Larger vacuum brake booster

[jauguston]

Does anyone know if there is a larger diameter vacuum brake booster that will fit or can be adapted to fit my '86 E-350? The one on there now appears to be 8" in diameter. The vacuum pump has been checked and is fine.This is a motorhome chassis with a 6.9 I am at 15,000# pretty much all the time with the Samurai toad behind. I have toad braking on the Samurai but a larger booster would be a nice addition. I don't want to go to the hassle of a hydro booster as working in the engine compartment is a nightmare!

Jim

 

[Agnem]

Jim, you might look into a booster/master cylinder for a 93. I don't know if they are bigger, but they are different, at least with the F series. My 93 stops a lot better than my 83 (which is the same as your 86).

 

[Mr_Roboto]

As far as I know any of the larger trucks ( F-Superduty, F-450 and up) use hydroboost or a remote vacuum booster.

Some things I can think of to improve braking are to make sure that your drums and rotors are not glazed, make sure rear brakes are adjusted properly, and make sure that the vacuum pump is giving MAXIMUM vacuum (not just "OK"). Also the use of premium brake pads and shoes for maximum friction.

 

[jauguston]

Mel,

Great tip!!!

I went and talked to my local auto parts sales friend. We did some cross checking and the news is good. The '86 booster is listed as 9 1/4" and the '93 is 10 3/4". His book had pictures and descriptions. They are both Bendix and both dual diaphram and both look the same in the picture. The only difference I can see is a slight offset in the pushrod that hooks to the brake pedal. I can swap them. I ordered one and it will be here in the morning. It was only $63.00 exchange and he said he could give them my '86 booster as the core.. This is just what I was hoping was possible. That 1 1/2" of additional diameter will mean a huge increase in area for the vacuum to act on. We checked the master cylinder bore to see if that might be different and they are the same (1 1/8"). I will follow up with another post when I get into installing it.

Jim

 

[towcat]

save yourself the grief and go hydro. You'll be glad you did. Only twist I can see headed your way is figuring out which E-series hydro lines will best fist your truck. Check out Monte's article in the tech section.

 

[krawlr]

I'm surprised the hydro wasn't mentioned earlier. But I'm curious to see how the '93 vac booster works out.

 

[jauguston]

Didn't anybody read my original post? The hydro booster has been mentioned - I said I didn't want one.

Jim

 

[towcat]

I did.
Honestly, the hydro doesn't get in the way as much as you think.
But hey, if you don't want to do it, that's ok too.

 

[jauguston]

TOWCAT,

I may be wrong but I am guessing you have never looked or worked under the hood of a "E" series with a 6.9 (-: It is literally crammed in there. You can hardly see the PS pump or steering gear or the lines between them. I had looked at the hydro booster entry in the tech section. The article says he paid $250.00 from a recycler for some of what he needed - I am paying $63.00 for a rebuilt booster and that will be all I need. I have no idea where I would find a recycler in my area to get the parts he got. I went to a local autoparts store to get the booster I am hoping to use. For me, if this all works out, it seemed like a better way to go. The booster is fairly accessable and it only took me about 1/2 hour last night to get the old one out. More later.

I would not have attempted this if Mel had not posted that he had both a '83 like my '86 and a '93 and there was a big difference in how they stopped. Thanks again Mel!

Jim

 

[towcat]

believe me.....
there's no diesel large or small that I haven't gone through at least twice. Compared to a e-series that has a psd in it, the IDI is roomy. Care to get a "walk through" on how injectors are changed out on a AMR ambulance? I've done it more times than I can count and still hate the job every time. moving the hydro out of the way on one of those is nothing compared to pulling the body off the frame.

 

[jauguston]

Progress report.

Got the booster and it looked like it was going to be a bolt in but in is not quite that easy. I didn't check other years other than the '93 Mel mentioned. Two things are different. The push rod that connects to the brake pedal is 3/4" too short. I cut it off in the flat part hear where the rod transitions from round to flat and tig welded in a piece of 1/4" flat stock I cut to 9/16" by 3/4". Beveled both welds for 100% penetration.

The other issue is the studs to mount the master cylinder are 1/4" center to center closer together. I could slot the mounting lugs on the existing master cylinder to make it fit but decided to replace the master cylinder with the one for a '93. No problem - right - - - - wrong(-: The line ports on the '93 are completely different. I am now waiting until tomorrow (Friday) to get the proper adapter fittings.

The booster is bolted in place and that part is done. I should have the rest done tomorrow afternoon unless some other glitch jumps up. More later.

Jim

 

[icanfixall]

Sorry about all the glitches your encountering. Replacing the master cylinder with a F450 one that has a 1 5/16th bore will really help too. Maybe it will bolt right up if you don't have to rotate the lines any.

 

[jauguston]

ICANFIXIT,

Better recheck your hydralics 101 manual. A larger bore MC will REDUCE the downstream pressure. Bigger bore wheel cylinders would INCREASE the force applied to the brakes with a reduced overall travel potential.

Jim

 

[Full Monte]

It is literally crammed in there. You can hardly see the PS pump or steering gear or the lines between them. I had looked at the hydro booster entry in the tech section. The article says he paid $250.00 from a recycler for some of what he needed - I am paying $63.00 for a rebuilt booster and that will be all I need. I have no idea where I would find a recycler in my area to get the parts he got. I went to a local autoparts store to get the booster I am hoping to use. For me, if this all works out, it seemed like a better way to go. The booster is fairly accessable and it only took me about 1/2 hour last night to get the old one out. More later.

I would not have attempted this if Mel had not posted that he had both a '83 like my '86 and a '93 and there was a big difference in how they stopped. Thanks again Mel!

Jim

One thing that hasn't been mentioned is that the hydroboost system is a LOT smaller than that vacuum system. I couldn't believe how much more room it made in the engine compartment, but I don't have an E-series.

 

[icanfixall]

Pressure applied from the brake peddle will move the volume of a given diameter cylinder. Now if you have lets say a 1 1/8th inch dia cylinder it will move "x" volume. Now change the dia of that 1 1/8th inch cylinder to 1 4/16th and the same peddle movement moves a larger "volume" of fluid but at a lower pressure. In the end it just works better having a larger diameter master cylinder being pushed by the same foot the same distance. The increased need for peddle pressure is not noticed by those of us that have done this. Your information is taken in to concideration and I'm not offended because you are correct. I just know the larger master cylinder works because its pushing more fluid into the same space as the smaller mastercylinder can. Gas will compress but fluids wont. Its all just science. You can compress fluids but you cant make them occupy a smaller space. :Sly