My 53 chevy PU has horrible firewall flex with the manual brakes due to cowl rust over the years and repairs. Im running a dual bowl MC, drums out back and discs up front, truck stops pretty good but i feel could be better and stopping the flex may help some. I was looking into one of these billet firewall mounts to stiffen up the area. few guys i talked to on this say this will greatly affect pedal ratio because its pushing the master further out from the firewall and affects pushrod engagement, it somewhat makes sense but i am not sure because the pushrod length is adjustable and all. What do you guys think?
Pedal ratio is determined by the mechanical design. Firewall flex has nothing to do with it, although you're probably giving away some pedal 'feel' with the flex....
def its the pedal feel i can feel the firewall flex, just want to fix this but dont want to risk messing my brakes up.
lengthening the rod will not change the ratio. i think it would be better to bring a support back towards the dash board. one to the column mount and one to the base of the windshield will do it.
if you put your MC 10" from the firewall and added 10" to the pushrod your pedal ratio would not change. I'd just make one from some plate steel rather than buy one
i agree they got me confused as hell today at lunch, got me worried which is why i had to ask you guys
yeah my buddy came by just now who works for a machine shop, he made a cardboard template and will mill me one this week from 5/8 billet which should be perfect. i bet this sucker will stop the flex thats for sure
The guy that told it will affect pedal ratio is probably the same guy spread the rumor about too much horsepower on the street is illegal. A guy told me once about a supposed car he had that the cops made him take it off the street because it had too much horsepower and so he sold it.
I have a plate on my firewall to stiffen it up, locates the brake and clutch master as well. I made up 2 aluminum ones, too flimsy, went to 1/4" steel... much better. It had zero impact on the pedal ratio.
What sort of pedal assembly do you have? Is your brake pedal mounted on the same structure that your mc bolts to? such as this pic... If so, stiffening that up with a large firewall plate or a couple added struts from the "backbone" to a couple of solid spots is simple. IF your brake pedal mount is not on the same structure or backbone that holds the mc, then stiffening it up gets more complicated. I hope your pedals are on the same backbone as the mc mount. why be ordinary?
Something like this would work for pendulum brakes as my Olds was designed with through floor pedals. I used 2 x parallel lengths of horizontal 1"RHS steel with 1/8" flat plates either end as there is no firewall support and I didn't want brakes in engine bay area. The flat ends bolt to cowl sides (3 x bolts each side) where OEM handbrake brackets are (LHD &RHD). The RHS fits flush against firewall and is secured with 3 x button head bolts after drilling and tapping holes. Everything bolts to this and can be removed as a complete unit if desired or items removed separately for servicing. Solid as a rock with no flex in firewall when in place and all the bolts are tightened. Just swap out the 90 degree booster with MC to a conventional pendulum assembly through firewall and you're good to go. Albeit a little more work but don't skimp on safety like brakes, steering or suspension..
...a pic of what you have would help, but a stiffener from the firewall back to the bottom of the dash is all you need, those dashes are plenty stiff there,..built many of these trucks that way.
Put your plate front or back it will work both ways, easier in the front. Adjust the pushrod and your done. Pedal ratio is determined from the pivot to the push rod to the foot pad. Adding a stiffner plate wont change that ratio.
Here's my opinion. The firewall is The same gauge sheet metal as the body in most cases, so adding a plate will only result in the firewall and plate flexing - especially if the firewall has been weakened by repair or modification. I'd think about adding a plate which covers more of the firewall around the master cylinder if possible, or engineering a stiffener to hold the firewall by counteracting the directional flex from pushing the brake pedal.
Like he says. If you add a shim/spacer between the firewall and the M/C add the same amount to your push rod. It will function just as it did before you put the shim/spacer on.
I made a plate similar to this ^^ for my AD . On the inside of the firewall I made two knee braces from 1/2" angle approx. 8" to 10" long and attached them to the bottom two bolts of the of the plate and the other ends to the steering column mounting brace. No flex. Hope this helps. Bill
if the firewall is flexing, a small plate, just a bit bigger than the master cylinder mount, is not going to be much more than a bandaid. A longer support, like a couple vertical pieces of angle iron mounted near the master cylinder is going to be more help. Just my thinking.
If there is enough room, a small diameter tube from one of the lower mount bolts to an inner fender mount should work. I used a strut on an OT vehicle and made a major difference in pedal feel/response.
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