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Auto trans issue after carb/ignition swap


Doug Burgoyne

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OK...just deleted all the smog stuff, ecu, smog pump and egr (PO pretty much cut and plugged much of that already, but was still hanging out in engine bay), etc, etc...installed points distributor from '74 mustang II, and new non-feedback carb. Starts great, idles fine (still a bit rich), timed, BUT now it doesn't want to shift into reverse (it did once right off the batt), but will drop into drive (but doesn't want to go forward really...acts like park brake is on but it's not). I did remove all vac lines and plugged stuff up, except for obvious ones like pcv, brakes, etc. There was one vac line, about 1/2" diam rubber that comes up along firewall behind distributor. It goes down about 8" or so and connects to hard line. I left that off intake vac tree (I'm sure that's where I yanked it from) in back under the carb, until I clean everything up and make sure my post-swap ducks are in a row. But got to thinking it may be a modulator valve vac line or something to do with transmission, so I hooked that back up to one of the intakes on the tree (back most one, as it seemed to fit best with curve of hose). I took a ton of pics during disassembly, but nothing that shows this clearly prior to pulling those lines. Dang. I'd say I must have gone too far on one thing or another that essentially disabled my trans from working correctly. I don't think it was electrical, but I'm pretty much stupid on most of this electrical stuff. I remember reading in duraspark swap write up about auto trans part of the conversion, but seemed that was only for A4LD overdrive issue...I have an 84 with what I believe to be stock and standard C5 transmission (3 speed), so that shouldn't apply to me, from what I understand.

Anyway folks...it runs finally, but no shifty! Somethings wrong, but before the swap the trans shifted and drove great. Thanks for any and all input and help! Doug
 


RobbieD

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Fluid level checked?

The only other thing that comes to mind is hard linkage to the carb for the passing gear kickdown; make sure that it's not trying to engage except for wide open throttle.
 

Doug Burgoyne

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Fluid good. Oh yeah, kickdown linkage just kind of hanging there at the moment, as just finished swap, and new carb didnt have proper attachment (something I need to mod). Perhaps engaged somehow that is keeping tranny from shifting, operating correctly. I'll look into that. Thanks for idea!
 

Shran

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Kickdown is not mandatory on the C5. I have a C5 in one of my Explorers and it has never been hooked up - it is only used to increase pressure a little bit when down shifting at WOT from my understanding. It certainly would not cause your issue but you should hook it back up just in case.

Make sure that your vacuum modulator hose and hard line is not plugged up. I'd pull it off both the engine & trans and blow air through it and see if you get any change.

Otherwise not sure what to say. C5's are all mechanical, there's not much outside of the transmission that can cause it to not function correctly other than the vacuum modulator and shift linkage.
 

Doug Burgoyne

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Thanks Shran, do you think that line I described coming up behind distributor that goes to steel line between engine and trans sound like the vac line for modulator valve? I will get under and physically trace back best I can....but curious if that sounds like the modulator line? Shifted and drove fine prior to dist/carb swap. Odd. Thx!
 

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It could be the vent tube too. I believe that one just goes up around the bellhousing and then back down... that should just be open to the atmosphere.

Modulator should look like this and the line should run up to the vacuum tree. 1/2" sounds awful large, usually they're quite a bit smaller than that. The vent tube is the bigger of the two.
 

Doug Burgoyne

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It could be the vent tube too. I believe that one just goes up around the bellhousing and then back down... that should just be open to the atmosphere.

Modulator should look like this and the line should run up to the vacuum tree. 1/2" sounds awful large, usually they're quite a bit smaller than that. The vent tube is the bigger of the two.
Thanks man! Some good things to look at when I get home. When I said 1/2" that is OD (may 1/4" ID). And that is a guess from memory. Does it sound right, that that black rubber hose connects to hard line 6"or so after it drops below distributor clamp level? If its modulator line that is. I'll report findings, and again thank you all!
 

