reads around 3.2. Am I figuring this correctly?

 

[BBShark]

For the frame nuts, maybe you could drill out the hole and weld some coupling nuts in there and then cut and grind them flush.

The transmission sounds like it needs to come up to match the diff. Are you measuring the diff angle on the yoke?

 

[Fuelie74]

Yes your right the trans needs to go up. I was alittle to tired last night and not thinking straight. I am about as high as I can go at 4 deg on the trans. I know ideally the angles should match exactly, but what is the allowable difference?

 

[Fuelie74]

Made my transmission mount today. I removed the lower 4 speed mount tabs off my old manual crossmember and used them on my auto crossmember. With everything bolted back together I was able to get my driveline angle at the trans to 3.2 matching my angle at the diff.



I also got my dash out and cut the firewall for manual M/C. Then installed my pedal assembly. While trying to figure out how I was going to cut it out I decided to try my rotozip. Wow did that work good on fiberglass.

 

[Fuelie74]

Well I decided to try 3/8 knurled rivet nuts for the bottom bolts of the crossmember. They are steel with a zink finish and weren't to badly priced from McMaster. I had to get the installer also, but I figured this won't be the last time I need them for something. They went in nicely and everything feels very solid, so with the top mount bolt I think I am good.

 

[Fuelie74]

I got my clutch master cylinder mounted. I made an adapter out out aluminum flat stock I had laying around. After measuring it I marked it out. Then carefully cut the angle with the band saw and sanded it smooth. When I take it back apart I will trim it up and polish it. I will also get some measurement of it in case anyone is interested in using an aftermarket M/C.

 

[Fuelie74]

I seem to be at the point of this project where there is a ton of stuff to do, but not a lot worth talking about. I have been spending large amounts of time under the car with a bottle of Purple Power and paper towels degreasing the bottom side of the car while the transmission is out. I also threw a new rear main seal in while everything is apart.

I Got my clutch M/C and linkage finished up. I also trimmed down the adapter and polished it.


I got my plumbing done for the hydraulic throwout bearing. My only complainant is that you have to install the transmission and bellhousing as one assembly.




I also got the brake M/C plumbed in along with a line lock that I really didn't need, but always wanted.

 

[BBShark]

I got my plumbing done for the hydraulic throwout bearing. My only complainant is that you have to install the transmission and bellhousing as one assembly.

I hadn't thought about that (putting the trans/bellhousing in assembled). I suppose that's the downside to a hydraulic bearing.

How difficult was that to do?