Doug Burgoyne

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Ok guys, last night I got the kick down linkage sorted, with no change to problem (wasn't expecting anything from that). Pulled my vac line off modulator and trans fluid immediately began dripping from vac line. So suspected diaphragm rupture (dont want to be sucking t fluid into my intake I suppose). To further test, I put my hand vacuum pump on the modulator nipple. Upon pumping, it began pulling fluid into my clear tubing attached to pump. Guessing its cooked, although it is holding pressure on gauge, probably just because of hydraulics of fluid in there as opposed to confirmation of sound diaphragm. Going to replace modulator and recheck. Sound like I'm on the right track? Still doesn't seem like modulator could create such sever symptoms like no reverse and extreme hesitation to roll in drive (acts just like park brake is on, and forcing it to overcome brake shoe to drum contact...I ruled out p-brake by rolling truck in neutral by hand no prob). I dont know how big of a role modulator typically plays in basic trans function.
 

Doug Burgoyne

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Boy, any help would be most appreciated. I replaced bad leaking modulator, checked vac line with gauge, adjusted both bands and linkage as per TRS guide for c5 trans (below). Also checked fluid visually and for smell, smells fresh. Dip stick looks factory with ford logo, etc., but dont know for sure. Cant check hot as I cant drive...so going by what appears to be cold check holes (my stick doesn't look exactly like one shown on guide). Still not engaging reverse. Engages in drive but acts as if parking brake fully engaged. I'm wondering if internal transmission brake is engaging for some reason. If that's possible sitting still? Only thing in guide I didnt do is pull the throttle valve out on other side of modulator. Guide doesn't say how to pull and make sure it operates smooth in bore. Magnet maybe? I drove this truck 20 miles home, it shifted and drove nice. Sat in driveway during ignition and carb conversion. Started this odd behavior as soon as I got engine back running. Sat less than a month in mild weather. Wtf? Hope someone has idea, besides trans replacement!
 
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RobbieD

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(my stick doesn't look exactly like one shown on guide)
Have you verified that you have a C5? C3 transmissions were also used, and I don't know if band adjustment, etc., would be the same as for a C5.
 

Doug Burgoyne

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Yes sir, 1st thing I confirmed. Got the 11 bolt pan with the big bump.
 

19Walt93

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It won't cause a no reverse problem but make sure to pull the hoses off the modulator tube, blow out the tube and replace the hoses. Fluid exposure will make the hoses swell and fall off soon.
The kickdown rod provides a forced downshift when you spike the throttle and isn't strictly needed if you don't mind pulling the lever into 2nd if the downshift is sluggish. The modulator will cause a downshift when the vacuum drops, too, so you may be happy with just that.
 

Doug Burgoyne

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Thanks for input! I did use compressed air to thoroughly blow out modulator line, from engine side. I can replace the rubber sections at end, but they dont seem swollen or oily. I did put vac gauge on modulator side, with line connected at intake tree...is pulling proper vacuum. Any thoughts on what, if any, role the throttle valve could be playing? As mentioned, I didnt remove from bore and check free movement as shown in c5 tech guide. Wasn't sure how to get it out. Could pull modulator again, and try to extract with magnet (unless aluminum or stainless). I suppose if that ain't moving, the new modulator is nothing more than a paperweight stuck in a hole. To beat the proverbial dead horse...the stumper is that I didnt mess with any of these tranny components while it sat after functioning fine prior to ignition/fuel conversions. I know from experience though that old cars can just have random and untimely coincidences sometimes.
 

19Walt93

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I did all our automatic transmissions from the late 70's through 1982 and never replaced one of those valves.
If you wait a few weeks,any rubber that was expposed to ATF will swell up like a ballon.
 

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Sounds to me like the line you left off is the vacuum line for the transmission.(reread your post and see you hooked it up.)
The booster and that line are the only vac lines I have hooked up to the vac tree.i also have a 84 with 3speed auto.
 

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